Merge branch 'master' into next

* master: (143 commits)
  Prepare 5.11.0-SNAPSHOT builds
  JGit v5.11.0.202102240950-m3
  [releng] japicmp: update last release version
  IgnoreNode: include path to file for invalid .gitignore patterns
  FastIgnoreRule: include bad pattern in log message
  init: add config option to set default for the initial branch name
  init: allow specifying the initial branch name for the new repository
  Fail clone if initial branch doesn't exist in remote repository
  GPG: fix reading unprotected old-format secret keys
  Update Orbit to S20210216215844
  Add missing bazel dependency for o.e.j.gpg.bc.test
  GPG: handle extended private key format
  dfs: handle short copies
  [GPG] Provide a factory for the BouncyCastleGpgSigner
  Fix boxing warnings
  GPG: compute the keygrip to find a secret key
  GPG signature verification via BouncyCastle
  Post commit hook failure should not cause commit failure
  Allow to define additional Hook classes outside JGit
  GitHook: use default charset for output and error streams
  ...

Change-Id: I689f4070e79f4a0ac1c02b35698ccaab68ad2f34

155 files changed, 4935 insertions, 7904 deletions

diff --git a/org.eclipse.jgit/.settings/.api_filters b/org.eclipse.jgit/.settings/.api_filters
index 538c6f7bfb..d389ac5888 100644
--- a/org.eclipse.jgit/.settings/.api_filters
+++ b/org.eclipse.jgit/.settings/.api_filters
@@ -1,38 +1,56 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <component id="org.eclipse.jgit" version="2">
-    <resource path="src/org/eclipse/jgit/lib/TypedConfigGetter.java" type="org.eclipse.jgit.lib.TypedConfigGetter">
-        <filter id="404000815">
+    <resource path="src/org/eclipse/jgit/lib/ConfigConstants.java" type="org.eclipse.jgit.lib.ConfigConstants">
+        <filter id="338755678">
             <message_arguments>
-                <message_argument value="org.eclipse.jgit.lib.TypedConfigGetter"/>
-                <message_argument value="getPath(Config, String, String, String, FS, File, Path)"/>
+                <message_argument value="org.eclipse.jgit.lib.ConfigConstants"/>
+                <message_argument value="CONFIG_REFSTORAGE_REFTREE"/>
             </message_arguments>
         </filter>
     </resource>
-    <resource path="src/org/eclipse/jgit/storage/pack/PackStatistics.java" type="org.eclipse.jgit.storage.pack.PackStatistics$Accumulator">
-        <filter id="336658481">
+    <resource path="src/org/eclipse/jgit/revwalk/ObjectWalk.java" type="org.eclipse.jgit.revwalk.ObjectWalk">
+        <filter id="421654647">
             <message_arguments>
-                <message_argument value="org.eclipse.jgit.storage.pack.PackStatistics.Accumulator"/>
-                <message_argument value="notAdvertisedWants"/>
+                <message_argument value="org.eclipse.jgit.revwalk.ObjectWalk"/>
+                <message_argument value="createObjectReachabilityChecker()"/>
             </message_arguments>
         </filter>
-        <filter id="336658481">
+    </resource>
+    <resource path="src/org/eclipse/jgit/revwalk/RevWalk.java" type="org.eclipse.jgit.revwalk.RevWalk">
+        <filter id="421654647">
             <message_arguments>
-                <message_argument value="org.eclipse.jgit.storage.pack.PackStatistics.Accumulator"/>
-                <message_argument value="reachabilityCheckDuration"/>
+                <message_argument value="org.eclipse.jgit.revwalk.RevWalk"/>
+                <message_argument value="createReachabilityChecker()"/>
             </message_arguments>
         </filter>
     </resource>
-    <resource path="src/org/eclipse/jgit/transport/HttpConfig.java" type="org.eclipse.jgit.transport.HttpConfig">
-        <filter id="336658481">
+    <resource path="src/org/eclipse/jgit/util/FS.java" type="org.eclipse.jgit.util.FS">
+        <filter id="338792546">
             <message_arguments>
-                <message_argument value="org.eclipse.jgit.transport.HttpConfig"/>
-                <message_argument value="EXTRA_HEADER"/>
+                <message_argument value="org.eclipse.jgit.util.FS"/>
+                <message_argument value="internalRunHookIfPresent(Repository, String, String[], PrintStream, PrintStream, String)"/>
             </message_arguments>
         </filter>
-        <filter id="336658481">
+        <filter id="338792546">
+            <message_arguments>
+                <message_argument value="org.eclipse.jgit.util.FS"/>
+                <message_argument value="runHookIfPresent(Repository, String, String[], PrintStream, PrintStream, String)"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/jgit/util/FS_POSIX.java" type="org.eclipse.jgit.util.FS_POSIX">
+        <filter id="338792546">
+            <message_arguments>
+                <message_argument value="org.eclipse.jgit.util.FS_POSIX"/>
+                <message_argument value="runHookIfPresent(Repository, String, String[], PrintStream, PrintStream, String)"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/jgit/util/FS_Win32_Cygwin.java" type="org.eclipse.jgit.util.FS_Win32_Cygwin">
+        <filter id="338792546">
             <message_arguments>
-                <message_argument value="org.eclipse.jgit.transport.HttpConfig"/>
-                <message_argument value="USER_AGENT"/>
+                <message_argument value="org.eclipse.jgit.util.FS_Win32_Cygwin"/>
+                <message_argument value="runHookIfPresent(Repository, String, String[], PrintStream, PrintStream, String)"/>
             </message_arguments>
         </filter>
     </resource>
diff --git a/org.eclipse.jgit/BUILD b/org.eclipse.jgit/BUILD
index 2083372248..04873b0c72 100644
--- a/org.eclipse.jgit/BUILD
+++ b/org.eclipse.jgit/BUILD
@@ -38,7 +38,7 @@ genrule(
         "cd $$TMP",
         "unzip -q $$ROOT/$<",
         "echo \"Implementation-Version: $$GEN_VERSION\n$$(cat META-INF/MANIFEST.MF)\" > META-INF/MANIFEST.MF",
-        "find . -exec touch '{}' ';'",
+        "find . -exec touch -t 198001010000 '{}' ';'",
         "zip -Xqr $$ROOT/$@ .",
         "rm -rf $$TMP",
     ]),
diff --git a/org.eclipse.jgit/META-INF/MANIFEST.MF b/org.eclipse.jgit/META-INF/MANIFEST.MF
index 403b8eed0f..d755f83626 100644
--- a/org.eclipse.jgit/META-INF/MANIFEST.MF
+++ b/org.eclipse.jgit/META-INF/MANIFEST.MF
@@ -72,11 +72,8 @@ Export-Package: org.eclipse.jgit.annotations;version="6.0.0",
    org.eclipse.jgit.http.test",
  org.eclipse.jgit.internal.fsck;version="6.0.0";
   x-friends:="org.eclipse.jgit.test",
- org.eclipse.jgit.internal.ketch;version="6.0.0";
-  x-friends:="org.eclipse.jgit.junit,
-   org.eclipse.jgit.test,
-   org.eclipse.jgit.pgm",
- org.eclipse.jgit.internal.revwalk;version="6.0.0";x-internal:=true,
+ org.eclipse.jgit.internal.revwalk;version="6.0.0";
+  x-friends:="org.eclipse.jgit.test",
  org.eclipse.jgit.internal.storage.dfs;version="6.0.0";
   x-friends:="org.eclipse.jgit.test,
    org.eclipse.jgit.http.server,
@@ -104,10 +101,6 @@ Export-Package: org.eclipse.jgit.annotations;version="6.0.0",
    org.eclipse.jgit.junit,
    org.eclipse.jgit.test,
    org.eclipse.jgit.pgm",
- org.eclipse.jgit.internal.storage.reftree;version="6.0.0";
-  x-friends:="org.eclipse.jgit.junit,
-   org.eclipse.jgit.test,
-   org.eclipse.jgit.pgm",
  org.eclipse.jgit.internal.submodule;version="6.0.0";x-internal:=true,
  org.eclipse.jgit.internal.transport.connectivity;version="6.0.0";
   x-friends:="org.eclipse.jgit.test",
diff --git a/org.eclipse.jgit/META-INF/SOURCE-MANIFEST.MF b/org.eclipse.jgit/META-INF/SOURCE-MANIFEST.MF
index e1904d5d3f..134cbacbee 100644
--- a/org.eclipse.jgit/META-INF/SOURCE-MANIFEST.MF
+++ b/org.eclipse.jgit/META-INF/SOURCE-MANIFEST.MF
@@ -5,4 +5,3 @@ Bundle-SymbolicName: org.eclipse.jgit.source
 Bundle-Vendor: Eclipse.org - JGit
 Bundle-Version: 6.0.0.qualifier
 Eclipse-SourceBundle: org.eclipse.jgit;version="6.0.0.qualifier";roots="."
-
diff --git a/org.eclipse.jgit/findBugs/FindBugsExcludeFilter.xml b/org.eclipse.jgit/findBugs/FindBugsExcludeFilter.xml
index 2efbb9c1a5..73a6685564 100644
--- a/org.eclipse.jgit/findBugs/FindBugsExcludeFilter.xml
+++ b/org.eclipse.jgit/findBugs/FindBugsExcludeFilter.xml
@@ -9,6 +9,12 @@
        <Bug pattern="DM_GC" />
      </Match>
 
+     <Match>
+       <Class name="org.eclipse.jgit.internal.storage.pack.PackOutputStream" />
+       <Method name="writeHeader" />
+       <Bug pattern="NS_DANGEROUS_NON_SHORT_CIRCUIT" />
+     </Match>
+
      <!-- Silence ignoring return value of mkdirs -->
      <Match>
        <Class name="org.eclipse.jgit.dircache.DirCacheCheckout" />
@@ -19,8 +25,26 @@
 	   <!-- Silence the construction of our magic String instance.
 	     -->
      <Match>
-	 <Class name="org.eclipse.jgit.lib.Config" />
-	 <Bug pattern="DM_STRING_VOID_CTOR"/>
+       <Class name="org.eclipse.jgit.lib.Config" />
+       <Bug pattern="DM_STRING_VOID_CTOR"/>
+     </Match>
+
+     <Match>
+       <Class name="org.eclipse.jgit.lib.Config" />
+       <Method name="isMissing" />
+       <Bug pattern="ES_COMPARING_PARAMETER_STRING_WITH_EQ"/>
+     </Match>
+
+     <Match>
+       <Class name="org.eclipse.jgit.transport.PacketLineIn" />
+       <Method name="isDelimiter" />
+       <Bug pattern="ES_COMPARING_PARAMETER_STRING_WITH_EQ"/>
+     </Match>
+
+     <Match>
+       <Class name="org.eclipse.jgit.transport.PacketLineIn" />
+       <Method name="isEnd" />
+       <Bug pattern="ES_COMPARING_PARAMETER_STRING_WITH_EQ"/>
      </Match>
 
      <!-- Silence comparison of string by == or !=.  This class is built
@@ -53,6 +77,12 @@
        <Bug pattern="NP_BOOLEAN_RETURN_NULL" />
      </Match>
 
+     <Match>
+       <Class name="org.eclipse.jgit.ignore.IgnoreNode" />
+       <Method name="checkIgnored" />
+       <Bug pattern="NP_BOOLEAN_RETURN_NULL" />
+     </Match>
+
      <!-- Transport initialization works like this -->
      <Match>
        <Class name="org.eclipse.jgit.transport.Transport" />
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
index 12902b9004..c00203dd07 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -30,6 +30,8 @@ badEntryDelimiter=Bad entry delimiter
 badEntryName=Bad entry name: {0}
 badEscape=Bad escape: {0}
 badGroupHeader=Bad group header
+badIgnorePattern=Cannot parse .gitignore pattern ''{0}''
+badIgnorePatternFull=File {0} line {1}: cannot parse pattern ''{2}'': {3}
 badObjectType=Bad object type: {0}
 badRef=Bad ref: {0}: {1}
 badSectionEntry=Bad section entry: {0}
@@ -233,6 +235,7 @@ downloadCancelled=Download cancelled
 downloadCancelledDuringIndexing=Download cancelled during indexing
 duplicateAdvertisementsOf=duplicate advertisements of {0}
 duplicateRef=Duplicate ref: {0}
+duplicateRefAttribute=Duplicate ref attribute: {0}
 duplicateRemoteRefUpdateIsIllegal=Duplicate remote ref update is illegal. Affected remote name: {0}
 duplicateStagesNotAllowed=Duplicate stages not allowed
 eitherGitDirOrWorkTreeRequired=One of setGitDir or setWorkTree must be called.
@@ -310,6 +313,10 @@ headRequiredToStash=HEAD required to stash local changes
 hoursAgo={0} hours ago
 httpConfigCannotNormalizeURL=Cannot normalize URL path {0}: too many .. segments
 httpConfigInvalidURL=Cannot parse URL from subsection http.{0} in git config; ignored.
+httpFactoryInUse=Changing the HTTP connection factory after an HTTP connection has already been opened is not allowed.
+httpPreAuthTooLate=HTTP Basic preemptive authentication cannot be set once an HTTP connection has already been opened.
+httpUserInfoDecodeError=Cannot decode user info from URL {}; ignored.
+httpWrongConnectionType=Wrong connection type: expected {0}, got {1}.
 hugeIndexesAreNotSupportedByJgitYet=Huge indexes are not supported by jgit, yet
 hunkBelongsToAnotherFile=Hunk belongs to another file
 hunkDisconnectedFromFile=Hunk disconnected from file
@@ -563,6 +570,7 @@ refNotResolved=Ref {0} cannot be resolved
 reftableDirExists=reftable dir exists and is nonempty
 reftableRecordsMustIncrease=records must be increasing: last {0}, this {1}
 refUpdateReturnCodeWas=RefUpdate return code was: {0}
+remoteBranchNotFound=Remote branch ''{0}'' not found in upstream origin
 remoteConfigHasNoURIAssociated=Remote config "{0}" has no URIs associated
 remoteDoesNotHaveSpec=Remote does not have {0} available for fetch.
 remoteDoesNotSupportSmartHTTPPush=remote does not support smart HTTP push
@@ -617,7 +625,9 @@ shortCompressedStreamAt=Short compressed stream at {0}
 shortReadOfBlock=Short read of block.
 shortReadOfOptionalDIRCExtensionExpectedAnotherBytes=Short read of optional DIRC extension {0}; expected another {1} bytes within the section.
 shortSkipOfBlock=Short skip of block.
-signingNotSupportedOnTag=Signing isn't supported on tag operations yet.
+signatureVerificationError=Signature verification failed
+signatureVerificationUnavailable=No signature verifier registered
+signedTagMessageNoLf=A non-empty message of a signed tag must end in LF.
 signingServiceUnavailable=Signing service is not available
 similarityScoreMustBeWithinBounds=Similarity score must be between 0 and 100.
 skipMustBeNonNegative=skip must be >= 0
@@ -758,6 +768,13 @@ uriNotFoundWithMessage={0} not found: {1}
 URINotSupported=URI not supported: {0}
 userConfigInvalid=Git config in the user's home directory {0} is invalid {1}
 validatingGitModules=Validating .gitmodules files
+verifySignatureBad=BAD signature from "{0}"
+verifySignatureExpired=Expired signature from "{0}"
+verifySignatureGood=Good signature from "{0}"
+verifySignatureIssuer=issuer "{0}"
+verifySignatureKey=using key {0}
+verifySignatureMade=Signature made {0}
+verifySignatureTrust=[{0}]
 walkFailure=Walk failure.
 wantNoSpaceWithCapabilities=No space between oid and first capability in first want line
 wantNotValid=want {0} not valid
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/ketch/KetchText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/ketch/KetchText.properties
deleted file mode 100644
index 1fbb7cb3b5..0000000000
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/ketch/KetchText.properties
+++ /dev/null
@@ -1,13 +0,0 @@
-accepted=accepted.
-cannotFetchFromLocalReplica=cannot fetch from LocalReplica
-failed=failed!
-invalidFollowerUri=invalid follower URI
-leaderFailedToStore=leader failed to store
-localReplicaRequired=LocalReplica instance is required
-mismatchedTxnNamespace=mismatched txnNamespace; expected {0} found {1}
-outsideTxnNamespace=ref {0} is outside of txnNamespace {1}
-proposingUpdates=Proposing updates
-queuedProposalFailedToApply=queued proposal failed to apply
-starting=starting!
-unsupportedVoterCount=unsupported voter count {0}, expected one of {1}
-waitingForQueue=Waiting for queue
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/ArchiveCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/ArchiveCommand.java
index 2c01c19c59..fdf8b80cd4 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/ArchiveCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/ArchiveCommand.java
@@ -19,7 +19,6 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
@@ -202,7 +201,7 @@ public class ArchiveCommand extends GitCommand<OutputStream> {
 	 * Available archival formats (corresponding to values for
 	 * the --format= option)
 	 */
-	private static final ConcurrentMap<String, FormatEntry> formats =
+	private static final Map<String, FormatEntry> formats =
 			new ConcurrentHashMap<>();
 
 	/**
@@ -215,7 +214,7 @@ public class ArchiveCommand extends GitCommand<OutputStream> {
 	 * @param newValue value to be associated with the key (null to remove).
 	 * @return true if the value was replaced
 	 */
-	private static <K, V> boolean replace(ConcurrentMap<K, V> map,
+	private static <K, V> boolean replace(Map<K, V> map,
 			K key, V oldValue, V newValue) {
 		if (oldValue == null && newValue == null) // Nothing to do.
 			return true;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CloneCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CloneCommand.java
index aba86fc361..cf7bc1f263 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CloneCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CloneCommand.java
@@ -297,6 +297,7 @@ public class CloneCommand extends TransportCommand<CloneCommand, Git> {
 			command.setTagOpt(
 					fetchAll ? TagOpt.FETCH_TAGS : TagOpt.AUTO_FOLLOW);
 		}
+		command.setInitialBranch(branch);
 		configure(command);
 
 		return command.call();
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
index b4f7175036..31f6a31c75 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
@@ -47,6 +47,7 @@ import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.GpgConfig;
 import org.eclipse.jgit.lib.GpgConfig.GpgFormat;
+import org.eclipse.jgit.lib.GpgObjectSigner;
 import org.eclipse.jgit.lib.GpgSigner;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
@@ -120,6 +121,8 @@ public class CommitCommand extends GitCommand<RevCommit> {
 
 	private GpgSigner gpgSigner;
 
+	private GpgConfig gpgConfig;
+
 	private CredentialsProvider credentialsProvider;
 
 	/**
@@ -247,8 +250,18 @@ public class CommitCommand extends GitCommand<RevCommit> {
 						throw new ServiceUnavailableException(
 								JGitText.get().signingServiceUnavailable);
 					}
-					gpgSigner.sign(commit, signingKey, committer,
-							credentialsProvider);
+					if (gpgSigner instanceof GpgObjectSigner) {
+						((GpgObjectSigner) gpgSigner).signObject(commit,
+								signingKey, committer, credentialsProvider,
+								gpgConfig);
+					} else {
+						if (gpgConfig.getKeyFormat() != GpgFormat.OPENPGP) {
+							throw new UnsupportedSigningFormatException(JGitText
+									.get().onlyOpenPgpSupportedForSigning);
+						}
+						gpgSigner.sign(commit, signingKey, committer,
+								credentialsProvider);
+					}
 				}
 
 				ObjectId commitId = odi.insert(commit);
@@ -576,7 +589,9 @@ public class CommitCommand extends GitCommand<RevCommit> {
 			// an explicit message
 			throw new NoMessageException(JGitText.get().commitMessageNotSpecified);
 
-		GpgConfig gpgConfig = new GpgConfig(repo.getConfig());
+		if (gpgConfig == null) {
+			gpgConfig = new GpgConfig(repo.getConfig());
+		}
 		if (signCommit == null) {
 			signCommit = gpgConfig.isSignCommits() ? Boolean.TRUE
 					: Boolean.FALSE;
@@ -585,10 +600,6 @@ public class CommitCommand extends GitCommand<RevCommit> {
 			signingKey = gpgConfig.getSigningKey();
 		}
 		if (gpgSigner == null) {
-			if (gpgConfig.getKeyFormat() != GpgFormat.OPENPGP) {
-				throw new UnsupportedSigningFormatException(
-						JGitText.get().onlyOpenPgpSupportedForSigning);
-			}
 			gpgSigner = GpgSigner.getDefault();
 		}
 	}
@@ -973,6 +984,36 @@ public class CommitCommand extends GitCommand<RevCommit> {
 	}
 
 	/**
+	 * Sets the {@link GpgSigner} to use if the commit is to be signed.
+	 *
+	 * @param signer
+	 *            to use; if {@code null}, the default signer will be used
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public CommitCommand setGpgSigner(GpgSigner signer) {
+		checkCallable();
+		this.gpgSigner = signer;
+		return this;
+	}
+
+	/**
+	 * Sets an external {@link GpgConfig} to use. Whether it will be used is at
+	 * the discretion of the {@link #setGpgSigner(GpgSigner)}.
+	 *
+	 * @param config
+	 *            to set; if {@code null}, the config will be loaded from the
+	 *            git config of the repository
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public CommitCommand setGpgConfig(GpgConfig config) {
+		checkCallable();
+		this.gpgConfig = config;
+		return this;
+	}
+
+	/**
 	 * Sets a {@link CredentialsProvider}
 	 *
 	 * @param credentialsProvider
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/FetchCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/FetchCommand.java
index 033dd60c3b..90c1515b06 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/FetchCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/FetchCommand.java
@@ -74,6 +74,8 @@ public class FetchCommand extends TransportCommand<FetchCommand, FetchResult> {
 
 	private boolean isForceUpdate;
 
+	private String initialBranch;
+
 	/**
 	 * Callback for status of fetch operation.
 	 *
@@ -209,7 +211,7 @@ public class FetchCommand extends TransportCommand<FetchCommand, FetchResult> {
 			transport.setFetchThin(thin);
 			configure(transport);
 			FetchResult result = transport.fetch(monitor,
-					applyOptions(refSpecs));
+					applyOptions(refSpecs), initialBranch);
 			if (!repo.isBare()) {
 				fetchSubmodules(result);
 			}
@@ -488,6 +490,24 @@ public class FetchCommand extends TransportCommand<FetchCommand, FetchResult> {
 	}
 
 	/**
+	 * Set the initial branch
+	 *
+	 * @param branch
+	 *            the initial branch to check out when cloning the repository.
+	 *            Can be specified as ref name (<code>refs/heads/master</code>),
+	 *            branch name (<code>master</code>) or tag name
+	 *            (<code>v1.2.3</code>). The default is to use the branch
+	 *            pointed to by the cloned repository's HEAD and can be
+	 *            requested by passing {@code null} or <code>HEAD</code>.
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public FetchCommand setInitialBranch(String branch) {
+		this.initialBranch = branch;
+		return this;
+	}
+
+	/**
 	 * Register a progress callback.
 	 *
 	 * @param callback
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
index 64314772b7..3b3e10e7b2 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2010, Christian Halstrick <christian.halstrick@sap.com>
- * Copyright (C) 2010, Chris Aniszczyk <caniszczyk@gmail.com> and others
+ * Copyright (C) 2010, 2021 Chris Aniszczyk <caniszczyk@gmail.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -773,6 +773,16 @@ public class Git implements AutoCloseable {
 	}
 
 	/**
+	 * Return a command to verify signatures of tags or commits.
+	 *
+	 * @return a {@link VerifySignatureCommand}
+	 * @since 5.11
+	 */
+	public VerifySignatureCommand verifySignature() {
+		return new VerifySignatureCommand(repo);
+	}
+
+	/**
 	 * Get repository
 	 *
 	 * @return the git repository this class is interacting with; see
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/InitCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/InitCommand.java
index 41fcf29ed0..240290f4f9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/InitCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/InitCommand.java
@@ -15,12 +15,16 @@ import java.text.MessageFormat;
 import java.util.concurrent.Callable;
 
 import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.api.errors.InvalidRefNameException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryBuilder;
 import org.eclipse.jgit.util.FS;
+import org.eclipse.jgit.util.StringUtils;
 import org.eclipse.jgit.util.SystemReader;
 
 /**
@@ -38,6 +42,8 @@ public class InitCommand implements Callable<Git> {
 
 	private FS fs;
 
+	private String initialBranch;
+
 	/**
 	 * {@inheritDoc}
 	 * <p>
@@ -87,11 +93,16 @@ public class InitCommand implements Callable<Git> {
 					builder.setWorkTree(new File(dStr));
 				}
 			}
+			builder.setInitialBranch(StringUtils.isEmptyOrNull(initialBranch)
+					? SystemReader.getInstance().getUserConfig().getString(
+							ConfigConstants.CONFIG_INIT_SECTION, null,
+							ConfigConstants.CONFIG_KEY_DEFAULT_BRANCH)
+					: initialBranch);
 			Repository repository = builder.build();
 			if (!repository.getObjectDatabase().exists())
 				repository.create(bare);
 			return new Git(repository, true);
-		} catch (IOException e) {
+		} catch (IOException | ConfigInvalidException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		}
 	}
@@ -184,4 +195,23 @@ public class InitCommand implements Callable<Git> {
 		this.fs = fs;
 		return this;
 	}
+
+	/**
+	 * Set the initial branch of the new repository. If not specified
+	 * ({@code null} or empty), fall back to the default name (currently
+	 * master).
+	 *
+	 * @param branch
+	 *            initial branch name of the new repository
+	 * @return {@code this}
+	 * @throws InvalidRefNameException
+	 *             if the branch name is not valid
+	 *
+	 * @since 5.11
+	 */
+	public InitCommand setInitialBranch(String branch)
+			throws InvalidRefNameException {
+		this.initialBranch = branch;
+		return this;
+	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/LsRemoteCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/LsRemoteCommand.java
index a4ca309095..0c691062f9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/LsRemoteCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/LsRemoteCommand.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2011, Christoph Brill <egore911@egore911.de> and others
+ * Copyright (C) 2011, 2020 Christoph Brill <egore911@egore911.de> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -164,7 +164,7 @@ public class LsRemoteCommand extends
 				refSpecs.add(new RefSpec("refs/heads/*:refs/remotes/origin/*")); //$NON-NLS-1$
 			Collection<Ref> refs;
 			Map<String, Ref> refmap = new HashMap<>();
-			try (FetchConnection fc = transport.openFetch()) {
+			try (FetchConnection fc = transport.openFetch(refSpecs)) {
 				refs = fc.getRefs();
 				if (refSpecs.isEmpty())
 					for (Ref r : refs)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/RebaseCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/RebaseCommand.java
index 6678af163a..836175dcea 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/RebaseCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/RebaseCommand.java
@@ -67,6 +67,7 @@ import org.eclipse.jgit.lib.RefUpdate.Result;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.merge.MergeStrategy;
 import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevSort;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.revwalk.filter.RevFilter;
 import org.eclipse.jgit.submodule.SubmoduleWalk.IgnoreSubmoduleMode;
@@ -1137,15 +1138,19 @@ public class RebaseCommand extends GitCommand<RebaseResult> {
 
 	private List<RevCommit> calculatePickList(RevCommit headCommit)
 			throws GitAPIException, NoHeadException, IOException {
-		Iterable<RevCommit> commitsToUse;
-		try (Git git = new Git(repo)) {
-			LogCommand cmd = git.log().addRange(upstreamCommit, headCommit);
-			commitsToUse = cmd.call();
-		}
 		List<RevCommit> cherryPickList = new ArrayList<>();
-		for (RevCommit commit : commitsToUse) {
-			if (preserveMerges || commit.getParentCount() == 1)
-				cherryPickList.add(commit);
+		try (RevWalk r = new RevWalk(repo)) {
+			r.sort(RevSort.TOPO_KEEP_BRANCH_TOGETHER, true);
+			r.sort(RevSort.COMMIT_TIME_DESC, true);
+			r.markUninteresting(r.lookupCommit(upstreamCommit));
+			r.markStart(r.lookupCommit(headCommit));
+			Iterator<RevCommit> commitsToUse = r.iterator();
+			while (commitsToUse.hasNext()) {
+				RevCommit commit = commitsToUse.next();
+				if (preserveMerges || commit.getParentCount() == 1) {
+					cherryPickList.add(commit);
+				}
+			}
 		}
 		Collections.reverse(cherryPickList);
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/TagCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/TagCommand.java
index 9a328a6eaa..58c18b38d1 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/TagCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/TagCommand.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, 2013 Chris Aniszczyk <caniszczyk@gmail.com> and others
+ * Copyright (C) 2010, 2020 Chris Aniszczyk <caniszczyk@gmail.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -18,8 +18,14 @@ import org.eclipse.jgit.api.errors.InvalidTagNameException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
 import org.eclipse.jgit.api.errors.NoHeadException;
 import org.eclipse.jgit.api.errors.RefAlreadyExistsException;
+import org.eclipse.jgit.api.errors.ServiceUnavailableException;
+import org.eclipse.jgit.api.errors.UnsupportedSigningFormatException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.GpgConfig;
+import org.eclipse.jgit.lib.GpgConfig.GpgFormat;
+import org.eclipse.jgit.lib.GpgObjectSigner;
+import org.eclipse.jgit.lib.GpgSigner;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.PersonIdent;
@@ -31,6 +37,7 @@ import org.eclipse.jgit.lib.RepositoryState;
 import org.eclipse.jgit.lib.TagBuilder;
 import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.transport.CredentialsProvider;
 
 /**
  * Create/update an annotated tag object or a simple unannotated tag
@@ -56,6 +63,7 @@ import org.eclipse.jgit.revwalk.RevWalk;
  *      >Git documentation about Tag</a>
  */
 public class TagCommand extends GitCommand<Ref> {
+
 	private RevObject id;
 
 	private String name;
@@ -64,11 +72,19 @@ public class TagCommand extends GitCommand<Ref> {
 
 	private PersonIdent tagger;
 
-	private boolean signed;
+	private Boolean signed;
 
 	private boolean forceUpdate;
 
-	private boolean annotated = true;
+	private Boolean annotated;
+
+	private String signingKey;
+
+	private GpgConfig gpgConfig;
+
+	private GpgObjectSigner gpgSigner;
+
+	private CredentialsProvider credentialsProvider;
 
 	/**
 	 * <p>Constructor for TagCommand.</p>
@@ -77,6 +93,7 @@ public class TagCommand extends GitCommand<Ref> {
 	 */
 	protected TagCommand(Repository repo) {
 		super(repo);
+		this.credentialsProvider = CredentialsProvider.getDefault();
 	}
 
 	/**
@@ -108,10 +125,7 @@ public class TagCommand extends GitCommand<Ref> {
 				id = revWalk.parseCommit(objectId);
 			}
 
-			if (!annotated) {
-				if (message != null || tagger != null)
-					throw new JGitInternalException(
-							JGitText.get().messageAndTaggerNotAllowedInUnannotatedTags);
+			if (!isAnnotated()) {
 				return updateTagRef(id, revWalk, name,
 						"SimpleTag[" + name + " : " + id //$NON-NLS-1$ //$NON-NLS-2$
 								+ "]"); //$NON-NLS-1$
@@ -124,6 +138,11 @@ public class TagCommand extends GitCommand<Ref> {
 			newTag.setTagger(tagger);
 			newTag.setObjectId(id);
 
+			if (gpgSigner != null) {
+				gpgSigner.signObject(newTag, signingKey, tagger,
+						credentialsProvider, gpgConfig);
+			}
+
 			// write the tag object
 			try (ObjectInserter inserter = repo.newObjectInserter()) {
 				ObjectId tagId = inserter.insert(newTag);
@@ -158,9 +177,17 @@ public class TagCommand extends GitCommand<Ref> {
 			throw new ConcurrentRefUpdateException(
 					JGitText.get().couldNotLockHEAD, tagRef.getRef(),
 					updateResult);
+		case NO_CHANGE:
+			if (forceUpdate) {
+				return repo.exactRef(refName);
+			}
+			throw new RefAlreadyExistsException(MessageFormat
+					.format(JGitText.get().tagAlreadyExists, newTagToString),
+					updateResult);
 		case REJECTED:
 			throw new RefAlreadyExistsException(MessageFormat.format(
-					JGitText.get().tagAlreadyExists, newTagToString));
+					JGitText.get().tagAlreadyExists, newTagToString),
+					updateResult);
 		default:
 			throw new JGitInternalException(MessageFormat.format(
 					JGitText.get().updatingRefFailed, refName, newTagToString,
@@ -177,20 +204,60 @@ public class TagCommand extends GitCommand<Ref> {
 	 *
 	 * @throws InvalidTagNameException
 	 *             if the tag name is null or invalid
-	 * @throws UnsupportedOperationException
-	 *             if the tag is signed (not supported yet)
+	 * @throws ServiceUnavailableException
+	 *             if the tag should be signed but no signer can be found
+	 * @throws UnsupportedSigningFormatException
+	 *             if the tag should be signed but {@code gpg.format} is not
+	 *             {@link GpgFormat#OPENPGP}
 	 */
 	private void processOptions(RepositoryState state)
-			throws InvalidTagNameException {
-		if (tagger == null && annotated)
-			tagger = new PersonIdent(repo);
-		if (name == null || !Repository.isValidRefName(Constants.R_TAGS + name))
+			throws InvalidTagNameException, ServiceUnavailableException,
+			UnsupportedSigningFormatException {
+		if (name == null
+				|| !Repository.isValidRefName(Constants.R_TAGS + name)) {
 			throw new InvalidTagNameException(
 					MessageFormat.format(JGitText.get().tagNameInvalid,
 							name == null ? "<null>" : name)); //$NON-NLS-1$
-		if (signed)
-			throw new UnsupportedOperationException(
-					JGitText.get().signingNotSupportedOnTag);
+		}
+		if (!isAnnotated()) {
+			if ((message != null && !message.isEmpty()) || tagger != null) {
+				throw new JGitInternalException(JGitText
+						.get().messageAndTaggerNotAllowedInUnannotatedTags);
+			}
+		} else {
+			if (tagger == null) {
+				tagger = new PersonIdent(repo);
+			}
+			// Figure out whether to sign.
+			if (!(Boolean.FALSE.equals(signed) && signingKey == null)) {
+				if (gpgConfig == null) {
+					gpgConfig = new GpgConfig(repo.getConfig());
+				}
+				boolean doSign = isSigned() || gpgConfig.isSignAllTags();
+				if (!Boolean.TRUE.equals(annotated) && !doSign) {
+					doSign = gpgConfig.isSignAnnotated();
+				}
+				if (doSign) {
+					if (signingKey == null) {
+						signingKey = gpgConfig.getSigningKey();
+					}
+					if (gpgSigner == null) {
+						GpgSigner signer = GpgSigner.getDefault();
+						if (!(signer instanceof GpgObjectSigner)) {
+							throw new ServiceUnavailableException(
+									JGitText.get().signingServiceUnavailable);
+						}
+						gpgSigner = (GpgObjectSigner) signer;
+					}
+					// The message of a signed tag must end in a newline because
+					// the signature will be appended.
+					if (message != null && !message.isEmpty()
+							&& !message.endsWith("\n")) { //$NON-NLS-1$
+						message += '\n';
+					}
+				}
+			}
+		}
 	}
 
 	/**
@@ -238,24 +305,61 @@ public class TagCommand extends GitCommand<Ref> {
 	}
 
 	/**
-	 * Whether this tag is signed
+	 * Whether {@link #setSigned(boolean) setSigned(true)} has been called or
+	 * whether a {@link #setSigningKey(String) signing key ID} has been set;
+	 * i.e., whether -s or -u was specified explicitly.
 	 *
 	 * @return whether the tag is signed
 	 */
 	public boolean isSigned() {
-		return signed;
+		return Boolean.TRUE.equals(signed) || signingKey != null;
 	}
 
 	/**
 	 * If set to true the Tag command creates a signed tag object. This
-	 * corresponds to the parameter -s on the command line.
+	 * corresponds to the parameter -s (--sign or --no-sign) on the command
+	 * line.
+	 * <p>
+	 * If {@code true}, the tag will be a signed annotated tag.
+	 * </p>
 	 *
 	 * @param signed
-	 *            a boolean.
+	 *            whether to sign
 	 * @return {@code this}
 	 */
 	public TagCommand setSigned(boolean signed) {
-		this.signed = signed;
+		checkCallable();
+		this.signed = Boolean.valueOf(signed);
+		return this;
+	}
+
+	/**
+	 * Sets the {@link GpgSigner} to use if the commit is to be signed.
+	 *
+	 * @param signer
+	 *            to use; if {@code null}, the default signer will be used
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public TagCommand setGpgSigner(GpgObjectSigner signer) {
+		checkCallable();
+		this.gpgSigner = signer;
+		return this;
+	}
+
+	/**
+	 * Sets an external {@link GpgConfig} to use. Whether it will be used is at
+	 * the discretion of the {@link #setGpgSigner(GpgObjectSigner)}.
+	 *
+	 * @param config
+	 *            to set; if {@code null}, the config will be loaded from the
+	 *            git config of the repository
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public TagCommand setGpgConfig(GpgConfig config) {
+		checkCallable();
+		this.gpgConfig = config;
 		return this;
 	}
 
@@ -268,6 +372,7 @@ public class TagCommand extends GitCommand<Ref> {
 	 * @return {@code this}
 	 */
 	public TagCommand setTagger(PersonIdent tagger) {
+		checkCallable();
 		this.tagger = tagger;
 		return this;
 	}
@@ -291,14 +396,15 @@ public class TagCommand extends GitCommand<Ref> {
 	}
 
 	/**
-	 * Sets the object id of the tag. If the object id is null, the commit
-	 * pointed to from HEAD will be used.
+	 * Sets the object id of the tag. If the object id is {@code null}, the
+	 * commit pointed to from HEAD will be used.
 	 *
 	 * @param id
 	 *            a {@link org.eclipse.jgit.revwalk.RevObject} object.
 	 * @return {@code this}
 	 */
 	public TagCommand setObjectId(RevObject id) {
+		checkCallable();
 		this.id = id;
 		return this;
 	}
@@ -321,6 +427,7 @@ public class TagCommand extends GitCommand<Ref> {
 	 * @return {@code this}
 	 */
 	public TagCommand setForceUpdate(boolean forceUpdate) {
+		checkCallable();
 		this.forceUpdate = forceUpdate;
 		return this;
 	}
@@ -334,18 +441,77 @@ public class TagCommand extends GitCommand<Ref> {
 	 * @since 3.0
 	 */
 	public TagCommand setAnnotated(boolean annotated) {
-		this.annotated = annotated;
+		checkCallable();
+		this.annotated = Boolean.valueOf(annotated);
 		return this;
 	}
 
 	/**
-	 * Whether this will create an annotated command
+	 * Whether this will create an annotated tag.
 	 *
 	 * @return true if this command will create an annotated tag (default is
 	 *         true)
 	 * @since 3.0
 	 */
 	public boolean isAnnotated() {
-		return annotated;
+		boolean setExplicitly = Boolean.TRUE.equals(annotated) || isSigned();
+		if (setExplicitly) {
+			return true;
+		}
+		// Annotated at default (not set explicitly)
+		return annotated == null;
 	}
+
+	/**
+	 * Sets the signing key.
+	 * <p>
+	 * Per spec of {@code user.signingKey}: this will be sent to the GPG program
+	 * as is, i.e. can be anything supported by the GPG program.
+	 * </p>
+	 * <p>
+	 * Note, if none was set or {@code null} is specified a default will be
+	 * obtained from the configuration.
+	 * </p>
+	 * <p>
+	 * If set to a non-{@code null} value, the tag will be a signed annotated
+	 * tag.
+	 * </p>
+	 *
+	 * @param signingKey
+	 *            signing key; {@code null} allowed
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public TagCommand setSigningKey(String signingKey) {
+		checkCallable();
+		this.signingKey = signingKey;
+		return this;
+	}
+
+	/**
+	 * Retrieves the signing key ID.
+	 *
+	 * @return the key ID set, or {@code null} if none is set
+	 * @since 5.11
+	 */
+	public String getSigningKey() {
+		return signingKey;
+	}
+
+	/**
+	 * Sets a {@link CredentialsProvider}
+	 *
+	 * @param credentialsProvider
+	 *            the provider to use when querying for credentials (eg., during
+	 *            signing)
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public TagCommand setCredentialsProvider(
+			CredentialsProvider credentialsProvider) {
+		checkCallable();
+		this.credentialsProvider = credentialsProvider;
+		return this;
+	}
+
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/VerificationResult.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/VerificationResult.java
new file mode 100644
index 0000000000..21cddf75b7
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/VerificationResult.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.api;
+
+import org.eclipse.jgit.lib.GpgSignatureVerifier;
+import org.eclipse.jgit.revwalk.RevObject;
+
+/**
+ * A {@code VerificationResult} describes the outcome of a signature
+ * verification.
+ *
+ * @see VerifySignatureCommand
+ *
+ * @since 5.11
+ */
+public interface VerificationResult {
+
+	/**
+	 * If an error occurred during signature verification, this retrieves the
+	 * exception.
+	 *
+	 * @return the exception, or {@code null} if none occurred
+	 */
+	Throwable getException();
+
+	/**
+	 * Retrieves the signature verification result.
+	 *
+	 * @return the result, or {@code null} if none was computed
+	 */
+	GpgSignatureVerifier.SignatureVerification getVerification();
+
+	/**
+	 * Retrieves the git object of which the signature was verified.
+	 *
+	 * @return the git object
+	 */
+	RevObject getObject();
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/VerifySignatureCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/VerifySignatureCommand.java
new file mode 100644
index 0000000000..6a2a44ea2d
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/VerifySignatureCommand.java
@@ -0,0 +1,307 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.api;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.api.errors.ServiceUnavailableException;
+import org.eclipse.jgit.api.errors.WrongObjectTypeException;
+import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.GpgConfig;
+import org.eclipse.jgit.lib.GpgSignatureVerifier;
+import org.eclipse.jgit.lib.GpgSignatureVerifier.SignatureVerification;
+import org.eclipse.jgit.lib.GpgSignatureVerifierFactory;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevObject;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+/**
+ * A command to verify GPG signatures on tags or commits.
+ *
+ * @since 5.11
+ */
+public class VerifySignatureCommand extends GitCommand<Map<String, VerificationResult>> {
+
+	/**
+	 * Describes what kind of objects shall be handled by a
+	 * {@link VerifySignatureCommand}.
+	 */
+	public enum VerifyMode {
+		/**
+		 * Handle any object type, ignore anything that is not a commit or tag.
+		 */
+		ANY,
+		/**
+		 * Handle only commits; throw a {@link WrongObjectTypeException} for
+		 * anything else.
+		 */
+		COMMITS,
+		/**
+		 * Handle only tags; throw a {@link WrongObjectTypeException} for
+		 * anything else.
+		 */
+		TAGS
+	}
+
+	private final Set<String> namesToCheck = new HashSet<>();
+
+	private VerifyMode mode = VerifyMode.ANY;
+
+	private GpgSignatureVerifier verifier;
+
+	private GpgConfig config;
+
+	private boolean ownVerifier;
+
+	/**
+	 * Creates a new {@link VerifySignatureCommand} for the given {@link Repository}.
+	 *
+	 * @param repo
+	 *            to operate on
+	 */
+	public VerifySignatureCommand(Repository repo) {
+		super(repo);
+	}
+
+	/**
+	 * Add a name of an object (SHA-1, ref name; anything that can be
+	 * {@link Repository#resolve(String) resolved}) to the command to have its
+	 * signature verified.
+	 *
+	 * @param name
+	 *            to add
+	 * @return {@code this}
+	 */
+	public VerifySignatureCommand addName(String name) {
+		checkCallable();
+		namesToCheck.add(name);
+		return this;
+	}
+
+	/**
+	 * Add names of objects (SHA-1, ref name; anything that can be
+	 * {@link Repository#resolve(String) resolved}) to the command to have their
+	 * signatures verified.
+	 *
+	 * @param names
+	 *            to add; duplicates will be ignored
+	 * @return {@code this}
+	 */
+	public VerifySignatureCommand addNames(String... names) {
+		checkCallable();
+		namesToCheck.addAll(Arrays.asList(names));
+		return this;
+	}
+
+	/**
+	 * Add names of objects (SHA-1, ref name; anything that can be
+	 * {@link Repository#resolve(String) resolved}) to the command to have their
+	 * signatures verified.
+	 *
+	 * @param names
+	 *            to add; duplicates will be ignored
+	 * @return {@code this}
+	 */
+	public VerifySignatureCommand addNames(Collection<String> names) {
+		checkCallable();
+		namesToCheck.addAll(names);
+		return this;
+	}
+
+	/**
+	 * Sets the mode of operation for this command.
+	 *
+	 * @param mode
+	 *            the {@link VerifyMode} to set
+	 * @return {@code this}
+	 */
+	public VerifySignatureCommand setMode(@NonNull VerifyMode mode) {
+		checkCallable();
+		this.mode = mode;
+		return this;
+	}
+
+	/**
+	 * Sets the {@link GpgSignatureVerifier} to use.
+	 *
+	 * @param verifier
+	 *            the {@link GpgSignatureVerifier} to use, or {@code null} to
+	 *            use the default verifier
+	 * @return {@code this}
+	 */
+	public VerifySignatureCommand setVerifier(GpgSignatureVerifier verifier) {
+		checkCallable();
+		this.verifier = verifier;
+		return this;
+	}
+
+	/**
+	 * Sets an external {@link GpgConfig} to use. Whether it will be used it at
+	 * the discretion of the {@link #setVerifier(GpgSignatureVerifier)}.
+	 *
+	 * @param config
+	 *            to set; if {@code null}, the config will be loaded from the
+	 *            git config of the repository
+	 * @return {@code this}
+	 * @since 5.11
+	 */
+	public VerifySignatureCommand setGpgConfig(GpgConfig config) {
+		checkCallable();
+		this.config = config;
+		return this;
+	}
+
+	/**
+	 * Retrieves the currently set {@link GpgSignatureVerifier}. Can be used
+	 * after a successful {@link #call()} to get the verifier that was used.
+	 *
+	 * @return the {@link GpgSignatureVerifier}
+	 */
+	public GpgSignatureVerifier getVerifier() {
+		return verifier;
+	}
+
+	/**
+	 * {@link Repository#resolve(String) Resolves} all names added to the
+	 * command to git objects and verifies their signature. Non-existing objects
+	 * are ignored.
+	 * <p>
+	 * Depending on the {@link #setMode(VerifyMode)}, only tags or commits or
+	 * any kind of objects are allowed.
+	 * </p>
+	 * <p>
+	 * Unsigned objects are silently skipped.
+	 * </p>
+	 *
+	 * @return a map of the given names to the corresponding
+	 *         {@link VerificationResult}, excluding ignored or skipped objects.
+	 * @throws ServiceUnavailableException
+	 *             if no {@link GpgSignatureVerifier} was set and no
+	 *             {@link GpgSignatureVerifierFactory} is available
+	 * @throws WrongObjectTypeException
+	 *             if a name resolves to an object of a type not allowed by the
+	 *             {@link #setMode(VerifyMode)} mode
+	 */
+	@Override
+	@NonNull
+	public Map<String, VerificationResult> call()
+			throws ServiceUnavailableException, WrongObjectTypeException {
+		checkCallable();
+		setCallable(false);
+		Map<String, VerificationResult> result = new HashMap<>();
+		if (verifier == null) {
+			GpgSignatureVerifierFactory factory = GpgSignatureVerifierFactory
+					.getDefault();
+			if (factory == null) {
+				throw new ServiceUnavailableException(
+						JGitText.get().signatureVerificationUnavailable);
+			}
+			verifier = factory.getVerifier();
+			ownVerifier = true;
+		}
+		if (config == null) {
+			config = new GpgConfig(repo.getConfig());
+		}
+		try (RevWalk walk = new RevWalk(repo)) {
+			for (String toCheck : namesToCheck) {
+				ObjectId id = repo.resolve(toCheck);
+				if (id != null && !ObjectId.zeroId().equals(id)) {
+					RevObject object;
+					try {
+						object = walk.parseAny(id);
+					} catch (MissingObjectException e) {
+						continue;
+					}
+					VerificationResult verification = verifyOne(object);
+					if (verification != null) {
+						result.put(toCheck, verification);
+					}
+				}
+			}
+		} catch (IOException e) {
+			throw new JGitInternalException(
+					JGitText.get().signatureVerificationError, e);
+		} finally {
+			if (ownVerifier) {
+				verifier.clear();
+			}
+		}
+		return result;
+	}
+
+	private VerificationResult verifyOne(RevObject object)
+			throws WrongObjectTypeException, IOException {
+		int type = object.getType();
+		if (VerifyMode.TAGS.equals(mode) && type != Constants.OBJ_TAG) {
+			throw new WrongObjectTypeException(object, Constants.OBJ_TAG);
+		} else if (VerifyMode.COMMITS.equals(mode)
+				&& type != Constants.OBJ_COMMIT) {
+			throw new WrongObjectTypeException(object, Constants.OBJ_COMMIT);
+		}
+		if (type == Constants.OBJ_COMMIT || type == Constants.OBJ_TAG) {
+			try {
+				GpgSignatureVerifier.SignatureVerification verification = verifier
+						.verifySignature(object, config);
+				if (verification == null) {
+					// Not signed
+					return null;
+				}
+				// Create new result
+				return new Result(object, verification, null);
+			} catch (JGitInternalException e) {
+				return new Result(object, null, e);
+			}
+		}
+		return null;
+	}
+
+	private static class Result implements VerificationResult {
+
+		private final Throwable throwable;
+
+		private final SignatureVerification verification;
+
+		private final RevObject object;
+
+		public Result(RevObject object, SignatureVerification verification,
+				Throwable throwable) {
+			this.object = object;
+			this.verification = verification;
+			this.throwable = throwable;
+		}
+
+		@Override
+		public Throwable getException() {
+			return throwable;
+		}
+
+		@Override
+		public SignatureVerification getVerification() {
+			return verification;
+		}
+
+		@Override
+		public RevObject getObject() {
+			return object;
+		}
+
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/RefAlreadyExistsException.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/RefAlreadyExistsException.java
index 7e39361eff..81b7bd84cb 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/RefAlreadyExistsException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/RefAlreadyExistsException.java
@@ -1,42 +1,17 @@
 /*
- * Copyright (C) 2010,Mathias Kinzler <mathias.kinzler@sap.com> and
- * other copyright owners as documented in the project's IP log.
+ * Copyright (C) 2010, 2020 Mathias Kinzler <mathias.kinzler@sap.com> and others
  *
  * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v1.0 which accompanies this
- * distribution, is reproduced below, and is available at
- * http://www.eclipse.org/org/documents/edl-v10.php
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
  *
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are met:
- *
- * - Redistributions of source code must retain the above copyright notice, this
- * list of conditions and the following disclaimer.
- *
- * - Redistributions in binary form must reproduce the above copyright notice,
- * this list of conditions and the following disclaimer in the documentation
- * and/or other materials provided with the distribution.
- *
- * - Neither the name of the Eclipse Foundation, Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from this
- * software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
- * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
+ * SPDX-License-Identifier: BSD-3-Clause
  */
 package org.eclipse.jgit.api.errors;
 
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.lib.RefUpdate;
+
 /**
  * Thrown when trying to create a {@link org.eclipse.jgit.lib.Ref} with the same
  * name as an existing one
@@ -44,13 +19,43 @@ package org.eclipse.jgit.api.errors;
 public class RefAlreadyExistsException extends GitAPIException {
 	private static final long serialVersionUID = 1L;
 
+	private final RefUpdate.Result updateResult;
+
 	/**
-	 * Constructor for RefAlreadyExistsException
+	 * Creates a new instance with the given message.
 	 *
 	 * @param message
 	 *            error message
 	 */
 	public RefAlreadyExistsException(String message) {
+		this(message, null);
+	}
+
+	/**
+	 * Constructor for RefAlreadyExistsException
+	 *
+	 * @param message
+	 *            error message
+	 * @param updateResult
+	 *            that caused the exception; may be {@code null}
+	 * @since 5.11
+	 */
+	public RefAlreadyExistsException(String message,
+			@Nullable RefUpdate.Result updateResult) {
 		super(message);
+		this.updateResult = updateResult;
+	}
+
+	/**
+	 * Retrieves the {@link org.eclipse.jgit.lib.RefUpdate.Result
+	 * RefUpdate.Result} that caused the exception.
+	 *
+	 * @return the {@link org.eclipse.jgit.lib.RefUpdate.Result
+	 *         RefUpdate.Result} or {@code null} if unknown
+	 * @since 5.11
+	 */
+	@Nullable
+	public RefUpdate.Result getUpdateResult() {
+		return updateResult;
 	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/WrongObjectTypeException.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/WrongObjectTypeException.java
new file mode 100644
index 0000000000..f639c2f838
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/errors/WrongObjectTypeException.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.api.errors;
+
+import java.text.MessageFormat;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+
+/**
+ * A given object is not of an expected object type.
+ *
+ * @since 5.11
+ */
+public class WrongObjectTypeException extends GitAPIException {
+
+	private static final long serialVersionUID = 1L;
+
+	private String name;
+
+	private int type;
+
+	/**
+	 * Construct a {@link WrongObjectTypeException} for the specified object id,
+	 * giving the expected type.
+	 *
+	 * @param id
+	 *            {@link ObjectId} of the object with the unexpected type
+	 * @param type
+	 *            expected object type code; see
+	 *            {@link Constants}{@code .OBJ_*}.
+	 */
+	public WrongObjectTypeException(ObjectId id, int type) {
+		super(MessageFormat.format(JGitText.get().objectIsNotA, id.name(),
+				Constants.typeString(type)));
+		this.name = id.name();
+		this.type = type;
+	}
+
+	/**
+	 * Retrieves the name (SHA-1) of the object.
+	 *
+	 * @return the name
+	 */
+	public String getObjectId() {
+		return name;
+	}
+
+	/**
+	 * Retrieves the expected type code. See {@link Constants}{@code .OBJ_*}.
+	 *
+	 * @return the type code
+	 */
+	public int getExpectedType() {
+		return type;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java
index 2698e23035..1c9e9d7f71 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java
@@ -12,6 +12,7 @@ package org.eclipse.jgit.attributes;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -23,7 +24,7 @@ import org.eclipse.jgit.lib.Repository;
  * @since 4.6
  */
 public class FilterCommandRegistry {
-	private static ConcurrentHashMap<String, FilterCommandFactory> filterCommandRegistry = new ConcurrentHashMap<>();
+	private static Map<String, FilterCommandFactory> filterCommandRegistry = new ConcurrentHashMap<>();
 
 	/**
 	 * Register a {@link org.eclipse.jgit.attributes.FilterCommandFactory}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java
index 8c51a7ac2f..671475ed47 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java
@@ -946,12 +946,14 @@ public class DirCacheCheckout {
 				// called before). Ignore the cached deletion and use what we
 				// find in Merge. Potentially updates the file.
 				if (equalIdAndMode(hId, hMode, mId, mMode)) {
-					if (initialCheckout)
+					if (initialCheckout || force) {
 						update(name, mId, mMode);
-					else
+					} else {
 						keep(name, dce, f);
-				} else
+					}
+				} else {
 					conflict(name, dce, h, m);
+				}
 			}
 		} else {
 			// Something in Index
@@ -1214,8 +1216,12 @@ public class DirCacheCheckout {
 
 	private void keep(String path, DirCacheEntry e, WorkingTreeIterator f)
 			throws IOException {
-		if (e != null && !FileMode.TREE.equals(e.getFileMode()))
+		if (e == null) {
+			return;
+		}
+		if (!FileMode.TREE.equals(e.getFileMode())) {
 			builder.add(e);
+		}
 		if (force) {
 			if (f == null || f.isModified(e, true, walk.getObjectReader())) {
 				kept.add(path);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/errors/NoPackSignatureException.java b/org.eclipse.jgit/src/org/eclipse/jgit/errors/NoPackSignatureException.java
index c3b1df9928..a37b8bee24 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/errors/NoPackSignatureException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/errors/NoPackSignatureException.java
@@ -13,8 +13,7 @@ package org.eclipse.jgit.errors;
 import java.io.IOException;
 
 /**
- * Thrown when a PackFile is found not to contain the pack signature defined by
- * git.
+ * Thrown when a Pack is found not to contain the pack signature defined by git.
  *
  * @since 4.5
  */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackInvalidException.java b/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackInvalidException.java
index c484984f82..1fd80867b9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackInvalidException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackInvalidException.java
@@ -17,7 +17,7 @@ import java.text.MessageFormat;
 import org.eclipse.jgit.internal.JGitText;
 
 /**
- * Thrown when a PackFile previously failed and is known to be unusable
+ * Thrown when a Pack previously failed and is known to be unusable
  */
 public class PackInvalidException extends IOException {
 	private static final long serialVersionUID = 1L;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackMismatchException.java b/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackMismatchException.java
index ad5664ceb2..44b8e0193c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackMismatchException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/errors/PackMismatchException.java
@@ -13,7 +13,7 @@ package org.eclipse.jgit.errors;
 import java.io.IOException;
 
 /**
- * Thrown when a PackFile no longer matches the PackIndex.
+ * Thrown when a Pack no longer matches the PackIndex.
  */
 public class PackMismatchException extends IOException {
 	private static final long serialVersionUID = 1L;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/errors/UnsupportedPackVersionException.java b/org.eclipse.jgit/src/org/eclipse/jgit/errors/UnsupportedPackVersionException.java
index 7538229950..07aa7564dd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/errors/UnsupportedPackVersionException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/errors/UnsupportedPackVersionException.java
@@ -16,7 +16,7 @@ import java.text.MessageFormat;
 import org.eclipse.jgit.internal.JGitText;
 
 /**
- * Thrown when a PackFile uses a pack version not supported by JGit.
+ * Thrown when a Pack uses a pack version not supported by JGit.
  *
  * @since 4.5
  */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/events/ListenerList.java b/org.eclipse.jgit/src/org/eclipse/jgit/events/ListenerList.java
index 32c3a1d28f..476c37c1c3 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/events/ListenerList.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/events/ListenerList.java
@@ -11,15 +11,15 @@
 package org.eclipse.jgit.events;
 
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 /**
  * Manages a thread-safe list of {@link org.eclipse.jgit.events.RepositoryListener}s.
  */
 public class ListenerList {
-	private final ConcurrentMap<Class<? extends RepositoryListener>, CopyOnWriteArrayList<ListenerHandle>> lists = new ConcurrentHashMap<>();
+	private final Map<Class<? extends RepositoryListener>, CopyOnWriteArrayList<ListenerHandle>> lists = new ConcurrentHashMap<>();
 
 	/**
 	 * Register a {@link org.eclipse.jgit.events.WorkingTreeModifiedListener}.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
index 4059b16b39..ce3ad2239a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/GitHook.java
@@ -9,12 +9,10 @@
  */
 package org.eclipse.jgit.hooks;
 
-import static java.nio.charset.StandardCharsets.UTF_8;
-
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.PrintStream;
-import java.io.UnsupportedEncodingException;
+import java.io.OutputStream;
+import java.nio.charset.Charset;
 import java.util.concurrent.Callable;
 
 import org.eclipse.jgit.api.errors.AbortedByHookException;
@@ -35,21 +33,21 @@ import org.eclipse.jgit.util.io.TeeOutputStream;
  *            the return type which is expected from {@link #call()}
  * @see <a href="http://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks">Git
  *      Hooks on the git-scm official site</a>
- * @since 4.0
+ * @since 5.11
  */
-abstract class GitHook<T> implements Callable<T> {
+public abstract class GitHook<T> implements Callable<T> {
 
 	private final Repository repo;
 
 	/**
 	 * The output stream to be used by the hook.
 	 */
-	protected final PrintStream outputStream;
+	private final OutputStream outputStream;
 
 	/**
 	 * The error stream to be used by the hook.
 	 */
-	protected final PrintStream errorStream;
+	private final OutputStream errorStream;
 
 	/**
 	 * Constructor for GitHook.
@@ -63,7 +61,7 @@ abstract class GitHook<T> implements Callable<T> {
 	 *            The output stream the hook must use. {@code null} is allowed,
 	 *            in which case the hook will use {@code System.out}.
 	 */
-	protected GitHook(Repository repo, PrintStream outputStream) {
+	protected GitHook(Repository repo, OutputStream outputStream) {
 		this(repo, outputStream, null);
 	}
 
@@ -79,8 +77,8 @@ abstract class GitHook<T> implements Callable<T> {
 	 *            The error stream the hook must use. {@code null} is allowed,
 	 *            in which case the hook will use {@code System.err}.
 	 */
-	protected GitHook(Repository repo, PrintStream outputStream,
-			PrintStream errorStream) {
+	protected GitHook(Repository repo, OutputStream outputStream,
+			OutputStream errorStream) {
 		this.repo = repo;
 		this.outputStream = outputStream;
 		this.errorStream = errorStream;
@@ -137,7 +135,7 @@ abstract class GitHook<T> implements Callable<T> {
 	 * @return The output stream the hook must use. Never {@code null},
 	 *         {@code System.out} is returned by default.
 	 */
-	protected PrintStream getOutputStream() {
+	protected OutputStream getOutputStream() {
 		return outputStream == null ? System.out : outputStream;
 	}
 
@@ -147,7 +145,7 @@ abstract class GitHook<T> implements Callable<T> {
 	 * @return The error stream the hook must use. Never {@code null},
 	 *         {@code System.err} is returned by default.
 	 */
-	protected PrintStream getErrorStream() {
+	protected OutputStream getErrorStream() {
 		return errorStream == null ? System.err : errorStream;
 	}
 
@@ -156,34 +154,48 @@ abstract class GitHook<T> implements Callable<T> {
 	 *
 	 * @throws org.eclipse.jgit.api.errors.AbortedByHookException
 	 *             If the underlying hook script exited with non-zero.
+	 * @throws IOException
+	 *             if an IO error occurred
 	 */
-	protected void doRun() throws AbortedByHookException {
+	protected void doRun() throws AbortedByHookException, IOException {
 		final ByteArrayOutputStream errorByteArray = new ByteArrayOutputStream();
 		final TeeOutputStream stderrStream = new TeeOutputStream(errorByteArray,
 				getErrorStream());
-		PrintStream hookErrRedirect = null;
-		try {
-			hookErrRedirect = new PrintStream(stderrStream, false,
-					UTF_8.name());
-		} catch (UnsupportedEncodingException e) {
-			// UTF-8 is guaranteed to be available
-		}
 		Repository repository = getRepository();
 		FS fs = repository.getFS();
 		if (fs == null) {
 			fs = FS.DETECTED;
 		}
 		ProcessResult result = fs.runHookIfPresent(repository, getHookName(),
-				getParameters(), getOutputStream(), hookErrRedirect,
+				getParameters(), getOutputStream(), stderrStream,
 				getStdinArgs());
 		if (result.isExecutedWithError()) {
-			throw new AbortedByHookException(
-					new String(errorByteArray.toByteArray(), UTF_8),
-					getHookName(), result.getExitCode());
+			handleError(new String(errorByteArray.toByteArray(),
+					Charset.defaultCharset().name()), result);
 		}
 	}
 
 	/**
+	 * Process that the hook exited with an error. This default implementation
+	 * throws an {@link AbortedByHookException }. Hooks which need a different
+	 * behavior can overwrite this method.
+	 *
+	 * @param message
+	 *            error message
+	 * @param result
+	 *            The process result of the hook
+	 * @throws AbortedByHookException
+	 *             When the hook should be aborted
+	 * @since 5.11
+	 */
+	protected void handleError(String message,
+			final ProcessResult result)
+			throws AbortedByHookException {
+		throw new AbortedByHookException(message, getHookName(),
+				result.getExitCode());
+	}
+
+	/**
 	 * Check whether a 'native' (i.e. script) hook is installed in the
 	 * repository.
 	 *
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PostCommitHook.java b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PostCommitHook.java
index 0b61ebea3f..b9dafcca31 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PostCommitHook.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PostCommitHook.java
@@ -14,6 +14,7 @@ import java.io.PrintStream;
 
 import org.eclipse.jgit.api.errors.AbortedByHookException;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.util.ProcessResult;
 
 /**
  * The <code>post-commit</code> hook implementation. This hook is run after the
@@ -73,4 +74,16 @@ public class PostCommitHook extends GitHook<Void> {
 		return NAME;
 	}
 
+
+	/**
+	 * Overwrites the default implementation to never throw an
+	 * {@link AbortedByHookException}, as the commit has already been done and
+	 * the exit code of the post-commit hook has no effect.
+	 */
+	@Override
+	protected void handleError(String message, ProcessResult result)
+			throws AbortedByHookException {
+		// Do nothing as the exit code of the post-commit hook has no effect.
+	}
+
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/ignore/FastIgnoreRule.java b/org.eclipse.jgit/src/org/eclipse/jgit/ignore/FastIgnoreRule.java
index d7e4f79d26..9dd565ff0a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/ignore/FastIgnoreRule.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/ignore/FastIgnoreRule.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014, Andrey Loskutov <loskutov@gmx.de> and others
+ * Copyright (C) 2014, 2021 Andrey Loskutov <loskutov@gmx.de> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -14,8 +14,11 @@ import static org.eclipse.jgit.ignore.internal.Strings.isDirectoryPattern;
 import static org.eclipse.jgit.ignore.internal.Strings.stripTrailing;
 import static org.eclipse.jgit.ignore.internal.Strings.stripTrailingWhitespace;
 
+import java.text.MessageFormat;
+
 import org.eclipse.jgit.errors.InvalidPatternException;
 import org.eclipse.jgit.ignore.internal.PathMatcher;
+import org.eclipse.jgit.internal.JGitText;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -36,11 +39,11 @@ public class FastIgnoreRule {
 	 */
 	public static final char PATH_SEPARATOR = '/';
 
-	private final IMatcher matcher;
+	private IMatcher matcher;
 
-	private final boolean inverse;
+	private boolean inverse;
 
-	private final boolean dirOnly;
+	private boolean dirOnly;
 
 	/**
 	 * Constructor for FastIgnoreRule
@@ -52,8 +55,23 @@ public class FastIgnoreRule {
 	 *            (comment), this rule doesn't match anything.
 	 */
 	public FastIgnoreRule(String pattern) {
-		if (pattern == null)
+		this();
+		try {
+			parse(pattern);
+		} catch (InvalidPatternException e) {
+			LOG.error(MessageFormat.format(JGitText.get().badIgnorePattern,
+					e.getPattern()), e);
+		}
+	}
+
+	FastIgnoreRule() {
+		matcher = IMatcher.NO_MATCH;
+	}
+
+	void parse(String pattern) throws InvalidPatternException {
+		if (pattern == null) {
 			throw new IllegalArgumentException("Pattern must not be null!"); //$NON-NLS-1$
+		}
 		if (pattern.length() == 0) {
 			dirOnly = false;
 			inverse = false;
@@ -90,15 +108,8 @@ public class FastIgnoreRule {
 				return;
 			}
 		}
-		IMatcher m;
-		try {
-			m = PathMatcher.createPathMatcher(pattern,
-					Character.valueOf(PATH_SEPARATOR), dirOnly);
-		} catch (InvalidPatternException e) {
-			m = NO_MATCH;
-			LOG.error(e.getMessage(), e);
-		}
-		this.matcher = m;
+		this.matcher = PathMatcher.createPathMatcher(pattern,
+				Character.valueOf(PATH_SEPARATOR), dirOnly);
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/ignore/IgnoreNode.java b/org.eclipse.jgit/src/org/eclipse/jgit/ignore/IgnoreNode.java
index 0bc6124912..4e7f126a60 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/ignore/IgnoreNode.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/ignore/IgnoreNode.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, Red Hat Inc. and others
+ * Copyright (C) 2010, 2021 Red Hat Inc. and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -15,16 +15,26 @@ import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.errors.InvalidPatternException;
+import org.eclipse.jgit.internal.JGitText;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * Represents a bundle of ignore rules inherited from a base directory.
  *
  * This class is not thread safe, it maintains state about the last match.
  */
 public class IgnoreNode {
+
+	private static final Logger LOG = LoggerFactory.getLogger(IgnoreNode.class);
+
 	/** Result from {@link IgnoreNode#isIgnored(String, boolean)}. */
 	public enum MatchResult {
 		/** The file is not ignored, due to a rule saying its not ignored. */
@@ -52,7 +62,7 @@ public class IgnoreNode {
 	 * Create an empty ignore node with no rules.
 	 */
 	public IgnoreNode() {
-		rules = new ArrayList<>();
+		this(new ArrayList<>());
 	}
 
 	/**
@@ -75,15 +85,47 @@ public class IgnoreNode {
 	 *             Error thrown when reading an ignore file.
 	 */
 	public void parse(InputStream in) throws IOException {
+		parse(null, in);
+	}
+
+	/**
+	 * Parse files according to gitignore standards.
+	 *
+	 * @param sourceName
+	 *            identifying the source of the stream
+	 * @param in
+	 *            input stream holding the standard ignore format. The caller is
+	 *            responsible for closing the stream.
+	 * @throws java.io.IOException
+	 *             Error thrown when reading an ignore file.
+	 * @since 5.11
+	 */
+	public void parse(String sourceName, InputStream in) throws IOException {
 		BufferedReader br = asReader(in);
 		String txt;
+		int lineNumber = 1;
 		while ((txt = br.readLine()) != null) {
 			if (txt.length() > 0 && !txt.startsWith("#") && !txt.equals("/")) { //$NON-NLS-1$ //$NON-NLS-2$
-				FastIgnoreRule rule = new FastIgnoreRule(txt);
+				FastIgnoreRule rule = new FastIgnoreRule();
+				try {
+					rule.parse(txt);
+				} catch (InvalidPatternException e) {
+					if (sourceName != null) {
+						LOG.error(MessageFormat.format(
+								JGitText.get().badIgnorePatternFull, sourceName,
+								Integer.toString(lineNumber), e.getPattern(),
+								e.getLocalizedMessage()), e);
+					} else {
+						LOG.error(MessageFormat.format(
+								JGitText.get().badIgnorePattern,
+								e.getPattern()), e);
+					}
+				}
 				if (!rule.isEmpty()) {
 					rules.add(rule);
 				}
 			}
+			lineNumber++;
 		}
 	}
 
@@ -135,7 +177,8 @@ public class IgnoreNode {
 	 *         undetermined
 	 * @since 4.11
 	 */
-	public Boolean checkIgnored(String entryPath, boolean isDirectory) {
+	public @Nullable Boolean checkIgnored(String entryPath,
+			boolean isDirectory) {
 		// Parse rules in the reverse order that they were read because later
 		// rules have higher priority
 		for (int i = rules.size() - 1; i > -1; i--) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
index 892657d5d3..9d215ca455 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2010, 2013 Sasa Zivkov <sasa.zivkov@sap.com>
- * Copyright (C) 2012, Research In Motion Limited and others
+ * Copyright (C) 2012, 2021 Research In Motion Limited and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -58,6 +58,8 @@ public class JGitText extends TranslationBundle {
 	/***/ public String badEntryName;
 	/***/ public String badEscape;
 	/***/ public String badGroupHeader;
+	/***/ public String badIgnorePattern;
+	/***/ public String badIgnorePatternFull;
 	/***/ public String badObjectType;
 	/***/ public String badRef;
 	/***/ public String badSectionEntry;
@@ -261,6 +263,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String downloadCancelledDuringIndexing;
 	/***/ public String duplicateAdvertisementsOf;
 	/***/ public String duplicateRef;
+	/***/ public String duplicateRefAttribute;
 	/***/ public String duplicateRemoteRefUpdateIsIllegal;
 	/***/ public String duplicateStagesNotAllowed;
 	/***/ public String eitherGitDirOrWorkTreeRequired;
@@ -338,6 +341,10 @@ public class JGitText extends TranslationBundle {
 	/***/ public String hoursAgo;
 	/***/ public String httpConfigCannotNormalizeURL;
 	/***/ public String httpConfigInvalidURL;
+	/***/ public String httpFactoryInUse;
+	/***/ public String httpPreAuthTooLate;
+	/***/ public String httpUserInfoDecodeError;
+	/***/ public String httpWrongConnectionType;
 	/***/ public String hugeIndexesAreNotSupportedByJgitYet;
 	/***/ public String hunkBelongsToAnotherFile;
 	/***/ public String hunkDisconnectedFromFile;
@@ -591,6 +598,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String reftableDirExists;
 	/***/ public String reftableRecordsMustIncrease;
 	/***/ public String refUpdateReturnCodeWas;
+	/***/ public String remoteBranchNotFound;
 	/***/ public String remoteConfigHasNoURIAssociated;
 	/***/ public String remoteDoesNotHaveSpec;
 	/***/ public String remoteDoesNotSupportSmartHTTPPush;
@@ -645,7 +653,9 @@ public class JGitText extends TranslationBundle {
 	/***/ public String shortReadOfBlock;
 	/***/ public String shortReadOfOptionalDIRCExtensionExpectedAnotherBytes;
 	/***/ public String shortSkipOfBlock;
-	/***/ public String signingNotSupportedOnTag;
+	/***/ public String signatureVerificationError;
+	/***/ public String signatureVerificationUnavailable;
+	/***/ public String signedTagMessageNoLf;
 	/***/ public String signingServiceUnavailable;
 	/***/ public String similarityScoreMustBeWithinBounds;
 	/***/ public String skipMustBeNonNegative;
@@ -786,6 +796,13 @@ public class JGitText extends TranslationBundle {
 	/***/ public String URINotSupported;
 	/***/ public String userConfigInvalid;
 	/***/ public String validatingGitModules;
+	/***/ public String verifySignatureBad;
+	/***/ public String verifySignatureExpired;
+	/***/ public String verifySignatureGood;
+	/***/ public String verifySignatureIssuer;
+	/***/ public String verifySignatureKey;
+	/***/ public String verifySignatureMade;
+	/***/ public String verifySignatureTrust;
 	/***/ public String walkFailure;
 	/***/ public String wantNoSpaceWithCapabilities;
 	/***/ public String wantNotValid;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ElectionRound.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ElectionRound.java
deleted file mode 100644
index 5ddbcbd0ed..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ElectionRound.java
+++ /dev/null
@@ -1,126 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static java.util.concurrent.TimeUnit.SECONDS;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.TERM;
-
-import java.io.IOException;
-import java.util.List;
-import java.util.concurrent.TimeoutException;
-
-import org.eclipse.jgit.lib.CommitBuilder;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.lib.TreeFormatter;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.util.time.ProposedTimestamp;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * The initial {@link Round} for a leaderless repository, used to establish a
- * leader.
- */
-class ElectionRound extends Round {
-	private static final Logger log = LoggerFactory.getLogger(ElectionRound.class);
-
-	private long term;
-
-	ElectionRound(KetchLeader leader, LogIndex head) {
-		super(leader, head);
-	}
-
-	@Override
-	void start() throws IOException {
-		ObjectId id;
-		try (Repository git = leader.openRepository();
-				ProposedTimestamp ts = getSystem().getClock().propose();
-				ObjectInserter inserter = git.newObjectInserter()) {
-			id = bumpTerm(git, ts, inserter);
-			inserter.flush();
-			blockUntil(ts);
-		}
-		runAsync(id);
-	}
-
-	@Override
-	void success() {
-		// Do nothing upon election, KetchLeader will copy the term.
-	}
-
-	long getTerm() {
-		return term;
-	}
-
-	private ObjectId bumpTerm(Repository git, ProposedTimestamp ts,
-			ObjectInserter inserter) throws IOException {
-		CommitBuilder b = new CommitBuilder();
-		if (!ObjectId.zeroId().equals(acceptedOldIndex)) {
-			try (RevWalk rw = new RevWalk(git)) {
-				RevCommit c = rw.parseCommit(acceptedOldIndex);
-				if (getSystem().requireMonotonicLeaderElections()) {
-					if (ts.read(SECONDS) < c.getCommitTime()) {
-						throw new TimeIsUncertainException();
-					}
-				}
-				b.setTreeId(c.getTree());
-				b.setParentId(acceptedOldIndex);
-				term = parseTerm(c.getFooterLines(TERM)) + 1;
-			}
-		} else {
-			term = 1;
-			b.setTreeId(inserter.insert(new TreeFormatter()));
-		}
-
-		StringBuilder msg = new StringBuilder();
-		msg.append(KetchConstants.TERM.getName())
-				.append(": ") //$NON-NLS-1$
-				.append(term);
-
-		String tag = leader.getSystem().newLeaderTag();
-		if (tag != null && !tag.isEmpty()) {
-			msg.append(' ').append(tag);
-		}
-
-		b.setAuthor(leader.getSystem().newCommitter(ts));
-		b.setCommitter(b.getAuthor());
-		b.setMessage(msg.toString());
-
-		if (log.isDebugEnabled()) {
-			log.debug("Trying to elect myself " + b.getMessage()); //$NON-NLS-1$
-		}
-		return inserter.insert(b);
-	}
-
-	private static long parseTerm(List<String> footer) {
-		if (footer.isEmpty()) {
-			return 0;
-		}
-
-		String s = footer.get(0);
-		int p = s.indexOf(' ');
-		if (p > 0) {
-			s = s.substring(0, p);
-		}
-		return Long.parseLong(s, 10);
-	}
-
-	private void blockUntil(ProposedTimestamp ts) throws IOException {
-		try {
-			ts.blockUntil(getSystem().getMaxWaitForMonotonicClock());
-		} catch (InterruptedException | TimeoutException e) {
-			throw new TimeIsUncertainException(e);
-		}
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchConstants.java
deleted file mode 100644
index f4a7f592f0..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchConstants.java
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import org.eclipse.jgit.revwalk.FooterKey;
-
-/**
- * Frequently used constants in a Ketch system.
- */
-public class KetchConstants {
-	/**
-	 * Default reference namespace holding {@link #ACCEPTED} and
-	 * {@link #COMMITTED} references and the {@link #STAGE} sub-namespace.
-	 */
-	public static final String DEFAULT_TXN_NAMESPACE = "refs/txn/"; //$NON-NLS-1$
-
-	/** Reference name holding the RefTree accepted by a follower. */
-	public static final String ACCEPTED = "accepted"; //$NON-NLS-1$
-
-	/** Reference name holding the RefTree known to be committed. */
-	public static final String COMMITTED = "committed"; //$NON-NLS-1$
-
-	/** Reference subdirectory holding proposed heads. */
-	public static final String STAGE = "stage/"; //$NON-NLS-1$
-
-	/** Footer containing the current term. */
-	public static final FooterKey TERM = new FooterKey("Term"); //$NON-NLS-1$
-
-	/** Section for Ketch configuration ({@code ketch}). */
-	public static final String CONFIG_SECTION_KETCH = "ketch"; //$NON-NLS-1$
-
-	/** Behavior for a replica ({@code remote.$name.ketch-type}) */
-	public static final String CONFIG_KEY_TYPE = "ketch-type"; //$NON-NLS-1$
-
-	/** Behavior for a replica ({@code remote.$name.ketch-commit}) */
-	public static final String CONFIG_KEY_COMMIT = "ketch-commit"; //$NON-NLS-1$
-
-	/** Behavior for a replica ({@code remote.$name.ketch-speed}) */
-	public static final String CONFIG_KEY_SPEED = "ketch-speed"; //$NON-NLS-1$
-
-	private KetchConstants() {
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeader.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeader.java
deleted file mode 100644
index 743d1939c8..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeader.java
+++ /dev/null
@@ -1,604 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchLeader.State.CANDIDATE;
-import static org.eclipse.jgit.internal.ketch.KetchLeader.State.LEADER;
-import static org.eclipse.jgit.internal.ketch.KetchLeader.State.SHUTDOWN;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.Participation.FOLLOWER_ONLY;
-import static org.eclipse.jgit.internal.ketch.Proposal.State.QUEUED;
-
-import java.io.IOException;
-import java.text.MessageFormat;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.List;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
-
-import org.eclipse.jgit.internal.storage.reftree.RefTree;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * A leader managing consensus across remote followers.
- * <p>
- * A leader instance starts up in
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader.State#CANDIDATE} and tries
- * to begin a new term by sending an
- * {@link org.eclipse.jgit.internal.ketch.ElectionRound} to all replicas. Its
- * term starts if a majority of replicas have accepted this leader instance for
- * the term.
- * <p>
- * Once elected by a majority the instance enters
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader.State#LEADER} and runs
- * proposals offered to {@link #queueProposal(Proposal)}. This continues until
- * the leader is timed out for inactivity, or is deposed by a competing leader
- * gaining its own majority.
- * <p>
- * Once timed out or deposed this {@code KetchLeader} instance should be
- * discarded, and a new instance takes over.
- * <p>
- * Each leader instance coordinates a group of
- * {@link org.eclipse.jgit.internal.ketch.KetchReplica}s. Replica instances are
- * owned by the leader instance and must be discarded when the leader is
- * discarded.
- * <p>
- * In Ketch all push requests are issued through the leader. The steps are as
- * follows (see {@link org.eclipse.jgit.internal.ketch.KetchPreReceive} for an
- * example):
- * <ul>
- * <li>Create a {@link org.eclipse.jgit.internal.ketch.Proposal} with the
- * {@link org.eclipse.jgit.transport.ReceiveCommand}s that represent the push.
- * <li>Invoke {@link #queueProposal(Proposal)} on the leader instance.
- * <li>Wait for consensus with
- * {@link org.eclipse.jgit.internal.ketch.Proposal#await()}.
- * <li>To examine the status of the push, check
- * {@link org.eclipse.jgit.internal.ketch.Proposal#getCommands()}, looking at
- * {@link org.eclipse.jgit.internal.storage.reftree.Command#getResult()}.
- * </ul>
- * <p>
- * The leader gains consensus by first pushing the needed objects and a
- * {@link org.eclipse.jgit.internal.storage.reftree.RefTree} representing the
- * desired target repository state to the {@code refs/txn/accepted} branch on
- * each of the replicas. Once a majority has succeeded, the leader commits the
- * state by either pushing the {@code refs/txn/accepted} value to
- * {@code refs/txn/committed} (for Ketch-aware replicas) or by pushing updates
- * to {@code refs/heads/master}, etc. for stock Git replicas.
- * <p>
- * Internally, the actual transport to replicas is performed on background
- * threads via the {@link org.eclipse.jgit.internal.ketch.KetchSystem}'s
- * executor service. For performance, the
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader},
- * {@link org.eclipse.jgit.internal.ketch.KetchReplica} and
- * {@link org.eclipse.jgit.internal.ketch.Proposal} objects share some state,
- * and may invoke each other's methods on different threads. This access is
- * protected by the leader's {@link #lock} object. Care must be taken to prevent
- * concurrent access by correctly obtaining the leader's lock.
- */
-public abstract class KetchLeader {
-	private static final Logger log = LoggerFactory.getLogger(KetchLeader.class);
-
-	/** Current state of the leader instance. */
-	public enum State {
-		/** Newly created instance trying to elect itself leader. */
-		CANDIDATE,
-
-		/** Leader instance elected by a majority. */
-		LEADER,
-
-		/** Instance has been deposed by another with a more recent term. */
-		DEPOSED,
-
-		/** Leader has been gracefully shutdown, e.g. due to inactivity. */
-		SHUTDOWN;
-	}
-
-	private final KetchSystem system;
-
-	/** Leader's knowledge of replicas for this repository. */
-	private KetchReplica[] voters;
-	private KetchReplica[] followers;
-	private LocalReplica self;
-
-	/**
-	 * Lock protecting all data within this leader instance.
-	 * <p>
-	 * This lock extends into the {@link KetchReplica} instances used by the
-	 * leader. They share the same lock instance to simplify concurrency.
-	 */
-	final Lock lock;
-
-	private State state = CANDIDATE;
-
-	/** Term of this leader, once elected. */
-	private long term;
-
-	/**
-	 * Pending proposals accepted into the queue in FIFO order.
-	 * <p>
-	 * These proposals were preflighted and do not contain any conflicts with
-	 * each other and their expectations matched the leader's local view of the
-	 * agreed upon {@code refs/txn/accepted} tree.
-	 */
-	private final List<Proposal> queued;
-
-	/**
-	 * State of the repository's RefTree after applying all entries in
-	 * {@link #queued}. New proposals must be consistent with this tree to be
-	 * appended to the end of {@link #queued}.
-	 * <p>
-	 * Must be deep-copied with {@link RefTree#copy()} if
-	 * {@link #roundHoldsReferenceToRefTree} is {@code true}.
-	 */
-	private RefTree refTree;
-
-	/**
-	 * If {@code true} {@link #refTree} must be duplicated before queuing the
-	 * next proposal. The {@link #refTree} was passed into the constructor of a
-	 * {@link ProposalRound}, and that external reference to the {@link RefTree}
-	 * object is held by the proposal until it materializes the tree object in
-	 * the object store. This field is set {@code true} when the proposal begins
-	 * execution and set {@code false} once tree objects are persisted in the
-	 * local repository's object store or {@link #refTree} is replaced with a
-	 * copy to isolate it from any running rounds.
-	 * <p>
-	 * If proposals arrive less frequently than the {@code RefTree} is written
-	 * out to the repository the {@link #roundHoldsReferenceToRefTree} behavior
-	 * avoids duplicating {@link #refTree}, reducing both time and memory used.
-	 * However if proposals arrive more frequently {@link #refTree} must be
-	 * duplicated to prevent newly queued proposals from corrupting the
-	 * {@link #runningRound}.
-	 */
-	volatile boolean roundHoldsReferenceToRefTree;
-
-	/** End of the leader's log. */
-	private LogIndex headIndex;
-
-	/** Leader knows this (and all prior) states are committed. */
-	private LogIndex committedIndex;
-
-	/**
-	 * Is the leader idle with no work pending? If {@code true} there is no work
-	 * for the leader (normal state). This field is {@code false} when the
-	 * leader thread is scheduled for execution, or while {@link #runningRound}
-	 * defines a round in progress.
-	 */
-	private boolean idle;
-
-	/** Current round the leader is preparing and waiting for a vote on. */
-	private Round runningRound;
-
-	/**
-	 * Construct a leader for a Ketch instance.
-	 *
-	 * @param system
-	 *            Ketch system configuration the leader must adhere to.
-	 */
-	protected KetchLeader(KetchSystem system) {
-		this.system = system;
-		this.lock = new ReentrantLock(true /* fair */);
-		this.queued = new ArrayList<>(4);
-		this.idle = true;
-	}
-
-	/** @return system configuration. */
-	KetchSystem getSystem() {
-		return system;
-	}
-
-	/**
-	 * Configure the replicas used by this Ketch instance.
-	 * <p>
-	 * Replicas should be configured once at creation before any proposals are
-	 * executed. Once elections happen, <b>reconfiguration is a complicated
-	 * concept that is not currently supported</b>.
-	 *
-	 * @param replicas
-	 *            members participating with the same repository.
-	 */
-	public void setReplicas(Collection<KetchReplica> replicas) {
-		List<KetchReplica> v = new ArrayList<>(5);
-		List<KetchReplica> f = new ArrayList<>(5);
-		for (KetchReplica r : replicas) {
-			switch (r.getParticipation()) {
-			case FULL:
-				v.add(r);
-				break;
-
-			case FOLLOWER_ONLY:
-				f.add(r);
-				break;
-			}
-		}
-
-		Collection<Integer> validVoters = validVoterCounts();
-		if (!validVoters.contains(Integer.valueOf(v.size()))) {
-			throw new IllegalArgumentException(MessageFormat.format(
-					KetchText.get().unsupportedVoterCount,
-					Integer.valueOf(v.size()),
-					validVoters));
-		}
-
-		LocalReplica me = findLocal(v);
-		if (me == null) {
-			throw new IllegalArgumentException(
-					KetchText.get().localReplicaRequired);
-		}
-
-		lock.lock();
-		try {
-			voters = v.toArray(new KetchReplica[0]);
-			followers = f.toArray(new KetchReplica[0]);
-			self = me;
-		} finally {
-			lock.unlock();
-		}
-	}
-
-	private static Collection<Integer> validVoterCounts() {
-		@SuppressWarnings("boxing")
-		Integer[] valid = {
-				// An odd number of voting replicas is required.
-				1, 3, 5, 7, 9 };
-		return Arrays.asList(valid);
-	}
-
-	private static LocalReplica findLocal(Collection<KetchReplica> voters) {
-		for (KetchReplica r : voters) {
-			if (r instanceof LocalReplica) {
-				return (LocalReplica) r;
-			}
-		}
-		return null;
-	}
-
-	/**
-	 * Get an instance of the repository for use by a leader thread.
-	 * <p>
-	 * The caller will close the repository.
-	 *
-	 * @return opened repository for use by the leader thread.
-	 * @throws java.io.IOException
-	 *             cannot reopen the repository for the leader.
-	 */
-	protected abstract Repository openRepository() throws IOException;
-
-	/**
-	 * Queue a reference update proposal for consensus.
-	 * <p>
-	 * This method does not wait for consensus to be reached. The proposal is
-	 * checked to look for risks of conflicts, and then submitted into the queue
-	 * for distribution as soon as possible.
-	 * <p>
-	 * Callers must use {@link org.eclipse.jgit.internal.ketch.Proposal#await()}
-	 * to see if the proposal is done.
-	 *
-	 * @param proposal
-	 *            the proposed reference updates to queue for consideration.
-	 *            Once execution is complete the individual reference result
-	 *            fields will be populated with the outcome.
-	 * @throws java.lang.InterruptedException
-	 *             current thread was interrupted. The proposal may have been
-	 *             aborted if it was not yet queued for execution.
-	 * @throws java.io.IOException
-	 *             unrecoverable error preventing proposals from being attempted
-	 *             by this leader.
-	 */
-	public void queueProposal(Proposal proposal)
-			throws InterruptedException, IOException {
-		try {
-			lock.lockInterruptibly();
-		} catch (InterruptedException e) {
-			proposal.abort();
-			throw e;
-		}
-		try {
-			if (refTree == null) {
-				initialize();
-				for (Proposal p : queued) {
-					refTree.apply(p.getCommands());
-				}
-			} else if (roundHoldsReferenceToRefTree) {
-				refTree = refTree.copy();
-				roundHoldsReferenceToRefTree = false;
-			}
-
-			if (!refTree.apply(proposal.getCommands())) {
-				// A conflict exists so abort the proposal.
-				proposal.abort();
-				return;
-			}
-
-			queued.add(proposal);
-			proposal.notifyState(QUEUED);
-
-			if (idle) {
-				scheduleLeader();
-			}
-		} finally {
-			lock.unlock();
-		}
-	}
-
-	private void initialize() throws IOException {
-		try (Repository git = openRepository(); RevWalk rw = new RevWalk(git)) {
-			self.initialize(git);
-
-			ObjectId accepted = self.getTxnAccepted();
-			if (!ObjectId.zeroId().equals(accepted)) {
-				RevCommit c = rw.parseCommit(accepted);
-				headIndex = LogIndex.unknown(accepted);
-				refTree = RefTree.read(rw.getObjectReader(), c.getTree());
-			} else {
-				headIndex = LogIndex.unknown(ObjectId.zeroId());
-				refTree = RefTree.newEmptyTree();
-			}
-		}
-	}
-
-	private void scheduleLeader() {
-		idle = false;
-		system.getExecutor().execute(this::runLeader);
-	}
-
-	private void runLeader() {
-		Round round;
-		lock.lock();
-		try {
-			switch (state) {
-			case CANDIDATE:
-				round = new ElectionRound(this, headIndex);
-				break;
-
-			case LEADER:
-				round = newProposalRound();
-				break;
-
-			case DEPOSED:
-			case SHUTDOWN:
-			default:
-				log.warn("Leader cannot run {}", state); //$NON-NLS-1$
-				// TODO(sop): Redirect proposals.
-				return;
-			}
-		} finally {
-			lock.unlock();
-		}
-
-		try {
-			round.start();
-		} catch (IOException e) {
-			// TODO(sop) Depose leader if it cannot use its repository.
-			log.error(KetchText.get().leaderFailedToStore, e);
-			lock.lock();
-			try {
-				nextRound();
-			} finally {
-				lock.unlock();
-			}
-		}
-	}
-
-	private ProposalRound newProposalRound() {
-		List<Proposal> todo = new ArrayList<>(queued);
-		queued.clear();
-		roundHoldsReferenceToRefTree = true;
-		return new ProposalRound(this, headIndex, todo, refTree);
-	}
-
-	/** @return term of this leader's reign. */
-	long getTerm() {
-		return term;
-	}
-
-	/** @return end of the leader's log. */
-	LogIndex getHead() {
-		return headIndex;
-	}
-
-	/**
-	 * @return state leader knows it has committed across a quorum of replicas.
-	 */
-	LogIndex getCommitted() {
-		return committedIndex;
-	}
-
-	boolean isIdle() {
-		return idle;
-	}
-
-	void runAsync(Round round) {
-		lock.lock();
-		try {
-			// End of the log is this round. Once transport begins it is
-			// reasonable to assume at least one replica will eventually get
-			// this, and there is reasonable probability it commits.
-			headIndex = round.acceptedNewIndex;
-			runningRound = round;
-
-			for (KetchReplica replica : voters) {
-				replica.pushTxnAcceptedAsync(round);
-			}
-			for (KetchReplica replica : followers) {
-				replica.pushTxnAcceptedAsync(round);
-			}
-		} finally {
-			lock.unlock();
-		}
-	}
-
-	/**
-	 * Asynchronous signal from a replica after completion.
-	 * <p>
-	 * Must be called while {@link #lock} is held by the replica.
-	 *
-	 * @param replica
-	 *            replica posting a completion event.
-	 */
-	void onReplicaUpdate(KetchReplica replica) {
-		if (log.isDebugEnabled()) {
-			log.debug("Replica {} finished:\n{}", //$NON-NLS-1$
-					replica.describeForLog(), snapshot());
-		}
-
-		if (replica.getParticipation() == FOLLOWER_ONLY) {
-			// Followers cannot vote, so votes haven't changed.
-			return;
-		} else if (runningRound == null) {
-			// No round running, no need to tally votes.
-			return;
-		}
-
-		assert headIndex.equals(runningRound.acceptedNewIndex);
-		int matching = 0;
-		for (KetchReplica r : voters) {
-			if (r.hasAccepted(headIndex)) {
-				matching++;
-			}
-		}
-
-		int quorum = voters.length / 2 + 1;
-		boolean success = matching >= quorum;
-		if (!success) {
-			return;
-		}
-
-		switch (state) {
-		case CANDIDATE:
-			term = ((ElectionRound) runningRound).getTerm();
-			state = LEADER;
-			if (log.isDebugEnabled()) {
-				log.debug("Won election, running term " + term); //$NON-NLS-1$
-			}
-
-			//$FALL-THROUGH$
-		case LEADER:
-			committedIndex = headIndex;
-			if (log.isDebugEnabled()) {
-				log.debug("Committed {} in term {}", //$NON-NLS-1$
-						committedIndex.describeForLog(),
-						Long.valueOf(term));
-			}
-			nextRound();
-			commitAsync(replica);
-			notifySuccess(runningRound);
-			if (log.isDebugEnabled()) {
-				log.debug("Leader state:\n{}", snapshot()); //$NON-NLS-1$
-			}
-			break;
-
-		default:
-			log.debug("Leader ignoring replica while in {}", state); //$NON-NLS-1$
-			break;
-		}
-	}
-
-	private void notifySuccess(Round round) {
-		// Drop the leader lock while notifying Proposal listeners.
-		lock.unlock();
-		try {
-			round.success();
-		} finally {
-			lock.lock();
-		}
-	}
-
-	private void commitAsync(KetchReplica caller) {
-		for (KetchReplica r : voters) {
-			if (r == caller) {
-				continue;
-			}
-			if (r.shouldPushUnbatchedCommit(committedIndex, isIdle())) {
-				r.pushCommitAsync(committedIndex);
-			}
-		}
-		for (KetchReplica r : followers) {
-			if (r == caller) {
-				continue;
-			}
-			if (r.shouldPushUnbatchedCommit(committedIndex, isIdle())) {
-				r.pushCommitAsync(committedIndex);
-			}
-		}
-	}
-
-	/** Schedule the next round; invoked while {@link #lock} is held. */
-	void nextRound() {
-		runningRound = null;
-
-		if (queued.isEmpty()) {
-			idle = true;
-		} else {
-			// Caller holds lock. Reschedule leader on a new thread so
-			// the call stack can unwind and lock is not held unexpectedly
-			// during prepare for the next round.
-			scheduleLeader();
-		}
-	}
-
-	/**
-	 * Snapshot this leader
-	 *
-	 * @return snapshot of this leader
-	 */
-	public LeaderSnapshot snapshot() {
-		lock.lock();
-		try {
-			LeaderSnapshot s = new LeaderSnapshot();
-			s.state = state;
-			s.term = term;
-			s.headIndex = headIndex;
-			s.committedIndex = committedIndex;
-			s.idle = isIdle();
-			for (KetchReplica r : voters) {
-				s.replicas.add(r.snapshot());
-			}
-			for (KetchReplica r : followers) {
-				s.replicas.add(r.snapshot());
-			}
-			return s;
-		} finally {
-			lock.unlock();
-		}
-	}
-
-	/**
-	 * Gracefully shutdown this leader and cancel outstanding operations.
-	 */
-	public void shutdown() {
-		lock.lock();
-		try {
-			if (state != SHUTDOWN) {
-				state = SHUTDOWN;
-				for (KetchReplica r : voters) {
-					r.shutdown();
-				}
-				for (KetchReplica r : followers) {
-					r.shutdown();
-				}
-			}
-		} finally {
-			lock.unlock();
-		}
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public String toString() {
-		return snapshot().toString();
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeaderCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeaderCache.java
deleted file mode 100644
index e01fb3ae53..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchLeaderCache.java
+++ /dev/null
@@ -1,93 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.net.URISyntaxException;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
-
-import org.eclipse.jgit.internal.storage.dfs.DfsRepository;
-import org.eclipse.jgit.lib.Repository;
-
-/**
- * A cache of live leader instances, keyed by repository.
- * <p>
- * Ketch only assigns a leader to a repository when needed. If
- * {@link #get(Repository)} is called for a repository that does not have a
- * leader, the leader is created and added to the cache.
- */
-public class KetchLeaderCache {
-	private final KetchSystem system;
-	private final ConcurrentMap<String, KetchLeader> leaders;
-	private final Lock startLock;
-
-	/**
-	 * Initialize a new leader cache.
-	 *
-	 * @param system
-	 *            system configuration for the leaders
-	 */
-	public KetchLeaderCache(KetchSystem system) {
-		this.system = system;
-		leaders = new ConcurrentHashMap<>();
-		startLock = new ReentrantLock(true /* fair */);
-	}
-
-	/**
-	 * Lookup the leader instance for a given repository.
-	 *
-	 * @param repo
-	 *            repository to get the leader for.
-	 * @return the leader instance for the repository.
-	 * @throws java.net.URISyntaxException
-	 *             remote configuration contains an invalid URL.
-	 */
-	public KetchLeader get(Repository repo)
-			throws URISyntaxException {
-		String key = computeKey(repo);
-		KetchLeader leader = leaders.get(key);
-		if (leader != null) {
-			return leader;
-		}
-		return startLeader(key, repo);
-	}
-
-	private KetchLeader startLeader(String key, Repository repo)
-			throws URISyntaxException {
-		startLock.lock();
-		try {
-			KetchLeader leader = leaders.get(key);
-			if (leader != null) {
-				return leader;
-			}
-			leader = system.createLeader(repo);
-			leaders.put(key, leader);
-			return leader;
-		} finally {
-			startLock.unlock();
-		}
-	}
-
-	private static String computeKey(Repository repo) {
-		if (repo instanceof DfsRepository) {
-			DfsRepository dfs = (DfsRepository) repo;
-			return dfs.getDescription().getRepositoryName();
-		}
-
-		if (repo.getDirectory() != null) {
-			return repo.getDirectory().toURI().toString();
-		}
-
-		throw new IllegalArgumentException();
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchPreReceive.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchPreReceive.java
deleted file mode 100644
index 1c9535f7be..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchPreReceive.java
+++ /dev/null
@@ -1,125 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-import static java.util.concurrent.TimeUnit.SECONDS;
-import static org.eclipse.jgit.internal.ketch.Proposal.State.EXECUTED;
-import static org.eclipse.jgit.internal.ketch.Proposal.State.QUEUED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-
-import java.io.IOException;
-import java.util.Collection;
-
-import org.eclipse.jgit.internal.JGitText;
-import org.eclipse.jgit.transport.PreReceiveHook;
-import org.eclipse.jgit.transport.ProgressSpinner;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.transport.ReceivePack;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * PreReceiveHook for handling push traffic in a Ketch system.
- * <p>
- * Install an instance on {@link org.eclipse.jgit.transport.ReceivePack} to
- * capture the commands and other connection state and relay them through the
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader}, allowing the leader to
- * gain consensus about the new reference state.
- */
-public class KetchPreReceive implements PreReceiveHook {
-	private static final Logger log = LoggerFactory.getLogger(KetchPreReceive.class);
-
-	private final KetchLeader leader;
-
-	/**
-	 * Construct a hook executing updates through a
-	 * {@link org.eclipse.jgit.internal.ketch.KetchLeader}.
-	 *
-	 * @param leader
-	 *            leader for this repository.
-	 */
-	public KetchPreReceive(KetchLeader leader) {
-		this.leader = leader;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void onPreReceive(ReceivePack rp, Collection<ReceiveCommand> cmds) {
-		cmds = ReceiveCommand.filter(cmds, NOT_ATTEMPTED);
-		if (cmds.isEmpty()) {
-			return;
-		}
-
-		try {
-			Proposal proposal = new Proposal(rp.getRevWalk(), cmds)
-				.setPushCertificate(rp.getPushCertificate())
-				.setAuthor(rp.getRefLogIdent())
-				.setMessage("push"); //$NON-NLS-1$
-			leader.queueProposal(proposal);
-			if (proposal.isDone()) {
-				// This failed fast, e.g. conflict or bad precondition.
-				return;
-			}
-
-			ProgressSpinner spinner = new ProgressSpinner(
-					rp.getMessageOutputStream());
-			if (proposal.getState() == QUEUED) {
-				waitForQueue(proposal, spinner);
-			}
-			if (!proposal.isDone()) {
-				waitForPropose(proposal, spinner);
-			}
-		} catch (IOException | InterruptedException e) {
-			String msg = JGitText.get().transactionAborted;
-			for (ReceiveCommand cmd : cmds) {
-				if (cmd.getResult() == NOT_ATTEMPTED) {
-					cmd.setResult(REJECTED_OTHER_REASON, msg);
-				}
-			}
-			log.error(msg, e);
-		}
-	}
-
-	private void waitForQueue(Proposal proposal, ProgressSpinner spinner)
-			throws InterruptedException {
-		spinner.beginTask(KetchText.get().waitingForQueue, 1, SECONDS);
-		while (!proposal.awaitStateChange(QUEUED, 250, MILLISECONDS)) {
-			spinner.update();
-		}
-		switch (proposal.getState()) {
-		case RUNNING:
-		default:
-			spinner.endTask(KetchText.get().starting);
-			break;
-
-		case EXECUTED:
-			spinner.endTask(KetchText.get().accepted);
-			break;
-
-		case ABORTED:
-			spinner.endTask(KetchText.get().failed);
-			break;
-		}
-	}
-
-	private void waitForPropose(Proposal proposal, ProgressSpinner spinner)
-			throws InterruptedException {
-		spinner.beginTask(KetchText.get().proposingUpdates, 2, SECONDS);
-		while (!proposal.await(250, MILLISECONDS)) {
-			spinner.update();
-		}
-		spinner.endTask(proposal.getState() == EXECUTED
-				? KetchText.get().accepted
-				: KetchText.get().failed);
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchReplica.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchReplica.java
deleted file mode 100644
index a9a694a565..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchReplica.java
+++ /dev/null
@@ -1,758 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitSpeed.BATCHED;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitSpeed.FAST;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.CURRENT;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.LAGGING;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.OFFLINE;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.UNKNOWN;
-import static org.eclipse.jgit.lib.Constants.HEAD;
-import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Type.CREATE;
-
-import java.io.IOException;
-import java.lang.ref.WeakReference;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.Callable;
-import java.util.concurrent.Future;
-
-import org.eclipse.jgit.annotations.NonNull;
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.internal.storage.reftree.RefTree;
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.treewalk.TreeWalk;
-import org.eclipse.jgit.util.FileUtils;
-import org.eclipse.jgit.util.SystemReader;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * A Ketch replica, either {@link org.eclipse.jgit.internal.ketch.LocalReplica}
- * or {@link org.eclipse.jgit.internal.ketch.RemoteGitReplica}.
- * <p>
- * Replicas can be either a stock Git replica, or a Ketch-aware replica.
- * <p>
- * A stock Git replica has no special knowledge of Ketch and simply stores
- * objects and references. Ketch communicates with the stock Git replica using
- * the Git push wire protocol. The
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader} commits an agreed upon
- * state by pushing all references to the Git replica, for example
- * {@code "refs/heads/master"} is pushed during commit. Stock Git replicas use
- * {@link org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod#ALL_REFS} to
- * record the final state.
- * <p>
- * Ketch-aware replicas understand the {@code RefTree} sent during the proposal
- * and during commit are able to update their own reference space to match the
- * state represented by the {@code RefTree}. Ketch-aware replicas typically use
- * a {@link org.eclipse.jgit.internal.storage.reftree.RefTreeDatabase} and
- * {@link org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod#TXN_COMMITTED}
- * to record the final state.
- * <p>
- * KetchReplica instances are tightly coupled with a single
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader}. Some state may be
- * accessed by the leader thread and uses the leader's own
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader#lock} to protect shared
- * data.
- */
-public abstract class KetchReplica {
-	static final Logger log = LoggerFactory.getLogger(KetchReplica.class);
-	private static final byte[] PEEL = { ' ', '^' };
-
-	/** Participation of a replica in establishing consensus. */
-	public enum Participation {
-		/** Replica can vote. */
-		FULL,
-
-		/** Replica does not vote, but tracks leader. */
-		FOLLOWER_ONLY;
-	}
-
-	/** How this replica wants to receive Ketch commit operations. */
-	public enum CommitMethod {
-		/** All references are pushed to the peer as standard Git. */
-		ALL_REFS,
-
-		/** Only {@code refs/txn/committed} is written/updated. */
-		TXN_COMMITTED;
-	}
-
-	/** Delay before committing to a replica. */
-	public enum CommitSpeed {
-		/**
-		 * Send the commit immediately, even if it could be batched with the
-		 * next proposal.
-		 */
-		FAST,
-
-		/**
-		 * If the next proposal is available, batch the commit with it,
-		 * otherwise just send the commit. This generates less network use, but
-		 * may provide slower consistency on the replica.
-		 */
-		BATCHED;
-	}
-
-	/** Current state of a replica. */
-	public enum State {
-		/** Leader has not yet contacted the replica. */
-		UNKNOWN,
-
-		/** Replica is behind the consensus. */
-		LAGGING,
-
-		/** Replica matches the consensus. */
-		CURRENT,
-
-		/** Replica has a different (or unknown) history. */
-		DIVERGENT,
-
-		/** Replica's history contains the leader's history. */
-		AHEAD,
-
-		/** Replica can not be contacted. */
-		OFFLINE;
-	}
-
-	private final KetchLeader leader;
-	private final String replicaName;
-	private final Participation participation;
-	private final CommitMethod commitMethod;
-	private final CommitSpeed commitSpeed;
-	private final long minRetryMillis;
-	private final long maxRetryMillis;
-	private final Map<ObjectId, List<ReceiveCommand>> staged;
-	private final Map<String, ReceiveCommand> running;
-	private final Map<String, ReceiveCommand> waiting;
-	private final List<ReplicaPushRequest> queued;
-
-	/**
-	 * Value known for {@code "refs/txn/accepted"}.
-	 * <p>
-	 * Raft literature refers to this as {@code matchIndex}.
-	 */
-	private ObjectId txnAccepted;
-
-	/**
-	 * Value known for {@code "refs/txn/committed"}.
-	 * <p>
-	 * Raft literature refers to this as {@code commitIndex}. In traditional
-	 * Raft this is a state variable inside the follower implementation, but
-	 * Ketch keeps it in the leader.
-	 */
-	private ObjectId txnCommitted;
-
-	/** What is happening with this replica. */
-	private State state = UNKNOWN;
-	private String error;
-
-	/** Scheduled retry due to communication failure. */
-	private Future<?> retryFuture;
-	private long lastRetryMillis;
-	private long retryAtMillis;
-
-	/**
-	 * Configure a replica representation.
-	 *
-	 * @param leader
-	 *            instance this replica follows.
-	 * @param name
-	 *            unique-ish name identifying this replica for debugging.
-	 * @param cfg
-	 *            how Ketch should treat the replica.
-	 */
-	protected KetchReplica(KetchLeader leader, String name, ReplicaConfig cfg) {
-		this.leader = leader;
-		this.replicaName = name;
-		this.participation = cfg.getParticipation();
-		this.commitMethod = cfg.getCommitMethod();
-		this.commitSpeed = cfg.getCommitSpeed();
-		this.minRetryMillis = cfg.getMinRetry(MILLISECONDS);
-		this.maxRetryMillis = cfg.getMaxRetry(MILLISECONDS);
-		this.staged = new HashMap<>();
-		this.running = new HashMap<>();
-		this.waiting = new HashMap<>();
-		this.queued = new ArrayList<>(4);
-	}
-
-	/**
-	 * Get system configuration.
-	 *
-	 * @return system configuration.
-	 */
-	public KetchSystem getSystem() {
-		return getLeader().getSystem();
-	}
-
-	/**
-	 * Get leader instance this replica follows.
-	 *
-	 * @return leader instance this replica follows.
-	 */
-	public KetchLeader getLeader() {
-		return leader;
-	}
-
-	/**
-	 * Get unique-ish name for debugging.
-	 *
-	 * @return unique-ish name for debugging.
-	 */
-	public String getName() {
-		return replicaName;
-	}
-
-	/**
-	 * Get description of this replica for error/debug logging purposes.
-	 *
-	 * @return description of this replica for error/debug logging purposes.
-	 */
-	protected String describeForLog() {
-		return getName();
-	}
-
-	/**
-	 * Get how the replica participates in this Ketch system.
-	 *
-	 * @return how the replica participates in this Ketch system.
-	 */
-	public Participation getParticipation() {
-		return participation;
-	}
-
-	/**
-	 * Get how Ketch will commit to the repository.
-	 *
-	 * @return how Ketch will commit to the repository.
-	 */
-	public CommitMethod getCommitMethod() {
-		return commitMethod;
-	}
-
-	/**
-	 * Get when Ketch will commit to the repository.
-	 *
-	 * @return when Ketch will commit to the repository.
-	 */
-	public CommitSpeed getCommitSpeed() {
-		return commitSpeed;
-	}
-
-	/**
-	 * Called by leader to perform graceful shutdown.
-	 * <p>
-	 * Default implementation cancels any scheduled retry. Subclasses may add
-	 * additional logic before or after calling {@code super.shutdown()}.
-	 * <p>
-	 * Called with {@link org.eclipse.jgit.internal.ketch.KetchLeader#lock} held
-	 * by caller.
-	 */
-	protected void shutdown() {
-		Future<?> f = retryFuture;
-		if (f != null) {
-			retryFuture = null;
-			f.cancel(true);
-		}
-	}
-
-	ReplicaSnapshot snapshot() {
-		ReplicaSnapshot s = new ReplicaSnapshot(this);
-		s.accepted = txnAccepted;
-		s.committed = txnCommitted;
-		s.state = state;
-		s.error = error;
-		s.retryAtMillis = waitingForRetry() ? retryAtMillis : 0;
-		return s;
-	}
-
-	/**
-	 * Update the leader's view of the replica after a poll.
-	 * <p>
-	 * Called with {@link KetchLeader#lock} held by caller.
-	 *
-	 * @param refs
-	 *            map of refs from the replica.
-	 */
-	void initialize(Map<String, Ref> refs) {
-		if (txnAccepted == null) {
-			txnAccepted = getId(refs.get(getSystem().getTxnAccepted()));
-		}
-		if (txnCommitted == null) {
-			txnCommitted = getId(refs.get(getSystem().getTxnCommitted()));
-		}
-	}
-
-	ObjectId getTxnAccepted() {
-		return txnAccepted;
-	}
-
-	boolean hasAccepted(LogIndex id) {
-		return equals(txnAccepted, id);
-	}
-
-	private static boolean equals(@Nullable ObjectId a, LogIndex b) {
-		return a != null && b != null && AnyObjectId.isEqual(a, b);
-	}
-
-	/**
-	 * Schedule a proposal round with the replica.
-	 * <p>
-	 * Called with {@link KetchLeader#lock} held by caller.
-	 *
-	 * @param round
-	 *            current round being run by the leader.
-	 */
-	void pushTxnAcceptedAsync(Round round) {
-		List<ReceiveCommand> cmds = new ArrayList<>();
-		if (commitSpeed == BATCHED) {
-			LogIndex committedIndex = leader.getCommitted();
-			if (equals(txnAccepted, committedIndex)
-					&& !equals(txnCommitted, committedIndex)) {
-				prepareTxnCommitted(cmds, committedIndex);
-			}
-		}
-
-		// TODO(sop) Lagging replicas should build accept on the fly.
-		if (round.stageCommands != null) {
-			for (ReceiveCommand cmd : round.stageCommands) {
-				// TODO(sop): Do not send certain object graphs to replica.
-				cmds.add(copy(cmd));
-			}
-		}
-		cmds.add(new ReceiveCommand(
-				round.acceptedOldIndex, round.acceptedNewIndex,
-				getSystem().getTxnAccepted()));
-		pushAsync(new ReplicaPushRequest(this, cmds));
-	}
-
-	private static ReceiveCommand copy(ReceiveCommand c) {
-		return new ReceiveCommand(c.getOldId(), c.getNewId(), c.getRefName());
-	}
-
-	boolean shouldPushUnbatchedCommit(LogIndex committed, boolean leaderIdle) {
-		return (leaderIdle || commitSpeed == FAST) && hasAccepted(committed);
-	}
-
-	void pushCommitAsync(LogIndex committed) {
-		List<ReceiveCommand> cmds = new ArrayList<>();
-		prepareTxnCommitted(cmds, committed);
-		pushAsync(new ReplicaPushRequest(this, cmds));
-	}
-
-	private void prepareTxnCommitted(List<ReceiveCommand> cmds,
-			ObjectId committed) {
-		removeStaged(cmds, committed);
-		cmds.add(new ReceiveCommand(
-				txnCommitted, committed,
-				getSystem().getTxnCommitted()));
-	}
-
-	private void removeStaged(List<ReceiveCommand> cmds, ObjectId committed) {
-		List<ReceiveCommand> a = staged.remove(committed);
-		if (a != null) {
-			delete(cmds, a);
-		}
-		if (staged.isEmpty() || !(committed instanceof LogIndex)) {
-			return;
-		}
-
-		LogIndex committedIndex = (LogIndex) committed;
-		Iterator<Map.Entry<ObjectId, List<ReceiveCommand>>> itr = staged
-				.entrySet().iterator();
-		while (itr.hasNext()) {
-			Map.Entry<ObjectId, List<ReceiveCommand>> e = itr.next();
-			if (e.getKey() instanceof LogIndex) {
-				LogIndex stagedIndex = (LogIndex) e.getKey();
-				if (stagedIndex.isBefore(committedIndex)) {
-					delete(cmds, e.getValue());
-					itr.remove();
-				}
-			}
-		}
-	}
-
-	private static void delete(List<ReceiveCommand> cmds,
-			List<ReceiveCommand> createCmds) {
-		for (ReceiveCommand cmd : createCmds) {
-			ObjectId id = cmd.getNewId();
-			String name = cmd.getRefName();
-			cmds.add(new ReceiveCommand(id, ObjectId.zeroId(), name));
-		}
-	}
-
-	/**
-	 * Determine the next push for this replica (if any) and start it.
-	 * <p>
-	 * If the replica has successfully accepted the committed state of the
-	 * leader, this method will push all references to the replica using the
-	 * configured {@link CommitMethod}.
-	 * <p>
-	 * If the replica is {@link State#LAGGING} this method will begin catch up
-	 * by sending a more recent {@code refs/txn/accepted}.
-	 * <p>
-	 * Must be invoked with {@link KetchLeader#lock} held by caller.
-	 */
-	private void runNextPushRequest() {
-		LogIndex committed = leader.getCommitted();
-		if (!equals(txnCommitted, committed)
-				&& shouldPushUnbatchedCommit(committed, leader.isIdle())) {
-			pushCommitAsync(committed);
-		}
-
-		if (queued.isEmpty() || !running.isEmpty() || waitingForRetry()) {
-			return;
-		}
-
-		// Collapse all queued requests into a single request.
-		Map<String, ReceiveCommand> cmdMap = new HashMap<>();
-		for (ReplicaPushRequest req : queued) {
-			for (ReceiveCommand cmd : req.getCommands()) {
-				String name = cmd.getRefName();
-				ReceiveCommand old = cmdMap.remove(name);
-				if (old != null) {
-					cmd = new ReceiveCommand(
-							old.getOldId(), cmd.getNewId(),
-							name);
-				}
-				cmdMap.put(name, cmd);
-			}
-		}
-		queued.clear();
-		waiting.clear();
-
-		List<ReceiveCommand> next = new ArrayList<>(cmdMap.values());
-		for (ReceiveCommand cmd : next) {
-			running.put(cmd.getRefName(), cmd);
-		}
-		startPush(new ReplicaPushRequest(this, next));
-	}
-
-	private void pushAsync(ReplicaPushRequest req) {
-		if (defer(req)) {
-			// TODO(sop) Collapse during long retry outage.
-			for (ReceiveCommand cmd : req.getCommands()) {
-				waiting.put(cmd.getRefName(), cmd);
-			}
-			queued.add(req);
-		} else {
-			for (ReceiveCommand cmd : req.getCommands()) {
-				running.put(cmd.getRefName(), cmd);
-			}
-			startPush(req);
-		}
-	}
-
-	private boolean defer(ReplicaPushRequest req) {
-		if (waitingForRetry()) {
-			// Prior communication failure; everything is deferred.
-			return true;
-		}
-
-		for (ReceiveCommand nextCmd : req.getCommands()) {
-			ReceiveCommand priorCmd = waiting.get(nextCmd.getRefName());
-			if (priorCmd == null) {
-				priorCmd = running.get(nextCmd.getRefName());
-			}
-			if (priorCmd != null) {
-				// Another request pending on same ref; that must go first.
-				// Verify priorCmd.newId == nextCmd.oldId?
-				return true;
-			}
-		}
-		return false;
-	}
-
-	private boolean waitingForRetry() {
-		Future<?> f = retryFuture;
-		return f != null && !f.isDone();
-	}
-
-	private void retryLater(ReplicaPushRequest req) {
-		Collection<ReceiveCommand> cmds = req.getCommands();
-		for (ReceiveCommand cmd : cmds) {
-			cmd.setResult(NOT_ATTEMPTED, null);
-			if (!waiting.containsKey(cmd.getRefName())) {
-				waiting.put(cmd.getRefName(), cmd);
-			}
-		}
-		queued.add(0, new ReplicaPushRequest(this, cmds));
-
-		if (!waitingForRetry()) {
-			long delay = FileUtils
-				.delay(lastRetryMillis, minRetryMillis, maxRetryMillis);
-			if (log.isDebugEnabled()) {
-				log.debug("Retrying {} after {} ms", //$NON-NLS-1$
-						describeForLog(), Long.valueOf(delay));
-			}
-			lastRetryMillis = delay;
-			retryAtMillis = SystemReader.getInstance().getCurrentTime() + delay;
-			retryFuture = getSystem().getExecutor()
-					.schedule(new WeakRetryPush(this), delay, MILLISECONDS);
-		}
-	}
-
-	/** Weakly holds a retrying replica, allowing it to garbage collect. */
-	static class WeakRetryPush extends WeakReference<KetchReplica>
-			implements Callable<Void> {
-		WeakRetryPush(KetchReplica r) {
-			super(r);
-		}
-
-		@Override
-		public Void call() throws Exception {
-			KetchReplica r = get();
-			if (r != null) {
-				r.doRetryPush();
-			}
-			return null;
-		}
-	}
-
-	private void doRetryPush() {
-		leader.lock.lock();
-		try {
-			retryFuture = null;
-			runNextPushRequest();
-		} finally {
-			leader.lock.unlock();
-		}
-	}
-
-	/**
-	 * Begin executing a single push.
-	 * <p>
-	 * This method must move processing onto another thread. Called with
-	 * {@link org.eclipse.jgit.internal.ketch.KetchLeader#lock} held by caller.
-	 *
-	 * @param req
-	 *            the request to send to the replica.
-	 */
-	protected abstract void startPush(ReplicaPushRequest req);
-
-	/**
-	 * Callback from {@link ReplicaPushRequest} upon success or failure.
-	 * <p>
-	 * Acquires the {@link KetchLeader#lock} and updates the leader's internal
-	 * knowledge about this replica to reflect what has been learned during a
-	 * push to the replica. In some cases of divergence this method may take
-	 * some time to determine how the replica has diverged; to reduce contention
-	 * this is evaluated before acquiring the leader lock.
-	 *
-	 * @param repo
-	 *            local repository instance used by the push thread.
-	 * @param req
-	 *            push request just attempted.
-	 */
-	void afterPush(@Nullable Repository repo, ReplicaPushRequest req) {
-		ReceiveCommand acceptCmd = null;
-		ReceiveCommand commitCmd = null;
-		List<ReceiveCommand> stages = null;
-
-		for (ReceiveCommand cmd : req.getCommands()) {
-			String name = cmd.getRefName();
-			if (name.equals(getSystem().getTxnAccepted())) {
-				acceptCmd = cmd;
-			} else if (name.equals(getSystem().getTxnCommitted())) {
-				commitCmd = cmd;
-			} else if (cmd.getResult() == OK && cmd.getType() == CREATE
-					&& name.startsWith(getSystem().getTxnStage())) {
-				if (stages == null) {
-					stages = new ArrayList<>();
-				}
-				stages.add(cmd);
-			}
-		}
-
-		State newState = null;
-		ObjectId acceptId = readId(req, acceptCmd);
-		if (repo != null && acceptCmd != null && acceptCmd.getResult() != OK
-				&& req.getException() == null) {
-			try (LagCheck lag = new LagCheck(this, repo)) {
-				newState = lag.check(acceptId, acceptCmd);
-				acceptId = lag.getRemoteId();
-			}
-		}
-
-		leader.lock.lock();
-		try {
-			for (ReceiveCommand cmd : req.getCommands()) {
-				running.remove(cmd.getRefName());
-			}
-
-			Throwable err = req.getException();
-			if (err != null) {
-				state = OFFLINE;
-				error = err.toString();
-				retryLater(req);
-				leader.onReplicaUpdate(this);
-				return;
-			}
-
-			lastRetryMillis = 0;
-			error = null;
-			updateView(req, acceptId, commitCmd);
-
-			if (acceptCmd != null && acceptCmd.getResult() == OK) {
-				state = hasAccepted(leader.getHead()) ? CURRENT : LAGGING;
-				if (stages != null) {
-					staged.put(acceptCmd.getNewId(), stages);
-				}
-			} else if (newState != null) {
-				state = newState;
-			}
-
-			leader.onReplicaUpdate(this);
-			runNextPushRequest();
-		} finally {
-			leader.lock.unlock();
-		}
-	}
-
-	private void updateView(ReplicaPushRequest req, @Nullable ObjectId acceptId,
-			ReceiveCommand commitCmd) {
-		if (acceptId != null) {
-			txnAccepted = acceptId;
-		}
-
-		ObjectId committed = readId(req, commitCmd);
-		if (committed != null) {
-			txnCommitted = committed;
-		} else if (acceptId != null && txnCommitted == null) {
-			// Initialize during first conversation.
-			Map<String, Ref> adv = req.getRefs();
-			if (adv != null) {
-				Ref refs = adv.get(getSystem().getTxnCommitted());
-				txnCommitted = getId(refs);
-			}
-		}
-	}
-
-	@Nullable
-	private static ObjectId readId(ReplicaPushRequest req,
-			@Nullable ReceiveCommand cmd) {
-		if (cmd == null) {
-			// Ref was not in the command list, do not trust advertisement.
-			return null;
-
-		} else if (cmd.getResult() == OK) {
-			// Currently at newId.
-			return cmd.getNewId();
-		}
-
-		Map<String, Ref> refs = req.getRefs();
-		return refs != null ? getId(refs.get(cmd.getRefName())) : null;
-	}
-
-	/**
-	 * Fetch objects from the remote using the calling thread.
-	 * <p>
-	 * Called without {@link org.eclipse.jgit.internal.ketch.KetchLeader#lock}.
-	 *
-	 * @param repo
-	 *            local repository to fetch objects into.
-	 * @param req
-	 *            the request to fetch from a replica.
-	 * @throws java.io.IOException
-	 *             communication with the replica was not possible.
-	 */
-	protected abstract void blockingFetch(Repository repo,
-			ReplicaFetchRequest req) throws IOException;
-
-	/**
-	 * Build a list of commands to commit
-	 * {@link org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod#ALL_REFS}.
-	 *
-	 * @param git
-	 *            local leader repository to read committed state from.
-	 * @param current
-	 *            all known references in the replica's repository. Typically
-	 *            this comes from a push advertisement.
-	 * @param committed
-	 *            state being pushed to {@code refs/txn/committed}.
-	 * @return commands to update during commit.
-	 * @throws java.io.IOException
-	 *             cannot read the committed state.
-	 */
-	protected Collection<ReceiveCommand> prepareCommit(Repository git,
-			Map<String, Ref> current, ObjectId committed) throws IOException {
-		List<ReceiveCommand> delta = new ArrayList<>();
-		Map<String, Ref> remote = new HashMap<>(current);
-		try (RevWalk rw = new RevWalk(git);
-				TreeWalk tw = new TreeWalk(rw.getObjectReader())) {
-			tw.setRecursive(true);
-			tw.addTree(rw.parseCommit(committed).getTree());
-			while (tw.next()) {
-				if (tw.getRawMode(0) != TYPE_GITLINK
-						|| tw.isPathSuffix(PEEL, 2)) {
-					// Symbolic references cannot be pushed.
-					// Caching peeled values is handled remotely.
-					continue;
-				}
-
-				// TODO(sop) Do not send certain ref names to replica.
-				String name = RefTree.refName(tw.getPathString());
-				Ref oldRef = remote.remove(name);
-				ObjectId oldId = getId(oldRef);
-				ObjectId newId = tw.getObjectId(0);
-				if (!AnyObjectId.isEqual(oldId, newId)) {
-					delta.add(new ReceiveCommand(oldId, newId, name));
-				}
-			}
-		}
-
-		// Delete any extra references not in the committed state.
-		for (Ref ref : remote.values()) {
-			if (canDelete(ref)) {
-				delta.add(new ReceiveCommand(
-					ref.getObjectId(), ObjectId.zeroId(),
-					ref.getName()));
-			}
-		}
-		return delta;
-	}
-
-	boolean canDelete(Ref ref) {
-		String name = ref.getName();
-		if (HEAD.equals(name)) {
-			return false;
-		}
-		if (name.startsWith(getSystem().getTxnNamespace())) {
-			return false;
-		}
-		// TODO(sop) Do not delete precious names from replica.
-		return true;
-	}
-
-	@NonNull
-	static ObjectId getId(@Nullable Ref ref) {
-		if (ref != null) {
-			ObjectId id = ref.getObjectId();
-			if (id != null) {
-				return id;
-			}
-		}
-		return ObjectId.zeroId();
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchSystem.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchSystem.java
deleted file mode 100644
index 8ad1d6033a..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchSystem.java
+++ /dev/null
@@ -1,320 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchConstants.ACCEPTED;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.COMMITTED;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.CONFIG_KEY_TYPE;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.CONFIG_SECTION_KETCH;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.DEFAULT_TXN_NAMESPACE;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.STAGE;
-import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_NAME;
-import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_REMOTE;
-
-import java.net.URISyntaxException;
-import java.time.Duration;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Random;
-import java.util.concurrent.Executors;
-import java.util.concurrent.ScheduledExecutorService;
-import java.util.concurrent.ThreadFactory;
-import java.util.concurrent.atomic.AtomicInteger;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.Config;
-import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.transport.RemoteConfig;
-import org.eclipse.jgit.transport.URIish;
-import org.eclipse.jgit.util.time.MonotonicClock;
-import org.eclipse.jgit.util.time.MonotonicSystemClock;
-import org.eclipse.jgit.util.time.ProposedTimestamp;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * Ketch system-wide configuration.
- * <p>
- * This class provides useful defaults for testing and small proof of concepts.
- * Full scale installations are expected to subclass and override methods to
- * provide consistent configuration across all managed repositories.
- * <p>
- * Servers should configure their own
- * {@link java.util.concurrent.ScheduledExecutorService}.
- */
-public class KetchSystem {
-	private static final Random RNG = new Random();
-
-	/**
-	 * Get default executor, one thread per available processor.
-	 *
-	 * @return default executor, one thread per available processor.
-	 */
-	public static ScheduledExecutorService defaultExecutor() {
-		return DefaultExecutorHolder.I;
-	}
-
-	private final ScheduledExecutorService executor;
-	private final MonotonicClock clock;
-	private final String txnNamespace;
-	private final String txnAccepted;
-	private final String txnCommitted;
-	private final String txnStage;
-
-	/**
-	 * Create a default system with a thread pool of 1 thread per CPU.
-	 */
-	public KetchSystem() {
-		this(defaultExecutor(), new MonotonicSystemClock(), DEFAULT_TXN_NAMESPACE);
-	}
-
-	/**
-	 * Create a Ketch system with the provided executor service.
-	 *
-	 * @param executor
-	 *            thread pool to run background operations.
-	 * @param clock
-	 *            clock to create timestamps.
-	 * @param txnNamespace
-	 *            reference namespace for the RefTree graph and associated
-	 *            transaction state. Must begin with {@code "refs/"} and end
-	 *            with {@code '/'}, for example {@code "refs/txn/"}.
-	 */
-	public KetchSystem(ScheduledExecutorService executor, MonotonicClock clock,
-			String txnNamespace) {
-		this.executor = executor;
-		this.clock = clock;
-		this.txnNamespace = txnNamespace;
-		this.txnAccepted = txnNamespace + ACCEPTED;
-		this.txnCommitted = txnNamespace + COMMITTED;
-		this.txnStage = txnNamespace + STAGE;
-	}
-
-	/**
-	 * Get executor to perform background operations.
-	 *
-	 * @return executor to perform background operations.
-	 */
-	public ScheduledExecutorService getExecutor() {
-		return executor;
-	}
-
-	/**
-	 * Get clock to obtain timestamps from.
-	 *
-	 * @return clock to obtain timestamps from.
-	 */
-	public MonotonicClock getClock() {
-		return clock;
-	}
-
-	/**
-	 * Get how long the leader will wait for the {@link #getClock()}'s
-	 * {@code ProposedTimestamp} used in commits proposed to the RefTree graph
-	 * ({@link #getTxnAccepted()})
-	 *
-	 * @return how long the leader will wait for the {@link #getClock()}'s
-	 *         {@code ProposedTimestamp} used in commits proposed to the RefTree
-	 *         graph ({@link #getTxnAccepted()}). Defaults to 5 seconds.
-	 */
-	public Duration getMaxWaitForMonotonicClock() {
-		return Duration.ofSeconds(5);
-	}
-
-	/**
-	 * Whether elections should require monotonically increasing commit
-	 * timestamps
-	 *
-	 * @return {@code true} if elections should require monotonically increasing
-	 *         commit timestamps. This requires a very good
-	 *         {@link org.eclipse.jgit.util.time.MonotonicClock}.
-	 */
-	public boolean requireMonotonicLeaderElections() {
-		return false;
-	}
-
-	/**
-	 * Get the namespace used for the RefTree graph and transaction management.
-	 *
-	 * @return reference namespace such as {@code "refs/txn/"}.
-	 */
-	public String getTxnNamespace() {
-		return txnNamespace;
-	}
-
-	/**
-	 * Get name of the accepted RefTree graph.
-	 *
-	 * @return name of the accepted RefTree graph.
-	 */
-	public String getTxnAccepted() {
-		return txnAccepted;
-	}
-
-	/**
-	 * Get name of the committed RefTree graph.
-	 *
-	 * @return name of the committed RefTree graph.
-	 */
-	public String getTxnCommitted() {
-		return txnCommitted;
-	}
-
-	/**
-	 * Get prefix for staged objects, e.g. {@code "refs/txn/stage/"}.
-	 *
-	 * @return prefix for staged objects, e.g. {@code "refs/txn/stage/"}.
-	 */
-	public String getTxnStage() {
-		return txnStage;
-	}
-
-	/**
-	 * Create new committer {@code PersonIdent} for ketch system
-	 *
-	 * @param time
-	 *            timestamp for the committer.
-	 * @return identity line for the committer header of a RefTreeGraph.
-	 */
-	public PersonIdent newCommitter(ProposedTimestamp time) {
-		String name = "ketch"; //$NON-NLS-1$
-		String email = "ketch@system"; //$NON-NLS-1$
-		return new PersonIdent(name, email, time);
-	}
-
-	/**
-	 * Construct a random tag to identify a candidate during leader election.
-	 * <p>
-	 * Multiple processes trying to elect themselves leaders at exactly the same
-	 * time (rounded to seconds) using the same
-	 * {@link #newCommitter(ProposedTimestamp)} identity strings, for the same
-	 * term, may generate the same ObjectId for the election commit and falsely
-	 * assume they have both won.
-	 * <p>
-	 * Candidates add this tag to their election ballot commit to disambiguate
-	 * the election. The tag only needs to be unique for a given triplet of
-	 * {@link #newCommitter(ProposedTimestamp)}, system time (rounded to
-	 * seconds), and term. If every replica in the system uses a unique
-	 * {@code newCommitter} (such as including the host name after the
-	 * {@code "@"} in the email address) the tag could be the empty string.
-	 * <p>
-	 * The default implementation generates a few bytes of random data.
-	 *
-	 * @return unique tag; null or empty string if {@code newCommitter()} is
-	 *         sufficiently unique to identify the leader.
-	 */
-	@Nullable
-	public String newLeaderTag() {
-		int n = RNG.nextInt(1 << (6 * 4));
-		return String.format("%06x", Integer.valueOf(n)); //$NON-NLS-1$
-	}
-
-	/**
-	 * Construct the KetchLeader instance of a repository.
-	 *
-	 * @param repo
-	 *            local repository stored by the leader.
-	 * @return leader instance.
-	 * @throws java.net.URISyntaxException
-	 *             a follower configuration contains an unsupported URI.
-	 */
-	public KetchLeader createLeader(Repository repo)
-			throws URISyntaxException {
-		KetchLeader leader = new KetchLeader(this) {
-			@Override
-			protected Repository openRepository() {
-				repo.incrementOpen();
-				return repo;
-			}
-		};
-		leader.setReplicas(createReplicas(leader, repo));
-		return leader;
-	}
-
-	/**
-	 * Get the collection of replicas for a repository.
-	 * <p>
-	 * The collection of replicas must include the local repository.
-	 *
-	 * @param leader
-	 *            the leader driving these replicas.
-	 * @param repo
-	 *            repository to get the replicas of.
-	 * @return collection of replicas for the specified repository.
-	 * @throws java.net.URISyntaxException
-	 *             a configured URI is invalid.
-	 */
-	protected List<KetchReplica> createReplicas(KetchLeader leader,
-			Repository repo) throws URISyntaxException {
-		List<KetchReplica> replicas = new ArrayList<>();
-		Config cfg = repo.getConfig();
-		String localName = getLocalName(cfg);
-		for (String name : cfg.getSubsections(CONFIG_KEY_REMOTE)) {
-			if (!hasParticipation(cfg, name)) {
-				continue;
-			}
-
-			ReplicaConfig kc = ReplicaConfig.newFromConfig(cfg, name);
-			if (name.equals(localName)) {
-				replicas.add(new LocalReplica(leader, name, kc));
-				continue;
-			}
-
-			RemoteConfig rc = new RemoteConfig(cfg, name);
-			List<URIish> uris = rc.getPushURIs();
-			if (uris.isEmpty()) {
-				uris = rc.getURIs();
-			}
-			for (URIish uri : uris) {
-				String n = uris.size() == 1 ? name : uri.getHost();
-				replicas.add(new RemoteGitReplica(leader, n, uri, kc, rc));
-			}
-		}
-		return replicas;
-	}
-
-	private static boolean hasParticipation(Config cfg, String name) {
-		return cfg.getString(CONFIG_KEY_REMOTE, name, CONFIG_KEY_TYPE) != null;
-	}
-
-	private static String getLocalName(Config cfg) {
-		return cfg.getString(CONFIG_SECTION_KETCH, null, CONFIG_KEY_NAME);
-	}
-
-	static class DefaultExecutorHolder {
-		private static final Logger log = LoggerFactory.getLogger(KetchSystem.class);
-		static final ScheduledExecutorService I = create();
-
-		private static ScheduledExecutorService create() {
-			int cores = Runtime.getRuntime().availableProcessors();
-			int threads = Math.max(5, cores);
-			log.info("Using {} threads", Integer.valueOf(threads)); //$NON-NLS-1$
-			return Executors.newScheduledThreadPool(
-				threads,
-				new ThreadFactory() {
-					private final AtomicInteger threadCnt = new AtomicInteger();
-
-					@Override
-					public Thread newThread(Runnable r) {
-						int id = threadCnt.incrementAndGet();
-						Thread thr = new Thread(r);
-						thr.setName("KetchExecutor-" + id); //$NON-NLS-1$
-						return thr;
-					}
-				});
-		}
-
-		private DefaultExecutorHolder() {
-		}
-	}
-
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchText.java
deleted file mode 100644
index 6f9038bbdf..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/KetchText.java
+++ /dev/null
@@ -1,43 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import org.eclipse.jgit.nls.NLS;
-import org.eclipse.jgit.nls.TranslationBundle;
-
-/**
- * Translation bundle for the Ketch implementation.
- */
-public class KetchText extends TranslationBundle {
-	/**
-	 * Get an instance of this translation bundle.
-	 *
-	 * @return instance of this translation bundle.
-	 */
-	public static KetchText get() {
-		return NLS.getBundleFor(KetchText.class);
-	}
-
-	// @formatter:off
-	/***/ public String accepted;
-	/***/ public String cannotFetchFromLocalReplica;
-	/***/ public String failed;
-	/***/ public String invalidFollowerUri;
-	/***/ public String leaderFailedToStore;
-	/***/ public String localReplicaRequired;
-	/***/ public String mismatchedTxnNamespace;
-	/***/ public String outsideTxnNamespace;
-	/***/ public String proposingUpdates;
-	/***/ public String queuedProposalFailedToApply;
-	/***/ public String starting;
-	/***/ public String unsupportedVoterCount;
-	/***/ public String waitingForQueue;
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LagCheck.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LagCheck.java
deleted file mode 100644
index 1f8384ff76..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LagCheck.java
+++ /dev/null
@@ -1,151 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.AHEAD;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.DIVERGENT;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.LAGGING;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.UNKNOWN;
-import static org.eclipse.jgit.lib.Constants.OBJ_COMMIT;
-
-import java.io.IOException;
-import java.util.Collections;
-import java.util.Map;
-
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-
-/**
- * A helper to check if a {@link KetchReplica} is ahead or behind the leader.
- */
-class LagCheck implements AutoCloseable {
-	private final KetchReplica replica;
-	private final Repository repo;
-	private RevWalk rw;
-	private ObjectId remoteId;
-
-	LagCheck(KetchReplica replica, Repository repo) {
-		this.replica = replica;
-		this.repo = repo;
-		initRevWalk();
-	}
-
-	private void initRevWalk() {
-		if (rw != null) {
-			rw.close();
-		}
-
-		rw = new RevWalk(repo);
-		rw.setRetainBody(false);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void close() {
-		if (rw != null) {
-			rw.close();
-			rw = null;
-		}
-	}
-
-	ObjectId getRemoteId() {
-		return remoteId;
-	}
-
-	KetchReplica.State check(ObjectId acceptId, ReceiveCommand acceptCmd) {
-		remoteId = acceptId;
-		if (remoteId == null) {
-			// Nothing advertised by the replica, value is unknown.
-			return UNKNOWN;
-		}
-
-		if (AnyObjectId.isEqual(remoteId, ObjectId.zeroId())) {
-			// Replica does not have the txnAccepted reference.
-			return LAGGING;
-		}
-
-		try {
-			RevCommit remote;
-			try {
-				remote = parseRemoteCommit(acceptCmd.getRefName());
-			} catch (RefGoneException gone) {
-				// Replica does not have the txnAccepted reference.
-				return LAGGING;
-			} catch (MissingObjectException notFound) {
-				// Local repository does not know this commit so it cannot
-				// be including the replica's log.
-				return DIVERGENT;
-			}
-
-			RevCommit head = rw.parseCommit(acceptCmd.getNewId());
-			if (rw.isMergedInto(remote, head)) {
-				return LAGGING;
-			}
-
-			// TODO(sop) Check term to see if my leader was deposed.
-			if (rw.isMergedInto(head, remote)) {
-				return AHEAD;
-			}
-			return DIVERGENT;
-		} catch (IOException err) {
-			KetchReplica.log.error(String.format(
-					"Cannot compare %s", //$NON-NLS-1$
-					acceptCmd.getRefName()), err);
-			return UNKNOWN;
-		}
-	}
-
-	private RevCommit parseRemoteCommit(String refName)
-			throws IOException, MissingObjectException, RefGoneException {
-		try {
-			return rw.parseCommit(remoteId);
-		} catch (MissingObjectException notLocal) {
-			// Fall through and try to acquire the object by fetching it.
-		}
-
-		ReplicaFetchRequest fetch = new ReplicaFetchRequest(
-				Collections.singleton(refName),
-				Collections.<ObjectId> emptySet());
-		try {
-			replica.blockingFetch(repo, fetch);
-		} catch (IOException fetchErr) {
-			KetchReplica.log.error(String.format(
-					"Cannot fetch %s (%s) from %s", //$NON-NLS-1$
-					remoteId.abbreviate(8).name(), refName,
-					replica.describeForLog()), fetchErr);
-			throw new MissingObjectException(remoteId, OBJ_COMMIT);
-		}
-
-		Map<String, Ref> adv = fetch.getRefs();
-		if (adv == null) {
-			throw new MissingObjectException(remoteId, OBJ_COMMIT);
-		}
-
-		Ref ref = adv.get(refName);
-		if (ref == null || ref.getObjectId() == null) {
-			throw new RefGoneException();
-		}
-
-		initRevWalk();
-		remoteId = ref.getObjectId();
-		return rw.parseCommit(remoteId);
-	}
-
-	private static class RefGoneException extends Exception {
-		private static final long serialVersionUID = 1L;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LeaderSnapshot.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LeaderSnapshot.java
deleted file mode 100644
index ce0672c168..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LeaderSnapshot.java
+++ /dev/null
@@ -1,153 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchReplica.State.OFFLINE;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.List;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.ObjectId;
-
-/**
- * A snapshot of a leader and its view of the world.
- */
-public class LeaderSnapshot {
-	final List<ReplicaSnapshot> replicas = new ArrayList<>();
-	KetchLeader.State state;
-	long term;
-	LogIndex headIndex;
-	LogIndex committedIndex;
-	boolean idle;
-
-	LeaderSnapshot() {
-	}
-
-	/**
-	 * Get unmodifiable view of configured replicas.
-	 *
-	 * @return unmodifiable view of configured replicas.
-	 */
-	public Collection<ReplicaSnapshot> getReplicas() {
-		return Collections.unmodifiableList(replicas);
-	}
-
-	/**
-	 * Get current state of the leader.
-	 *
-	 * @return current state of the leader.
-	 */
-	public KetchLeader.State getState() {
-		return state;
-	}
-
-	/**
-	 * Whether the leader is not running a round to reach consensus, and has no
-	 * rounds queued.
-	 *
-	 * @return {@code true} if the leader is not running a round to reach
-	 *         consensus, and has no rounds queued.
-	 */
-	public boolean isIdle() {
-		return idle;
-	}
-
-	/**
-	 * Get term of this leader
-	 *
-	 * @return term of this leader. Valid only if {@link #getState()} is
-	 *         currently
-	 *         {@link org.eclipse.jgit.internal.ketch.KetchLeader.State#LEADER}.
-	 */
-	public long getTerm() {
-		return term;
-	}
-
-	/**
-	 * Get end of the leader's log
-	 *
-	 * @return end of the leader's log; null if leader hasn't started up enough
-	 *         to begin its own election.
-	 */
-	@Nullable
-	public LogIndex getHead() {
-		return headIndex;
-	}
-
-	/**
-	 * Get state the leader knows is committed on a majority of participant
-	 * replicas
-	 *
-	 * @return state the leader knows is committed on a majority of participant
-	 *         replicas. Null until the leader instance has committed a log
-	 *         index within its own term.
-	 */
-	@Nullable
-	public LogIndex getCommitted() {
-		return committedIndex;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public String toString() {
-		StringBuilder s = new StringBuilder();
-		s.append(isIdle() ? "IDLE" : "RUNNING"); //$NON-NLS-1$ //$NON-NLS-2$
-		s.append(" state ").append(getState()); //$NON-NLS-1$
-		if (getTerm() > 0) {
-			s.append(" term ").append(getTerm()); //$NON-NLS-1$
-		}
-		s.append('\n');
-		s.append(String.format(
-				"%-10s %12s %12s\n", //$NON-NLS-1$
-				"Replica", "Accepted", "Committed")); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
-		s.append("------------------------------------\n"); //$NON-NLS-1$
-		debug(s, "(leader)", getHead(), getCommitted()); //$NON-NLS-1$
-		s.append('\n');
-		for (ReplicaSnapshot r : getReplicas()) {
-			debug(s, r);
-			s.append('\n');
-		}
-		s.append('\n');
-		return s.toString();
-	}
-
-	private static void debug(StringBuilder b, ReplicaSnapshot s) {
-		KetchReplica replica = s.getReplica();
-		debug(b, replica.getName(), s.getAccepted(), s.getCommitted());
-		b.append(String.format(" %-8s %s", //$NON-NLS-1$
-				replica.getParticipation(), s.getState()));
-		if (s.getState() == OFFLINE) {
-			String err = s.getErrorMessage();
-			if (err != null) {
-				b.append(" (").append(err).append(')'); //$NON-NLS-1$
-			}
-		}
-	}
-
-	private static void debug(StringBuilder s, String name,
-			ObjectId accepted, ObjectId committed) {
-		s.append(String.format(
-				"%-10s %-12s %-12s", //$NON-NLS-1$
-				name, str(accepted), str(committed)));
-	}
-
-	static String str(ObjectId c) {
-		if (c instanceof LogIndex) {
-			return ((LogIndex) c).describeForLog();
-		} else if (c != null) {
-			return c.abbreviate(8).name();
-		}
-		return "-"; //$NON-NLS-1$
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LocalReplica.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LocalReplica.java
deleted file mode 100644
index b2d59d77da..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LocalReplica.java
+++ /dev/null
@@ -1,204 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod.ALL_REFS;
-import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod.TXN_COMMITTED;
-import static org.eclipse.jgit.lib.RefDatabase.ALL;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-
-import java.io.IOException;
-import java.text.MessageFormat;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.List;
-import java.util.Map;
-
-import org.eclipse.jgit.internal.storage.reftree.RefTreeDatabase;
-import org.eclipse.jgit.lib.BatchRefUpdate;
-import org.eclipse.jgit.lib.NullProgressMonitor;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefDatabase;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.util.time.MonotonicClock;
-import org.eclipse.jgit.util.time.ProposedTimestamp;
-
-/**
- * Ketch replica running on the same system as the
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader}.
- */
-public class LocalReplica extends KetchReplica {
-	/**
-	 * Configure a local replica.
-	 *
-	 * @param leader
-	 *            instance this replica follows.
-	 * @param name
-	 *            unique-ish name identifying this replica for debugging.
-	 * @param cfg
-	 *            how Ketch should treat the local system.
-	 */
-	public LocalReplica(KetchLeader leader, String name, ReplicaConfig cfg) {
-		super(leader, name, cfg);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected String describeForLog() {
-		return String.format("%s (leader)", getName()); //$NON-NLS-1$
-	}
-
-	/**
-	 * Initializes local replica by reading accepted and committed references.
-	 * <p>
-	 * Loads accepted and committed references from the reference database of
-	 * the local replica and stores their current ObjectIds in memory.
-	 *
-	 * @param repo
-	 *            repository to initialize state from.
-	 * @throws IOException
-	 *             cannot read repository state.
-	 */
-	void initialize(Repository repo) throws IOException {
-		RefDatabase refdb = repo.getRefDatabase();
-		if (refdb instanceof RefTreeDatabase) {
-			RefTreeDatabase treeDb = (RefTreeDatabase) refdb;
-			String txnNamespace = getSystem().getTxnNamespace();
-			if (!txnNamespace.equals(treeDb.getTxnNamespace())) {
-				throw new IOException(MessageFormat.format(
-						KetchText.get().mismatchedTxnNamespace,
-						txnNamespace, treeDb.getTxnNamespace()));
-			}
-			refdb = treeDb.getBootstrap();
-		}
-		initialize(refdb.exactRef(
-				getSystem().getTxnAccepted(),
-				getSystem().getTxnCommitted()));
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void startPush(ReplicaPushRequest req) {
-		getSystem().getExecutor().execute(() -> {
-			MonotonicClock clk = getSystem().getClock();
-			try (Repository git = getLeader().openRepository();
-					ProposedTimestamp ts = clk.propose()) {
-				try {
-					update(git, req, ts);
-					req.done(git);
-				} catch (Throwable err) {
-					req.setException(git, err);
-				}
-			} catch (IOException err) {
-				req.setException(null, err);
-			}
-		});
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void blockingFetch(Repository repo, ReplicaFetchRequest req)
-			throws IOException {
-		throw new IOException(KetchText.get().cannotFetchFromLocalReplica);
-	}
-
-	private void update(Repository git, ReplicaPushRequest req,
-			ProposedTimestamp ts) throws IOException {
-		RefDatabase refdb = git.getRefDatabase();
-		CommitMethod method = getCommitMethod();
-
-		// Local replica probably uses RefTreeDatabase, the request should
-		// be only for the txnNamespace, so drop to the bootstrap layer.
-		if (refdb instanceof RefTreeDatabase) {
-			if (!isOnlyTxnNamespace(req.getCommands())) {
-				return;
-			}
-
-			refdb = ((RefTreeDatabase) refdb).getBootstrap();
-			method = TXN_COMMITTED;
-		}
-
-		BatchRefUpdate batch = refdb.newBatchUpdate();
-		batch.addProposedTimestamp(ts);
-		batch.setRefLogIdent(getSystem().newCommitter(ts));
-		batch.setRefLogMessage("ketch", false); //$NON-NLS-1$
-		batch.setAllowNonFastForwards(true);
-
-		// RefDirectory updates multiple references sequentially.
-		// Run everything else first, then accepted (if present),
-		// then committed (if present). This ensures an earlier
-		// failure will not update these critical references.
-		ReceiveCommand accepted = null;
-		ReceiveCommand committed = null;
-		for (ReceiveCommand cmd : req.getCommands()) {
-			String name = cmd.getRefName();
-			if (name.equals(getSystem().getTxnAccepted())) {
-				accepted = cmd;
-			} else if (name.equals(getSystem().getTxnCommitted())) {
-				committed = cmd;
-			} else {
-				batch.addCommand(cmd);
-			}
-		}
-		if (committed != null && method == ALL_REFS) {
-			Map<String, Ref> refs = refdb.getRefs(ALL);
-			batch.addCommand(prepareCommit(git, refs, committed.getNewId()));
-		}
-		if (accepted != null) {
-			batch.addCommand(accepted);
-		}
-		if (committed != null) {
-			batch.addCommand(committed);
-		}
-
-		try (RevWalk rw = new RevWalk(git)) {
-			batch.execute(rw, NullProgressMonitor.INSTANCE);
-		}
-
-		// KetchReplica only cares about accepted and committed in
-		// advertisement. If they failed, store the current values
-		// back in the ReplicaPushRequest.
-		List<String> failed = new ArrayList<>(2);
-		checkFailed(failed, accepted);
-		checkFailed(failed, committed);
-		if (!failed.isEmpty()) {
-			String[] arr = failed.toArray(new String[0]);
-			req.setRefs(refdb.exactRef(arr));
-		}
-	}
-
-	private static void checkFailed(List<String> failed, ReceiveCommand cmd) {
-		if (cmd != null && cmd.getResult() != OK) {
-			failed.add(cmd.getRefName());
-		}
-	}
-
-	private boolean isOnlyTxnNamespace(Collection<ReceiveCommand> cmdList) {
-		// Be paranoid and reject non txnNamespace names, this
-		// is a programming error in Ketch that should not occur.
-
-		String txnNamespace = getSystem().getTxnNamespace();
-		for (ReceiveCommand cmd : cmdList) {
-			if (!cmd.getRefName().startsWith(txnNamespace)) {
-				cmd.setResult(REJECTED_OTHER_REASON,
-						MessageFormat.format(
-								KetchText.get().outsideTxnNamespace,
-								cmd.getRefName(), txnNamespace));
-				ReceiveCommand.abort(cmdList);
-				return false;
-			}
-		}
-		return true;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LogIndex.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LogIndex.java
deleted file mode 100644
index ed65c06fae..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LogIndex.java
+++ /dev/null
@@ -1,95 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.ObjectId;
-
-/**
- * An ObjectId for a commit extended with incrementing log index.
- * <p>
- * For any two LogIndex instances, {@code A} is an ancestor of {@code C}
- * reachable through parent edges in the graph if {@code A.index < C.index}.
- * LogIndex provides a performance optimization for Ketch, the same information
- * can be obtained from {@link org.eclipse.jgit.revwalk.RevWalk}.
- * <p>
- * Index values are only valid within a single
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader} instance after it has won
- * an election. By restricting scope to a single leader new leaders do not need
- * to traverse the entire history to determine the next {@code index} for new
- * proposals. This differs from Raft, where leader election uses the log index
- * and the term number to determine which replica holds a sufficiently
- * up-to-date log. Since Ketch uses Git objects for storage of its replicated
- * log, it keeps the term number as Raft does but uses standard Git operations
- * to imply the log index.
- * <p>
- * {@link org.eclipse.jgit.internal.ketch.Round#runAsync(AnyObjectId)} bumps the
- * index as each new round is constructed.
- */
-public class LogIndex extends ObjectId {
-	static LogIndex unknown(AnyObjectId id) {
-		return new LogIndex(id, 0);
-	}
-
-	private final long index;
-
-	private LogIndex(AnyObjectId id, long index) {
-		super(id);
-		this.index = index;
-	}
-
-	LogIndex nextIndex(AnyObjectId id) {
-		return new LogIndex(id, index + 1);
-	}
-
-	/**
-	 * Get index provided by the current leader instance.
-	 *
-	 * @return index provided by the current leader instance.
-	 */
-	public long getIndex() {
-		return index;
-	}
-
-	/**
-	 * Check if this log position committed before another log position.
-	 * <p>
-	 * Only valid for log positions in memory for the current leader.
-	 *
-	 * @param c
-	 *            other (more recent) log position.
-	 * @return true if this log position was before {@code c} or equal to c and
-	 *         therefore any agreement of {@code c} implies agreement on this
-	 *         log position.
-	 */
-	boolean isBefore(LogIndex c) {
-		return index <= c.index;
-	}
-
-	/**
-	 * Create string suitable for debug logging containing the log index and
-	 * abbreviated ObjectId.
-	 *
-	 * @return string suitable for debug logging containing the log index and
-	 *         abbreviated ObjectId.
-	 */
-	@SuppressWarnings("boxing")
-	public String describeForLog() {
-		return String.format("%5d/%s", index, abbreviate(6).name()); //$NON-NLS-1$
-	}
-
-	/** {@inheritDoc} */
-	@SuppressWarnings("boxing")
-	@Override
-	public String toString() {
-		return String.format("LogId[%5d/%s]", index, name()); //$NON-NLS-1$
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Proposal.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Proposal.java
deleted file mode 100644
index ca27281a8e..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Proposal.java
+++ /dev/null
@@ -1,415 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.Proposal.State.ABORTED;
-import static org.eclipse.jgit.internal.ketch.Proposal.State.EXECUTED;
-import static org.eclipse.jgit.internal.ketch.Proposal.State.NEW;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.List;
-import java.util.concurrent.CopyOnWriteArrayList;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicReference;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.internal.storage.reftree.Command;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.PushCertificate;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.util.time.ProposedTimestamp;
-
-/**
- * A proposal to be applied in a Ketch system.
- * <p>
- * Pushing to a Ketch leader results in the leader making a proposal. The
- * proposal includes the list of reference updates. The leader attempts to send
- * the proposal to a quorum of replicas by pushing the proposal to a "staging"
- * area under the {@code refs/txn/stage/} namespace. If the proposal succeeds
- * then the changes are durable and the leader can commit the proposal.
- * <p>
- * Proposals are executed by
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader#queueProposal(Proposal)},
- * which runs them asynchronously in the background. Proposals are thread-safe
- * futures allowing callers to {@link #await()} for results or be notified by
- * callback using {@link #addListener(Runnable)}.
- */
-public class Proposal {
-	/** Current state of the proposal. */
-	public enum State {
-		/** Proposal has not yet been given to a {@link KetchLeader}. */
-		NEW(false),
-
-		/**
-		 * Proposal was validated and has entered the queue, but a round
-		 * containing this proposal has not started yet.
-		 */
-		QUEUED(false),
-
-		/** Round containing the proposal has begun and is in progress. */
-		RUNNING(false),
-
-		/**
-		 * Proposal was executed through a round. Individual results from
-		 * {@link Proposal#getCommands()}, {@link Command#getResult()} explain
-		 * the success or failure outcome.
-		 */
-		EXECUTED(true),
-
-		/** Proposal was aborted and did not reach consensus. */
-		ABORTED(true);
-
-		private final boolean done;
-
-		private State(boolean done) {
-			this.done = done;
-		}
-
-		/** @return true if this is a terminal state. */
-		public boolean isDone() {
-			return done;
-		}
-	}
-
-	private final List<Command> commands;
-	private PersonIdent author;
-	private String message;
-	private PushCertificate pushCert;
-
-	private List<ProposedTimestamp> timestamps;
-	private final List<Runnable> listeners = new CopyOnWriteArrayList<>();
-	private final AtomicReference<State> state = new AtomicReference<>(NEW);
-
-	/**
-	 * Create a proposal from a list of Ketch commands.
-	 *
-	 * @param cmds
-	 *            prepared list of commands.
-	 */
-	public Proposal(List<Command> cmds) {
-		commands = Collections.unmodifiableList(new ArrayList<>(cmds));
-	}
-
-	/**
-	 * Create a proposal from a collection of received commands.
-	 *
-	 * @param rw
-	 *            walker to assist in preparing commands.
-	 * @param cmds
-	 *            list of pending commands.
-	 * @throws org.eclipse.jgit.errors.MissingObjectException
-	 *             newId of a command is not found locally.
-	 * @throws java.io.IOException
-	 *             local objects cannot be accessed.
-	 */
-	public Proposal(RevWalk rw, Collection<ReceiveCommand> cmds)
-			throws MissingObjectException, IOException {
-		commands = asCommandList(rw, cmds);
-	}
-
-	private static List<Command> asCommandList(RevWalk rw,
-			Collection<ReceiveCommand> cmds)
-					throws MissingObjectException, IOException {
-		List<Command> commands = new ArrayList<>(cmds.size());
-		for (ReceiveCommand cmd : cmds) {
-			commands.add(new Command(rw, cmd));
-		}
-		return Collections.unmodifiableList(commands);
-	}
-
-	/**
-	 * Get commands from this proposal.
-	 *
-	 * @return commands from this proposal.
-	 */
-	public Collection<Command> getCommands() {
-		return commands;
-	}
-
-	/**
-	 * Get optional author of the proposal.
-	 *
-	 * @return optional author of the proposal.
-	 */
-	@Nullable
-	public PersonIdent getAuthor() {
-		return author;
-	}
-
-	/**
-	 * Set the author for the proposal.
-	 *
-	 * @param who
-	 *            optional identity of the author of the proposal.
-	 * @return {@code this}
-	 */
-	public Proposal setAuthor(@Nullable PersonIdent who) {
-		author = who;
-		return this;
-	}
-
-	/**
-	 * Get optional message for the commit log of the RefTree.
-	 *
-	 * @return optional message for the commit log of the RefTree.
-	 */
-	@Nullable
-	public String getMessage() {
-		return message;
-	}
-
-	/**
-	 * Set the message to appear in the commit log of the RefTree.
-	 *
-	 * @param msg
-	 *            message text for the commit.
-	 * @return {@code this}
-	 */
-	public Proposal setMessage(@Nullable String msg) {
-		message = msg != null && !msg.isEmpty() ? msg : null;
-		return this;
-	}
-
-	/**
-	 * Get optional certificate signing the references.
-	 *
-	 * @return optional certificate signing the references.
-	 */
-	@Nullable
-	public PushCertificate getPushCertificate() {
-		return pushCert;
-	}
-
-	/**
-	 * Set the push certificate signing the references.
-	 *
-	 * @param cert
-	 *            certificate, may be null.
-	 * @return {@code this}
-	 */
-	public Proposal setPushCertificate(@Nullable PushCertificate cert) {
-		pushCert = cert;
-		return this;
-	}
-
-	/**
-	 * Get timestamps that Ketch must block for.
-	 *
-	 * @return timestamps that Ketch must block for. These may have been used as
-	 *         commit times inside the objects involved in the proposal.
-	 */
-	public List<ProposedTimestamp> getProposedTimestamps() {
-		if (timestamps != null) {
-			return timestamps;
-		}
-		return Collections.emptyList();
-	}
-
-	/**
-	 * Request the proposal to wait for the affected timestamps to resolve.
-	 *
-	 * @param ts
-	 *            a {@link org.eclipse.jgit.util.time.ProposedTimestamp} object.
-	 * @return {@code this}.
-	 */
-	public Proposal addProposedTimestamp(ProposedTimestamp ts) {
-		if (timestamps == null) {
-			timestamps = new ArrayList<>(4);
-		}
-		timestamps.add(ts);
-		return this;
-	}
-
-	/**
-	 * Add a callback to be invoked when the proposal is done.
-	 * <p>
-	 * A proposal is done when it has entered either
-	 * {@link org.eclipse.jgit.internal.ketch.Proposal.State#EXECUTED} or
-	 * {@link org.eclipse.jgit.internal.ketch.Proposal.State#ABORTED} state. If
-	 * the proposal is already done {@code callback.run()} is immediately
-	 * invoked on the caller's thread.
-	 *
-	 * @param callback
-	 *            method to run after the proposal is done. The callback may be
-	 *            run on a Ketch system thread and should be completed quickly.
-	 */
-	public void addListener(Runnable callback) {
-		boolean runNow = false;
-		synchronized (state) {
-			if (state.get().isDone()) {
-				runNow = true;
-			} else {
-				listeners.add(callback);
-			}
-		}
-		if (runNow) {
-			callback.run();
-		}
-	}
-
-	/** Set command result as OK. */
-	void success() {
-		for (Command c : commands) {
-			if (c.getResult() == NOT_ATTEMPTED) {
-				c.setResult(OK);
-			}
-		}
-		notifyState(EXECUTED);
-	}
-
-	/** Mark commands as "transaction aborted". */
-	void abort() {
-		Command.abort(commands, null);
-		notifyState(ABORTED);
-	}
-
-	/**
-	 * Read the current state of the proposal.
-	 *
-	 * @return read the current state of the proposal.
-	 */
-	public State getState() {
-		return state.get();
-	}
-
-	/**
-	 * Whether the proposal was attempted
-	 *
-	 * @return {@code true} if the proposal was attempted. A true value does not
-	 *         mean consensus was reached, only that the proposal was considered
-	 *         and will not be making any more progress beyond its current
-	 *         state.
-	 */
-	public boolean isDone() {
-		return state.get().isDone();
-	}
-
-	/**
-	 * Wait for the proposal to be attempted and {@link #isDone()} to be true.
-	 *
-	 * @throws java.lang.InterruptedException
-	 *             caller was interrupted before proposal executed.
-	 */
-	public void await() throws InterruptedException {
-		synchronized (state) {
-			while (!state.get().isDone()) {
-				state.wait();
-			}
-		}
-	}
-
-	/**
-	 * Wait for the proposal to be attempted and {@link #isDone()} to be true.
-	 *
-	 * @param wait
-	 *            how long to wait.
-	 * @param unit
-	 *            unit describing the wait time.
-	 * @return true if the proposal is done; false if the method timed out.
-	 * @throws java.lang.InterruptedException
-	 *             caller was interrupted before proposal executed.
-	 */
-	public boolean await(long wait, TimeUnit unit) throws InterruptedException {
-		synchronized (state) {
-			if (state.get().isDone()) {
-				return true;
-			}
-			state.wait(unit.toMillis(wait));
-			return state.get().isDone();
-		}
-	}
-
-	/**
-	 * Wait for the proposal to exit a state.
-	 *
-	 * @param notIn
-	 *            state the proposal should not be in to return.
-	 * @param wait
-	 *            how long to wait.
-	 * @param unit
-	 *            unit describing the wait time.
-	 * @return true if the proposal exited the state; false on time out.
-	 * @throws java.lang.InterruptedException
-	 *             caller was interrupted before proposal executed.
-	 */
-	public boolean awaitStateChange(State notIn, long wait, TimeUnit unit)
-			throws InterruptedException {
-		synchronized (state) {
-			if (state.get() != notIn) {
-				return true;
-			}
-			state.wait(unit.toMillis(wait));
-			return state.get() != notIn;
-		}
-	}
-
-	void notifyState(State s) {
-		synchronized (state) {
-			state.set(s);
-			state.notifyAll();
-		}
-		if (s.isDone()) {
-			for (Runnable callback : listeners) {
-				callback.run();
-			}
-			listeners.clear();
-		}
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public String toString() {
-		StringBuilder s = new StringBuilder();
-		s.append("Ketch Proposal {\n"); //$NON-NLS-1$
-		s.append("  ").append(state.get()).append('\n'); //$NON-NLS-1$
-		if (author != null) {
-			s.append("  author ").append(author).append('\n'); //$NON-NLS-1$
-		}
-		if (message != null) {
-			s.append("  message ").append(message).append('\n'); //$NON-NLS-1$
-		}
-		for (Command c : commands) {
-			s.append("  "); //$NON-NLS-1$
-			format(s, c.getOldRef(), "CREATE"); //$NON-NLS-1$
-			s.append(' ');
-			format(s, c.getNewRef(), "DELETE"); //$NON-NLS-1$
-			s.append(' ').append(c.getRefName());
-			if (c.getResult() != ReceiveCommand.Result.NOT_ATTEMPTED) {
-				s.append(' ').append(c.getResult()); // $NON-NLS-1$
-			}
-			s.append('\n');
-		}
-		s.append('}');
-		return s.toString();
-	}
-
-	private static void format(StringBuilder s, @Nullable Ref r, String n) {
-		if (r == null) {
-			s.append(n);
-		} else if (r.isSymbolic()) {
-			s.append(r.getTarget().getName());
-		} else {
-			ObjectId id = r.getObjectId();
-			if (id != null) {
-				s.append(id.abbreviate(8).name());
-			}
-		}
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ProposalRound.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ProposalRound.java
deleted file mode 100644
index b73183abd0..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ProposalRound.java
+++ /dev/null
@@ -1,289 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.Proposal.State.RUNNING;
-
-import java.io.IOException;
-import java.time.Duration;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-import java.util.concurrent.TimeoutException;
-import java.util.stream.Collectors;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.internal.storage.reftree.Command;
-import org.eclipse.jgit.internal.storage.reftree.RefTree;
-import org.eclipse.jgit.lib.CommitBuilder;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.util.time.ProposedTimestamp;
-
-/** A {@link Round} that aggregates and sends user {@link Proposal}s. */
-class ProposalRound extends Round {
-	private final List<Proposal> todo;
-	private RefTree queuedTree;
-
-	ProposalRound(KetchLeader leader, LogIndex head, List<Proposal> todo,
-			@Nullable RefTree tree) {
-		super(leader, head);
-		this.todo = todo;
-
-		if (tree != null && canCombine(todo)) {
-			this.queuedTree = tree;
-		} else {
-			leader.roundHoldsReferenceToRefTree = false;
-		}
-	}
-
-	private static boolean canCombine(List<Proposal> todo) {
-		Proposal first = todo.get(0);
-		for (int i = 1; i < todo.size(); i++) {
-			if (!canCombine(first, todo.get(i))) {
-				return false;
-			}
-		}
-		return true;
-	}
-
-	private static boolean canCombine(Proposal a, Proposal b) {
-		String aMsg = nullToEmpty(a.getMessage());
-		String bMsg = nullToEmpty(b.getMessage());
-		return aMsg.equals(bMsg) && canCombine(a.getAuthor(), b.getAuthor());
-	}
-
-	private static String nullToEmpty(@Nullable String str) {
-		return str != null ? str : ""; //$NON-NLS-1$
-	}
-
-	private static boolean canCombine(@Nullable PersonIdent a,
-			@Nullable PersonIdent b) {
-		if (a != null && b != null) {
-			// Same name and email address. Combine timestamp as the two
-			// proposals are running concurrently and appear together or
-			// not at all from the point of view of an outside reader.
-			return a.getName().equals(b.getName())
-					&& a.getEmailAddress().equals(b.getEmailAddress());
-		}
-
-		// If a and b are null, both will be the system identity.
-		return a == null && b == null;
-	}
-
-	@Override
-	void start() throws IOException {
-		for (Proposal p : todo) {
-			p.notifyState(RUNNING);
-		}
-		try {
-			ObjectId id;
-			try (Repository git = leader.openRepository();
-					ProposedTimestamp ts = getSystem().getClock().propose()) {
-				id = insertProposals(git, ts);
-				blockUntil(ts);
-			}
-			runAsync(id);
-		} catch (NoOp e) {
-			for (Proposal p : todo) {
-				p.success();
-			}
-			leader.lock.lock();
-			try {
-				leader.nextRound();
-			} finally {
-				leader.lock.unlock();
-			}
-		} catch (IOException e) {
-			abort();
-			throw e;
-		}
-	}
-
-	private ObjectId insertProposals(Repository git, ProposedTimestamp ts)
-			throws IOException, NoOp {
-		ObjectId id;
-		try (ObjectInserter inserter = git.newObjectInserter()) {
-			// TODO(sop) Process signed push certificates.
-
-			if (queuedTree != null) {
-				id = insertSingleProposal(git, ts, inserter);
-			} else {
-				id = insertMultiProposal(git, ts, inserter);
-			}
-
-			stageCommands = makeStageList(git, inserter);
-			inserter.flush();
-		}
-		return id;
-	}
-
-	private ObjectId insertSingleProposal(Repository git, ProposedTimestamp ts,
-			ObjectInserter inserter) throws IOException, NoOp {
-		// Fast path: tree is passed in with all proposals applied.
-		ObjectId treeId = queuedTree.writeTree(inserter);
-		queuedTree = null;
-		leader.roundHoldsReferenceToRefTree = false;
-
-		if (!ObjectId.zeroId().equals(acceptedOldIndex)) {
-			try (RevWalk rw = new RevWalk(git)) {
-				RevCommit c = rw.parseCommit(acceptedOldIndex);
-				if (treeId.equals(c.getTree())) {
-					throw new NoOp();
-				}
-			}
-		}
-
-		Proposal p = todo.get(0);
-		CommitBuilder b = new CommitBuilder();
-		b.setTreeId(treeId);
-		if (!ObjectId.zeroId().equals(acceptedOldIndex)) {
-			b.setParentId(acceptedOldIndex);
-		}
-		b.setCommitter(leader.getSystem().newCommitter(ts));
-		b.setAuthor(p.getAuthor() != null ? p.getAuthor() : b.getCommitter());
-		b.setMessage(message(p));
-		return inserter.insert(b);
-	}
-
-	private ObjectId insertMultiProposal(Repository git, ProposedTimestamp ts,
-			ObjectInserter inserter) throws IOException, NoOp {
-		// The tree was not passed in, or there are multiple proposals
-		// each needing their own commit. Reset the tree and replay each
-		// proposal in order as individual commits.
-		ObjectId lastIndex = acceptedOldIndex;
-		ObjectId oldTreeId;
-		RefTree tree;
-		if (ObjectId.zeroId().equals(lastIndex)) {
-			oldTreeId = ObjectId.zeroId();
-			tree = RefTree.newEmptyTree();
-		} else {
-			try (RevWalk rw = new RevWalk(git)) {
-				RevCommit c = rw.parseCommit(lastIndex);
-				oldTreeId = c.getTree();
-				tree = RefTree.read(rw.getObjectReader(), c.getTree());
-			}
-		}
-
-		PersonIdent committer = leader.getSystem().newCommitter(ts);
-		for (Proposal p : todo) {
-			if (!tree.apply(p.getCommands())) {
-				// This should not occur, previously during queuing the
-				// commands were successfully applied to the pending tree.
-				// Abort the entire round.
-				throw new IOException(
-						KetchText.get().queuedProposalFailedToApply);
-			}
-
-			ObjectId treeId = tree.writeTree(inserter);
-			if (treeId.equals(oldTreeId)) {
-				continue;
-			}
-
-			CommitBuilder b = new CommitBuilder();
-			b.setTreeId(treeId);
-			if (!ObjectId.zeroId().equals(lastIndex)) {
-				b.setParentId(lastIndex);
-			}
-			b.setAuthor(p.getAuthor() != null ? p.getAuthor() : committer);
-			b.setCommitter(committer);
-			b.setMessage(message(p));
-			lastIndex = inserter.insert(b);
-		}
-		if (lastIndex.equals(acceptedOldIndex)) {
-			throw new NoOp();
-		}
-		return lastIndex;
-	}
-
-	private String message(Proposal p) {
-		StringBuilder m = new StringBuilder();
-		String msg = p.getMessage();
-		if (msg != null && !msg.isEmpty()) {
-			m.append(msg);
-			while (m.length() < 2 || m.charAt(m.length() - 2) != '\n'
-					|| m.charAt(m.length() - 1) != '\n') {
-				m.append('\n');
-			}
-		}
-		m.append(KetchConstants.TERM.getName())
-				.append(": ") //$NON-NLS-1$
-				.append(leader.getTerm());
-		return m.toString();
-	}
-
-	void abort() {
-		for (Proposal p : todo) {
-			p.abort();
-		}
-	}
-
-	@Override
-	void success() {
-		for (Proposal p : todo) {
-			p.success();
-		}
-	}
-
-	private List<ReceiveCommand> makeStageList(Repository git,
-			ObjectInserter inserter) throws IOException {
-		// For each branch, collapse consecutive updates to only most recent,
-		// avoiding sending multiple objects in a rapid fast-forward chain, or
-		// rewritten content.
-		Map<String, ObjectId> byRef = new HashMap<>();
-		for (Proposal p : todo) {
-			for (Command c : p.getCommands()) {
-				Ref n = c.getNewRef();
-				if (n != null && !n.isSymbolic()) {
-					byRef.put(n.getName(), n.getObjectId());
-				}
-			}
-		}
-		if (byRef.isEmpty()) {
-			return Collections.emptyList();
-		}
-
-		Set<ObjectId> newObjs = new HashSet<>(byRef.values());
-		StageBuilder b = new StageBuilder(
-				leader.getSystem().getTxnStage(),
-				acceptedNewIndex);
-		return b.makeStageList(newObjs, git, inserter);
-	}
-
-	private void blockUntil(ProposedTimestamp ts)
-			throws TimeIsUncertainException {
-		List<ProposedTimestamp> times = todo.stream()
-				.flatMap(p -> p.getProposedTimestamps().stream())
-				.collect(Collectors.toCollection(ArrayList::new));
-		times.add(ts);
-
-		try {
-			Duration maxWait = getSystem().getMaxWaitForMonotonicClock();
-			ProposedTimestamp.blockUntil(times, maxWait);
-		} catch (InterruptedException | TimeoutException e) {
-			throw new TimeIsUncertainException(e);
-		}
-	}
-
-	private static class NoOp extends Exception {
-		private static final long serialVersionUID = 1L;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/RemoteGitReplica.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/RemoteGitReplica.java
deleted file mode 100644
index fac93c84b3..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/RemoteGitReplica.java
+++ /dev/null
@@ -1,293 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod.ALL_REFS;
-import static org.eclipse.jgit.lib.Ref.Storage.NETWORK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.LOCK_FAILURE;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_NODELETE;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_NONFASTFORWARD;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.errors.NotSupportedException;
-import org.eclipse.jgit.errors.TransportException;
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.NullProgressMonitor;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.transport.FetchConnection;
-import org.eclipse.jgit.transport.PushConnection;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.transport.RemoteConfig;
-import org.eclipse.jgit.transport.RemoteRefUpdate;
-import org.eclipse.jgit.transport.Transport;
-import org.eclipse.jgit.transport.URIish;
-
-/**
- * Representation of a Git repository on a remote replica system.
- * <p>
- * {@link org.eclipse.jgit.internal.ketch.KetchLeader} will contact the replica
- * using the Git wire protocol.
- * <p>
- * The remote replica may be fully Ketch-aware, or a standard Git server.
- */
-public class RemoteGitReplica extends KetchReplica {
-	private final URIish uri;
-	private final RemoteConfig remoteConfig;
-
-	/**
-	 * Configure a new remote.
-	 *
-	 * @param leader
-	 *            instance this replica follows.
-	 * @param name
-	 *            unique-ish name identifying this remote for debugging.
-	 * @param uri
-	 *            URI to connect to the follower's repository.
-	 * @param cfg
-	 *            how Ketch should treat the remote system.
-	 * @param rc
-	 *            optional remote configuration describing how to contact the
-	 *            peer repository.
-	 */
-	public RemoteGitReplica(KetchLeader leader, String name, URIish uri,
-			ReplicaConfig cfg, @Nullable RemoteConfig rc) {
-		super(leader, name, cfg);
-		this.uri = uri;
-		this.remoteConfig = rc;
-	}
-
-	/**
-	 * Get URI to contact the remote peer repository.
-	 *
-	 * @return URI to contact the remote peer repository.
-	 */
-	public URIish getURI() {
-		return uri;
-	}
-
-	/**
-	 * Get optional configuration describing how to contact the peer.
-	 *
-	 * @return optional configuration describing how to contact the peer.
-	 */
-	@Nullable
-	protected RemoteConfig getRemoteConfig() {
-		return remoteConfig;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected String describeForLog() {
-		return String.format("%s @ %s", getName(), getURI()); //$NON-NLS-1$
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void startPush(ReplicaPushRequest req) {
-		getSystem().getExecutor().execute(() -> {
-			try (Repository git = getLeader().openRepository()) {
-				try {
-					push(git, req);
-					req.done(git);
-				} catch (Throwable err) {
-					req.setException(git, err);
-				}
-			} catch (IOException err) {
-				req.setException(null, err);
-			}
-		});
-	}
-
-	private void push(Repository repo, ReplicaPushRequest req)
-			throws NotSupportedException, TransportException, IOException {
-		Map<String, Ref> adv;
-		List<RemoteCommand> cmds = asUpdateList(req.getCommands());
-		try (Transport transport = Transport.open(repo, uri)) {
-			RemoteConfig rc = getRemoteConfig();
-			if (rc != null) {
-				transport.applyConfig(rc);
-			}
-			transport.setPushAtomic(true);
-			adv = push(repo, transport, cmds);
-		}
-		for (RemoteCommand c : cmds) {
-			c.copyStatusToResult();
-		}
-		req.setRefs(adv);
-	}
-
-	private Map<String, Ref> push(Repository git, Transport transport,
-			List<RemoteCommand> cmds) throws IOException {
-		Map<String, RemoteRefUpdate> updates = asUpdateMap(cmds);
-		try (PushConnection connection = transport.openPush()) {
-			Map<String, Ref> adv = connection.getRefsMap();
-			RemoteRefUpdate accepted = updates.get(getSystem().getTxnAccepted());
-			if (accepted != null && !isExpectedValue(adv, accepted)) {
-				abort(cmds);
-				return adv;
-			}
-
-			RemoteRefUpdate committed = updates.get(getSystem().getTxnCommitted());
-			if (committed != null && !isExpectedValue(adv, committed)) {
-				abort(cmds);
-				return adv;
-			}
-			if (committed != null && getCommitMethod() == ALL_REFS) {
-				prepareCommit(git, cmds, updates, adv,
-						committed.getNewObjectId());
-			}
-
-			connection.push(NullProgressMonitor.INSTANCE, updates);
-			return adv;
-		}
-	}
-
-	private static boolean isExpectedValue(Map<String, Ref> adv,
-			RemoteRefUpdate u) {
-		Ref r = adv.get(u.getRemoteName());
-		if (!AnyObjectId.isEqual(getId(r), u.getExpectedOldObjectId())) {
-			((RemoteCommand) u).cmd.setResult(LOCK_FAILURE);
-			return false;
-		}
-		return true;
-	}
-
-	private void prepareCommit(Repository git, List<RemoteCommand> cmds,
-			Map<String, RemoteRefUpdate> updates, Map<String, Ref> adv,
-			ObjectId committed) throws IOException {
-		for (ReceiveCommand cmd : prepareCommit(git, adv, committed)) {
-			RemoteCommand c = new RemoteCommand(cmd);
-			cmds.add(c);
-			updates.put(c.getRemoteName(), c);
-		}
-	}
-
-	private static List<RemoteCommand> asUpdateList(
-			Collection<ReceiveCommand> cmds) {
-		try {
-			List<RemoteCommand> toPush = new ArrayList<>(cmds.size());
-			for (ReceiveCommand cmd : cmds) {
-				toPush.add(new RemoteCommand(cmd));
-			}
-			return toPush;
-		} catch (IOException e) {
-			// Cannot occur as no IO was required to build the command.
-			throw new IllegalStateException(e);
-		}
-	}
-
-	private static Map<String, RemoteRefUpdate> asUpdateMap(
-			List<RemoteCommand> cmds) {
-		Map<String, RemoteRefUpdate> m = new LinkedHashMap<>();
-		for (RemoteCommand cmd : cmds) {
-			m.put(cmd.getRemoteName(), cmd);
-		}
-		return m;
-	}
-
-	private static void abort(List<RemoteCommand> cmds) {
-		List<ReceiveCommand> tmp = new ArrayList<>(cmds.size());
-		for (RemoteCommand cmd : cmds) {
-			tmp.add(cmd.cmd);
-		}
-		ReceiveCommand.abort(tmp);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void blockingFetch(Repository repo, ReplicaFetchRequest req)
-			throws NotSupportedException, TransportException {
-		try (Transport transport = Transport.open(repo, uri)) {
-			RemoteConfig rc = getRemoteConfig();
-			if (rc != null) {
-				transport.applyConfig(rc);
-			}
-			fetch(transport, req);
-		}
-	}
-
-	private void fetch(Transport transport, ReplicaFetchRequest req)
-			throws NotSupportedException, TransportException {
-		try (FetchConnection conn = transport.openFetch()) {
-			Map<String, Ref> remoteRefs = conn.getRefsMap();
-			req.setRefs(remoteRefs);
-
-			List<Ref> want = new ArrayList<>();
-			for (String name : req.getWantRefs()) {
-				Ref ref = remoteRefs.get(name);
-				if (ref != null && ref.getObjectId() != null) {
-					want.add(ref);
-				}
-			}
-			for (ObjectId id : req.getWantObjects()) {
-				want.add(new ObjectIdRef.Unpeeled(NETWORK, id.name(), id));
-			}
-
-			conn.fetch(NullProgressMonitor.INSTANCE, want,
-					Collections.<ObjectId> emptySet());
-		}
-	}
-
-	static class RemoteCommand extends RemoteRefUpdate {
-		final ReceiveCommand cmd;
-
-		RemoteCommand(ReceiveCommand cmd) throws IOException {
-			super(null, null,
-					cmd.getNewId(), cmd.getRefName(),
-					true /* force update */,
-					null /* no local tracking ref */,
-					cmd.getOldId());
-			this.cmd = cmd;
-		}
-
-		void copyStatusToResult() {
-			if (cmd.getResult() == NOT_ATTEMPTED) {
-				switch (getStatus()) {
-				case OK:
-				case UP_TO_DATE:
-				case NON_EXISTING:
-					cmd.setResult(OK);
-					break;
-
-				case REJECTED_NODELETE:
-					cmd.setResult(REJECTED_NODELETE);
-					break;
-
-				case REJECTED_NONFASTFORWARD:
-					cmd.setResult(REJECTED_NONFASTFORWARD);
-					break;
-
-				case REJECTED_OTHER_REASON:
-					cmd.setResult(REJECTED_OTHER_REASON, getMessage());
-					break;
-
-				default:
-					cmd.setResult(REJECTED_OTHER_REASON, getStatus().name());
-					break;
-				}
-			}
-		}
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaConfig.java
deleted file mode 100644
index 1d323b8490..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaConfig.java
+++ /dev/null
@@ -1,214 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static java.util.concurrent.TimeUnit.DAYS;
-import static java.util.concurrent.TimeUnit.HOURS;
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-import static java.util.concurrent.TimeUnit.MINUTES;
-import static java.util.concurrent.TimeUnit.SECONDS;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.CONFIG_KEY_COMMIT;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.CONFIG_KEY_SPEED;
-import static org.eclipse.jgit.internal.ketch.KetchConstants.CONFIG_KEY_TYPE;
-import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_REMOTE;
-
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Map;
-import java.util.concurrent.TimeUnit;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
-
-import org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod;
-import org.eclipse.jgit.internal.ketch.KetchReplica.CommitSpeed;
-import org.eclipse.jgit.internal.ketch.KetchReplica.Participation;
-import org.eclipse.jgit.lib.Config;
-
-/**
- * Configures a {@link org.eclipse.jgit.internal.ketch.KetchReplica}.
- */
-public class ReplicaConfig {
-	/**
-	 * Read a configuration from a config block.
-	 *
-	 * @param cfg
-	 *            configuration to read.
-	 * @param name
-	 *            of the replica being configured.
-	 * @return replica configuration for {@code name}.
-	 */
-	public static ReplicaConfig newFromConfig(Config cfg, String name) {
-		return new ReplicaConfig().fromConfig(cfg, name);
-	}
-
-	private Participation participation = Participation.FULL;
-	private CommitMethod commitMethod = CommitMethod.ALL_REFS;
-	private CommitSpeed commitSpeed = CommitSpeed.BATCHED;
-	private long minRetry = SECONDS.toMillis(5);
-	private long maxRetry = MINUTES.toMillis(1);
-
-	/**
-	 * Get participation of the replica in the system.
-	 *
-	 * @return participation of the replica in the system.
-	 */
-	public Participation getParticipation() {
-		return participation;
-	}
-
-	/**
-	 * Get how Ketch should apply committed changes.
-	 *
-	 * @return how Ketch should apply committed changes.
-	 */
-	public CommitMethod getCommitMethod() {
-		return commitMethod;
-	}
-
-	/**
-	 * Get how quickly should Ketch commit.
-	 *
-	 * @return how quickly should Ketch commit.
-	 */
-	public CommitSpeed getCommitSpeed() {
-		return commitSpeed;
-	}
-
-	/**
-	 * Returns the minimum wait delay before retrying a failure.
-	 *
-	 * @param unit
-	 *            to get retry delay in.
-	 * @return minimum delay before retrying a failure.
-	 */
-	public long getMinRetry(TimeUnit unit) {
-		return unit.convert(minRetry, MILLISECONDS);
-	}
-
-	/**
-	 * Returns the maximum wait delay before retrying a failure.
-	 *
-	 * @param unit
-	 *            to get retry delay in.
-	 * @return maximum delay before retrying a failure.
-	 */
-	public long getMaxRetry(TimeUnit unit) {
-		return unit.convert(maxRetry, MILLISECONDS);
-	}
-
-	/**
-	 * Update the configuration from a config block.
-	 *
-	 * @param cfg
-	 *            configuration to read.
-	 * @param name
-	 *            of the replica being configured.
-	 * @return {@code this}
-	 */
-	public ReplicaConfig fromConfig(Config cfg, String name) {
-		participation = cfg.getEnum(
-				CONFIG_KEY_REMOTE, name, CONFIG_KEY_TYPE,
-				participation);
-		commitMethod = cfg.getEnum(
-				CONFIG_KEY_REMOTE, name, CONFIG_KEY_COMMIT,
-				commitMethod);
-		commitSpeed = cfg.getEnum(
-				CONFIG_KEY_REMOTE, name, CONFIG_KEY_SPEED,
-				commitSpeed);
-		minRetry = getMillis(cfg, name, "ketch-minRetry", minRetry); //$NON-NLS-1$
-		maxRetry = getMillis(cfg, name, "ketch-maxRetry", maxRetry); //$NON-NLS-1$
-		return this;
-	}
-
-	private static long getMillis(Config cfg, String name, String key,
-			long defaultValue) {
-		String valStr = cfg.getString(CONFIG_KEY_REMOTE, name, key);
-		if (valStr == null) {
-			return defaultValue;
-		}
-
-		valStr = valStr.trim();
-		if (valStr.isEmpty()) {
-			return defaultValue;
-		}
-
-		Matcher m = UnitMap.PATTERN.matcher(valStr);
-		if (!m.matches()) {
-			return defaultValue;
-		}
-
-		String digits = m.group(1);
-		String unitName = m.group(2).trim();
-		TimeUnit unit = UnitMap.UNITS.get(unitName);
-		if (unit == null) {
-			return defaultValue;
-		}
-
-		try {
-			if (digits.indexOf('.') == -1) {
-				return unit.toMillis(Long.parseLong(digits));
-			}
-
-			double val = Double.parseDouble(digits);
-			return (long) (val * unit.toMillis(1));
-		} catch (NumberFormatException nfe) {
-			return defaultValue;
-		}
-	}
-
-	static class UnitMap {
-		static final Pattern PATTERN = Pattern
-				.compile("^([1-9][0-9]*(?:\\.[0-9]*)?)\\s*(.*)$"); //$NON-NLS-1$
-
-		static final Map<String, TimeUnit> UNITS;
-
-		static {
-			Map<String, TimeUnit> m = new HashMap<>();
-			TimeUnit u = MILLISECONDS;
-			m.put("", u); //$NON-NLS-1$
-			m.put("ms", u); //$NON-NLS-1$
-			m.put("millis", u); //$NON-NLS-1$
-			m.put("millisecond", u); //$NON-NLS-1$
-			m.put("milliseconds", u); //$NON-NLS-1$
-
-			u = SECONDS;
-			m.put("s", u); //$NON-NLS-1$
-			m.put("sec", u); //$NON-NLS-1$
-			m.put("secs", u); //$NON-NLS-1$
-			m.put("second", u); //$NON-NLS-1$
-			m.put("seconds", u); //$NON-NLS-1$
-
-			u = MINUTES;
-			m.put("m", u); //$NON-NLS-1$
-			m.put("min", u); //$NON-NLS-1$
-			m.put("mins", u); //$NON-NLS-1$
-			m.put("minute", u); //$NON-NLS-1$
-			m.put("minutes", u); //$NON-NLS-1$
-
-			u = HOURS;
-			m.put("h", u); //$NON-NLS-1$
-			m.put("hr", u); //$NON-NLS-1$
-			m.put("hrs", u); //$NON-NLS-1$
-			m.put("hour", u); //$NON-NLS-1$
-			m.put("hours", u); //$NON-NLS-1$
-
-			u = DAYS;
-			m.put("d", u); //$NON-NLS-1$
-			m.put("day", u); //$NON-NLS-1$
-			m.put("days", u); //$NON-NLS-1$
-
-			UNITS = Collections.unmodifiableMap(m);
-		}
-
-		private UnitMap() {
-		}
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaFetchRequest.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaFetchRequest.java
deleted file mode 100644
index f50ad62c80..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaFetchRequest.java
+++ /dev/null
@@ -1,79 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.util.Map;
-import java.util.Set;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.Ref;
-
-/**
- * A fetch request to obtain objects from a replica, and its result.
- */
-public class ReplicaFetchRequest {
-	private final Set<String> wantRefs;
-	private final Set<ObjectId> wantObjects;
-	private Map<String, Ref> refs;
-
-	/**
-	 * Construct a new fetch request for a replica.
-	 *
-	 * @param wantRefs
-	 *            named references to be fetched.
-	 * @param wantObjects
-	 *            specific objects to be fetched.
-	 */
-	public ReplicaFetchRequest(Set<String> wantRefs,
-			Set<ObjectId> wantObjects) {
-		this.wantRefs = wantRefs;
-		this.wantObjects = wantObjects;
-	}
-
-	/**
-	 * Get references to be fetched.
-	 *
-	 * @return references to be fetched.
-	 */
-	public Set<String> getWantRefs() {
-		return wantRefs;
-	}
-
-	/**
-	 * Get objects to be fetched.
-	 *
-	 * @return objects to be fetched.
-	 */
-	public Set<ObjectId> getWantObjects() {
-		return wantObjects;
-	}
-
-	/**
-	 * Get remote references, usually from the advertisement.
-	 *
-	 * @return remote references, usually from the advertisement.
-	 */
-	@Nullable
-	public Map<String, Ref> getRefs() {
-		return refs;
-	}
-
-	/**
-	 * Set references observed from the replica.
-	 *
-	 * @param refs
-	 *            references observed from the replica.
-	 */
-	public void setRefs(Map<String, Ref> refs) {
-		this.refs = refs;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaPushRequest.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaPushRequest.java
deleted file mode 100644
index 273760bc6e..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaPushRequest.java
+++ /dev/null
@@ -1,149 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.util.Collection;
-import java.util.Map;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.transport.ReceiveCommand;
-
-/**
- * A push request sending objects to a replica, and its result.
- * <p>
- * Implementors of {@link org.eclipse.jgit.internal.ketch.KetchReplica} must
- * populate the command result fields, {@link #setRefs(Map)}, and call one of
- * {@link #setException(Repository, Throwable)} or {@link #done(Repository)} to
- * finish processing.
- */
-public class ReplicaPushRequest {
-	private final KetchReplica replica;
-	private final Collection<ReceiveCommand> commands;
-	private Map<String, Ref> refs;
-	private Throwable exception;
-	private boolean notified;
-
-	/**
-	 * Construct a new push request for a replica.
-	 *
-	 * @param replica
-	 *            the replica being pushed to.
-	 * @param commands
-	 *            commands to be executed.
-	 */
-	public ReplicaPushRequest(KetchReplica replica,
-			Collection<ReceiveCommand> commands) {
-		this.replica = replica;
-		this.commands = commands;
-	}
-
-	/**
-	 * Get commands to be executed, and their results.
-	 *
-	 * @return commands to be executed, and their results.
-	 */
-	public Collection<ReceiveCommand> getCommands() {
-		return commands;
-	}
-
-	/**
-	 * Get remote references, usually from the advertisement.
-	 *
-	 * @return remote references, usually from the advertisement.
-	 */
-	@Nullable
-	public Map<String, Ref> getRefs() {
-		return refs;
-	}
-
-	/**
-	 * Set references observed from the replica.
-	 *
-	 * @param refs
-	 *            references observed from the replica.
-	 */
-	public void setRefs(Map<String, Ref> refs) {
-		this.refs = refs;
-	}
-
-	/**
-	 * Get exception thrown, if any.
-	 *
-	 * @return exception thrown, if any.
-	 */
-	@Nullable
-	public Throwable getException() {
-		return exception;
-	}
-
-	/**
-	 * Mark the request as crashing with a communication error.
-	 * <p>
-	 * This method may take significant time acquiring the leader lock and
-	 * updating the Ketch state machine with the failure.
-	 *
-	 * @param repo
-	 *            local repository reference used by the push attempt.
-	 * @param err
-	 *            exception thrown during communication.
-	 */
-	public void setException(@Nullable Repository repo, Throwable err) {
-		if (KetchReplica.log.isErrorEnabled()) {
-			KetchReplica.log.error(describe("failed"), err); //$NON-NLS-1$
-		}
-		if (!notified) {
-			notified = true;
-			exception = err;
-			replica.afterPush(repo, this);
-		}
-	}
-
-	/**
-	 * Mark the request as completed without exception.
-	 * <p>
-	 * This method may take significant time acquiring the leader lock and
-	 * updating the Ketch state machine with results from this replica.
-	 *
-	 * @param repo
-	 *            local repository reference used by the push attempt.
-	 */
-	public void done(Repository repo) {
-		if (KetchReplica.log.isDebugEnabled()) {
-			KetchReplica.log.debug(describe("completed")); //$NON-NLS-1$
-		}
-		if (!notified) {
-			notified = true;
-			replica.afterPush(repo, this);
-		}
-	}
-
-	private String describe(String heading) {
-		StringBuilder b = new StringBuilder();
-		b.append("push to "); //$NON-NLS-1$
-		b.append(replica.describeForLog());
-		b.append(' ').append(heading).append(":\n"); //$NON-NLS-1$
-		for (ReceiveCommand cmd : commands) {
-			b.append(String.format(
-					"  %-12s %-12s %s %s", //$NON-NLS-1$
-					LeaderSnapshot.str(cmd.getOldId()),
-					LeaderSnapshot.str(cmd.getNewId()),
-					cmd.getRefName(),
-					cmd.getResult()));
-			if (cmd.getMessage() != null) {
-				b.append(' ').append(cmd.getMessage());
-			}
-			b.append('\n');
-		}
-		return b.toString();
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaSnapshot.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaSnapshot.java
deleted file mode 100644
index 05e4ed693a..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/ReplicaSnapshot.java
+++ /dev/null
@@ -1,98 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.util.Date;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.ObjectId;
-
-/**
- * A snapshot of a replica.
- *
- * @see LeaderSnapshot
- */
-public class ReplicaSnapshot {
-	final KetchReplica replica;
-	ObjectId accepted;
-	ObjectId committed;
-	KetchReplica.State state;
-	String error;
-	long retryAtMillis;
-
-	ReplicaSnapshot(KetchReplica replica) {
-		this.replica = replica;
-	}
-
-	/**
-	 * Get the replica this snapshot describes the state of
-	 *
-	 * @return the replica this snapshot describes the state of
-	 */
-	public KetchReplica getReplica() {
-		return replica;
-	}
-
-	/**
-	 * Get current state of the replica
-	 *
-	 * @return current state of the replica
-	 */
-	public KetchReplica.State getState() {
-		return state;
-	}
-
-	/**
-	 * Get last known Git commit at {@code refs/txn/accepted}
-	 *
-	 * @return last known Git commit at {@code refs/txn/accepted}
-	 */
-	@Nullable
-	public ObjectId getAccepted() {
-		return accepted;
-	}
-
-	/**
-	 * Get last known Git commit at {@code refs/txn/committed}
-	 *
-	 * @return last known Git commit at {@code refs/txn/committed}
-	 */
-	@Nullable
-	public ObjectId getCommitted() {
-		return committed;
-	}
-
-	/**
-	 * Get error message
-	 *
-	 * @return if {@link #getState()} ==
-	 *         {@link org.eclipse.jgit.internal.ketch.KetchReplica.State#OFFLINE}
-	 *         an optional human-readable message from the transport system
-	 *         explaining the failure.
-	 */
-	@Nullable
-	public String getErrorMessage() {
-		return error;
-	}
-
-	/**
-	 * Get when the leader will retry communication with the offline or lagging
-	 * replica
-	 *
-	 * @return time (usually in the future) when the leader will retry
-	 *         communication with the offline or lagging replica; null if no
-	 *         retry is scheduled or necessary.
-	 */
-	@Nullable
-	public Date getRetryAt() {
-		return retryAtMillis > 0 ? new Date(retryAtMillis) : null;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Round.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Round.java
deleted file mode 100644
index 05da5be056..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/Round.java
+++ /dev/null
@@ -1,87 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.io.IOException;
-import java.util.List;
-
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.transport.ReceiveCommand;
-
-/**
- * One round-trip to all replicas proposing a log entry.
- * <p>
- * In Raft a log entry represents a state transition at a specific index in the
- * replicated log. The leader can only append log entries to the log.
- * <p>
- * In Ketch a log entry is recorded under the {@code refs/txn} namespace. This
- * occurs when:
- * <ul>
- * <li>a replica wants to establish itself as a new leader by proposing a new
- * term (see {@link ElectionRound})
- * <li>an established leader wants to gain consensus on new {@link Proposal}s
- * (see {@link ProposalRound})
- * </ul>
- */
-abstract class Round {
-	final KetchLeader leader;
-	final LogIndex acceptedOldIndex;
-	LogIndex acceptedNewIndex;
-	List<ReceiveCommand> stageCommands;
-
-	Round(KetchLeader leader, LogIndex head) {
-		this.leader = leader;
-		this.acceptedOldIndex = head;
-	}
-
-	KetchSystem getSystem() {
-		return leader.getSystem();
-	}
-
-	/**
-	 * Creates a commit for {@code refs/txn/accepted} and calls
-	 * {@link #runAsync(AnyObjectId)} to begin execution of the round across
-	 * the system.
-	 * <p>
-	 * If references are being updated (such as in a {@link ProposalRound}) the
-	 * RefTree may be modified.
-	 * <p>
-	 * Invoked without {@link KetchLeader#lock} to build objects.
-	 *
-	 * @throws IOException
-	 *             the round cannot build new objects within the leader's
-	 *             repository. The leader may be unable to execute.
-	 */
-	abstract void start() throws IOException;
-
-	/**
-	 * Asynchronously distribute the round's new value for
-	 * {@code refs/txn/accepted} to all replicas.
-	 * <p>
-	 * Invoked by {@link #start()} after new commits have been created for the
-	 * log. The method passes {@code newId} to {@link KetchLeader} to be
-	 * distributed to all known replicas.
-	 *
-	 * @param newId
-	 *            new value for {@code refs/txn/accepted}.
-	 */
-	void runAsync(AnyObjectId newId) {
-		acceptedNewIndex = acceptedOldIndex.nextIndex(newId);
-		leader.runAsync(this);
-	}
-
-	/**
-	 * Notify the round it was accepted by a majority of the system.
-	 * <p>
-	 * Invoked by the leader with {@link KetchLeader#lock} held by the caller.
-	 */
-	abstract void success();
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/StageBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/StageBuilder.java
deleted file mode 100644
index 40d86e1a85..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/StageBuilder.java
+++ /dev/null
@@ -1,240 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Set;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.CommitBuilder;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevObject;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.treewalk.EmptyTreeIterator;
-import org.eclipse.jgit.treewalk.TreeWalk;
-import org.eclipse.jgit.treewalk.filter.TreeFilter;
-
-/**
- * Constructs a set of commands to stage content during a proposal.
- */
-public class StageBuilder {
-	/**
-	 * Acceptable number of references to send in a single stage transaction.
-	 * <p>
-	 * If the number of unique objects exceeds this amount the builder will
-	 * attempt to decrease the reference count by chaining commits..
-	 */
-	private static final int SMALL_BATCH_SIZE = 5;
-
-	/**
-	 * Acceptable number of commits to chain together using parent pointers.
-	 * <p>
-	 * When staging many unique commits the {@link StageBuilder} batches
-	 * together unrelated commits as parents of a temporary commit. After the
-	 * proposal completes the temporary commit is discarded and can be garbage
-	 * collected by all replicas.
-	 */
-	private static final int TEMP_PARENT_BATCH_SIZE = 128;
-
-	private static final byte[] PEEL = { ' ', '^' };
-
-	private final String txnStage;
-	private final String txnId;
-
-	/**
-	 * Construct a stage builder for a transaction.
-	 *
-	 * @param txnStageNamespace
-	 *            namespace for transaction references to build
-	 *            {@code "txnStageNamespace/txnId.n"} style names.
-	 * @param txnId
-	 *            identifier used to name temporary staging refs.
-	 */
-	public StageBuilder(String txnStageNamespace, ObjectId txnId) {
-		this.txnStage = txnStageNamespace;
-		this.txnId = txnId.name();
-	}
-
-	/**
-	 * Compare two RefTrees and return commands to stage new objects.
-	 * <p>
-	 * This method ignores the lineage between the two RefTrees and does a
-	 * straight diff on the two trees. New objects will be staged. The diff
-	 * strategy is useful to catch-up a lagging replica, without sending every
-	 * intermediate step. This may mean the replica does not have the same
-	 * object set as other replicas if there are rewinds or branch deletes.
-	 *
-	 * @param git
-	 *            source repository to read {@code oldTree} and {@code newTree}
-	 *            from.
-	 * @param oldTree
-	 *            accepted RefTree on the replica ({@code refs/txn/accepted}).
-	 *            Use {@link org.eclipse.jgit.lib.ObjectId#zeroId()} if the
-	 *            remote does not have any ref tree, e.g. a new replica catching
-	 *            up.
-	 * @param newTree
-	 *            RefTree being sent to the replica. The trees will be compared.
-	 * @return list of commands to create {@code "refs/txn/stage/..."}
-	 *         references on replicas anchoring new objects into the repository
-	 *         while a transaction gains consensus.
-	 * @throws java.io.IOException
-	 *             {@code git} cannot be accessed to compare {@code oldTree} and
-	 *             {@code newTree} to build the object set.
-	 */
-	public List<ReceiveCommand> makeStageList(Repository git, ObjectId oldTree,
-			ObjectId newTree) throws IOException {
-		try (RevWalk rw = new RevWalk(git);
-				TreeWalk tw = new TreeWalk(rw.getObjectReader());
-				ObjectInserter ins = git.newObjectInserter()) {
-			if (AnyObjectId.isEqual(oldTree, ObjectId.zeroId())) {
-				tw.addTree(new EmptyTreeIterator());
-			} else {
-				tw.addTree(rw.parseTree(oldTree));
-			}
-			tw.addTree(rw.parseTree(newTree));
-			tw.setFilter(TreeFilter.ANY_DIFF);
-			tw.setRecursive(true);
-
-			Set<ObjectId> newObjs = new HashSet<>();
-			while (tw.next()) {
-				if (tw.getRawMode(1) == TYPE_GITLINK
-						&& !tw.isPathSuffix(PEEL, 2)) {
-					newObjs.add(tw.getObjectId(1));
-				}
-			}
-
-			List<ReceiveCommand> cmds = makeStageList(newObjs, git, ins);
-			ins.flush();
-			return cmds;
-		}
-	}
-
-	/**
-	 * Construct a set of commands to stage objects on a replica.
-	 *
-	 * @param newObjs
-	 *            objects to send to a replica.
-	 * @param git
-	 *            local repository to read source objects from. Required to
-	 *            perform minification of {@code newObjs}.
-	 * @param inserter
-	 *            inserter to write temporary commit objects during minification
-	 *            if many new branches are created by {@code newObjs}.
-	 * @return list of commands to create {@code "refs/txn/stage/..."}
-	 *         references on replicas anchoring {@code newObjs} into the
-	 *         repository while a transaction gains consensus.
-	 * @throws java.io.IOException
-	 *             {@code git} cannot be accessed to perform minification of
-	 *             {@code newObjs}.
-	 */
-	public List<ReceiveCommand> makeStageList(Set<ObjectId> newObjs,
-			@Nullable Repository git, @Nullable ObjectInserter inserter)
-					throws IOException {
-		if (git == null || newObjs.size() <= SMALL_BATCH_SIZE) {
-			// Without a source repository can only construct unique set.
-			List<ReceiveCommand> cmds = new ArrayList<>(newObjs.size());
-			for (ObjectId id : newObjs) {
-				stage(cmds, id);
-			}
-			return cmds;
-		}
-
-		List<ReceiveCommand> cmds = new ArrayList<>();
-		List<RevCommit> commits = new ArrayList<>();
-		reduceObjects(cmds, commits, git, newObjs);
-
-		if (inserter == null || commits.size() <= 1
-				|| (cmds.size() + commits.size()) <= SMALL_BATCH_SIZE) {
-			// Without an inserter to aggregate commits, or for a small set of
-			// commits just send one stage ref per commit.
-			for (RevCommit c : commits) {
-				stage(cmds, c.copy());
-			}
-			return cmds;
-		}
-
-		// 'commits' is sorted most recent to least recent commit.
-		// Group batches of commits and build a chain.
-		// TODO(sop) Cluster by restricted graphs to support filtering.
-		ObjectId tip = null;
-		for (int end = commits.size(); end > 0;) {
-			int start = Math.max(0, end - TEMP_PARENT_BATCH_SIZE);
-			List<RevCommit> batch = commits.subList(start, end);
-			List<ObjectId> parents = new ArrayList<>(1 + batch.size());
-			if (tip != null) {
-				parents.add(tip);
-			}
-			parents.addAll(batch);
-
-			CommitBuilder b = new CommitBuilder();
-			b.setTreeId(batch.get(0).getTree());
-			b.setParentIds(parents);
-			b.setAuthor(tmpAuthor(batch));
-			b.setCommitter(b.getAuthor());
-			tip = inserter.insert(b);
-			end = start;
-		}
-		stage(cmds, tip);
-		return cmds;
-	}
-
-	private static PersonIdent tmpAuthor(List<RevCommit> commits) {
-		// Construct a predictable author using most recent commit time.
-		int t = 0;
-		for (int i = 0; i < commits.size();) {
-			t = Math.max(t, commits.get(i).getCommitTime());
-		}
-		String name = "Ketch Stage"; //$NON-NLS-1$
-		String email = "tmp@tmp"; //$NON-NLS-1$
-		return new PersonIdent(name, email, t * 1000L, 0);
-	}
-
-	private void reduceObjects(List<ReceiveCommand> cmds,
-			List<RevCommit> commits, Repository git,
-			Set<ObjectId> newObjs) throws IOException {
-		try (RevWalk rw = new RevWalk(git)) {
-			rw.setRetainBody(false);
-
-			for (ObjectId id : newObjs) {
-				RevObject obj = rw.parseAny(id);
-				if (obj instanceof RevCommit) {
-					rw.markStart((RevCommit) obj);
-				} else {
-					stage(cmds, id);
-				}
-			}
-
-			for (RevCommit c; (c = rw.next()) != null;) {
-				commits.add(c);
-				rw.markUninteresting(c);
-			}
-		}
-	}
-
-	private void stage(List<ReceiveCommand> cmds, ObjectId id) {
-		int estLen = txnStage.length() + txnId.length() + 5;
-		StringBuilder n = new StringBuilder(estLen);
-		n.append(txnStage).append(txnId).append('.');
-		n.append(Integer.toHexString(cmds.size()));
-		cmds.add(new ReceiveCommand(ObjectId.zeroId(), id, n.toString()));
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/TimeIsUncertainException.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/TimeIsUncertainException.java
deleted file mode 100644
index f665e6a438..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/TimeIsUncertainException.java
+++ /dev/null
@@ -1,27 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.ketch;
-
-import java.io.IOException;
-
-import org.eclipse.jgit.internal.JGitText;
-
-class TimeIsUncertainException extends IOException {
-	private static final long serialVersionUID = 1L;
-
-	TimeIsUncertainException() {
-		super(JGitText.get().timeIsUncertain);
-	}
-
-	TimeIsUncertainException(Exception e) {
-		super(JGitText.get().timeIsUncertain, e);
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/package-info.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/package-info.java
deleted file mode 100644
index dfe03752ca..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/package-info.java
+++ /dev/null
@@ -1,4 +0,0 @@
-/**
- * Distributed consensus system built on Git.
- */
-package org.eclipse.jgit.internal.ketch;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/BitmappedObjectReachabilityChecker.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/BitmappedObjectReachabilityChecker.java
index 89aef7dc41..d8056490aa 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/BitmappedObjectReachabilityChecker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/BitmappedObjectReachabilityChecker.java
@@ -7,7 +7,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-package org.eclipse.jgit.revwalk;
+package org.eclipse.jgit.internal.revwalk;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -21,12 +21,16 @@ import java.util.stream.Stream;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
+import org.eclipse.jgit.revwalk.BitmapWalker;
+import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
+import org.eclipse.jgit.revwalk.ObjectWalk;
+import org.eclipse.jgit.revwalk.RevObject;
 
 /**
  * Checks if all objects are reachable from certain starting points using
  * bitmaps.
  */
-class BitmappedObjectReachabilityChecker
+public class BitmappedObjectReachabilityChecker
 		implements ObjectReachabilityChecker {
 
 	private final ObjectWalk walk;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/BitmappedReachabilityChecker.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/BitmappedReachabilityChecker.java
index 0d9c4593bf..37721ad1ea 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/BitmappedReachabilityChecker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/BitmappedReachabilityChecker.java
@@ -7,7 +7,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-package org.eclipse.jgit.revwalk;
+package org.eclipse.jgit.internal.revwalk;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -23,12 +23,17 @@ import org.eclipse.jgit.lib.BitmapIndex;
 import org.eclipse.jgit.lib.BitmapIndex.Bitmap;
 import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.revwalk.ReachabilityChecker;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevFlag;
+import org.eclipse.jgit.revwalk.RevSort;
+import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.revwalk.filter.RevFilter;
 
 /**
  * Checks the reachability using bitmaps.
  */
-class BitmappedReachabilityChecker implements ReachabilityChecker {
+public class BitmappedReachabilityChecker implements ReachabilityChecker {
 
 	private final RevWalk walk;
 
@@ -42,7 +47,7 @@ class BitmappedReachabilityChecker implements ReachabilityChecker {
 	 * @throws IOException
 	 *             if the index or the object reader cannot be opened.
 	 */
-	BitmappedReachabilityChecker(RevWalk walk)
+	public BitmappedReachabilityChecker(RevWalk walk)
 			throws IOException {
 		this.walk = walk;
 		if (walk.getObjectReader().getBitmapIndex() == null) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/PedestrianObjectReachabilityChecker.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/PedestrianObjectReachabilityChecker.java
index df5d68a66e..1d1f5fddaf 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/PedestrianObjectReachabilityChecker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/PedestrianObjectReachabilityChecker.java
@@ -7,7 +7,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-package org.eclipse.jgit.revwalk;
+package org.eclipse.jgit.internal.revwalk;
 
 import java.io.IOException;
 import java.io.InvalidObjectException;
@@ -17,12 +17,18 @@ import java.util.Optional;
 import java.util.stream.Stream;
 
 import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
+import org.eclipse.jgit.revwalk.ObjectWalk;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevObject;
+import org.eclipse.jgit.revwalk.RevSort;
 
 /**
  * Checks if all objects are reachable from certain starting points doing a
  * walk.
  */
-class PedestrianObjectReachabilityChecker implements ObjectReachabilityChecker {
+public class PedestrianObjectReachabilityChecker
+		implements ObjectReachabilityChecker {
 	private final ObjectWalk walk;
 
 	/**
@@ -31,7 +37,7 @@ class PedestrianObjectReachabilityChecker implements ObjectReachabilityChecker {
 	 * @param walk
 	 *            ObjectWalk instance to reuse. Caller retains ownership.
 	 */
-	PedestrianObjectReachabilityChecker(ObjectWalk walk) {
+	public PedestrianObjectReachabilityChecker(ObjectWalk walk) {
 		this.walk = walk;
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/PedestrianReachabilityChecker.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/PedestrianReachabilityChecker.java
index 5dc03776c2..a03306b6ee 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/PedestrianReachabilityChecker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/revwalk/PedestrianReachabilityChecker.java
@@ -7,7 +7,7 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-package org.eclipse.jgit.revwalk;
+package org.eclipse.jgit.internal.revwalk;
 
 import java.io.IOException;
 import java.util.Collection;
@@ -17,12 +17,16 @@ import java.util.stream.Stream;
 
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.revwalk.ReachabilityChecker;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevSort;
+import org.eclipse.jgit.revwalk.RevWalk;
 
 /**
  * Checks the reachability walking the graph from the starters towards the
  * target.
  */
-class PedestrianReachabilityChecker implements ReachabilityChecker {
+public class PedestrianReachabilityChecker implements ReachabilityChecker {
 
 	private final boolean topoSort;
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
index 876cbec161..26d5b5b176 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
@@ -13,7 +13,6 @@ package org.eclipse.jgit.internal.storage.dfs;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.COMPACT;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC_REST;
-import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC_TXN;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.INSERT;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.RECEIVE;
 import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.UNREACHABLE_GARBAGE;
@@ -45,7 +44,6 @@ import org.eclipse.jgit.internal.storage.pack.PackWriter;
 import org.eclipse.jgit.internal.storage.reftable.ReftableCompactor;
 import org.eclipse.jgit.internal.storage.reftable.ReftableConfig;
 import org.eclipse.jgit.internal.storage.reftable.ReftableWriter;
-import org.eclipse.jgit.internal.storage.reftree.RefTreeNames;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.NullProgressMonitor;
@@ -95,7 +93,6 @@ public class DfsGarbageCollector {
 	private Set<ObjectId> allHeadsAndTags;
 	private Set<ObjectId> allTags;
 	private Set<ObjectId> nonHeads;
-	private Set<ObjectId> txnHeads;
 	private Set<ObjectId> tagTargets;
 
 	/**
@@ -318,7 +315,6 @@ public class DfsGarbageCollector {
 			allHeadsAndTags = new HashSet<>();
 			allTags = new HashSet<>();
 			nonHeads = new HashSet<>();
-			txnHeads = new HashSet<>();
 			tagTargets = new HashSet<>();
 			for (Ref ref : refsBefore) {
 				if (ref.isSymbolic() || ref.getObjectId() == null) {
@@ -328,8 +324,6 @@ public class DfsGarbageCollector {
 					allHeads.add(ref.getObjectId());
 				} else if (isTag(ref)) {
 					allTags.add(ref.getObjectId());
-				} else if (RefTreeNames.isRefTree(refdb, ref.getName())) {
-					txnHeads.add(ref.getObjectId());
 				} else {
 					nonHeads.add(ref.getObjectId());
 				}
@@ -355,7 +349,6 @@ public class DfsGarbageCollector {
 			try {
 				packHeads(pm);
 				packRest(pm);
-				packRefTreeGraph(pm);
 				packGarbage(pm);
 				objdb.commitPack(newPackDesc, toPrune());
 				rollback = false;
@@ -559,19 +552,6 @@ public class DfsGarbageCollector {
 		}
 	}
 
-	private void packRefTreeGraph(ProgressMonitor pm) throws IOException {
-		if (txnHeads.isEmpty())
-			return;
-
-		try (PackWriter pw = newPackWriter()) {
-			for (ObjectIdSet packedObjs : newPackObj)
-				pw.excludeObjects(packedObjs);
-			pw.preparePack(pm, txnHeads, NONE);
-			if (0 < pw.getObjectCount())
-				writePack(GC_TXN, pw, pm, 0 /* unknown pack size */);
-		}
-	}
-
 	private void packGarbage(ProgressMonitor pm) throws IOException {
 		PackConfig cfg = new PackConfig(packConfig);
 		cfg.setReuseDeltas(true);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjDatabase.java
index 4dab3b20c5..46ec87df54 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjDatabase.java
@@ -105,13 +105,6 @@ public abstract class DfsObjDatabase extends ObjectDatabase {
 		GC_REST,
 
 		/**
-		 * RefTreeGraph pack was created by Git garbage collection.
-		 *
-		 * @see DfsGarbageCollector
-		 */
-		GC_TXN,
-
-		/**
 		 * Pack was created by Git garbage collection.
 		 * <p>
 		 * This pack contains only unreachable garbage that was found during the
@@ -133,7 +126,6 @@ public abstract class DfsObjDatabase extends ObjectDatabase {
 						.add(COMPACT)
 						.add(GC)
 						.add(GC_REST)
-						.add(GC_TXN)
 						.add(UNREACHABLE_GARBAGE)
 						.build();
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjectRepresentation.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjectRepresentation.java
index 3f113a3ee3..8e124e3c20 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjectRepresentation.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsObjectRepresentation.java
@@ -48,7 +48,6 @@ class DfsObjectRepresentation extends StoredObjectRepresentation {
 		switch (pack.getPackDescription().getPackSource()) {
 		case GC:
 		case GC_REST:
-		case GC_TXN:
 			return true;
 		default:
 			return false;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
index 0c8755fca3..4f418ab4db 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
@@ -533,7 +533,6 @@ public class DfsPackDescription {
 		switch (s) {
 		case GC:
 		case GC_REST:
-		case GC_TXN:
 			return true;
 		default:
 			return false;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
index b1e95520cc..96ca690c1c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
@@ -607,8 +607,15 @@ public final class DfsPackFile extends BlockBasedFile {
 
 	private void readFully(long position, byte[] dstbuf, int dstoff, int cnt,
 			DfsReader ctx) throws IOException {
-		if (ctx.copy(this, position, dstbuf, dstoff, cnt) != cnt)
-			throw new EOFException();
+		while (cnt > 0) {
+			int copied = ctx.copy(this, position, dstbuf, dstoff, cnt);
+			if (copied == 0) {
+				throw new EOFException();
+			}
+			position += copied;
+			dstoff += copied;
+			cnt -= copied;
+		}
 	}
 
 	ObjectLoader load(DfsReader ctx, long pos)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java
index 8a54431d5c..6c3b056efd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReftableDatabase.java
@@ -17,6 +17,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
 import org.eclipse.jgit.annotations.Nullable;
@@ -62,11 +63,12 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 		reftableDatabase = new ReftableDatabase() {
 			@Override
 			public MergedReftable openMergedReftable() throws IOException {
-				DfsReftableDatabase.this.getLock().lock();
+				Lock l = DfsReftableDatabase.this.getLock();
+				l.lock();
 				try {
 					return new MergedReftable(stack().readers());
 				} finally {
-					DfsReftableDatabase.this.getLock().unlock();
+					l.unlock();
 				}
 			}
 		};
@@ -176,6 +178,13 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 
 	/** {@inheritDoc} */
 	@Override
+	public List<Ref> getRefsByPrefixWithExclusions(String include, Set<String> excludes)
+			throws IOException {
+		return reftableDatabase.getRefsByPrefixWithExclusions(include, excludes);
+	}
+
+	/** {@inheritDoc} */
+	@Override
 	public Set<Ref> getTipsWithSha1(ObjectId id) throws IOException {
 		if (!getReftableConfig().isIndexObjects()) {
 			return super.getTipsWithSha1(id);
@@ -207,7 +216,8 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 
 	@Override
 	void clearCache() {
-		getLock().lock();
+		ReentrantLock l = getLock();
+		l.lock();
 		try {
 			if (ctx != null) {
 				ctx.close();
@@ -219,7 +229,7 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 				stack = null;
 			}
 		} finally {
-			getLock().unlock();
+			l.unlock();
 		}
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteArrayWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteArrayWindow.java
index 45d9c85c8c..1036535423 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteArrayWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteArrayWindow.java
@@ -25,7 +25,7 @@ import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
 final class ByteArrayWindow extends ByteWindow {
 	private final byte[] array;
 
-	ByteArrayWindow(PackFile pack, long o, byte[] b) {
+	ByteArrayWindow(Pack pack, long o, byte[] b) {
 		super(pack, o, b.length);
 		array = b;
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteBufferWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteBufferWindow.java
index 8703216322..b6877578c9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteBufferWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteBufferWindow.java
@@ -27,7 +27,7 @@ import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
 final class ByteBufferWindow extends ByteWindow {
 	private final ByteBuffer buffer;
 
-	ByteBufferWindow(PackFile pack, long o, ByteBuffer b) {
+	ByteBufferWindow(Pack pack, long o, ByteBuffer b) {
 		super(pack, o, b.capacity());
 		buffer = b;
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteWindow.java
index 159f31c971..31e7eadd8a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ByteWindow.java
@@ -27,7 +27,7 @@ import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
  * </p>
  */
 abstract class ByteWindow {
-	protected final PackFile pack;
+	protected final Pack pack;
 
 	protected final long start;
 
@@ -37,13 +37,13 @@ abstract class ByteWindow {
 	 * Constructor for ByteWindow.
 	 *
 	 * @param p
-	 *            a {@link org.eclipse.jgit.internal.storage.file.PackFile}.
+	 *            a {@link org.eclipse.jgit.internal.storage.file.Pack}.
 	 * @param s
 	 *            where the byte window starts in the pack file
 	 * @param n
 	 *            size of the byte window
 	 */
-	protected ByteWindow(PackFile p, long s, int n) {
+	protected ByteWindow(Pack p, long s, int n) {
 		pack = p;
 		start = s;
 		end = start + n;
@@ -53,8 +53,8 @@ abstract class ByteWindow {
 		return (int) (end - start);
 	}
 
-	final boolean contains(PackFile neededFile, long neededPos) {
-		return pack == neededFile && start <= neededPos && neededPos < end;
+	final boolean contains(Pack neededPack, long neededPos) {
+		return pack == neededPack && start <= neededPos && neededPos < end;
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
index 9c7a2e7111..7dedeb57ab 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
@@ -239,7 +239,7 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	}
 
 	@Override
-	PackFile openPack(File pack) throws IOException {
+	Pack openPack(File pack) throws IOException {
 		return wrapped.openPack(pack);
 	}
 
@@ -250,7 +250,7 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	}
 
 	@Override
-	Collection<PackFile> getPacks() {
+	Collection<Pack> getPacks() {
 		return wrapped.getPacks();
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/DeltaBaseCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/DeltaBaseCache.java
index cef5a330f2..69cebadf1e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/DeltaBaseCache.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/DeltaBaseCache.java
@@ -49,7 +49,7 @@ class DeltaBaseCache {
 		cache = new Slot[CACHE_SZ];
 	}
 
-	Entry get(PackFile pack, long position) {
+	Entry get(Pack pack, long position) {
 		Slot e = cache[hash(position)];
 		if (e == null)
 			return null;
@@ -63,7 +63,7 @@ class DeltaBaseCache {
 		return null;
 	}
 
-	void store(final PackFile pack, final long position,
+	void store(final Pack pack, final long position,
 			final byte[] data, final int objectType) {
 		if (data.length > maxByteCount)
 			return; // Too large to cache.
@@ -146,7 +146,7 @@ class DeltaBaseCache {
 
 		Slot lruNext;
 
-		PackFile provider;
+		Pack provider;
 
 		long position;
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
index 11ed10c90a..01dd27d9fb 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
@@ -71,7 +71,7 @@ abstract class FileObjectDatabase extends ObjectDatabase {
 	abstract InsertLooseObjectResult insertUnpackedObject(File tmp,
 			ObjectId id, boolean createDuplicate) throws IOException;
 
-	abstract PackFile openPack(File pack) throws IOException;
+	abstract Pack openPack(File pack) throws IOException;
 
-	abstract Collection<PackFile> getPacks();
+	abstract Collection<Pack> getPacks();
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableDatabase.java
index e613a58062..a80fa837b7 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableDatabase.java
@@ -21,7 +21,9 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.TreeSet;
+import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Collectors;
 
@@ -107,12 +109,13 @@ public class FileReftableDatabase extends RefDatabase {
 	 * @throws IOException on I/O errors
 	 */
 	public void compactFully() throws IOException {
-		reftableDatabase.getLock().lock();
+		Lock l = reftableDatabase.getLock();
+		l.lock();
 		try {
 			reftableStack.compactFully();
 			reftableDatabase.clearCache();
 		} finally {
-			reftableDatabase.getLock().unlock();
+			l.unlock();
 		}
 	}
 
@@ -179,6 +182,13 @@ public class FileReftableDatabase extends RefDatabase {
 
 	/** {@inheritDoc} */
 	@Override
+	public List<Ref> getRefsByPrefixWithExclusions(String include, Set<String> excludes)
+			throws IOException {
+		return reftableDatabase.getRefsByPrefixWithExclusions(include, excludes);
+	}
+
+	/** {@inheritDoc} */
+	@Override
 	public List<Ref> getAdditionalRefs() throws IOException {
 		return Collections.emptyList();
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
index bc2039c56b..b5e3927bcc 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.io.InputStreamReader;
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
+import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
@@ -65,6 +66,8 @@ public class FileReftableStack implements AutoCloseable {
 
 	private final Runnable onChange;
 
+	private final SecureRandom random = new SecureRandom();
+
 	private final Supplier<Config> configSupplier;
 
 	// Used for stats & testing.
@@ -365,8 +368,9 @@ public class FileReftableStack implements AutoCloseable {
 	}
 
 	private String filename(long low, long high) {
-		return String.format("%012x-%012x", //$NON-NLS-1$
-				Long.valueOf(low), Long.valueOf(high));
+		return String.format("%012x-%012x-%08x", //$NON-NLS-1$
+				Long.valueOf(low), Long.valueOf(high),
+				Integer.valueOf(random.nextInt()));
 	}
 
 	/**
@@ -636,6 +640,9 @@ public class FileReftableStack implements AutoCloseable {
 
 		@Override
 		public boolean equals(Object other) {
+			if (other == null) {
+				return false;
+			}
 			Segment o = (Segment) other;
 			return o.bytes == bytes && o.log == log && o.start == start
 					&& o.end == end;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
index fd052cec28..fecced1ae6 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
@@ -40,7 +40,6 @@ import org.eclipse.jgit.events.IndexChangedEvent;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.file.ObjectDirectory.AlternateHandle;
 import org.eclipse.jgit.internal.storage.file.ObjectDirectory.AlternateRepository;
-import org.eclipse.jgit.internal.storage.reftree.RefTreeDatabase;
 import org.eclipse.jgit.lib.BaseRepositoryBuilder;
 import org.eclipse.jgit.lib.BatchRefUpdate;
 import org.eclipse.jgit.lib.ConfigConstants;
@@ -182,9 +181,6 @@ public class FileRepository extends Repository {
 			if (StringUtils.equalsIgnoreCase(reftype,
 					ConfigConstants.CONFIG_REF_STORAGE_REFTABLE)) {
 				refs = new FileReftableDatabase(this);
-			} else if (StringUtils.equalsIgnoreCase(reftype,
-					ConfigConstants.CONFIG_REFSTORAGE_REFTREE)) {
-				refs = new RefTreeDatabase(this, new RefDirectory(this));
 			} else {
 				throw new IOException(JGitText.get().unknownRepositoryFormat);
 			}
@@ -247,7 +243,7 @@ public class FileRepository extends Repository {
 
 		RefUpdate head = updateRef(Constants.HEAD);
 		head.disableRefLog();
-		head.link(Constants.R_HEADS + Constants.MASTER);
+		head.link(Constants.R_HEADS + getInitialBranch());
 
 		final boolean fileMode;
 		if (getFS().supportsExecute()) {
@@ -640,7 +636,7 @@ public class FileRepository extends Repository {
 		refsHeadsFile.delete();
 		// RefDirectory wants to create the refs/ directory from scratch, so
 		// remove that too.
-		refsFile.delete();
+			refsFile.delete();
 		// remove HEAD so its previous invalid value doesn't cause issues.
 		headFile.delete();
 
@@ -668,7 +664,7 @@ public class FileRepository extends Repository {
 				for (ReflogEntry e : logs) {
 					logWriter.log(r.getName(), e);
 				}
-			}
+		}
 		}
 
 		try (RevWalk rw = new RevWalk(this)) {
@@ -731,7 +727,7 @@ public class FileRepository extends Repository {
 			throws IOException {
 		File reftableDir = new File(getDirectory(), Constants.REFTABLE);
 		File headFile = new File(getDirectory(), Constants.HEAD);
-		if (reftableDir.exists() && reftableDir.listFiles().length > 0) {
+		if (reftableDir.exists() && FileUtils.hasFiles(reftableDir.toPath())) {
 			throw new IOException(JGitText.get().reftableDirExists);
 		}
 
@@ -763,9 +759,11 @@ public class FileRepository extends Repository {
 			}
 		} else {
 			FileUtils.delete(packedRefs, FileUtils.SKIP_MISSING);
-			FileUtils.delete(headFile);
-			FileUtils.delete(logsDir, FileUtils.RECURSIVE);
-			FileUtils.delete(refsFile, FileUtils.RECURSIVE);
+			FileUtils.delete(headFile, FileUtils.SKIP_MISSING);
+			FileUtils.delete(logsDir,
+					FileUtils.RECURSIVE | FileUtils.SKIP_MISSING);
+			FileUtils.delete(refsFile,
+					FileUtils.RECURSIVE | FileUtils.SKIP_MISSING);
 			for (String r : additional) {
 				new File(getDirectory(), r).delete();
 			}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java
index 54ff7d29c6..8c48cd94b0 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java
@@ -12,8 +12,10 @@ package org.eclipse.jgit.internal.storage.file;
 
 import static org.eclipse.jgit.util.FS.FileStoreAttributes.FALLBACK_FILESTORE_ATTRIBUTES;
 import static org.eclipse.jgit.util.FS.FileStoreAttributes.FALLBACK_TIMESTAMP_RESOLUTION;
+
 import java.io.File;
 import java.io.IOException;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.time.Duration;
 import java.time.Instant;
@@ -221,14 +223,20 @@ public class FileSnapshot {
 		this.file = file;
 		this.lastRead = Instant.now();
 		this.fileStoreAttributeCache = useConfig
-				? FS.getFileStoreAttributes(file.toPath().getParent())
+				? FS.getFileStoreAttributes(file.toPath())
 				: FALLBACK_FILESTORE_ATTRIBUTES;
 		BasicFileAttributes fileAttributes = null;
 		try {
 			fileAttributes = FS.DETECTED.fileAttributes(file);
+		} catch (NoSuchFileException e) {
+			this.lastModified = Instant.EPOCH;
+			this.size = 0L;
+			this.fileKey = MISSING_FILEKEY;
+			return;
 		} catch (IOException e) {
-			this.lastModified = Instant.ofEpochMilli(file.lastModified());
-			this.size = file.length();
+			LOG.error(e.getMessage(), e);
+			this.lastModified = Instant.EPOCH;
+			this.size = 0L;
 			this.fileKey = MISSING_FILEKEY;
 			return;
 		}
@@ -309,9 +317,14 @@ public class FileSnapshot {
 			currLastModified = fileAttributes.lastModifiedTime().toInstant();
 			currSize = fileAttributes.size();
 			currFileKey = getFileKey(fileAttributes);
+		} catch (NoSuchFileException e) {
+			currLastModified = Instant.EPOCH;
+			currSize = 0L;
+			currFileKey = MISSING_FILEKEY;
 		} catch (IOException e) {
-			currLastModified = Instant.ofEpochMilli(path.lastModified());
-			currSize = path.length();
+			LOG.error(e.getMessage(), e);
+			currLastModified = Instant.EPOCH;
+			currSize = 0L;
 			currFileKey = MISSING_FILEKEY;
 		}
 		sizeChanged = isSizeChanged(currSize);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
index 1f2fe1057f..75de3be89e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
@@ -60,7 +60,6 @@ import org.eclipse.jgit.errors.NoWorkTreeException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.pack.PackExt;
 import org.eclipse.jgit.internal.storage.pack.PackWriter;
-import org.eclipse.jgit.internal.storage.reftree.RefTreeNames;
 import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
@@ -206,16 +205,16 @@ public class GC {
 	 * gc.log.
 	 *
 	 * @return the collection of
-	 *         {@link org.eclipse.jgit.internal.storage.file.PackFile}'s which
+	 *         {@link org.eclipse.jgit.internal.storage.file.Pack}'s which
 	 *         are newly created
 	 * @throws java.io.IOException
 	 * @throws java.text.ParseException
 	 *             If the configuration parameter "gc.pruneexpire" couldn't be
 	 *             parsed
 	 */
-	// TODO(ms): change signature and return Future<Collection<PackFile>>
+	// TODO(ms): change signature and return Future<Collection<Pack>>
 	@SuppressWarnings("FutureReturnValueIgnored")
-	public Collection<PackFile> gc() throws IOException, ParseException {
+	public Collection<Pack> gc() throws IOException, ParseException {
 		if (!background) {
 			return doGc();
 		}
@@ -225,9 +224,9 @@ public class GC {
 			return Collections.emptyList();
 		}
 
-		Callable<Collection<PackFile>> gcTask = () -> {
+		Callable<Collection<Pack>> gcTask = () -> {
 			try {
-				Collection<PackFile> newPacks = doGc();
+				Collection<Pack> newPacks = doGc();
 				if (automatic && tooManyLooseObjects()) {
 					String message = JGitText.get().gcTooManyUnpruned;
 					gcLog.write(message);
@@ -259,14 +258,14 @@ public class GC {
 		return (executor != null) ? executor : WorkQueue.getExecutor();
 	}
 
-	private Collection<PackFile> doGc() throws IOException, ParseException {
+	private Collection<Pack> doGc() throws IOException, ParseException {
 		if (automatic && !needGc()) {
 			return Collections.emptyList();
 		}
 		pm.start(6 /* tasks */);
 		packRefs();
 		// TODO: implement reflog_expire(pm, repo);
-		Collection<PackFile> newPacks = repack();
+		Collection<Pack> newPacks = repack();
 		prune(Collections.emptySet());
 		// TODO: implement rerere_gc(pm);
 		return newPacks;
@@ -282,7 +281,7 @@ public class GC {
 	 * @param existing
 	 * @throws IOException
 	 */
-	private void loosen(ObjectDirectoryInserter inserter, ObjectReader reader, PackFile pack, HashSet<ObjectId> existing)
+	private void loosen(ObjectDirectoryInserter inserter, ObjectReader reader, Pack pack, HashSet<ObjectId> existing)
 			throws IOException {
 		for (PackIndex.MutableEntry entry : pack) {
 			ObjectId oid = entry.toObjectId();
@@ -314,10 +313,10 @@ public class GC {
 	 * @throws ParseException
 	 * @throws IOException
 	 */
-	private void deleteOldPacks(Collection<PackFile> oldPacks,
-			Collection<PackFile> newPacks) throws ParseException, IOException {
+	private void deleteOldPacks(Collection<Pack> oldPacks,
+			Collection<Pack> newPacks) throws ParseException, IOException {
 		HashSet<ObjectId> ids = new HashSet<>();
-		for (PackFile pack : newPacks) {
+		for (Pack pack : newPacks) {
 			for (PackIndex.MutableEntry entry : pack) {
 				ids.add(entry.toObjectId());
 			}
@@ -330,12 +329,12 @@ public class GC {
 
 		prunePreserved();
 		long packExpireDate = getPackExpireDate();
-		oldPackLoop: for (PackFile oldPack : oldPacks) {
+		oldPackLoop: for (Pack oldPack : oldPacks) {
 			checkCancelled();
 			String oldName = oldPack.getPackName();
 			// check whether an old pack file is also among the list of new
 			// pack files. Then we must not delete it.
-			for (PackFile newPack : newPacks)
+			for (Pack newPack : newPacks)
 				if (oldName.equals(newPack.getPackName()))
 					continue oldPackLoop;
 
@@ -439,7 +438,7 @@ public class GC {
 	 */
 	public void prunePacked() throws IOException {
 		ObjectDirectory objdb = repo.getObjectDatabase();
-		Collection<PackFile> packs = objdb.getPacks();
+		Collection<Pack> packs = objdb.getPacks();
 		File objects = repo.getObjectsDirectory();
 		String[] fanout = objects.list();
 
@@ -467,7 +466,7 @@ public class GC {
 							continue;
 						}
 						boolean found = false;
-						for (PackFile p : packs) {
+						for (Pack p : packs) {
 							checkCancelled();
 							if (p.hasObject(id)) {
 								found = true;
@@ -789,8 +788,8 @@ public class GC {
 	 *             reflog-entries or during writing to the packfiles
 	 *             {@link java.io.IOException} occurs
 	 */
-	public Collection<PackFile> repack() throws IOException {
-		Collection<PackFile> toBeDeleted = repo.getObjectDatabase().getPacks();
+	public Collection<Pack> repack() throws IOException {
+		Collection<Pack> toBeDeleted = repo.getObjectDatabase().getPacks();
 
 		long time = System.currentTimeMillis();
 		Collection<Ref> refsBefore = getAllRefs();
@@ -802,7 +801,6 @@ public class GC {
 		Set<ObjectId> txnHeads = new HashSet<>();
 		Set<ObjectId> tagTargets = new HashSet<>();
 		Set<ObjectId> indexObjects = listNonHEADIndexObjects();
-		RefDatabase refdb = repo.getRefDatabase();
 
 		for (Ref ref : refsBefore) {
 			checkCancelled();
@@ -814,8 +812,6 @@ public class GC {
 				allHeads.add(ref.getObjectId());
 			} else if (isTag(ref)) {
 				allTags.add(ref.getObjectId());
-			} else if (RefTreeNames.isRefTree(refdb, ref.getName())) {
-				txnHeads.add(ref.getObjectId());
 			} else {
 				nonHeads.add(ref.getObjectId());
 			}
@@ -825,10 +821,10 @@ public class GC {
 		}
 
 		List<ObjectIdSet> excluded = new LinkedList<>();
-		for (PackFile f : repo.getObjectDatabase().getPacks()) {
+		for (Pack p : repo.getObjectDatabase().getPacks()) {
 			checkCancelled();
-			if (f.shouldBeKept())
-				excluded.add(f.getIndex());
+			if (p.shouldBeKept())
+				excluded.add(p.getIndex());
 		}
 
 		// Don't exclude tags that are also branch tips
@@ -846,8 +842,8 @@ public class GC {
 			nonHeads.clear();
 		}
 
-		List<PackFile> ret = new ArrayList<>(2);
-		PackFile heads = null;
+		List<Pack> ret = new ArrayList<>(2);
+		Pack heads = null;
 		if (!allHeadsAndTags.isEmpty()) {
 			heads = writePack(allHeadsAndTags, PackWriter.NONE, allTags,
 					tagTargets, excluded);
@@ -857,13 +853,13 @@ public class GC {
 			}
 		}
 		if (!nonHeads.isEmpty()) {
-			PackFile rest = writePack(nonHeads, allHeadsAndTags, PackWriter.NONE,
+			Pack rest = writePack(nonHeads, allHeadsAndTags, PackWriter.NONE,
 					tagTargets, excluded);
 			if (rest != null)
 				ret.add(rest);
 		}
 		if (!txnHeads.isEmpty()) {
-			PackFile txn = writePack(txnHeads, PackWriter.NONE, PackWriter.NONE,
+			Pack txn = writePack(txnHeads, PackWriter.NONE, PackWriter.NONE,
 					null, excluded);
 			if (txn != null)
 				ret.add(txn);
@@ -1133,7 +1129,7 @@ public class GC {
 		}
 	}
 
-	private PackFile writePack(@NonNull Set<? extends ObjectId> want,
+	private Pack writePack(@NonNull Set<? extends ObjectId> want,
 			@NonNull Set<? extends ObjectId> have, @NonNull Set<ObjectId> tags,
 			Set<ObjectId> tagTargets, List<ObjectIdSet> excludeObjects)
 			throws IOException {
@@ -1360,13 +1356,13 @@ public class GC {
 	 */
 	public RepoStatistics getStatistics() throws IOException {
 		RepoStatistics ret = new RepoStatistics();
-		Collection<PackFile> packs = repo.getObjectDatabase().getPacks();
-		for (PackFile f : packs) {
-			ret.numberOfPackedObjects += f.getIndex().getObjectCount();
+		Collection<Pack> packs = repo.getObjectDatabase().getPacks();
+		for (Pack p : packs) {
+			ret.numberOfPackedObjects += p.getIndex().getObjectCount();
 			ret.numberOfPackFiles++;
-			ret.sizeOfPackedObjects += f.getPackFile().length();
-			if (f.getBitmapIndex() != null)
-				ret.numberOfBitmaps += f.getBitmapIndex().getBitmapCount();
+			ret.sizeOfPackedObjects += p.getPackFile().length();
+			if (p.getBitmapIndex() != null)
+				ret.numberOfBitmaps += p.getBitmapIndex().getBitmapCount();
 		}
 		File objDir = repo.getObjectsDirectory();
 		String[] fanout = objDir.list();
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedWholeObject.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedWholeObject.java
index ee4bbc1964..e2fbd7a0b4 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedWholeObject.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedWholeObject.java
@@ -30,12 +30,12 @@ class LargePackedWholeObject extends ObjectLoader {
 
 	private final int headerLength;
 
-	private final PackFile pack;
+	private final Pack pack;
 
 	private final FileObjectDatabase db;
 
 	LargePackedWholeObject(int type, long size, long objectOffset,
-			int headerLength, PackFile pack, FileObjectDatabase db) {
+			int headerLength, Pack pack, FileObjectDatabase db) {
 		this.type = type;
 		this.size = size;
 		this.objectOffset = objectOffset;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalCachedPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalCachedPack.java
index 9d04062e37..ae5bce6985 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalCachedPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalCachedPack.java
@@ -25,31 +25,31 @@ class LocalCachedPack extends CachedPack {
 
 	private final String[] packNames;
 
-	private PackFile[] packs;
+	private Pack[] packs;
 
 	LocalCachedPack(ObjectDirectory odb, List<String> packNames) {
 		this.odb = odb;
 		this.packNames = packNames.toArray(new String[0]);
 	}
 
-	LocalCachedPack(List<PackFile> packs) {
+	LocalCachedPack(List<Pack> packs) {
 		odb = null;
 		packNames = null;
-		this.packs = packs.toArray(new PackFile[0]);
+		this.packs = packs.toArray(new Pack[0]);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public long getObjectCount() throws IOException {
 		long cnt = 0;
-		for (PackFile pack : getPacks())
+		for (Pack pack : getPacks())
 			cnt += pack.getObjectCount();
 		return cnt;
 	}
 
 	void copyAsIs(PackOutputStream out, WindowCursor wc)
 			throws IOException {
-		for (PackFile pack : getPacks())
+		for (Pack pack : getPacks())
 			pack.copyPackAsIs(out, wc);
 	}
 
@@ -58,7 +58,7 @@ class LocalCachedPack extends CachedPack {
 	public boolean hasObject(ObjectToPack obj, StoredObjectRepresentation rep) {
 		try {
 			LocalObjectRepresentation local = (LocalObjectRepresentation) rep;
-			for (PackFile pack : getPacks()) {
+			for (Pack pack : getPacks()) {
 				if (local.pack == pack)
 					return true;
 			}
@@ -68,9 +68,9 @@ class LocalCachedPack extends CachedPack {
 		}
 	}
 
-	private PackFile[] getPacks() throws FileNotFoundException {
+	private Pack[] getPacks() throws FileNotFoundException {
 		if (packs == null) {
-			PackFile[] p = new PackFile[packNames.length];
+			Pack[] p = new Pack[packNames.length];
 			for (int i = 0; i < packNames.length; i++)
 				p[i] = getPackFile(packNames[i]);
 			packs = p;
@@ -78,8 +78,8 @@ class LocalCachedPack extends CachedPack {
 		return packs;
 	}
 
-	private PackFile getPackFile(String packName) throws FileNotFoundException {
-		for (PackFile pack : odb.getPacks()) {
+	private Pack getPackFile(String packName) throws FileNotFoundException {
+		for (Pack pack : odb.getPacks()) {
 			if (packName.equals(pack.getPackName()))
 				return pack;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectRepresentation.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectRepresentation.java
index 3950dde4a5..559718af3a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectRepresentation.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectRepresentation.java
@@ -16,40 +16,40 @@ import org.eclipse.jgit.internal.storage.pack.StoredObjectRepresentation;
 import org.eclipse.jgit.lib.ObjectId;
 
 class LocalObjectRepresentation extends StoredObjectRepresentation {
-	static LocalObjectRepresentation newWhole(PackFile f, long p, long length) {
+	static LocalObjectRepresentation newWhole(Pack pack, long offset, long length) {
 		LocalObjectRepresentation r = new LocalObjectRepresentation() {
 			@Override
 			public int getFormat() {
 				return PACK_WHOLE;
 			}
 		};
-		r.pack = f;
-		r.offset = p;
+		r.pack = pack;
+		r.offset = offset;
 		r.length = length;
 		return r;
 	}
 
-	static LocalObjectRepresentation newDelta(PackFile f, long p, long n,
+	static LocalObjectRepresentation newDelta(Pack pack, long offset, long length,
 			ObjectId base) {
 		LocalObjectRepresentation r = new Delta();
-		r.pack = f;
-		r.offset = p;
-		r.length = n;
+		r.pack = pack;
+		r.offset = offset;
+		r.length = length;
 		r.baseId = base;
 		return r;
 	}
 
-	static LocalObjectRepresentation newDelta(PackFile f, long p, long n,
+	static LocalObjectRepresentation newDelta(Pack pack, long offset, long length,
 			long base) {
 		LocalObjectRepresentation r = new Delta();
-		r.pack = f;
-		r.offset = p;
-		r.length = n;
+		r.pack = pack;
+		r.offset = offset;
+		r.length = length;
 		r.baseOffset = base;
 		return r;
 	}
 
-	PackFile pack;
+	Pack pack;
 
 	long offset;
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectToPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectToPack.java
index 4a0ac1fd84..ac6cd212d5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectToPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LocalObjectToPack.java
@@ -17,7 +17,7 @@ import org.eclipse.jgit.lib.AnyObjectId;
 /** {@link ObjectToPack} for {@link ObjectDirectory}. */
 class LocalObjectToPack extends ObjectToPack {
 	/** Pack to reuse compressed data from, otherwise null. */
-	PackFile pack;
+	Pack pack;
 
 	/** Offset of the object's header in {@link #pack}. */
 	long offset;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LooseObjects.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LooseObjects.java
new file mode 100644
index 0000000000..e7cb285c34
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LooseObjects.java
@@ -0,0 +1,227 @@
+/*
+ * Copyright (C) 2009, Google Inc. and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.storage.file;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.StandardCopyOption;
+import java.util.Set;
+
+import org.eclipse.jgit.internal.storage.file.FileObjectDatabase.InsertLooseObjectResult;
+import org.eclipse.jgit.lib.AbbreviatedObjectId;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.util.FileUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Traditional file system based loose objects handler.
+ * <p>
+ * This is the loose object representation for a Git object database, where
+ * objects are stored loose by hashing them into directories by their
+ * {@link org.eclipse.jgit.lib.ObjectId}.
+ */
+class LooseObjects {
+	private static final Logger LOG = LoggerFactory
+			.getLogger(LooseObjects.class);
+
+	private final File directory;
+
+	private final UnpackedObjectCache unpackedObjectCache;
+
+	/**
+	 * Initialize a reference to an on-disk object directory.
+	 *
+	 * @param dir
+	 *            the location of the <code>objects</code> directory.
+	 */
+	LooseObjects(File dir) {
+		directory = dir;
+		unpackedObjectCache = new UnpackedObjectCache();
+	}
+
+	/**
+	 * Getter for the field <code>directory</code>.
+	 *
+	 * @return the location of the <code>objects</code> directory.
+	 */
+	File getDirectory() {
+		return directory;
+	}
+
+	void create() throws IOException {
+		FileUtils.mkdirs(directory);
+	}
+
+	void close() {
+		unpackedObjectCache.clear();
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public String toString() {
+		return "LooseObjects[" + directory + "]"; //$NON-NLS-1$ //$NON-NLS-2$
+	}
+
+	boolean hasCached(AnyObjectId id) {
+		return unpackedObjectCache.isUnpacked(id);
+	}
+
+	/**
+	 * Does the requested object exist as a loose object?
+	 *
+	 * @param objectId
+	 *            identity of the object to test for existence of.
+	 * @return {@code true} if the specified object is stored as a loose object.
+	 */
+	boolean has(AnyObjectId objectId) {
+		return fileFor(objectId).exists();
+	}
+
+	/**
+	 * Find objects matching the prefix abbreviation.
+	 *
+	 * @param matches
+	 *            set to add any located ObjectIds to. This is an output
+	 *            parameter.
+	 * @param id
+	 *            prefix to search for.
+	 * @param matchLimit
+	 *            maximum number of results to return. At most this many
+	 *            ObjectIds should be added to matches before returning.
+	 * @return {@code true} if the matches were exhausted before reaching
+	 *         {@code maxLimit}.
+	 */
+	boolean resolve(Set<ObjectId> matches, AbbreviatedObjectId id,
+			int matchLimit) {
+		String fanOut = id.name().substring(0, 2);
+		String[] entries = new File(directory, fanOut).list();
+		if (entries != null) {
+			for (String e : entries) {
+				if (e.length() != Constants.OBJECT_ID_STRING_LENGTH - 2) {
+					continue;
+				}
+				try {
+					ObjectId entId = ObjectId.fromString(fanOut + e);
+					if (id.prefixCompare(entId) == 0) {
+						matches.add(entId);
+					}
+				} catch (IllegalArgumentException notId) {
+					continue;
+				}
+				if (matches.size() > matchLimit) {
+					return false;
+				}
+			}
+		}
+		return true;
+	}
+
+	ObjectLoader open(WindowCursor curs, AnyObjectId id) throws IOException {
+		File path = fileFor(id);
+		try (FileInputStream in = new FileInputStream(path)) {
+			unpackedObjectCache.add(id);
+			return UnpackedObject.open(in, path, id, curs);
+		} catch (FileNotFoundException noFile) {
+			if (path.exists()) {
+				throw noFile;
+			}
+			unpackedObjectCache.remove(id);
+			return null;
+		}
+	}
+
+	long getSize(WindowCursor curs, AnyObjectId id) throws IOException {
+		File f = fileFor(id);
+		try (FileInputStream in = new FileInputStream(f)) {
+			unpackedObjectCache.add(id);
+			return UnpackedObject.getSize(in, id, curs);
+		} catch (FileNotFoundException noFile) {
+			if (f.exists()) {
+				throw noFile;
+			}
+			unpackedObjectCache.remove(id);
+			return -1;
+		}
+	}
+
+	InsertLooseObjectResult insert(File tmp, ObjectId id) throws IOException {
+		final File dst = fileFor(id);
+		if (dst.exists()) {
+			// We want to be extra careful and avoid replacing an object
+			// that already exists. We can't be sure renameTo() would
+			// fail on all platforms if dst exists, so we check first.
+			//
+			FileUtils.delete(tmp, FileUtils.RETRY);
+			return InsertLooseObjectResult.EXISTS_LOOSE;
+		}
+
+		try {
+			return tryMove(tmp, dst, id);
+		} catch (NoSuchFileException e) {
+			// It's possible the directory doesn't exist yet as the object
+			// directories are always lazily created. Note that we try the
+			// rename/move first as the directory likely does exist.
+			//
+			// Create the directory.
+			//
+			FileUtils.mkdir(dst.getParentFile(), true);
+		} catch (IOException e) {
+			// Any other IO error is considered a failure.
+			//
+			LOG.error(e.getMessage(), e);
+			FileUtils.delete(tmp, FileUtils.RETRY);
+			return InsertLooseObjectResult.FAILURE;
+		}
+
+		try {
+			return tryMove(tmp, dst, id);
+		} catch (IOException e) {
+			// The object failed to be renamed into its proper location and
+			// it doesn't exist in the repository either. We really don't
+			// know what went wrong, so fail.
+			//
+			LOG.error(e.getMessage(), e);
+			FileUtils.delete(tmp, FileUtils.RETRY);
+			return InsertLooseObjectResult.FAILURE;
+		}
+	}
+
+	private InsertLooseObjectResult tryMove(File tmp, File dst, ObjectId id)
+			throws IOException {
+		Files.move(FileUtils.toPath(tmp), FileUtils.toPath(dst),
+				StandardCopyOption.ATOMIC_MOVE);
+		dst.setReadOnly();
+		unpackedObjectCache.add(id);
+		return InsertLooseObjectResult.INSERTED;
+	}
+
+	/**
+	 * Compute the location of a loose object file.
+	 *
+	 * @param objectId
+	 *            identity of the object to get the File location for.
+	 * @return {@link java.io.File} location of the specified loose object.
+	 */
+	File fileFor(AnyObjectId objectId) {
+		String n = objectId.name();
+		String d = n.substring(0, 2);
+		String f = n.substring(2);
+		return new File(new File(getDirectory(), d), f);
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
index d32182864a..e71a960603 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
@@ -16,28 +16,19 @@ import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
 
 import java.io.BufferedReader;
 import java.io.File;
-import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.file.Files;
-import java.nio.file.NoSuchFileException;
-import java.nio.file.StandardCopyOption;
 import java.text.MessageFormat;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
-import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicReference;
 
-import org.eclipse.jgit.errors.CorruptObjectException;
-import org.eclipse.jgit.errors.PackInvalidException;
-import org.eclipse.jgit.errors.PackMismatchException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
 import org.eclipse.jgit.internal.storage.pack.PackExt;
@@ -45,7 +36,6 @@ import org.eclipse.jgit.internal.storage.pack.PackWriter;
 import org.eclipse.jgit.lib.AbbreviatedObjectId;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Config;
-import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectDatabase;
 import org.eclipse.jgit.lib.ObjectId;
@@ -54,8 +44,6 @@ import org.eclipse.jgit.lib.RepositoryCache;
 import org.eclipse.jgit.lib.RepositoryCache.FileKey;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.FileUtils;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * Traditional file system based {@link org.eclipse.jgit.lib.ObjectDatabase}.
@@ -63,7 +51,7 @@ import org.slf4j.LoggerFactory;
  * This is the classical object database representation for a Git repository,
  * where objects are stored loose by hashing them into directories by their
  * {@link org.eclipse.jgit.lib.ObjectId}, or are stored in compressed containers
- * known as {@link org.eclipse.jgit.internal.storage.file.PackFile}s.
+ * known as {@link org.eclipse.jgit.internal.storage.file.Pack}s.
  * <p>
  * Optionally an object database can reference one or more alternates; other
  * ObjectDatabase instances that are searched in addition to the current
@@ -76,12 +64,6 @@ import org.slf4j.LoggerFactory;
  * considered.
  */
 public class ObjectDirectory extends FileObjectDatabase {
-	private static final Logger LOG = LoggerFactory
-			.getLogger(ObjectDirectory.class);
-
-	private static final PackList NO_PACKS = new PackList(
-			FileSnapshot.DIRTY, new PackFile[0]);
-
 	/** Maximum number of candidates offered as resolutions of abbreviation. */
 	private static final int RESOLVE_ABBREV_LIMIT = 256;
 
@@ -93,7 +75,9 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private final File infoDirectory;
 
-	private final File packDirectory;
+	private final LooseObjects loose;
+
+	private final PackDirectory packed;
 
 	private final File preservedDirectory;
 
@@ -103,16 +87,12 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private final AtomicReference<AlternateHandle[]> alternates;
 
-	private final UnpackedObjectCache unpackedObjectCache;
-
 	private final File shallowFile;
 
 	private FileSnapshot shallowFileSnapshot = FileSnapshot.DIRTY;
 
 	private Set<ObjectId> shallowCommitsIds;
 
-	final AtomicReference<PackList> packList;
-
 	/**
 	 * Initialize a reference to an on-disk object directory.
 	 *
@@ -136,11 +116,11 @@ public class ObjectDirectory extends FileObjectDatabase {
 		config = cfg;
 		objects = dir;
 		infoDirectory = new File(objects, "info"); //$NON-NLS-1$
-		packDirectory = new File(objects, "pack"); //$NON-NLS-1$
+		File packDirectory = new File(objects, "pack"); //$NON-NLS-1$
 		preservedDirectory = new File(packDirectory, "preserved"); //$NON-NLS-1$
 		alternatesFile = new File(objects, Constants.INFO_ALTERNATES);
-		packList = new AtomicReference<>(NO_PACKS);
-		unpackedObjectCache = new UnpackedObjectCache();
+		loose = new LooseObjects(objects);
+		packed = new PackDirectory(config, packDirectory);
 		this.fs = fs;
 		this.shallowFile = shallowFile;
 
@@ -158,7 +138,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	/** {@inheritDoc} */
 	@Override
 	public final File getDirectory() {
-		return objects;
+		return loose.getDirectory();
 	}
 
 	/**
@@ -167,7 +147,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	 * @return the location of the <code>pack</code> directory.
 	 */
 	public final File getPackDirectory() {
-		return packDirectory;
+		return packed.getDirectory();
 	}
 
 	/**
@@ -188,9 +168,9 @@ public class ObjectDirectory extends FileObjectDatabase {
 	/** {@inheritDoc} */
 	@Override
 	public void create() throws IOException {
-		FileUtils.mkdirs(objects);
+		loose.create();
 		FileUtils.mkdir(infoDirectory);
-		FileUtils.mkdir(packDirectory);
+		packed.create();
 	}
 
 	/** {@inheritDoc} */
@@ -212,13 +192,9 @@ public class ObjectDirectory extends FileObjectDatabase {
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
-		unpackedObjectCache.clear();
+		loose.close();
 
-		final PackList packs = packList.get();
-		if (packs != NO_PACKS && packList.compareAndSet(packs, NO_PACKS)) {
-			for (PackFile p : packs.packs)
-				p.close();
-		}
+		packed.close();
 
 		// Fully close all loaded alternates and clear the alternate list.
 		AlternateHandle[] alt = alternates.get();
@@ -230,12 +206,8 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	/** {@inheritDoc} */
 	@Override
-	public Collection<PackFile> getPacks() {
-		PackList list = packList.get();
-		if (list == NO_PACKS)
-			list = scanPacks(list);
-		PackFile[] packs = list.packs;
-		return Collections.unmodifiableCollection(Arrays.asList(packs));
+	public Collection<Pack> getPacks() {
+		return packed.getPacks();
 	}
 
 	/**
@@ -244,7 +216,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	 * Add a single existing pack to the list of available pack files.
 	 */
 	@Override
-	public PackFile openPack(File pack)
+	public Pack openPack(File pack)
 			throws IOException {
 		final String p = pack.getName();
 		if (p.length() != 50 || !p.startsWith("pack-") || !p.endsWith(".pack")) //$NON-NLS-1$ //$NON-NLS-2$
@@ -263,8 +235,8 @@ public class ObjectDirectory extends FileObjectDatabase {
 			}
 		}
 
-		PackFile res = new PackFile(pack, extensions);
-		insertPack(res);
+		Pack res = new Pack(pack, extensions);
+		packed.insert(res);
 		return res;
 	}
 
@@ -277,7 +249,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	/** {@inheritDoc} */
 	@Override
 	public boolean has(AnyObjectId objectId) {
-		return unpackedObjectCache.isUnpacked(objectId)
+		return loose.hasCached(objectId)
 				|| hasPackedInSelfOrAlternate(objectId, null)
 				|| hasLooseInSelfOrAlternate(objectId, null);
 	}
@@ -300,7 +272,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private boolean hasLooseInSelfOrAlternate(AnyObjectId objectId,
 			Set<AlternateHandle.Id> skips) {
-		if (fileFor(objectId).exists()) {
+		if (loose.has(objectId)) {
 			return true;
 		}
 		skips = addMe(skips);
@@ -315,25 +287,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	}
 
 	boolean hasPackedObject(AnyObjectId objectId) {
-		PackList pList;
-		do {
-			pList = packList.get();
-			for (PackFile p : pList.packs) {
-				try {
-					if (p.hasObject(objectId))
-						return true;
-				} catch (IOException e) {
-					// The hasObject call should have only touched the index,
-					// so any failure here indicates the index is unreadable
-					// by this process, and the pack is likewise not readable.
-					LOG.warn(MessageFormat.format(
-							JGitText.get().unableToReadPackfile,
-							p.getPackFile().getAbsolutePath()), e);
-					removePack(p);
-				}
-			}
-		} while (searchPacksAgain(pList));
-		return false;
+		return packed.has(objectId);
 	}
 
 	@Override
@@ -345,41 +299,11 @@ public class ObjectDirectory extends FileObjectDatabase {
 	private void resolve(Set<ObjectId> matches, AbbreviatedObjectId id,
 			Set<AlternateHandle.Id> skips)
 			throws IOException {
-		// Go through the packs once. If we didn't find any resolutions
-		// scan for new packs and check once more.
-		int oldSize = matches.size();
-		PackList pList;
-		do {
-			pList = packList.get();
-			for (PackFile p : pList.packs) {
-				try {
-					p.resolve(matches, id, RESOLVE_ABBREV_LIMIT);
-					p.resetTransientErrorCount();
-				} catch (IOException e) {
-					handlePackError(e, p);
-				}
-				if (matches.size() > RESOLVE_ABBREV_LIMIT)
-					return;
-			}
-		} while (matches.size() == oldSize && searchPacksAgain(pList));
-
-		String fanOut = id.name().substring(0, 2);
-		String[] entries = new File(getDirectory(), fanOut).list();
-		if (entries != null) {
-			for (String e : entries) {
-				if (e.length() != Constants.OBJECT_ID_STRING_LENGTH - 2)
-					continue;
-				try {
-					ObjectId entId = ObjectId.fromString(fanOut + e);
-					if (id.prefixCompare(entId) == 0)
-						matches.add(entId);
-				} catch (IllegalArgumentException notId) {
-					continue;
-				}
-				if (matches.size() > RESOLVE_ABBREV_LIMIT)
-					return;
-			}
-		}
+		if (!packed.resolve(matches, id, RESOLVE_ABBREV_LIMIT))
+			return;
+
+		if (!loose.resolve(matches, id, RESOLVE_ABBREV_LIMIT))
+			return;
 
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
@@ -395,7 +319,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 	@Override
 	ObjectLoader openObject(WindowCursor curs, AnyObjectId objectId)
 			throws IOException {
-		if (unpackedObjectCache.isUnpacked(objectId)) {
+		if (loose.hasCached(objectId)) {
 			ObjectLoader ldr = openLooseObject(curs, objectId);
 			if (ldr != null) {
 				return ldr;
@@ -446,51 +370,20 @@ public class ObjectDirectory extends FileObjectDatabase {
 	}
 
 	ObjectLoader openPackedObject(WindowCursor curs, AnyObjectId objectId) {
-		PackList pList;
-		do {
-			SEARCH: for (;;) {
-				pList = packList.get();
-				for (PackFile p : pList.packs) {
-					try {
-						ObjectLoader ldr = p.get(curs, objectId);
-						p.resetTransientErrorCount();
-						if (ldr != null)
-							return ldr;
-					} catch (PackMismatchException e) {
-						// Pack was modified; refresh the entire pack list.
-						if (searchPacksAgain(pList))
-							continue SEARCH;
-					} catch (IOException e) {
-						handlePackError(e, p);
-					}
-				}
-				break SEARCH;
-			}
-		} while (searchPacksAgain(pList));
-		return null;
+		return packed.open(curs, objectId);
 	}
 
 	@Override
 	ObjectLoader openLooseObject(WindowCursor curs, AnyObjectId id)
 			throws IOException {
-		File path = fileFor(id);
-		try (FileInputStream in = new FileInputStream(path)) {
-			unpackedObjectCache.add(id);
-			return UnpackedObject.open(in, path, id, curs);
-		} catch (FileNotFoundException noFile) {
-			if (path.exists()) {
-				throw noFile;
-			}
-			unpackedObjectCache.remove(id);
-			return null;
-		}
+		return loose.open(curs, id);
 	}
 
 	@Override
 	long getObjectSize(WindowCursor curs, AnyObjectId id)
 			throws IOException {
-		if (unpackedObjectCache.isUnpacked(id)) {
-			long len = getLooseObjectSize(curs, id);
+		if (loose.hasCached(id)) {
+			long len = loose.getSize(curs, id);
 			if (0 <= len) {
 				return len;
 			}
@@ -504,7 +397,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private long getPackedSizeFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId id, Set<AlternateHandle.Id> skips) {
-		long len = getPackedObjectSize(curs, id);
+		long len = packed.getSize(curs, id);
 		if (0 <= len) {
 			return len;
 		}
@@ -522,7 +415,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private long getLooseSizeFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId id, Set<AlternateHandle.Id> skips) throws IOException {
-		long len = getLooseObjectSize(curs, id);
+		long len = loose.getSize(curs, id);
 		if (0 <= len) {
 			return len;
 		}
@@ -538,46 +431,6 @@ public class ObjectDirectory extends FileObjectDatabase {
 		return -1;
 	}
 
-	private long getPackedObjectSize(WindowCursor curs, AnyObjectId id) {
-		PackList pList;
-		do {
-			SEARCH: for (;;) {
-				pList = packList.get();
-				for (PackFile p : pList.packs) {
-					try {
-						long len = p.getObjectSize(curs, id);
-						p.resetTransientErrorCount();
-						if (0 <= len)
-							return len;
-					} catch (PackMismatchException e) {
-						// Pack was modified; refresh the entire pack list.
-						if (searchPacksAgain(pList))
-							continue SEARCH;
-					} catch (IOException e) {
-						handlePackError(e, p);
-					}
-				}
-				break SEARCH;
-			}
-		} while (searchPacksAgain(pList));
-		return -1;
-	}
-
-	private long getLooseObjectSize(WindowCursor curs, AnyObjectId id)
-			throws IOException {
-		File f = fileFor(id);
-		try (FileInputStream in = new FileInputStream(f)) {
-			unpackedObjectCache.add(id);
-			return UnpackedObject.getSize(in, id, curs);
-		} catch (FileNotFoundException noFile) {
-			if (f.exists()) {
-				throw noFile;
-			}
-			unpackedObjectCache.remove(id);
-			return -1;
-		}
-	}
-
 	@Override
 	void selectObjectRepresentation(PackWriter packer, ObjectToPack otp,
 			WindowCursor curs) throws IOException {
@@ -586,25 +439,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	private void selectObjectRepresentation(PackWriter packer, ObjectToPack otp,
 			WindowCursor curs, Set<AlternateHandle.Id> skips) throws IOException {
-		PackList pList = packList.get();
-		SEARCH: for (;;) {
-			for (PackFile p : pList.packs) {
-				try {
-					LocalObjectRepresentation rep = p.representation(curs, otp);
-					p.resetTransientErrorCount();
-					if (rep != null)
-						packer.select(otp, rep);
-				} catch (PackMismatchException e) {
-					// Pack was modified; refresh the entire pack list.
-					//
-					pList = scanPacks(pList);
-					continue SEARCH;
-				} catch (IOException e) {
-					handlePackError(e, p);
-				}
-			}
-			break SEARCH;
-		}
+		packed.selectRepresentation(packer, otp, curs);
 
 		skips = addMe(skips);
 		for (AlternateHandle h : myAlternates()) {
@@ -614,60 +449,12 @@ public class ObjectDirectory extends FileObjectDatabase {
 		}
 	}
 
-	private void handlePackError(IOException e, PackFile p) {
-		String warnTmpl = null;
-		int transientErrorCount = 0;
-		String errTmpl = JGitText.get().exceptionWhileReadingPack;
-		if ((e instanceof CorruptObjectException)
-				|| (e instanceof PackInvalidException)) {
-			warnTmpl = JGitText.get().corruptPack;
-			LOG.warn(MessageFormat.format(warnTmpl,
-					p.getPackFile().getAbsolutePath()), e);
-			// Assume the pack is corrupted, and remove it from the list.
-			removePack(p);
-		} else if (e instanceof FileNotFoundException) {
-			if (p.getPackFile().exists()) {
-				errTmpl = JGitText.get().packInaccessible;
-				transientErrorCount = p.incrementTransientErrorCount();
-			} else {
-				warnTmpl = JGitText.get().packWasDeleted;
-				removePack(p);
-			}
-		} else if (FileUtils.isStaleFileHandleInCausalChain(e)) {
-			warnTmpl = JGitText.get().packHandleIsStale;
-			removePack(p);
-		} else {
-			transientErrorCount = p.incrementTransientErrorCount();
-		}
-		if (warnTmpl != null) {
-			LOG.warn(MessageFormat.format(warnTmpl,
-					p.getPackFile().getAbsolutePath()), e);
-		} else {
-			if (doLogExponentialBackoff(transientErrorCount)) {
-				// Don't remove the pack from the list, as the error may be
-				// transient.
-				LOG.error(MessageFormat.format(errTmpl,
-						p.getPackFile().getAbsolutePath(),
-						Integer.valueOf(transientErrorCount)), e);
-			}
-		}
-	}
-
-	/**
-	 * @param n
-	 *            count of consecutive failures
-	 * @return @{code true} if i is a power of 2
-	 */
-	private boolean doLogExponentialBackoff(int n) {
-		return (n & (n - 1)) == 0;
-	}
-
 	@Override
 	InsertLooseObjectResult insertUnpackedObject(File tmp, ObjectId id,
 			boolean createDuplicate) throws IOException {
 		// If the object is already in the repository, remove temporary file.
 		//
-		if (unpackedObjectCache.isUnpacked(id)) {
+		if (loose.hasCached(id)) {
 			FileUtils.delete(tmp, FileUtils.RETRY);
 			return InsertLooseObjectResult.EXISTS_LOOSE;
 		}
@@ -675,71 +462,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 			FileUtils.delete(tmp, FileUtils.RETRY);
 			return InsertLooseObjectResult.EXISTS_PACKED;
 		}
-
-		final File dst = fileFor(id);
-		if (dst.exists()) {
-			// We want to be extra careful and avoid replacing an object
-			// that already exists. We can't be sure renameTo() would
-			// fail on all platforms if dst exists, so we check first.
-			//
-			FileUtils.delete(tmp, FileUtils.RETRY);
-			return InsertLooseObjectResult.EXISTS_LOOSE;
-		}
-
-		try {
-			return tryMove(tmp, dst, id);
-		} catch (NoSuchFileException e) {
-			// It's possible the directory doesn't exist yet as the object
-			// directories are always lazily created. Note that we try the
-			// rename/move first as the directory likely does exist.
-			//
-			// Create the directory.
-			//
-			FileUtils.mkdir(dst.getParentFile(), true);
-		} catch (IOException e) {
-			// Any other IO error is considered a failure.
-			//
-			LOG.error(e.getMessage(), e);
-			FileUtils.delete(tmp, FileUtils.RETRY);
-			return InsertLooseObjectResult.FAILURE;
-		}
-
-		try {
-			return tryMove(tmp, dst, id);
-		} catch (IOException e) {
-			// The object failed to be renamed into its proper location and
-			// it doesn't exist in the repository either. We really don't
-			// know what went wrong, so fail.
-			//
-			LOG.error(e.getMessage(), e);
-			FileUtils.delete(tmp, FileUtils.RETRY);
-			return InsertLooseObjectResult.FAILURE;
-		}
-	}
-
-	private InsertLooseObjectResult tryMove(File tmp, File dst,
-			ObjectId id)
-			throws IOException {
-		Files.move(FileUtils.toPath(tmp), FileUtils.toPath(dst),
-				StandardCopyOption.ATOMIC_MOVE);
-		dst.setReadOnly();
-		unpackedObjectCache.add(id);
-		return InsertLooseObjectResult.INSERTED;
-	}
-
-	boolean searchPacksAgain(PackList old) {
-		// Whether to trust the pack folder's modification time. If set
-		// to false we will always scan the .git/objects/pack folder to
-		// check for new pack files. If set to true (default) we use the
-		// lastmodified attribute of the folder and assume that no new
-		// pack files can be in this folder if his modification time has
-		// not changed.
-		boolean trustFolderStat = config.getBoolean(
-				ConfigConstants.CONFIG_CORE_SECTION,
-				ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, true);
-
-		return ((!trustFolderStat) || old.snapshot.isModified(packDirectory))
-				&& old != scanPacks(old);
+		return loose.insert(tmp, id);
 	}
 
 	@Override
@@ -780,182 +503,13 @@ public class ObjectDirectory extends FileObjectDatabase {
 		return shallowCommitsIds;
 	}
 
-	private void insertPack(PackFile pf) {
-		PackList o, n;
-		do {
-			o = packList.get();
-
-			// If the pack in question is already present in the list
-			// (picked up by a concurrent thread that did a scan?) we
-			// do not want to insert it a second time.
-			//
-			final PackFile[] oldList = o.packs;
-			final String name = pf.getPackFile().getName();
-			for (PackFile p : oldList) {
-				if (name.equals(p.getPackFile().getName()))
-					return;
-			}
-
-			final PackFile[] newList = new PackFile[1 + oldList.length];
-			newList[0] = pf;
-			System.arraycopy(oldList, 0, newList, 1, oldList.length);
-			n = new PackList(o.snapshot, newList);
-		} while (!packList.compareAndSet(o, n));
-	}
-
-	private void removePack(PackFile deadPack) {
-		PackList o, n;
-		do {
-			o = packList.get();
-
-			final PackFile[] oldList = o.packs;
-			final int j = indexOf(oldList, deadPack);
-			if (j < 0)
-				break;
-
-			final PackFile[] newList = new PackFile[oldList.length - 1];
-			System.arraycopy(oldList, 0, newList, 0, j);
-			System.arraycopy(oldList, j + 1, newList, j, newList.length - j);
-			n = new PackList(o.snapshot, newList);
-		} while (!packList.compareAndSet(o, n));
-		deadPack.close();
-	}
-
-	private static int indexOf(PackFile[] list, PackFile pack) {
-		for (int i = 0; i < list.length; i++) {
-			if (list[i] == pack)
-				return i;
-		}
-		return -1;
-	}
-
-	private PackList scanPacks(PackList original) {
-		synchronized (packList) {
-			PackList o, n;
-			do {
-				o = packList.get();
-				if (o != original) {
-					// Another thread did the scan for us, while we
-					// were blocked on the monitor above.
-					//
-					return o;
-				}
-				n = scanPacksImpl(o);
-				if (n == o)
-					return n;
-			} while (!packList.compareAndSet(o, n));
-			return n;
-		}
-	}
-
-	private PackList scanPacksImpl(PackList old) {
-		final Map<String, PackFile> forReuse = reuseMap(old);
-		final FileSnapshot snapshot = FileSnapshot.save(packDirectory);
-		final Set<String> names = listPackDirectory();
-		final List<PackFile> list = new ArrayList<>(names.size() >> 2);
-		boolean foundNew = false;
-		for (String indexName : names) {
-			// Must match "pack-[0-9a-f]{40}.idx" to be an index.
-			//
-			if (indexName.length() != 49 || !indexName.endsWith(".idx")) //$NON-NLS-1$
-				continue;
-
-			final String base = indexName.substring(0, indexName.length() - 3);
-			int extensions = 0;
-			for (PackExt ext : PackExt.values()) {
-				if (names.contains(base + ext.getExtension()))
-					extensions |= ext.getBit();
-			}
-
-			if ((extensions & PACK.getBit()) == 0) {
-				// Sometimes C Git's HTTP fetch transport leaves a
-				// .idx file behind and does not download the .pack.
-				// We have to skip over such useless indexes.
-				//
-				continue;
-			}
-
-			final String packName = base + PACK.getExtension();
-			final File packFile = new File(packDirectory, packName);
-			final PackFile oldPack = forReuse.get(packName);
-			if (oldPack != null
-					&& !oldPack.getFileSnapshot().isModified(packFile)) {
-				forReuse.remove(packName);
-				list.add(oldPack);
-				continue;
-			}
-
-			list.add(new PackFile(packFile, extensions));
-			foundNew = true;
-		}
-
-		// If we did not discover any new files, the modification time was not
-		// changed, and we did not remove any files, then the set of files is
-		// the same as the set we were given. Instead of building a new object
-		// return the same collection.
-		//
-		if (!foundNew && forReuse.isEmpty() && snapshot.equals(old.snapshot)) {
-			old.snapshot.setClean(snapshot);
-			return old;
-		}
-
-		for (PackFile p : forReuse.values()) {
-			p.close();
-		}
-
-		if (list.isEmpty())
-			return new PackList(snapshot, NO_PACKS.packs);
-
-		final PackFile[] r = list.toArray(new PackFile[0]);
-		Arrays.sort(r, PackFile.SORT);
-		return new PackList(snapshot, r);
-	}
-
-	private static Map<String, PackFile> reuseMap(PackList old) {
-		final Map<String, PackFile> forReuse = new HashMap<>();
-		for (PackFile p : old.packs) {
-			if (p.invalid()) {
-				// The pack instance is corrupted, and cannot be safely used
-				// again. Do not include it in our reuse map.
-				//
-				p.close();
-				continue;
-			}
-
-			final PackFile prior = forReuse.put(p.getPackFile().getName(), p);
-			if (prior != null) {
-				// This should never occur. It should be impossible for us
-				// to have two pack files with the same name, as all of them
-				// came out of the same directory. If it does, we promised to
-				// close any PackFiles we did not reuse, so close the second,
-				// readers are likely to be actively using the first.
-				//
-				forReuse.put(prior.getPackFile().getName(), prior);
-				p.close();
-			}
-		}
-		return forReuse;
-	}
-
-	private Set<String> listPackDirectory() {
-		final String[] nameList = packDirectory.list();
-		if (nameList == null)
-			return Collections.emptySet();
-		final Set<String> nameSet = new HashSet<>(nameList.length << 1);
-		for (String name : nameList) {
-			if (name.startsWith("pack-")) //$NON-NLS-1$
-				nameSet.add(name);
-		}
-		return nameSet;
-	}
-
 	void closeAllPackHandles(File packFile) {
 		// if the packfile already exists (because we are rewriting a
 		// packfile for the same set of objects maybe with different
 		// PackConfig) then make sure we get rid of all handles on the file.
 		// Windows will not allow for rename otherwise.
 		if (packFile.exists()) {
-			for (PackFile p : getPacks()) {
+			for (Pack p : packed.getPacks()) {
 				if (packFile.getPath().equals(p.getPackFile().getPath())) {
 					p.close();
 					break;
@@ -1025,29 +579,11 @@ public class ObjectDirectory extends FileObjectDatabase {
 	}
 
 	/**
-	 * {@inheritDoc}
-	 * <p>
 	 * Compute the location of a loose object file.
 	 */
 	@Override
 	public File fileFor(AnyObjectId objectId) {
-		String n = objectId.name();
-		String d = n.substring(0, 2);
-		String f = n.substring(2);
-		return new File(new File(getDirectory(), d), f);
-	}
-
-	static final class PackList {
-		/** State just before reading the pack directory. */
-		final FileSnapshot snapshot;
-
-		/** All known packs, sorted by {@link PackFile#SORT}. */
-		final PackFile[] packs;
-
-		PackList(FileSnapshot monitor, PackFile[] packs) {
-			this.snapshot = monitor;
-			this.packs = packs;
-		}
+		return loose.fileFor(objectId);
 	}
 
 	static class AlternateHandle {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
index e27518690b..04d2ff8ab2 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
@@ -88,7 +88,7 @@ public class ObjectDirectoryPackParser extends PackParser {
 	private Deflater def;
 
 	/** The pack that was created, if parsing was successful. */
-	private PackFile newPack;
+	private Pack newPack;
 
 	private PackConfig pconfig;
 
@@ -129,14 +129,14 @@ public class ObjectDirectoryPackParser extends PackParser {
 	}
 
 	/**
-	 * Get the imported {@link org.eclipse.jgit.internal.storage.file.PackFile}.
+	 * Get the imported {@link org.eclipse.jgit.internal.storage.file.Pack}.
 	 * <p>
 	 * This method is supplied only to support testing; applications shouldn't
 	 * be using it directly to access the imported data.
 	 *
 	 * @return the imported PackFile, if parsing was successful.
 	 */
-	public PackFile getPackFile() {
+	public Pack getPack() {
 		return newPack;
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackFile.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/Pack.java
index 254c020237..d928633a73 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackFile.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/Pack.java
@@ -69,13 +69,13 @@ import org.slf4j.LoggerFactory;
  * delta packed format yielding high compression of lots of object where some
  * objects are similar.
  */
-public class PackFile implements Iterable<PackIndex.MutableEntry> {
-	private static final Logger LOG = LoggerFactory.getLogger(PackFile.class);
+public class Pack implements Iterable<PackIndex.MutableEntry> {
+	private static final Logger LOG = LoggerFactory.getLogger(Pack.class);
 
 	/**
 	 * Sorts PackFiles to be most recently created to least recently created.
 	 */
-	public static final Comparator<PackFile> SORT = (a, b) -> b.packLastModified
+	public static final Comparator<Pack> SORT = (a, b) -> b.packLastModified
 			.compareTo(a.packLastModified);
 
 	private final File packFile;
@@ -136,7 +136,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 	 * @param extensions
 	 *            additional pack file extensions with the same base as the pack
 	 */
-	public PackFile(File packFile, int extensions) {
+	public Pack(File packFile, int extensions) {
 		this.packFile = packFile;
 		this.fileSnapshot = PackFileSnapshot.save(packFile);
 		this.packLastModified = fileSnapshot.lastModifiedInstant();
@@ -650,6 +650,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 
 	private void doOpen() throws IOException {
 		if (invalid) {
+			openFail(true, invalidatingCause);
 			throw new PackInvalidException(packFile, invalidatingCause);
 		}
 		try {
@@ -1200,7 +1201,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 	@SuppressWarnings("nls")
 	@Override
 	public String toString() {
-		return "PackFile [packFileName=" + packFile.getName() + ", length="
+		return "Pack [packFileName=" + packFile.getName() + ", length="
 				+ packFile.length() + ", packChecksum="
 				+ ObjectId.fromRaw(packChecksum).name() + "]";
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackDirectory.java
new file mode 100644
index 0000000000..b2ba36bf91
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackDirectory.java
@@ -0,0 +1,516 @@
+/*
+ * Copyright (C) 2009, Google Inc. and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.storage.file;
+
+import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.text.MessageFormat;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.eclipse.jgit.errors.CorruptObjectException;
+import org.eclipse.jgit.errors.PackInvalidException;
+import org.eclipse.jgit.errors.PackMismatchException;
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
+import org.eclipse.jgit.internal.storage.pack.PackExt;
+import org.eclipse.jgit.internal.storage.pack.PackWriter;
+import org.eclipse.jgit.lib.AbbreviatedObjectId;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ConfigConstants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.util.FileUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Traditional file system packed objects directory handler.
+ * <p>
+ * This is the {@link org.eclipse.jgit.internal.storage.file.Pack}s object
+ * representation for a Git object database, where objects are stored in
+ * compressed containers known as
+ * {@link org.eclipse.jgit.internal.storage.file.Pack}s.
+ */
+class PackDirectory {
+	private final static Logger LOG = LoggerFactory
+			.getLogger(PackDirectory.class);
+
+	private static final PackList NO_PACKS = new PackList(FileSnapshot.DIRTY,
+			new Pack[0]);
+
+	private final Config config;
+
+	private final File directory;
+
+	private final AtomicReference<PackList> packList;
+
+	/**
+	 * Initialize a reference to an on-disk 'pack' directory.
+	 *
+	 * @param config
+	 *            configuration this directory consults for write settings.
+	 * @param directory
+	 *            the location of the {@code pack} directory.
+	 */
+	PackDirectory(Config config, File directory) {
+		this.config = config;
+		this.directory = directory;
+		packList = new AtomicReference<>(NO_PACKS);
+	}
+
+	/**
+	 * Getter for the field {@code directory}.
+	 *
+	 * @return the location of the {@code pack} directory.
+	 */
+	File getDirectory() {
+		return directory;
+	}
+
+	void create() throws IOException {
+		FileUtils.mkdir(directory);
+	}
+
+	void close() {
+		PackList packs = packList.get();
+		if (packs != NO_PACKS && packList.compareAndSet(packs, NO_PACKS)) {
+			for (Pack p : packs.packs) {
+				p.close();
+			}
+		}
+	}
+
+	Collection<Pack> getPacks() {
+		PackList list = packList.get();
+		if (list == NO_PACKS) {
+			list = scanPacks(list);
+		}
+		Pack[] packs = list.packs;
+		return Collections.unmodifiableCollection(Arrays.asList(packs));
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public String toString() {
+		return "PackDirectory[" + getDirectory() + "]"; //$NON-NLS-1$ //$NON-NLS-2$
+	}
+
+	/**
+	 * Does the requested object exist in this PackDirectory?
+	 *
+	 * @param objectId
+	 *            identity of the object to test for existence of.
+	 * @return true if the specified object is stored in this PackDirectory.
+	 */
+	boolean has(AnyObjectId objectId) {
+		PackList pList;
+		do {
+			pList = packList.get();
+			for (Pack p : pList.packs) {
+				try {
+					if (p.hasObject(objectId)) {
+						return true;
+					}
+				} catch (IOException e) {
+					// The hasObject call should have only touched the index,
+					// so any failure here indicates the index is unreadable
+					// by this process, and the pack is likewise not readable.
+					LOG.warn(MessageFormat.format(
+							JGitText.get().unableToReadPackfile,
+							p.getPackFile().getAbsolutePath()), e);
+					remove(p);
+				}
+			}
+		} while (searchPacksAgain(pList));
+		return false;
+	}
+
+	/**
+	 * Find objects matching the prefix abbreviation.
+	 *
+	 * @param matches
+	 *            set to add any located ObjectIds to. This is an output
+	 *            parameter.
+	 * @param id
+	 *            prefix to search for.
+	 * @param matchLimit
+	 *            maximum number of results to return. At most this many
+	 *            ObjectIds should be added to matches before returning.
+	 * @return {@code true} if the matches were exhausted before reaching
+	 *         {@code maxLimit}.
+	 */
+	boolean resolve(Set<ObjectId> matches, AbbreviatedObjectId id,
+			int matchLimit) {
+		// Go through the packs once. If we didn't find any resolutions
+		// scan for new packs and check once more.
+		int oldSize = matches.size();
+		PackList pList;
+		do {
+			pList = packList.get();
+			for (Pack p : pList.packs) {
+				try {
+					p.resolve(matches, id, matchLimit);
+					p.resetTransientErrorCount();
+				} catch (IOException e) {
+					handlePackError(e, p);
+				}
+				if (matches.size() > matchLimit) {
+					return false;
+				}
+			}
+		} while (matches.size() == oldSize && searchPacksAgain(pList));
+		return true;
+	}
+
+	ObjectLoader open(WindowCursor curs, AnyObjectId objectId) {
+		PackList pList;
+		do {
+			SEARCH: for (;;) {
+				pList = packList.get();
+				for (Pack p : pList.packs) {
+					try {
+						ObjectLoader ldr = p.get(curs, objectId);
+						p.resetTransientErrorCount();
+						if (ldr != null)
+							return ldr;
+					} catch (PackMismatchException e) {
+						// Pack was modified; refresh the entire pack list.
+						if (searchPacksAgain(pList)) {
+							continue SEARCH;
+						}
+					} catch (IOException e) {
+						handlePackError(e, p);
+					}
+				}
+				break SEARCH;
+			}
+		} while (searchPacksAgain(pList));
+		return null;
+	}
+
+	long getSize(WindowCursor curs, AnyObjectId id) {
+		PackList pList;
+		do {
+			SEARCH: for (;;) {
+				pList = packList.get();
+				for (Pack p : pList.packs) {
+					try {
+						long len = p.getObjectSize(curs, id);
+						p.resetTransientErrorCount();
+						if (0 <= len) {
+							return len;
+						}
+					} catch (PackMismatchException e) {
+						// Pack was modified; refresh the entire pack list.
+						if (searchPacksAgain(pList)) {
+							continue SEARCH;
+						}
+					} catch (IOException e) {
+						handlePackError(e, p);
+					}
+				}
+				break SEARCH;
+			}
+		} while (searchPacksAgain(pList));
+		return -1;
+	}
+
+	void selectRepresentation(PackWriter packer, ObjectToPack otp,
+			WindowCursor curs) {
+		PackList pList = packList.get();
+		SEARCH: for (;;) {
+			for (Pack p : pList.packs) {
+				try {
+					LocalObjectRepresentation rep = p.representation(curs, otp);
+					p.resetTransientErrorCount();
+					if (rep != null) {
+						packer.select(otp, rep);
+					}
+				} catch (PackMismatchException e) {
+					// Pack was modified; refresh the entire pack list.
+					//
+					pList = scanPacks(pList);
+					continue SEARCH;
+				} catch (IOException e) {
+					handlePackError(e, p);
+				}
+			}
+			break SEARCH;
+		}
+	}
+
+	private void handlePackError(IOException e, Pack p) {
+		String warnTmpl = null;
+		int transientErrorCount = 0;
+		String errTmpl = JGitText.get().exceptionWhileReadingPack;
+		if ((e instanceof CorruptObjectException)
+				|| (e instanceof PackInvalidException)) {
+			warnTmpl = JGitText.get().corruptPack;
+			LOG.warn(MessageFormat.format(warnTmpl,
+					p.getPackFile().getAbsolutePath()), e);
+			// Assume the pack is corrupted, and remove it from the list.
+			remove(p);
+		} else if (e instanceof FileNotFoundException) {
+			if (p.getPackFile().exists()) {
+				errTmpl = JGitText.get().packInaccessible;
+				transientErrorCount = p.incrementTransientErrorCount();
+			} else {
+				warnTmpl = JGitText.get().packWasDeleted;
+				remove(p);
+			}
+		} else if (FileUtils.isStaleFileHandleInCausalChain(e)) {
+			warnTmpl = JGitText.get().packHandleIsStale;
+			remove(p);
+		} else {
+			transientErrorCount = p.incrementTransientErrorCount();
+		}
+		if (warnTmpl != null) {
+			LOG.warn(MessageFormat.format(warnTmpl,
+					p.getPackFile().getAbsolutePath()), e);
+		} else {
+			if (doLogExponentialBackoff(transientErrorCount)) {
+				// Don't remove the pack from the list, as the error may be
+				// transient.
+				LOG.error(MessageFormat.format(errTmpl,
+						p.getPackFile().getAbsolutePath(),
+						Integer.valueOf(transientErrorCount)), e);
+			}
+		}
+	}
+
+	/**
+	 * @param n
+	 *            count of consecutive failures
+	 * @return @{code true} if i is a power of 2
+	 */
+	private boolean doLogExponentialBackoff(int n) {
+		return (n & (n - 1)) == 0;
+	}
+
+	boolean searchPacksAgain(PackList old) {
+		// Whether to trust the pack folder's modification time. If set
+		// to false we will always scan the .git/objects/pack folder to
+		// check for new pack files. If set to true (default) we use the
+		// lastmodified attribute of the folder and assume that no new
+		// pack files can be in this folder if his modification time has
+		// not changed.
+		boolean trustFolderStat = config.getBoolean(
+				ConfigConstants.CONFIG_CORE_SECTION,
+				ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, true);
+
+		return ((!trustFolderStat) || old.snapshot.isModified(directory))
+				&& old != scanPacks(old);
+	}
+
+	void insert(Pack pack) {
+		PackList o, n;
+		do {
+			o = packList.get();
+
+			// If the pack in question is already present in the list
+			// (picked up by a concurrent thread that did a scan?) we
+			// do not want to insert it a second time.
+			//
+			final Pack[] oldList = o.packs;
+			final String name = pack.getPackFile().getName();
+			for (Pack p : oldList) {
+				if (name.equals(p.getPackFile().getName())) {
+					return;
+				}
+			}
+
+			final Pack[] newList = new Pack[1 + oldList.length];
+			newList[0] = pack;
+			System.arraycopy(oldList, 0, newList, 1, oldList.length);
+			n = new PackList(o.snapshot, newList);
+		} while (!packList.compareAndSet(o, n));
+	}
+
+	private void remove(Pack deadPack) {
+		PackList o, n;
+		do {
+			o = packList.get();
+
+			final Pack[] oldList = o.packs;
+			final int j = indexOf(oldList, deadPack);
+			if (j < 0) {
+				break;
+			}
+
+			final Pack[] newList = new Pack[oldList.length - 1];
+			System.arraycopy(oldList, 0, newList, 0, j);
+			System.arraycopy(oldList, j + 1, newList, j, newList.length - j);
+			n = new PackList(o.snapshot, newList);
+		} while (!packList.compareAndSet(o, n));
+		deadPack.close();
+	}
+
+	private static int indexOf(Pack[] list, Pack pack) {
+		for (int i = 0; i < list.length; i++) {
+			if (list[i] == pack) {
+				return i;
+			}
+		}
+		return -1;
+	}
+
+	private PackList scanPacks(PackList original) {
+		synchronized (packList) {
+			PackList o, n;
+			do {
+				o = packList.get();
+				if (o != original) {
+					// Another thread did the scan for us, while we
+					// were blocked on the monitor above.
+					//
+					return o;
+				}
+				n = scanPacksImpl(o);
+				if (n == o) {
+					return n;
+				}
+			} while (!packList.compareAndSet(o, n));
+			return n;
+		}
+	}
+
+	private PackList scanPacksImpl(PackList old) {
+		final Map<String, Pack> forReuse = reuseMap(old);
+		final FileSnapshot snapshot = FileSnapshot.save(directory);
+		final Set<String> names = listPackDirectory();
+		final List<Pack> list = new ArrayList<>(names.size() >> 2);
+		boolean foundNew = false;
+		for (String indexName : names) {
+			// Must match "pack-[0-9a-f]{40}.idx" to be an index.
+			//
+			if (indexName.length() != 49 || !indexName.endsWith(".idx")) { //$NON-NLS-1$
+				continue;
+			}
+
+			final String base = indexName.substring(0, indexName.length() - 3);
+			int extensions = 0;
+			for (PackExt ext : PackExt.values()) {
+				if (names.contains(base + ext.getExtension())) {
+					extensions |= ext.getBit();
+				}
+			}
+
+			if ((extensions & PACK.getBit()) == 0) {
+				// Sometimes C Git's HTTP fetch transport leaves a
+				// .idx file behind and does not download the .pack.
+				// We have to skip over such useless indexes.
+				//
+				continue;
+			}
+
+			final String packName = base + PACK.getExtension();
+			final File packFile = new File(directory, packName);
+			final Pack oldPack = forReuse.get(packName);
+			if (oldPack != null
+					&& !oldPack.getFileSnapshot().isModified(packFile)) {
+				forReuse.remove(packName);
+				list.add(oldPack);
+				continue;
+			}
+
+			list.add(new Pack(packFile, extensions));
+			foundNew = true;
+		}
+
+		// If we did not discover any new files, the modification time was not
+		// changed, and we did not remove any files, then the set of files is
+		// the same as the set we were given. Instead of building a new object
+		// return the same collection.
+		//
+		if (!foundNew && forReuse.isEmpty() && snapshot.equals(old.snapshot)) {
+			old.snapshot.setClean(snapshot);
+			return old;
+		}
+
+		for (Pack p : forReuse.values()) {
+			p.close();
+		}
+
+		if (list.isEmpty()) {
+			return new PackList(snapshot, NO_PACKS.packs);
+		}
+
+		final Pack[] r = list.toArray(new Pack[0]);
+		Arrays.sort(r, Pack.SORT);
+		return new PackList(snapshot, r);
+	}
+
+	private static Map<String, Pack> reuseMap(PackList old) {
+		final Map<String, Pack> forReuse = new HashMap<>();
+		for (Pack p : old.packs) {
+			if (p.invalid()) {
+				// The pack instance is corrupted, and cannot be safely used
+				// again. Do not include it in our reuse map.
+				//
+				p.close();
+				continue;
+			}
+
+			final Pack prior = forReuse.put(p.getPackFile().getName(), p);
+			if (prior != null) {
+				// This should never occur. It should be impossible for us
+				// to have two pack files with the same name, as all of them
+				// came out of the same directory. If it does, we promised to
+				// close any PackFiles we did not reuse, so close the second,
+				// readers are likely to be actively using the first.
+				//
+				forReuse.put(prior.getPackFile().getName(), prior);
+				p.close();
+			}
+		}
+		return forReuse;
+	}
+
+	private Set<String> listPackDirectory() {
+		final String[] nameList = directory.list();
+		if (nameList == null) {
+			return Collections.emptySet();
+		}
+		final Set<String> nameSet = new HashSet<>(nameList.length << 1);
+		for (String name : nameList) {
+			if (name.startsWith("pack-")) { //$NON-NLS-1$
+				nameSet.add(name);
+			}
+		}
+		return nameSet;
+	}
+
+	static final class PackList {
+		/** State just before reading the pack directory. */
+		final FileSnapshot snapshot;
+
+		/** All known packs, sorted by {@link Pack#SORT}. */
+		final Pack[] packs;
+
+		PackList(FileSnapshot monitor, Pack[] packs) {
+			this.snapshot = monitor;
+			this.packs = packs;
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndex.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndex.java
index 31686befc9..942cc96745 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndex.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndex.java
@@ -34,7 +34,7 @@ import org.eclipse.jgit.util.io.SilentFileInputStream;
 
 /**
  * Access path to locate objects by {@link org.eclipse.jgit.lib.ObjectId} in a
- * {@link org.eclipse.jgit.internal.storage.file.PackFile}.
+ * {@link org.eclipse.jgit.internal.storage.file.Pack}.
  * <p>
  * Indexes are strictly redundant information in that we can rebuild all of the
  * data held in the index file from the on disk representation of the pack file
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndexWriter.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndexWriter.java
index 612b12366c..87e0b44d46 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndexWriter.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndexWriter.java
@@ -25,7 +25,7 @@ import org.eclipse.jgit.util.NB;
 
 /**
  * Creates a table of contents to support random access by
- * {@link org.eclipse.jgit.internal.storage.file.PackFile}.
+ * {@link org.eclipse.jgit.internal.storage.file.Pack}.
  * <p>
  * Pack index files (the <code>.idx</code> suffix in a pack file pair) provides
  * random access to any object in the pack by associating an ObjectId to the
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackInputStream.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackInputStream.java
index a9e0588885..0bceca72ea 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackInputStream.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackInputStream.java
@@ -16,11 +16,11 @@ import java.io.InputStream;
 class PackInputStream extends InputStream {
 	private final WindowCursor wc;
 
-	private final PackFile pack;
+	private final Pack pack;
 
 	private long pos;
 
-	PackInputStream(PackFile pack, long pos, WindowCursor wc)
+	PackInputStream(Pack pack, long pos, WindowCursor wc)
 			throws IOException {
 		this.pack = pack;
 		this.pos = pos;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackLock.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackLock.java
index 2c2f7911aa..482b143e33 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackLock.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackLock.java
@@ -18,7 +18,7 @@ import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.FileUtils;
 
 /**
- * Keeps track of a {@link org.eclipse.jgit.internal.storage.file.PackFile}'s
+ * Keeps track of a {@link org.eclipse.jgit.internal.storage.file.Pack}'s
  * associated <code>.keep</code> file.
  */
 public class PackLock {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackReverseIndex.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackReverseIndex.java
index 4d80a0312a..ee458e27ba 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackReverseIndex.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackReverseIndex.java
@@ -25,7 +25,7 @@ import org.eclipse.jgit.lib.ObjectId;
  * </p>
  *
  * @see PackIndex
- * @see PackFile
+ * @see Pack
  */
 public class PackReverseIndex {
 	/** Index we were created from, and that has our ObjectId data. */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectoryRename.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectoryRename.java
index 9dbdbc73f0..2c0ade681b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectoryRename.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectoryRename.java
@@ -51,9 +51,6 @@ class RefDirectoryRename extends RefRename {
 	 */
 	private ObjectId objId;
 
-	/** True if HEAD must be moved to the destination reference. */
-	private boolean updateHEAD;
-
 	/** A reference we backup {@link #objId} into during the rename. */
 	private RefDirectoryUpdate tmp;
 
@@ -69,7 +66,7 @@ class RefDirectoryRename extends RefRename {
 			return Result.IO_FAILURE; // not supported
 
 		objId = source.getOldObjectId();
-		updateHEAD = needToUpdateHEAD();
+		boolean updateHEAD = needToUpdateHEAD();
 		tmp = refdb.newTemporaryUpdate();
 		try (RevWalk rw = new RevWalk(refdb.getRepository())) {
 			// First backup the source so its never unreachable.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCache.java
index 3e8cb3a3f2..25653b3ce3 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCache.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCache.java
@@ -33,7 +33,7 @@ import org.eclipse.jgit.storage.file.WindowCacheStats;
 import org.eclipse.jgit.util.Monitoring;
 
 /**
- * Caches slices of a {@link org.eclipse.jgit.internal.storage.file.PackFile} in
+ * Caches slices of a {@link org.eclipse.jgit.internal.storage.file.Pack} in
  * memory for faster read access.
  * <p>
  * The WindowCache serves as a Java based "buffer cache", loading segments of a
@@ -41,7 +41,7 @@ import org.eclipse.jgit.util.Monitoring;
  * only tiny slices of a file, the WindowCache tries to smooth out these tiny
  * reads into larger block-sized IO operations.
  * <p>
- * Whenever a cache miss occurs, {@link #load(PackFile, long)} is invoked by
+ * Whenever a cache miss occurs, {@link #load(Pack, long)} is invoked by
  * exactly one thread for the given <code>(PackFile,position)</code> key tuple.
  * This is ensured by an array of locks, with the tuple hashed to a lock
  * instance.
@@ -80,10 +80,10 @@ import org.eclipse.jgit.util.Monitoring;
  * <p>
  * This cache has an implementation rule such that:
  * <ul>
- * <li>{@link #load(PackFile, long)} is invoked by at most one thread at a time
+ * <li>{@link #load(Pack, long)} is invoked by at most one thread at a time
  * for a given <code>(PackFile,position)</code> tuple.</li>
  * <li>For every <code>load()</code> invocation there is exactly one
- * {@link #createRef(PackFile, long, ByteWindow)} invocation to wrap a
+ * {@link #createRef(Pack, long, ByteWindow)} invocation to wrap a
  * SoftReference or a StrongReference around the cached entity.</li>
  * <li>For every Reference created by <code>createRef()</code> there will be
  * exactly one call to {@link #clear(PageRef)} to cleanup any resources associated
@@ -91,10 +91,10 @@ import org.eclipse.jgit.util.Monitoring;
  * </ul>
  * <p>
  * Therefore, it is safe to perform resource accounting increments during the
- * {@link #load(PackFile, long)} or
- * {@link #createRef(PackFile, long, ByteWindow)} methods, and matching
+ * {@link #load(Pack, long)} or
+ * {@link #createRef(Pack, long, ByteWindow)} methods, and matching
  * decrements during {@link #clear(PageRef)}. Implementors may need to override
- * {@link #createRef(PackFile, long, ByteWindow)} in order to embed additional
+ * {@link #createRef(Pack, long, ByteWindow)} in order to embed additional
  * accounting information into an implementation specific
  * {@link org.eclipse.jgit.internal.storage.file.WindowCache.PageRef} subclass, as
  * the cached entity may have already been evicted by the JRE's garbage
@@ -170,7 +170,7 @@ public class WindowCache {
 		 * @param delta
 		 *            delta of cached bytes
 		 */
-		void recordOpenBytes(PackFile pack, int delta);
+		void recordOpenBytes(Pack pack, int delta);
 
 		/**
 		 * Returns a snapshot of this recorder's stats. Note that this may be an
@@ -242,7 +242,7 @@ public class WindowCache {
 		}
 
 		@Override
-		public void recordOpenBytes(PackFile pack, int delta) {
+		public void recordOpenBytes(Pack pack, int delta) {
 			openByteCount.add(delta);
 			String repositoryId = repositoryId(pack);
 			LongAdder la = openByteCountPerRepository
@@ -254,9 +254,8 @@ public class WindowCache {
 			}
 		}
 
-		private static String repositoryId(PackFile pack) {
-			// use repository's gitdir since packfile doesn't know its
-			// repository
+		private static String repositoryId(Pack pack) {
+			// use repository's gitdir since Pack doesn't know its repository
 			return pack.getPackFile().getParentFile().getParentFile()
 					.getParent();
 		}
@@ -380,7 +379,7 @@ public class WindowCache {
 		return cache.publishMBeanIfNeeded();
 	}
 
-	static final ByteWindow get(PackFile pack, long offset)
+	static final ByteWindow get(Pack pack, long offset)
 			throws IOException {
 		final WindowCache c = cache;
 		final ByteWindow r = c.getOrLoad(pack, c.toStart(offset));
@@ -395,7 +394,7 @@ public class WindowCache {
 		return r;
 	}
 
-	static final void purge(PackFile pack) {
+	static final void purge(Pack pack) {
 		cache.removeAll(pack);
 	}
 
@@ -506,7 +505,7 @@ public class WindowCache {
 		return packHash + (int) (off >>> windowSizeShift);
 	}
 
-	private ByteWindow load(PackFile pack, long offset) throws IOException {
+	private ByteWindow load(Pack pack, long offset) throws IOException {
 		long startTime = System.nanoTime();
 		if (pack.beginWindowCache())
 			statsRecorder.recordOpenFiles(1);
@@ -525,7 +524,7 @@ public class WindowCache {
 		}
 	}
 
-	private PageRef<ByteWindow> createRef(PackFile p, long o, ByteWindow v) {
+	private PageRef<ByteWindow> createRef(Pack p, long o, ByteWindow v) {
 		final PageRef<ByteWindow> ref = useStrongRefs
 				? new StrongRef(p, o, v, queue)
 				: new SoftRef(p, o, v, (SoftCleanupQueue) queue);
@@ -539,7 +538,7 @@ public class WindowCache {
 		close(ref.getPack());
 	}
 
-	private void close(PackFile pack) {
+	private void close(Pack pack) {
 		if (pack.endWindowCache()) {
 			statsRecorder.recordOpenFiles(-1);
 		}
@@ -578,9 +577,9 @@ public class WindowCache {
 	 * @return the object reference.
 	 * @throws IOException
 	 *             the object reference was not in the cache and could not be
-	 *             obtained by {@link #load(PackFile, long)}.
+	 *             obtained by {@link #load(Pack, long)}.
 	 */
-	private ByteWindow getOrLoad(PackFile pack, long position)
+	private ByteWindow getOrLoad(Pack pack, long position)
 			throws IOException {
 		final int slot = slot(pack, position);
 		final Entry e1 = table.get(slot);
@@ -623,7 +622,7 @@ public class WindowCache {
 		return v;
 	}
 
-	private ByteWindow scan(Entry n, PackFile pack, long position) {
+	private ByteWindow scan(Entry n, Pack pack, long position) {
 		for (; n != null; n = n.next) {
 			final PageRef<ByteWindow> r = n.ref;
 			if (r.getPack() == pack && r.getPosition() == position) {
@@ -704,7 +703,7 @@ public class WindowCache {
 	/**
 	 * Clear all entries related to a single file.
 	 * <p>
-	 * Typically this method is invoked during {@link PackFile#close()}, when we
+	 * Typically this method is invoked during {@link Pack#close()}, when we
 	 * know the pack is never going to be useful to us again (for example, it no
 	 * longer exists on disk). A concurrent reader loading an entry from this
 	 * same pack may cause the pack to become stuck in the cache anyway.
@@ -712,7 +711,7 @@ public class WindowCache {
 	 * @param pack
 	 *            the file to purge all entries of.
 	 */
-	private void removeAll(PackFile pack) {
+	private void removeAll(Pack pack) {
 		for (int s = 0; s < tableSize; s++) {
 			final Entry e1 = table.get(s);
 			boolean hasDead = false;
@@ -733,11 +732,11 @@ public class WindowCache {
 		queue.gc();
 	}
 
-	private int slot(PackFile pack, long position) {
+	private int slot(Pack pack, long position) {
 		return (hash(pack.hash, position) >>> 1) % tableSize;
 	}
 
-	private Lock lock(PackFile pack, long position) {
+	private Lock lock(Pack pack, long position) {
 		return locks[(hash(pack.hash, position) >>> 1) % locks.length];
 	}
 
@@ -799,16 +798,20 @@ public class WindowCache {
 		boolean kill();
 
 		/**
-		 * Get the packfile the referenced cache page is allocated for
+		 * Get the {@link org.eclipse.jgit.internal.storage.file.Pack} the
+		 * referenced cache page is allocated for
 		 *
-		 * @return the packfile the referenced cache page is allocated for
+		 * @return the {@link org.eclipse.jgit.internal.storage.file.Pack} the
+		 *         referenced cache page is allocated for
 		 */
-		PackFile getPack();
+		Pack getPack();
 
 		/**
-		 * Get the position of the referenced cache page in the packfile
+		 * Get the position of the referenced cache page in the
+		 * {@link org.eclipse.jgit.internal.storage.file.Pack}
 		 *
-		 * @return the position of the referenced cache page in the packfile
+		 * @return the position of the referenced cache page in the
+		 *         {@link org.eclipse.jgit.internal.storage.file.Pack}
 		 */
 		long getPosition();
 
@@ -844,7 +847,7 @@ public class WindowCache {
 	/** A soft reference wrapped around a cached object. */
 	private static class SoftRef extends SoftReference<ByteWindow>
 			implements PageRef<ByteWindow> {
-		private final PackFile pack;
+		private final Pack pack;
 
 		private final long position;
 
@@ -852,7 +855,7 @@ public class WindowCache {
 
 		private long lastAccess;
 
-		protected SoftRef(final PackFile pack, final long position,
+		protected SoftRef(final Pack pack, final long position,
 				final ByteWindow v, final SoftCleanupQueue queue) {
 			super(v, queue);
 			this.pack = pack;
@@ -861,7 +864,7 @@ public class WindowCache {
 		}
 
 		@Override
-		public PackFile getPack() {
+		public Pack getPack() {
 			return pack;
 		}
 
@@ -900,7 +903,7 @@ public class WindowCache {
 	private static class StrongRef implements PageRef<ByteWindow> {
 		private ByteWindow referent;
 
-		private final PackFile pack;
+		private final Pack pack;
 
 		private final long position;
 
@@ -910,7 +913,7 @@ public class WindowCache {
 
 		private CleanupQueue queue;
 
-		protected StrongRef(final PackFile pack, final long position,
+		protected StrongRef(final Pack pack, final long position,
 				final ByteWindow v, final CleanupQueue queue) {
 			this.pack = pack;
 			this.position = position;
@@ -920,7 +923,7 @@ public class WindowCache {
 		}
 
 		@Override
-		public PackFile getPack() {
+		public Pack getPack() {
 			return pack;
 		}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java
index 6c975708a3..e7fd7b9e76 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/WindowCursor.java
@@ -86,7 +86,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	/** {@inheritDoc} */
 	@Override
 	public BitmapIndex getBitmapIndex() throws IOException {
-		for (PackFile pack : db.getPacks()) {
+		for (Pack pack : db.getPacks()) {
 			PackBitmapIndex index = pack.getBitmapIndex();
 			if (index != null)
 				return new BitmapIndexImpl(index);
@@ -98,7 +98,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	@Override
 	public Collection<CachedPack> getCachedPacksAndUpdate(
 			BitmapBuilder needBitmap) throws IOException {
-		for (PackFile pack : db.getPacks()) {
+		for (Pack pack : db.getPacks()) {
 			PackBitmapIndex index = pack.getBitmapIndex();
 			if (needBitmap.removeAllOrNone(index))
 				return Collections.<CachedPack> singletonList(
@@ -218,7 +218,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
 	 */
-	int copy(final PackFile pack, long position, final byte[] dstbuf,
+	int copy(final Pack pack, long position, final byte[] dstbuf,
 			int dstoff, final int cnt) throws IOException {
 		final long length = pack.length;
 		int need = cnt;
@@ -239,7 +239,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 		((LocalCachedPack) pack).copyAsIs(out, this);
 	}
 
-	void copyPackAsIs(final PackFile pack, final long length,
+	void copyPackAsIs(final Pack pack, final long length,
 			final PackOutputStream out) throws IOException {
 		long position = 12;
 		long remaining = length - (12 + 20);
@@ -275,7 +275,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 	 *             the inflater encountered an invalid chunk of data. Data
 	 *             stream corruption is likely.
 	 */
-	int inflate(final PackFile pack, long position, final byte[] dstbuf,
+	int inflate(final Pack pack, long position, final byte[] dstbuf,
 			boolean headerOnly) throws IOException, DataFormatException {
 		prepareInflater();
 		pin(pack, position);
@@ -293,7 +293,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 		}
 	}
 
-	ByteArrayWindow quickCopy(PackFile p, long pos, long cnt)
+	ByteArrayWindow quickCopy(Pack p, long pos, long cnt)
 			throws IOException {
 		pin(p, pos);
 		if (window instanceof ByteArrayWindow
@@ -314,7 +314,7 @@ final class WindowCursor extends ObjectReader implements ObjectReuseAsIs {
 			inf.reset();
 	}
 
-	void pin(PackFile pack, long position)
+	void pin(Pack pack, long position)
 			throws IOException {
 		final ByteWindow w = window;
 		if (w == null || !w.contains(pack, position)) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/MergedReftable.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/MergedReftable.java
index a78f4d24da..e210acf058 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/MergedReftable.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/MergedReftable.java
@@ -11,6 +11,7 @@
 package org.eclipse.jgit.internal.storage.reftable;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.PriorityQueue;
 
@@ -215,6 +216,23 @@ public class MergedReftable extends Reftable {
 			}
 		}
 
+		@Override
+		public void seekPastPrefix(String prefixName) throws IOException {
+			List<RefQueueEntry> entriesToAdd = new ArrayList<>();
+			entriesToAdd.addAll(queue);
+			if (head != null) {
+				entriesToAdd.add(head);
+			}
+
+			head = null;
+			queue.clear();
+
+			for(RefQueueEntry entry : entriesToAdd){
+				entry.rc.seekPastPrefix(prefixName);
+				add(entry);
+			}
+		}
+
 		private RefQueueEntry poll() {
 			RefQueueEntry e = head;
 			if (e != null) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/RefCursor.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/RefCursor.java
index d96648eb50..5e2c350883 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/RefCursor.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/RefCursor.java
@@ -29,6 +29,19 @@ public abstract class RefCursor implements AutoCloseable {
 	public abstract boolean next() throws IOException;
 
 	/**
+	 * Seeks forward to the first ref record lexicographically beyond
+	 * {@code prefixName} that doesn't start with {@code prefixName}. If there are
+	 * no more results, skipping some refs won't add new results. E.g if we create a
+	 * RefCursor that returns only results with a specific prefix, skipping that
+	 * prefix won't give results that are not part of the original prefix.
+	 *
+	 * @param prefixName prefix that should be skipped. All previous refs before it
+	 *                   will be skipped.
+	 * @throws java.io.IOException references cannot be read.
+	 */
+	public abstract void seekPastPrefix(String prefixName) throws IOException;
+
+	/**
 	 * Get reference at the current position.
 	 *
 	 * @return reference at the current position.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableDatabase.java
index 4747be3544..0c16828617 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableDatabase.java
@@ -14,10 +14,12 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.stream.Collectors;
 
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.lib.ObjectId;
@@ -266,6 +268,54 @@ public abstract class ReftableDatabase {
 	}
 
 	/**
+	 * Returns refs whose names start with a given prefix excluding all refs that
+	 * start with one of the given prefixes.
+	 *
+	 * @param include string that names of refs should start with; may be empty.
+	 * @param excludes strings that names of refs can't start with; may be empty.
+	 * @return immutable list of refs whose names start with {@code include} and
+	 *         none of the strings in {@code exclude}.
+	 * @throws java.io.IOException the reference space cannot be accessed.
+	 */
+	public List<Ref> getRefsByPrefixWithExclusions(String include, Set<String> excludes) throws IOException {
+		if (excludes.isEmpty()) {
+			return getRefsByPrefix(include);
+		}
+		List<Ref> results = new ArrayList<>();
+		lock.lock();
+		try {
+			Reftable table = reader();
+			Iterator<String> excludeIterator =
+					excludes.stream().sorted().collect(Collectors.toList()).iterator();
+			String currentExclusion = excludeIterator.hasNext() ? excludeIterator.next() : null;
+			try (RefCursor rc = RefDatabase.ALL.equals(include) ? table.allRefs() : table.seekRefsWithPrefix(include)) {
+				while (rc.next()) {
+					Ref ref = table.resolve(rc.getRef());
+					if (ref == null || ref.getObjectId() == null) {
+						continue;
+					}
+					// Skip prefixes that will never see since we are already further than those
+					// prefixes lexicographically.
+					while (excludeIterator.hasNext() && !ref.getName().startsWith(currentExclusion)
+							&& ref.getName().compareTo(currentExclusion) > 0) {
+						currentExclusion = excludeIterator.next();
+					}
+
+					if (currentExclusion != null && ref.getName().startsWith(currentExclusion)) {
+						rc.seekPastPrefix(currentExclusion);
+						continue;
+					}
+					results.add(ref);
+				}
+			}
+		} finally {
+			lock.unlock();
+		}
+
+		return Collections.unmodifiableList(results);
+	}
+
+	/**
 	 * @return whether there is a fast SHA1 to ref map.
 	 * @throws IOException in case of I/O problems.
 	 */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
index 095276f57b..9e2ae91608 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
@@ -509,6 +509,21 @@ public class ReftableReader extends Reftable implements AutoCloseable {
 		}
 
 		@Override
+		public void seekPastPrefix(String prefixName) throws IOException {
+			initRefIndex();
+			byte[] key = prefixName.getBytes(UTF_8);
+			ByteBuffer byteBuffer = ByteBuffer.allocate(key.length + 1);
+			byteBuffer.put(key);
+			// Add the representation of the last byte lexicographically. Based on how UTF_8
+			// representation works, this byte will be bigger lexicographically than any
+			// UTF_8 character when translated into bytes, since 0xFF can never be a part of
+			// a UTF_8 string.
+			byteBuffer.put((byte) 0xFF);
+
+			block = seek(REF_BLOCK_TYPE, byteBuffer.array(), refIndex, 0, refEnd);
+		}
+
+		@Override
 		public Ref getRef() {
 			return ref;
 		}
@@ -682,6 +697,17 @@ public class ReftableReader extends Reftable implements AutoCloseable {
 		}
 
 		@Override
+		/**
+		 * The implementation here would not be efficient complexity-wise since it
+		 * expected that there are a small number of refs that match the same object id.
+		 * In such case it's better to not even use this method (as the caller might
+		 * expect it to be efficient).
+		 */
+		public void seekPastPrefix(String prefixName) throws IOException {
+		    throw new UnsupportedOperationException();
+		}
+
+		@Override
 		public Ref getRef() {
 			return ref;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/AlwaysFailUpdate.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/AlwaysFailUpdate.java
deleted file mode 100644
index 5138636089..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/AlwaysFailUpdate.java
+++ /dev/null
@@ -1,72 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import java.io.IOException;
-
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefDatabase;
-import org.eclipse.jgit.lib.RefUpdate;
-import org.eclipse.jgit.lib.Repository;
-
-/** Update that always rejects with {@code LOCK_FAILURE}. */
-class AlwaysFailUpdate extends RefUpdate {
-	private final RefTreeDatabase refdb;
-
-	AlwaysFailUpdate(RefTreeDatabase refdb, String name) {
-		super(new ObjectIdRef.Unpeeled(Ref.Storage.NEW, name, null));
-		this.refdb = refdb;
-		setCheckConflicting(false);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected RefDatabase getRefDatabase() {
-		return refdb;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Repository getRepository() {
-		return refdb.getRepository();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected boolean tryLock(boolean deref) throws IOException {
-		return false;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void unlock() {
-		// No locks are held here.
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doUpdate(Result desiredResult) {
-		return Result.LOCK_FAILURE;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doDelete(Result desiredResult) {
-		return Result.LOCK_FAILURE;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doLink(String target) {
-		return Result.LOCK_FAILURE;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Command.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Command.java
deleted file mode 100644
index bb06a9e0cf..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Command.java
+++ /dev/null
@@ -1,309 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
-import static org.eclipse.jgit.lib.Constants.encode;
-import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
-import static org.eclipse.jgit.lib.FileMode.TYPE_SYMLINK;
-import static org.eclipse.jgit.lib.Ref.Storage.NETWORK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-
-import java.io.IOException;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.dircache.DirCacheEntry;
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.internal.JGitText;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevObject;
-import org.eclipse.jgit.revwalk.RevTag;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-import org.eclipse.jgit.transport.ReceiveCommand.Result;
-
-/**
- * Command to create, update or delete an entry inside a
- * {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
- * <p>
- * Unlike {@link org.eclipse.jgit.transport.ReceiveCommand} (which can only
- * update a reference to an {@link org.eclipse.jgit.lib.ObjectId}), a RefTree
- * Command can also create, modify or delete symbolic references to a target
- * reference.
- * <p>
- * RefTree Commands may wrap a {@code ReceiveCommand} to allow callers to
- * process an existing ReceiveCommand against a RefTree.
- * <p>
- * Commands should be passed into
- * {@link org.eclipse.jgit.internal.storage.reftree.RefTree#apply(java.util.Collection)}
- * for processing.
- */
-public class Command {
-	/**
-	 * Set unprocessed commands as failed due to transaction aborted.
-	 * <p>
-	 * If a command is still
-	 * {@link org.eclipse.jgit.transport.ReceiveCommand.Result#NOT_ATTEMPTED} it
-	 * will be set to
-	 * {@link org.eclipse.jgit.transport.ReceiveCommand.Result#REJECTED_OTHER_REASON}.
-	 * If {@code why} is non-null its contents will be used as the message for
-	 * the first command status.
-	 *
-	 * @param commands
-	 *            commands to mark as failed.
-	 * @param why
-	 *            optional message to set on the first aborted command.
-	 */
-	public static void abort(Iterable<Command> commands, @Nullable String why) {
-		if (why == null || why.isEmpty()) {
-			why = JGitText.get().transactionAborted;
-		}
-		for (Command c : commands) {
-			if (c.getResult() == NOT_ATTEMPTED) {
-				c.setResult(REJECTED_OTHER_REASON, why);
-				why = JGitText.get().transactionAborted;
-			}
-		}
-	}
-
-	private final Ref oldRef;
-	private final Ref newRef;
-	private final ReceiveCommand cmd;
-	private Result result;
-
-	/**
-	 * Create a command to create, update or delete a reference.
-	 * <p>
-	 * At least one of {@code oldRef} or {@code newRef} must be supplied.
-	 *
-	 * @param oldRef
-	 *            expected value. Null if the ref should not exist.
-	 * @param newRef
-	 *            desired value, must be peeled if not null and not symbolic.
-	 *            Null to delete the ref.
-	 */
-	public Command(@Nullable Ref oldRef, @Nullable Ref newRef) {
-		this.oldRef = oldRef;
-		this.newRef = newRef;
-		this.cmd = null;
-		this.result = NOT_ATTEMPTED;
-
-		if (oldRef == null && newRef == null) {
-			throw new IllegalArgumentException();
-		}
-		if (newRef != null && !newRef.isPeeled() && !newRef.isSymbolic()) {
-			throw new IllegalArgumentException();
-		}
-		if (oldRef != null && newRef != null
-				&& !oldRef.getName().equals(newRef.getName())) {
-			throw new IllegalArgumentException();
-		}
-	}
-
-	/**
-	 * Construct a RefTree command wrapped around a ReceiveCommand.
-	 *
-	 * @param rw
-	 *            walk instance to peel the {@code newId}.
-	 * @param cmd
-	 *            command received from a push client.
-	 * @throws org.eclipse.jgit.errors.MissingObjectException
-	 *             {@code oldId} or {@code newId} is missing.
-	 * @throws java.io.IOException
-	 *             {@code oldId} or {@code newId} cannot be peeled.
-	 */
-	public Command(RevWalk rw, ReceiveCommand cmd)
-			throws MissingObjectException, IOException {
-		this.oldRef = toRef(rw, cmd.getOldId(), cmd.getOldSymref(),
-				cmd.getRefName(), false);
-		this.newRef = toRef(rw, cmd.getNewId(), cmd.getNewSymref(),
-				cmd.getRefName(), true);
-		this.cmd = cmd;
-	}
-
-	static Ref toRef(RevWalk rw, ObjectId id, @Nullable String target,
-			String name, boolean mustExist)
-			throws MissingObjectException, IOException {
-		if (target != null) {
-			return new SymbolicRef(name,
-					new ObjectIdRef.Unpeeled(NETWORK, target, id));
-		} else if (ObjectId.zeroId().equals(id)) {
-			return null;
-		}
-
-		try {
-			RevObject o = rw.parseAny(id);
-			if (o instanceof RevTag) {
-				RevObject p = rw.peel(o);
-				return new ObjectIdRef.PeeledTag(NETWORK, name, id, p.copy());
-			}
-			return new ObjectIdRef.PeeledNonTag(NETWORK, name, id);
-		} catch (MissingObjectException e) {
-			if (mustExist) {
-				throw e;
-			}
-			return new ObjectIdRef.Unpeeled(NETWORK, name, id);
-		}
-	}
-
-	/**
-	 * Get name of the reference affected by this command.
-	 *
-	 * @return name of the reference affected by this command.
-	 */
-	public String getRefName() {
-		if (cmd != null) {
-			return cmd.getRefName();
-		} else if (newRef != null) {
-			return newRef.getName();
-		}
-		return oldRef.getName();
-	}
-
-	/**
-	 * Set the result of this command.
-	 *
-	 * @param result
-	 *            the command result.
-	 */
-	public void setResult(Result result) {
-		setResult(result, null);
-	}
-
-	/**
-	 * Set the result of this command.
-	 *
-	 * @param result
-	 *            the command result.
-	 * @param why
-	 *            optional message explaining the result status.
-	 */
-	public void setResult(Result result, @Nullable String why) {
-		if (cmd != null) {
-			cmd.setResult(result, why);
-		} else {
-			this.result = result;
-		}
-	}
-
-	/**
-	 * Get result of executing this command.
-	 *
-	 * @return result of executing this command.
-	 */
-	public Result getResult() {
-		return cmd != null ? cmd.getResult() : result;
-	}
-
-	/**
-	 * Get optional message explaining command failure.
-	 *
-	 * @return optional message explaining command failure.
-	 */
-	@Nullable
-	public String getMessage() {
-		return cmd != null ? cmd.getMessage() : null;
-	}
-
-	/**
-	 * Old peeled reference.
-	 *
-	 * @return the old reference; null if the command is creating the reference.
-	 */
-	@Nullable
-	public Ref getOldRef() {
-		return oldRef;
-	}
-
-	/**
-	 * New peeled reference.
-	 *
-	 * @return the new reference; null if the command is deleting the reference.
-	 */
-	@Nullable
-	public Ref getNewRef() {
-		return newRef;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public String toString() {
-		StringBuilder s = new StringBuilder();
-		append(s, oldRef, "CREATE"); //$NON-NLS-1$
-		s.append(' ');
-		append(s, newRef, "DELETE"); //$NON-NLS-1$
-		s.append(' ').append(getRefName());
-		s.append(' ').append(getResult());
-		if (getMessage() != null) {
-			s.append(' ').append(getMessage());
-		}
-		return s.toString();
-	}
-
-	private static void append(StringBuilder s, Ref r, String nullName) {
-		if (r == null) {
-			s.append(nullName);
-		} else if (r.isSymbolic()) {
-			s.append(r.getTarget().getName());
-		} else {
-			ObjectId id = r.getObjectId();
-			if (id != null) {
-				s.append(id.name());
-			}
-		}
-	}
-
-	/**
-	 * Check the entry is consistent with either the old or the new ref.
-	 *
-	 * @param entry
-	 *            current entry; null if the entry does not exist.
-	 * @return true if entry matches {@link #getOldRef()} or
-	 *         {@link #getNewRef()}; otherwise false.
-	 */
-	boolean checkRef(@Nullable DirCacheEntry entry) {
-		if (entry != null && entry.getRawMode() == 0) {
-			entry = null;
-		}
-		return check(entry, oldRef) || check(entry, newRef);
-	}
-
-	private static boolean check(@Nullable DirCacheEntry cur,
-			@Nullable Ref exp) {
-		if (cur == null) {
-			// Does not exist, ok if oldRef does not exist.
-			return exp == null;
-		} else if (exp == null) {
-			// Expected to not exist, but currently exists, fail.
-			return false;
-		}
-
-		if (exp.isSymbolic()) {
-			String dst = exp.getTarget().getName();
-			return cur.getRawMode() == TYPE_SYMLINK
-					&& cur.getObjectId().equals(symref(dst));
-		}
-
-		return cur.getRawMode() == TYPE_GITLINK
-				&& cur.getObjectId().equals(exp.getObjectId());
-	}
-
-	static ObjectId symref(String s) {
-		@SuppressWarnings("resource")
-		ObjectInserter.Formatter fmt = new ObjectInserter.Formatter();
-		return fmt.idFor(OBJ_BLOB, encode(s));
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTree.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTree.java
deleted file mode 100644
index 6f12e9ccb6..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTree.java
+++ /dev/null
@@ -1,384 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.HEAD;
-import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
-import static org.eclipse.jgit.lib.Constants.R_REFS;
-import static org.eclipse.jgit.lib.Constants.encode;
-import static org.eclipse.jgit.lib.FileMode.GITLINK;
-import static org.eclipse.jgit.lib.FileMode.SYMLINK;
-import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
-import static org.eclipse.jgit.lib.FileMode.TYPE_SYMLINK;
-import static org.eclipse.jgit.lib.Ref.Storage.NEW;
-import static org.eclipse.jgit.lib.Ref.Storage.PACKED;
-import static org.eclipse.jgit.lib.RefDatabase.MAX_SYMBOLIC_REF_DEPTH;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.LOCK_FAILURE;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-
-import java.io.IOException;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.Map;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.dircache.DirCache;
-import org.eclipse.jgit.dircache.DirCacheBuilder;
-import org.eclipse.jgit.dircache.DirCacheEditor;
-import org.eclipse.jgit.dircache.DirCacheEditor.DeletePath;
-import org.eclipse.jgit.dircache.DirCacheEditor.PathEdit;
-import org.eclipse.jgit.dircache.DirCacheEntry;
-import org.eclipse.jgit.errors.CorruptObjectException;
-import org.eclipse.jgit.errors.DirCacheNameConflictException;
-import org.eclipse.jgit.errors.IncorrectObjectTypeException;
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.internal.JGitText;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.ObjectReader;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevTree;
-import org.eclipse.jgit.util.RawParseUtils;
-
-/**
- * Tree of references in the reference graph.
- * <p>
- * The root corresponds to the {@code "refs/"} subdirectory, for example the
- * default reference {@code "refs/heads/master"} is stored at path
- * {@code "heads/master"} in a {@code RefTree}.
- * <p>
- * Normal references are stored as {@link org.eclipse.jgit.lib.FileMode#GITLINK}
- * tree entries. The ObjectId in the tree entry is the ObjectId the reference
- * refers to.
- * <p>
- * Symbolic references are stored as
- * {@link org.eclipse.jgit.lib.FileMode#SYMLINK} entries, with the blob storing
- * the name of the target reference.
- * <p>
- * Annotated tags also store the peeled object using a {@code GITLINK} entry
- * with the suffix <code>" ^"</code> (space carrot), for example
- * {@code "tags/v1.0"} stores the annotated tag object, while
- * <code>"tags/v1.0 ^"</code> stores the commit the tag annotates.
- * <p>
- * {@code HEAD} is a special case and stored as {@code "..HEAD"}.
- */
-public class RefTree {
-	/** Suffix applied to GITLINK to indicate its the peeled value of a tag. */
-	public static final String PEELED_SUFFIX = " ^"; //$NON-NLS-1$
-	static final String ROOT_DOTDOT = ".."; //$NON-NLS-1$
-
-	/**
-	 * Create an empty reference tree.
-	 *
-	 * @return a new empty reference tree.
-	 */
-	public static RefTree newEmptyTree() {
-		return new RefTree(DirCache.newInCore());
-	}
-
-	/**
-	 * Load a reference tree.
-	 *
-	 * @param reader
-	 *            reader to scan the reference tree with.
-	 * @param tree
-	 *            the tree to read.
-	 * @return the ref tree read from the commit.
-	 * @throws java.io.IOException
-	 *             the repository cannot be accessed through the reader.
-	 * @throws org.eclipse.jgit.errors.CorruptObjectException
-	 *             a tree object is corrupt and cannot be read.
-	 * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
-	 *             a tree object wasn't actually a tree.
-	 * @throws org.eclipse.jgit.errors.MissingObjectException
-	 *             a reference tree object doesn't exist.
-	 */
-	public static RefTree read(ObjectReader reader, RevTree tree)
-			throws MissingObjectException, IncorrectObjectTypeException,
-			CorruptObjectException, IOException {
-		return new RefTree(DirCache.read(reader, tree));
-	}
-
-	private DirCache contents;
-	private Map<ObjectId, String> pendingBlobs;
-
-	private RefTree(DirCache dc) {
-		this.contents = dc;
-	}
-
-	/**
-	 * Read one reference.
-	 * <p>
-	 * References are always returned peeled
-	 * ({@link org.eclipse.jgit.lib.Ref#isPeeled()} is true). If the reference
-	 * points to an annotated tag, the returned reference will be peeled and
-	 * contain {@link org.eclipse.jgit.lib.Ref#getPeeledObjectId()}.
-	 * <p>
-	 * If the reference is a symbolic reference and the chain depth is less than
-	 * {@link org.eclipse.jgit.lib.RefDatabase#MAX_SYMBOLIC_REF_DEPTH} the
-	 * returned reference is resolved. If the chain depth is longer, the
-	 * symbolic reference is returned without resolving.
-	 *
-	 * @param reader
-	 *            to access objects necessary to read the requested reference.
-	 * @param name
-	 *            name of the reference to read.
-	 * @return the reference; null if it does not exist.
-	 * @throws java.io.IOException
-	 *             cannot read a symbolic reference target.
-	 */
-	@Nullable
-	public Ref exactRef(ObjectReader reader, String name) throws IOException {
-		Ref r = readRef(reader, name);
-		if (r == null) {
-			return null;
-		} else if (r.isSymbolic()) {
-			return resolve(reader, r, 0);
-		}
-
-		DirCacheEntry p = contents.getEntry(peeledPath(name));
-		if (p != null && p.getRawMode() == TYPE_GITLINK) {
-			return new ObjectIdRef.PeeledTag(PACKED, r.getName(),
-					r.getObjectId(), p.getObjectId());
-		}
-		return r;
-	}
-
-	private Ref readRef(ObjectReader reader, String name) throws IOException {
-		DirCacheEntry e = contents.getEntry(refPath(name));
-		return e != null ? toRef(reader, e, name) : null;
-	}
-
-	private Ref toRef(ObjectReader reader, DirCacheEntry e, String name)
-			throws IOException {
-		int mode = e.getRawMode();
-		if (mode == TYPE_GITLINK) {
-			ObjectId id = e.getObjectId();
-			return new ObjectIdRef.PeeledNonTag(PACKED, name, id);
-		}
-
-		if (mode == TYPE_SYMLINK) {
-			ObjectId id = e.getObjectId();
-			String n = pendingBlobs != null ? pendingBlobs.get(id) : null;
-			if (n == null) {
-				byte[] bin = reader.open(id, OBJ_BLOB).getCachedBytes();
-				n = RawParseUtils.decode(bin);
-			}
-			Ref dst = new ObjectIdRef.Unpeeled(NEW, n, null);
-			return new SymbolicRef(name, dst);
-		}
-
-		return null; // garbage file or something; not a reference.
-	}
-
-	private Ref resolve(ObjectReader reader, Ref ref, int depth)
-			throws IOException {
-		if (ref.isSymbolic() && depth < MAX_SYMBOLIC_REF_DEPTH) {
-			Ref r = readRef(reader, ref.getTarget().getName());
-			if (r == null) {
-				return ref;
-			}
-			Ref dst = resolve(reader, r, depth + 1);
-			return new SymbolicRef(ref.getName(), dst);
-		}
-		return ref;
-	}
-
-	/**
-	 * Attempt a batch of commands against this RefTree.
-	 * <p>
-	 * The batch is applied atomically, either all commands apply at once, or
-	 * they all reject and the RefTree is left unmodified.
-	 * <p>
-	 * On success (when this method returns {@code true}) the command results
-	 * are left as-is (probably {@code NOT_ATTEMPTED}). Result fields are set
-	 * only when this method returns {@code false} to indicate failure.
-	 *
-	 * @param cmdList
-	 *            to apply. All commands should still have result NOT_ATTEMPTED.
-	 * @return true if the commands applied; false if they were rejected.
-	 */
-	public boolean apply(Collection<Command> cmdList) {
-		try {
-			DirCacheEditor ed = contents.editor();
-			for (Command cmd : cmdList) {
-				if (!isValidRef(cmd)) {
-					cmd.setResult(REJECTED_OTHER_REASON,
-							JGitText.get().funnyRefname);
-					Command.abort(cmdList, null);
-					return false;
-				}
-				apply(ed, cmd);
-			}
-			ed.finish();
-			return true;
-		} catch (DirCacheNameConflictException e) {
-			String r1 = refName(e.getPath1());
-			String r2 = refName(e.getPath2());
-			for (Command cmd : cmdList) {
-				if (r1.equals(cmd.getRefName())
-						|| r2.equals(cmd.getRefName())) {
-					cmd.setResult(LOCK_FAILURE);
-					break;
-				}
-			}
-			Command.abort(cmdList, null);
-			return false;
-		} catch (LockFailureException e) {
-			Command.abort(cmdList, null);
-			return false;
-		}
-	}
-
-	private static boolean isValidRef(Command cmd) {
-		String n = cmd.getRefName();
-		return HEAD.equals(n) || Repository.isValidRefName(n);
-	}
-
-	private void apply(DirCacheEditor ed, Command cmd) {
-		String path = refPath(cmd.getRefName());
-		Ref oldRef = cmd.getOldRef();
-		final Ref newRef = cmd.getNewRef();
-
-		if (newRef == null) {
-			checkRef(contents.getEntry(path), cmd);
-			ed.add(new DeletePath(path));
-			cleanupPeeledRef(ed, oldRef);
-			return;
-		}
-
-		if (newRef.isSymbolic()) {
-			final String dst = newRef.getTarget().getName();
-			ed.add(new PathEdit(path) {
-				@Override
-				public void apply(DirCacheEntry ent) {
-					checkRef(ent, cmd);
-					ObjectId id = Command.symref(dst);
-					ent.setFileMode(SYMLINK);
-					ent.setObjectId(id);
-					if (pendingBlobs == null) {
-						pendingBlobs = new HashMap<>(4);
-					}
-					pendingBlobs.put(id, dst);
-				}
-			}.setReplace(false));
-			cleanupPeeledRef(ed, oldRef);
-			return;
-		}
-
-		ed.add(new PathEdit(path) {
-			@Override
-			public void apply(DirCacheEntry ent) {
-				checkRef(ent, cmd);
-				ent.setFileMode(GITLINK);
-				ent.setObjectId(newRef.getObjectId());
-			}
-		}.setReplace(false));
-
-		if (newRef.getPeeledObjectId() != null) {
-			ed.add(new PathEdit(peeledPath(newRef.getName())) {
-				@Override
-				public void apply(DirCacheEntry ent) {
-					ent.setFileMode(GITLINK);
-					ent.setObjectId(newRef.getPeeledObjectId());
-				}
-			}.setReplace(false));
-		} else {
-			cleanupPeeledRef(ed, oldRef);
-		}
-	}
-
-	private static void checkRef(@Nullable DirCacheEntry ent, Command cmd) {
-		if (!cmd.checkRef(ent)) {
-			cmd.setResult(LOCK_FAILURE);
-			throw new LockFailureException();
-		}
-	}
-
-	private static void cleanupPeeledRef(DirCacheEditor ed, Ref ref) {
-		if (ref != null && !ref.isSymbolic()
-				&& (!ref.isPeeled() || ref.getPeeledObjectId() != null)) {
-			ed.add(new DeletePath(peeledPath(ref.getName())));
-		}
-	}
-
-	/**
-	 * Convert a path name in a RefTree to the reference name known by Git.
-	 *
-	 * @param path
-	 *            name read from the RefTree structure, for example
-	 *            {@code "heads/master"}.
-	 * @return reference name for the path, {@code "refs/heads/master"}.
-	 */
-	public static String refName(String path) {
-		if (path.startsWith(ROOT_DOTDOT)) {
-			return path.substring(2);
-		}
-		return R_REFS + path;
-	}
-
-	static String refPath(String name) {
-		if (name.startsWith(R_REFS)) {
-			return name.substring(R_REFS.length());
-		}
-		return ROOT_DOTDOT + name;
-	}
-
-	private static String peeledPath(String name) {
-		return refPath(name) + PEELED_SUFFIX;
-	}
-
-	/**
-	 * Write this reference tree.
-	 *
-	 * @param inserter
-	 *            inserter to use when writing trees to the object database.
-	 *            Caller is responsible for flushing the inserter before trying
-	 *            to read the objects, or exposing them through a reference.
-	 * @return the top level tree.
-	 * @throws java.io.IOException
-	 *             a tree could not be written.
-	 */
-	public ObjectId writeTree(ObjectInserter inserter) throws IOException {
-		if (pendingBlobs != null) {
-			for (String s : pendingBlobs.values()) {
-				inserter.insert(OBJ_BLOB, encode(s));
-			}
-			pendingBlobs = null;
-		}
-		return contents.writeTree(inserter);
-	}
-
-	/**
-	 * Create a deep copy of this RefTree.
-	 *
-	 * @return a deep copy of this RefTree.
-	 */
-	public RefTree copy() {
-		RefTree r = new RefTree(DirCache.newInCore());
-		DirCacheBuilder b = r.contents.builder();
-		for (int i = 0; i < contents.getEntryCount(); i++) {
-			b.add(new DirCacheEntry(contents.getEntry(i)));
-		}
-		b.finish();
-		if (pendingBlobs != null) {
-			r.pendingBlobs = new HashMap<>(pendingBlobs);
-		}
-		return r;
-	}
-
-	private static class LockFailureException extends RuntimeException {
-		private static final long serialVersionUID = 1L;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeBatch.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeBatch.java
deleted file mode 100644
index b154b95adc..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeBatch.java
+++ /dev/null
@@ -1,194 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.OBJ_TREE;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_NONFASTFORWARD;
-import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
-import static org.eclipse.jgit.transport.ReceiveCommand.Type.UPDATE;
-import static org.eclipse.jgit.transport.ReceiveCommand.Type.UPDATE_NONFASTFORWARD;
-
-import java.io.IOException;
-import java.text.MessageFormat;
-import java.util.ArrayList;
-import java.util.List;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.internal.JGitText;
-import org.eclipse.jgit.lib.BatchRefUpdate;
-import org.eclipse.jgit.lib.CommitBuilder;
-import org.eclipse.jgit.lib.NullProgressMonitor;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.ObjectReader;
-import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.lib.ProgressMonitor;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-
-/** Batch update a {@link RefTreeDatabase}. */
-class RefTreeBatch extends BatchRefUpdate {
-	private final RefTreeDatabase refdb;
-	private Ref src;
-	private ObjectId parentCommitId;
-	private ObjectId parentTreeId;
-	private RefTree tree;
-	private PersonIdent author;
-	private ObjectId newCommitId;
-
-	RefTreeBatch(RefTreeDatabase refdb) {
-		super(refdb);
-		this.refdb = refdb;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void execute(RevWalk rw, ProgressMonitor monitor)
-			throws IOException {
-		List<Command> todo = new ArrayList<>(getCommands().size());
-		for (ReceiveCommand c : getCommands()) {
-			if (!isAllowNonFastForwards()) {
-				if (c.getType() == UPDATE) {
-					c.updateType(rw);
-				}
-				if (c.getType() == UPDATE_NONFASTFORWARD) {
-					c.setResult(REJECTED_NONFASTFORWARD);
-					if (isAtomic()) {
-						ReceiveCommand.abort(getCommands());
-						return;
-					}
-					continue;
-				}
-			}
-			todo.add(new Command(rw, c));
-		}
-		init(rw);
-		execute(rw, todo);
-	}
-
-	void init(RevWalk rw) throws IOException {
-		src = refdb.getBootstrap().exactRef(refdb.getTxnCommitted());
-		if (src != null && src.getObjectId() != null) {
-			RevCommit c = rw.parseCommit(src.getObjectId());
-			parentCommitId = c;
-			parentTreeId = c.getTree();
-			tree = RefTree.read(rw.getObjectReader(), c.getTree());
-		} else {
-			parentCommitId = ObjectId.zeroId();
-			try (ObjectInserter.Formatter fmt = new ObjectInserter.Formatter()) {
-				parentTreeId = fmt.idFor(OBJ_TREE, new byte[] {});
-			}
-			tree = RefTree.newEmptyTree();
-		}
-	}
-
-	@Nullable
-	Ref exactRef(ObjectReader reader, String name) throws IOException {
-		return tree.exactRef(reader, name);
-	}
-
-	/**
-	 * Execute an update from {@link RefTreeUpdate} or {@link RefTreeRename}.
-	 *
-	 * @param rw
-	 *            current RevWalk handling the update or rename.
-	 * @param todo
-	 *            commands to execute. Must never be a bootstrap reference name.
-	 * @throws IOException
-	 *             the storage system is unable to read or write data.
-	 */
-	void execute(RevWalk rw, List<Command> todo) throws IOException {
-		for (Command c : todo) {
-			if (c.getResult() != NOT_ATTEMPTED) {
-				Command.abort(todo, null);
-				return;
-			}
-			if (refdb.conflictsWithBootstrap(c.getRefName())) {
-				c.setResult(REJECTED_OTHER_REASON, MessageFormat
-						.format(JGitText.get().invalidRefName, c.getRefName()));
-				Command.abort(todo, null);
-				return;
-			}
-		}
-
-		if (apply(todo) && newCommitId != null) {
-			commit(rw, todo);
-		}
-	}
-
-	private boolean apply(List<Command> todo) throws IOException {
-		if (!tree.apply(todo)) {
-			// apply set rejection information on commands.
-			return false;
-		}
-
-		Repository repo = refdb.getRepository();
-		try (ObjectInserter ins = repo.newObjectInserter()) {
-			CommitBuilder b = new CommitBuilder();
-			b.setTreeId(tree.writeTree(ins));
-			if (parentTreeId.equals(b.getTreeId())) {
-				for (Command c : todo) {
-					c.setResult(OK);
-				}
-				return true;
-			}
-			if (!parentCommitId.equals(ObjectId.zeroId())) {
-				b.setParentId(parentCommitId);
-			}
-
-			author = getRefLogIdent();
-			if (author == null) {
-				author = new PersonIdent(repo);
-			}
-			b.setAuthor(author);
-			b.setCommitter(author);
-			b.setMessage(getRefLogMessage());
-			newCommitId = ins.insert(b);
-			ins.flush();
-		}
-		return true;
-	}
-
-	private void commit(RevWalk rw, List<Command> todo) throws IOException {
-		ReceiveCommand commit = new ReceiveCommand(
-				parentCommitId, newCommitId,
-				refdb.getTxnCommitted());
-		updateBootstrap(rw, commit);
-
-		if (commit.getResult() == OK) {
-			for (Command c : todo) {
-				c.setResult(OK);
-			}
-		} else {
-			Command.abort(todo, commit.getResult().name());
-		}
-	}
-
-	private void updateBootstrap(RevWalk rw, ReceiveCommand commit)
-			throws IOException {
-		BatchRefUpdate u = refdb.getBootstrap().newBatchUpdate();
-		u.setAllowNonFastForwards(true);
-		u.setPushCertificate(getPushCertificate());
-		if (isRefLogDisabled()) {
-			u.disableRefLog();
-		} else {
-			u.setRefLogIdent(author);
-			u.setRefLogMessage(getRefLogMessage(), false);
-		}
-		u.addCommand(commit);
-		u.execute(rw, NullProgressMonitor.INSTANCE);
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeDatabase.java
deleted file mode 100644
index 34b8f2cd36..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeDatabase.java
+++ /dev/null
@@ -1,354 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.HEAD;
-import static org.eclipse.jgit.lib.Ref.Storage.LOOSE;
-import static org.eclipse.jgit.lib.Ref.Storage.PACKED;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.lib.BatchRefUpdate;
-import org.eclipse.jgit.lib.Config;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Ref.Storage;
-import org.eclipse.jgit.lib.RefDatabase;
-import org.eclipse.jgit.lib.RefRename;
-import org.eclipse.jgit.lib.RefUpdate;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevObject;
-import org.eclipse.jgit.revwalk.RevTag;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.util.RefList;
-import org.eclipse.jgit.util.RefMap;
-
-/**
- * Reference database backed by a
- * {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
- * <p>
- * The storage for RefTreeDatabase has two parts. The main part is a native Git
- * tree object stored under the {@code refs/txn} namespace. To avoid cycles,
- * references to {@code refs/txn} are not stored in that tree object, but
- * instead in a "bootstrap" layer, which is a separate
- * {@link org.eclipse.jgit.lib.RefDatabase} such as
- * {@link org.eclipse.jgit.internal.storage.file.RefDirectory} using local
- * reference files inside of {@code $GIT_DIR/refs}.
- */
-public class RefTreeDatabase extends RefDatabase {
-	private final Repository repo;
-	private final RefDatabase bootstrap;
-	private final String txnCommitted;
-
-	@Nullable
-	private final String txnNamespace;
-	private volatile Scanner.Result refs;
-
-	/**
-	 * Create a RefTreeDb for a repository.
-	 *
-	 * @param repo
-	 *            the repository using references in this database.
-	 * @param bootstrap
-	 *            bootstrap reference database storing the references that
-	 *            anchor the
-	 *            {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
-	 */
-	public RefTreeDatabase(Repository repo, RefDatabase bootstrap) {
-		Config cfg = repo.getConfig();
-		String committed = cfg.getString("reftree", null, "committedRef"); //$NON-NLS-1$ //$NON-NLS-2$
-		if (committed == null || committed.isEmpty()) {
-			committed = "refs/txn/committed"; //$NON-NLS-1$
-		}
-
-		this.repo = repo;
-		this.bootstrap = bootstrap;
-		this.txnNamespace = initNamespace(committed);
-		this.txnCommitted = committed;
-	}
-
-	/**
-	 * Create a RefTreeDb for a repository.
-	 *
-	 * @param repo
-	 *            the repository using references in this database.
-	 * @param bootstrap
-	 *            bootstrap reference database storing the references that
-	 *            anchor the
-	 *            {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
-	 * @param txnCommitted
-	 *            name of the bootstrap reference holding the committed RefTree.
-	 */
-	public RefTreeDatabase(Repository repo, RefDatabase bootstrap,
-			String txnCommitted) {
-		this.repo = repo;
-		this.bootstrap = bootstrap;
-		this.txnNamespace = initNamespace(txnCommitted);
-		this.txnCommitted = txnCommitted;
-	}
-
-	private static String initNamespace(String committed) {
-		int s = committed.lastIndexOf('/');
-		if (s < 0) {
-			return null;
-		}
-		return committed.substring(0, s + 1); // Keep trailing '/'.
-	}
-
-	Repository getRepository() {
-		return repo;
-	}
-
-	/**
-	 * Get the bootstrap reference database
-	 *
-	 * @return the bootstrap reference database, which must be used to access
-	 *         {@link #getTxnCommitted()}, {@link #getTxnNamespace()}.
-	 */
-	public RefDatabase getBootstrap() {
-		return bootstrap;
-	}
-
-	/**
-	 * Get name of bootstrap reference anchoring committed RefTree.
-	 *
-	 * @return name of bootstrap reference anchoring committed RefTree.
-	 */
-	public String getTxnCommitted() {
-		return txnCommitted;
-	}
-
-	/**
-	 * Get namespace used by bootstrap layer.
-	 *
-	 * @return namespace used by bootstrap layer, e.g. {@code refs/txn/}. Always
-	 *         ends in {@code '/'}.
-	 */
-	@Nullable
-	public String getTxnNamespace() {
-		return txnNamespace;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void create() throws IOException {
-		bootstrap.create();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public boolean performsAtomicTransactions() {
-		return true;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void refresh() {
-		bootstrap.refresh();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public void close() {
-		refs = null;
-		bootstrap.close();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public Ref exactRef(String name) throws IOException {
-		if (!repo.isBare() && name.indexOf('/') < 0 && !HEAD.equals(name)) {
-			// Pass through names like MERGE_HEAD, ORIG_HEAD, FETCH_HEAD.
-			return bootstrap.exactRef(name);
-		} else if (conflictsWithBootstrap(name)) {
-			return null;
-		}
-
-		boolean partial = false;
-		Ref src = bootstrap.exactRef(txnCommitted);
-		Scanner.Result c = refs;
-		if (c == null || !c.refTreeId.equals(idOf(src))) {
-			c = Scanner.scanRefTree(repo, src, prefixOf(name), false);
-			partial = true;
-		}
-
-		Ref r = c.all.get(name);
-		if (r != null && r.isSymbolic()) {
-			r = c.sym.get(name);
-			if (partial && r.getObjectId() == null) {
-				// Attempting exactRef("HEAD") with partial scan will leave
-				// an unresolved symref as its target e.g. refs/heads/master
-				// was not read by the partial scan. Scan everything instead.
-				return getRefs(ALL).get(name);
-			}
-		}
-		return r;
-	}
-
-	private static String prefixOf(String name) {
-		int s = name.lastIndexOf('/');
-		if (s >= 0) {
-			return name.substring(0, s);
-		}
-		return ""; //$NON-NLS-1$
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public Map<String, Ref> getRefs(String prefix) throws IOException {
-		if (!prefix.isEmpty() && prefix.charAt(prefix.length() - 1) != '/') {
-			return new HashMap<>(0);
-		}
-
-		Ref src = bootstrap.exactRef(txnCommitted);
-		Scanner.Result c = refs;
-		if (c == null || !c.refTreeId.equals(idOf(src))) {
-			c = Scanner.scanRefTree(repo, src, prefix, true);
-			if (prefix.isEmpty()) {
-				refs = c;
-			}
-		}
-		return new RefMap(prefix, RefList.<Ref> emptyList(), c.all, c.sym);
-	}
-
-	private static ObjectId idOf(@Nullable Ref src) {
-		return src != null && src.getObjectId() != null
-				? src.getObjectId()
-				: ObjectId.zeroId();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public List<Ref> getAdditionalRefs() throws IOException {
-		Collection<Ref> txnRefs;
-		if (txnNamespace != null) {
-			txnRefs = bootstrap.getRefsByPrefix(txnNamespace);
-		} else {
-			Ref r = bootstrap.exactRef(txnCommitted);
-			if (r != null && r.getObjectId() != null) {
-				txnRefs = Collections.singleton(r);
-			} else {
-				txnRefs = Collections.emptyList();
-			}
-		}
-
-		List<Ref> otherRefs = bootstrap.getAdditionalRefs();
-		List<Ref> all = new ArrayList<>(txnRefs.size() + otherRefs.size());
-		all.addAll(txnRefs);
-		all.addAll(otherRefs);
-		return all;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public Ref peel(Ref ref) throws IOException {
-		Ref i = ref.getLeaf();
-		ObjectId id = i.getObjectId();
-		if (i.isPeeled() || id == null) {
-			return ref;
-		}
-		try (RevWalk rw = new RevWalk(repo)) {
-			RevObject obj = rw.parseAny(id);
-			if (obj instanceof RevTag) {
-				ObjectId p = rw.peel(obj).copy();
-				i = new ObjectIdRef.PeeledTag(PACKED, i.getName(), id, p);
-			} else {
-				i = new ObjectIdRef.PeeledNonTag(PACKED, i.getName(), id);
-			}
-		}
-		return recreate(ref, i);
-	}
-
-	private static Ref recreate(Ref old, Ref leaf) {
-		if (old.isSymbolic()) {
-			Ref dst = recreate(old.getTarget(), leaf);
-			return new SymbolicRef(old.getName(), dst);
-		}
-		return leaf;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public boolean isNameConflicting(String name) throws IOException {
-		return conflictsWithBootstrap(name)
-				|| !getConflictingNames(name).isEmpty();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public BatchRefUpdate newBatchUpdate() {
-		return new RefTreeBatch(this);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public RefUpdate newUpdate(String name, boolean detach) throws IOException {
-		if (!repo.isBare() && name.indexOf('/') < 0 && !HEAD.equals(name)) {
-			return bootstrap.newUpdate(name, detach);
-		}
-		if (conflictsWithBootstrap(name)) {
-			return new AlwaysFailUpdate(this, name);
-		}
-
-		Ref r = exactRef(name);
-		if (r == null) {
-			r = new ObjectIdRef.Unpeeled(Storage.NEW, name, null);
-		}
-
-		boolean detaching = detach && r.isSymbolic();
-		if (detaching) {
-			r = new ObjectIdRef.Unpeeled(LOOSE, name, r.getObjectId());
-		}
-
-		RefTreeUpdate u = new RefTreeUpdate(this, r);
-		if (detaching) {
-			u.setDetachingSymbolicRef();
-		}
-		return u;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	public RefRename newRename(String fromName, String toName)
-			throws IOException {
-		RefUpdate from = newUpdate(fromName, true);
-		RefUpdate to = newUpdate(toName, true);
-		return new RefTreeRename(this, from, to);
-	}
-
-	boolean conflictsWithBootstrap(String name) {
-		if (txnNamespace != null && name.startsWith(txnNamespace)) {
-			return true;
-		} else if (txnCommitted.equals(name)) {
-			return true;
-		}
-
-		if (name.indexOf('/') < 0 && !HEAD.equals(name)) {
-			return true;
-		}
-
-		if (name.length() > txnCommitted.length()
-				&& name.charAt(txnCommitted.length()) == '/'
-				&& name.startsWith(txnCommitted)) {
-			return true;
-		}
-		return false;
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeNames.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeNames.java
deleted file mode 100644
index eec0da29e2..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeNames.java
+++ /dev/null
@@ -1,58 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import org.eclipse.jgit.lib.RefDatabase;
-
-/**
- * Magic reference name logic for RefTrees.
- */
-public class RefTreeNames {
-	/**
-	 * Suffix used on a {@link RefTreeDatabase#getTxnNamespace()} for user data.
-	 * <p>
-	 * A {@link RefTreeDatabase}'s namespace may include a subspace (e.g.
-	 * {@code "refs/txn/stage/"}) containing commit objects from the usual user
-	 * portion of the repository (e.g. {@code "refs/heads/"}). These should be
-	 * packed by the garbage collector alongside other user content rather than
-	 * with the RefTree.
-	 */
-	private static final String STAGE = "stage/"; //$NON-NLS-1$
-
-	/**
-	 * Determine if the reference is likely to be a RefTree.
-	 *
-	 * @param refdb
-	 *            database instance.
-	 * @param ref
-	 *            reference name.
-	 * @return {@code true} if the reference is a RefTree.
-	 */
-	public static boolean isRefTree(RefDatabase refdb, String ref) {
-		if (refdb instanceof RefTreeDatabase) {
-			RefTreeDatabase b = (RefTreeDatabase) refdb;
-			if (ref.equals(b.getTxnCommitted())) {
-				return true;
-			}
-
-			String namespace = b.getTxnNamespace();
-			if (namespace != null
-					&& ref.startsWith(namespace)
-					&& !ref.startsWith(namespace + STAGE)) {
-				return true;
-			}
-		}
-		return false;
-	}
-
-	private RefTreeNames() {
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeRename.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeRename.java
deleted file mode 100644
index ccf8f75e7d..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeRename.java
+++ /dev/null
@@ -1,89 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.HEAD;
-import static org.eclipse.jgit.lib.RefUpdate.Result.REJECTED;
-import static org.eclipse.jgit.lib.RefUpdate.Result.RENAMED;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
-
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefRename;
-import org.eclipse.jgit.lib.RefUpdate;
-import org.eclipse.jgit.lib.RefUpdate.Result;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevWalk;
-
-/** Single reference rename to {@link RefTreeDatabase}. */
-class RefTreeRename extends RefRename {
-	private final RefTreeDatabase refdb;
-
-	RefTreeRename(RefTreeDatabase refdb, RefUpdate src, RefUpdate dst) {
-		super(src, dst);
-		this.refdb = refdb;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doRename() throws IOException {
-		try (RevWalk rw = new RevWalk(refdb.getRepository())) {
-			RefTreeBatch batch = new RefTreeBatch(refdb);
-			batch.setRefLogIdent(getRefLogIdent());
-			batch.setRefLogMessage(getRefLogMessage(), false);
-			batch.init(rw);
-
-			Ref head = batch.exactRef(rw.getObjectReader(), HEAD);
-			Ref oldRef = batch.exactRef(rw.getObjectReader(), source.getName());
-			if (oldRef == null) {
-				return REJECTED;
-			}
-
-			Ref newRef = asNew(oldRef);
-			List<Command> mv = new ArrayList<>(3);
-			mv.add(new Command(oldRef, null));
-			mv.add(new Command(null, newRef));
-			if (head != null && head.isSymbolic()
-					&& head.getTarget().getName().equals(oldRef.getName())) {
-				mv.add(new Command(
-					head,
-					new SymbolicRef(head.getName(), newRef)));
-			}
-			batch.execute(rw, mv);
-			return RefTreeUpdate.translate(mv.get(1).getResult(), RENAMED);
-		}
-	}
-
-	private Ref asNew(Ref src) {
-		String name = destination.getName();
-		if (src.isSymbolic()) {
-			return new SymbolicRef(name, src.getTarget());
-		}
-
-		ObjectId peeled = src.getPeeledObjectId();
-		if (peeled != null) {
-			return new ObjectIdRef.PeeledTag(
-					src.getStorage(),
-					name,
-					src.getObjectId(),
-					peeled);
-		}
-
-		return new ObjectIdRef.PeeledNonTag(
-				src.getStorage(),
-				name,
-				src.getObjectId());
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeUpdate.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeUpdate.java
deleted file mode 100644
index 6e6ccd9986..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/RefTreeUpdate.java
+++ /dev/null
@@ -1,150 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Ref.Storage.LOOSE;
-import static org.eclipse.jgit.lib.Ref.Storage.NEW;
-
-import java.io.IOException;
-import java.util.Collections;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefDatabase;
-import org.eclipse.jgit.lib.RefUpdate;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevObject;
-import org.eclipse.jgit.revwalk.RevTag;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.ReceiveCommand;
-
-/** Single reference update to {@link RefTreeDatabase}. */
-class RefTreeUpdate extends RefUpdate {
-	private final RefTreeDatabase refdb;
-	private RevWalk rw;
-	private RefTreeBatch batch;
-	private Ref oldRef;
-
-	RefTreeUpdate(RefTreeDatabase refdb, Ref ref) {
-		super(ref);
-		this.refdb = refdb;
-		setCheckConflicting(false); // Done automatically by doUpdate.
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected RefDatabase getRefDatabase() {
-		return refdb;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Repository getRepository() {
-		return refdb.getRepository();
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected boolean tryLock(boolean deref) throws IOException {
-		rw = new RevWalk(getRepository());
-		batch = new RefTreeBatch(refdb);
-		batch.init(rw);
-		oldRef = batch.exactRef(rw.getObjectReader(), getName());
-		if (oldRef != null && oldRef.getObjectId() != null) {
-			setOldObjectId(oldRef.getObjectId());
-		} else if (oldRef == null && getExpectedOldObjectId() != null) {
-			setOldObjectId(ObjectId.zeroId());
-		}
-		return true;
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected void unlock() {
-		batch = null;
-		if (rw != null) {
-			rw.close();
-			rw = null;
-		}
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doUpdate(Result desiredResult) throws IOException {
-		return run(newRef(getName(), getNewObjectId()), desiredResult);
-	}
-
-	private Ref newRef(String name, ObjectId id)
-			throws MissingObjectException, IOException {
-		RevObject o = rw.parseAny(id);
-		if (o instanceof RevTag) {
-			RevObject p = rw.peel(o);
-			return new ObjectIdRef.PeeledTag(LOOSE, name, id, p.copy());
-		}
-		return new ObjectIdRef.PeeledNonTag(LOOSE, name, id);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doDelete(Result desiredResult) throws IOException {
-		return run(null, desiredResult);
-	}
-
-	/** {@inheritDoc} */
-	@Override
-	protected Result doLink(String target) throws IOException {
-		Ref dst = new ObjectIdRef.Unpeeled(NEW, target, null);
-		SymbolicRef n = new SymbolicRef(getName(), dst);
-		Result desiredResult = getRef().getStorage() == NEW
-			? Result.NEW
-			: Result.FORCED;
-		return run(n, desiredResult);
-	}
-
-	private Result run(@Nullable Ref newRef, Result desiredResult)
-			throws IOException {
-		Command c = new Command(oldRef, newRef);
-		batch.setRefLogIdent(getRefLogIdent());
-		batch.setRefLogMessage(getRefLogMessage(), isRefLogIncludingResult());
-		batch.execute(rw, Collections.singletonList(c));
-		return translate(c.getResult(), desiredResult);
-	}
-
-	static Result translate(ReceiveCommand.Result r, Result desiredResult) {
-		switch (r) {
-		case OK:
-			return desiredResult;
-
-		case LOCK_FAILURE:
-			return Result.LOCK_FAILURE;
-
-		case NOT_ATTEMPTED:
-			return Result.NOT_ATTEMPTED;
-
-		case REJECTED_MISSING_OBJECT:
-			return Result.IO_FAILURE;
-
-		case REJECTED_CURRENT_BRANCH:
-			return Result.REJECTED_CURRENT_BRANCH;
-
-		case REJECTED_OTHER_REASON:
-		case REJECTED_NOCREATE:
-		case REJECTED_NODELETE:
-		case REJECTED_NONFASTFORWARD:
-		default:
-			return Result.REJECTED;
-		}
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Scanner.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Scanner.java
deleted file mode 100644
index 3f5122911c..0000000000
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Scanner.java
+++ /dev/null
@@ -1,254 +0,0 @@
-/*
- * Copyright (C) 2016, Google Inc. and others
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Distribution License v. 1.0 which is available at
- * https://www.eclipse.org/org/documents/edl-v10.php.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-package org.eclipse.jgit.internal.storage.reftree;
-
-import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
-import static org.eclipse.jgit.lib.Constants.R_REFS;
-import static org.eclipse.jgit.lib.Constants.encode;
-import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
-import static org.eclipse.jgit.lib.FileMode.TYPE_SYMLINK;
-import static org.eclipse.jgit.lib.FileMode.TYPE_TREE;
-import static org.eclipse.jgit.lib.Ref.Storage.NEW;
-import static org.eclipse.jgit.lib.Ref.Storage.PACKED;
-import static org.eclipse.jgit.lib.RefDatabase.MAX_SYMBOLIC_REF_DEPTH;
-
-import java.io.IOException;
-
-import org.eclipse.jgit.annotations.Nullable;
-import org.eclipse.jgit.errors.IncorrectObjectTypeException;
-import org.eclipse.jgit.lib.AnyObjectId;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectIdRef;
-import org.eclipse.jgit.lib.ObjectReader;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.lib.SymbolicRef;
-import org.eclipse.jgit.revwalk.RevTree;
-import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.treewalk.AbstractTreeIterator;
-import org.eclipse.jgit.treewalk.CanonicalTreeParser;
-import org.eclipse.jgit.treewalk.TreeWalk;
-import org.eclipse.jgit.util.Paths;
-import org.eclipse.jgit.util.RawParseUtils;
-import org.eclipse.jgit.util.RefList;
-
-/** A tree parser that extracts references from a {@link RefTree}. */
-class Scanner {
-	private static final int MAX_SYMLINK_BYTES = 10 << 10;
-	private static final byte[] BINARY_R_REFS = encode(R_REFS);
-	private static final byte[] REFS_DOT_DOT = encode("refs/.."); //$NON-NLS-1$
-
-	static class Result {
-		final ObjectId refTreeId;
-		final RefList<Ref> all;
-		final RefList<Ref> sym;
-
-		Result(ObjectId id, RefList<Ref> all, RefList<Ref> sym) {
-			this.refTreeId = id;
-			this.all = all;
-			this.sym = sym;
-		}
-	}
-
-	/**
-	 * Scan a {@link RefTree} and parse entries into {@link Ref} instances.
-	 *
-	 * @param repo
-	 *            source repository containing the commit and tree objects that
-	 *            make up the RefTree.
-	 * @param src
-	 *            bootstrap reference such as {@code refs/txn/committed} to read
-	 *            the reference tree tip from. The current ObjectId will be
-	 *            included in {@link Result#refTreeId}.
-	 * @param prefix
-	 *            if non-empty a reference prefix to scan only a subdirectory.
-	 *            For example {@code prefix = "refs/heads/"} will limit the scan
-	 *            to only the {@code "heads"} directory of the RefTree, avoiding
-	 *            other directories like {@code "tags"}. Empty string reads all
-	 *            entries in the RefTree.
-	 * @param recursive
-	 *            if true recurse into subdirectories of the reference tree;
-	 *            false to read only one level. Callers may use false during an
-	 *            implementation of {@code exactRef(String)} where only one
-	 *            reference is needed out of a specific subtree.
-	 * @return sorted list of references after parsing.
-	 * @throws IOException
-	 *             tree cannot be accessed from the repository.
-	 */
-	static Result scanRefTree(Repository repo, @Nullable Ref src, String prefix,
-			boolean recursive) throws IOException {
-		RefList.Builder<Ref> all = new RefList.Builder<>();
-		RefList.Builder<Ref> sym = new RefList.Builder<>();
-
-		ObjectId srcId;
-		if (src != null && src.getObjectId() != null) {
-			try (ObjectReader reader = repo.newObjectReader()) {
-				srcId = src.getObjectId();
-				scan(reader, srcId, prefix, recursive, all, sym);
-			}
-		} else {
-			srcId = ObjectId.zeroId();
-		}
-
-		RefList<Ref> aList = all.toRefList();
-		for (int idx = 0; idx < sym.size();) {
-			Ref s = sym.get(idx);
-			Ref r = resolve(s, 0, aList);
-			if (r != null) {
-				sym.set(idx++, r);
-			} else {
-				// Remove broken symbolic reference, they don't exist.
-				sym.remove(idx);
-				int rm = aList.find(s.getName());
-				if (0 <= rm) {
-					aList = aList.remove(rm);
-				}
-			}
-		}
-		return new Result(srcId, aList, sym.toRefList());
-	}
-
-	private static void scan(ObjectReader reader, AnyObjectId srcId,
-			String prefix, boolean recursive,
-			RefList.Builder<Ref> all, RefList.Builder<Ref> sym)
-					throws IncorrectObjectTypeException, IOException {
-		CanonicalTreeParser p = createParserAtPath(reader, srcId, prefix);
-		if (p == null) {
-			return;
-		}
-
-		while (!p.eof()) {
-			int mode = p.getEntryRawMode();
-			if (mode == TYPE_TREE) {
-				if (recursive) {
-					p = p.createSubtreeIterator(reader);
-				} else {
-					p = p.next();
-				}
-				continue;
-			}
-
-			if (!curElementHasPeelSuffix(p)) {
-				Ref r = toRef(reader, mode, p);
-				if (r != null) {
-					all.add(r);
-					if (r.isSymbolic()) {
-						sym.add(r);
-					}
-				}
-			} else if (mode == TYPE_GITLINK) {
-				peel(all, p);
-			}
-			p = p.next();
-		}
-	}
-
-	private static CanonicalTreeParser createParserAtPath(ObjectReader reader,
-			AnyObjectId srcId, String prefix) throws IOException {
-		ObjectId root = toTree(reader, srcId);
-		if (prefix.isEmpty()) {
-			return new CanonicalTreeParser(BINARY_R_REFS, reader, root);
-		}
-
-		String dir = RefTree.refPath(Paths.stripTrailingSeparator(prefix));
-		TreeWalk tw = TreeWalk.forPath(reader, dir, root);
-		if (tw == null || !tw.isSubtree()) {
-			return null;
-		}
-
-		ObjectId id = tw.getObjectId(0);
-		return new CanonicalTreeParser(encode(prefix), reader, id);
-	}
-
-	private static Ref resolve(Ref ref, int depth, RefList<Ref> refs)
-			throws IOException {
-		if (!ref.isSymbolic()) {
-			return ref;
-		} else if (MAX_SYMBOLIC_REF_DEPTH <= depth) {
-			return null;
-		}
-
-		Ref r = refs.get(ref.getTarget().getName());
-		if (r == null) {
-			return ref;
-		}
-
-		Ref dst = resolve(r, depth + 1, refs);
-		if (dst == null) {
-			return null;
-		}
-		return new SymbolicRef(ref.getName(), dst);
-	}
-
-	private static RevTree toTree(ObjectReader reader, AnyObjectId id)
-			throws IOException {
-		try (RevWalk rw = new RevWalk(reader)) {
-			return rw.parseTree(id);
-		}
-	}
-
-	private static boolean curElementHasPeelSuffix(AbstractTreeIterator itr) {
-		int n = itr.getEntryPathLength();
-		byte[] c = itr.getEntryPathBuffer();
-		return n > 2 && c[n - 2] == ' ' && c[n - 1] == '^';
-	}
-
-	private static void peel(RefList.Builder<Ref> all, CanonicalTreeParser p) {
-		String name = refName(p, true);
-		for (int idx = all.size() - 1; 0 <= idx; idx--) {
-			Ref r = all.get(idx);
-			int cmp = r.getName().compareTo(name);
-			if (cmp == 0) {
-				all.set(idx, new ObjectIdRef.PeeledTag(PACKED, r.getName(),
-						r.getObjectId(), p.getEntryObjectId()));
-				break;
-			} else if (cmp < 0) {
-				// Stray peeled name without matching base name; skip entry.
-				break;
-			}
-		}
-	}
-
-	private static Ref toRef(ObjectReader reader, int mode,
-			CanonicalTreeParser p) throws IOException {
-		if (mode == TYPE_GITLINK) {
-			String name = refName(p, false);
-			ObjectId id = p.getEntryObjectId();
-			return new ObjectIdRef.PeeledNonTag(PACKED, name, id);
-
-		} else if (mode == TYPE_SYMLINK) {
-			ObjectId id = p.getEntryObjectId();
-			byte[] bin = reader.open(id, OBJ_BLOB)
-					.getCachedBytes(MAX_SYMLINK_BYTES);
-			String dst = RawParseUtils.decode(bin);
-			Ref trg = new ObjectIdRef.Unpeeled(NEW, dst, null);
-			String name = refName(p, false);
-			return new SymbolicRef(name, trg);
-		}
-		return null;
-	}
-
-	private static String refName(CanonicalTreeParser p, boolean peel) {
-		byte[] buf = p.getEntryPathBuffer();
-		int len = p.getEntryPathLength();
-		if (peel) {
-			len -= 2;
-		}
-		int ptr = 0;
-		if (RawParseUtils.match(buf, ptr, REFS_DOT_DOT) > 0) {
-			ptr = 7;
-		}
-		return RawParseUtils.decode(buf, ptr, len);
-	}
-
-	private Scanner() {
-	}
-}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BaseRepositoryBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BaseRepositoryBuilder.java
index e51995f93d..b2242a11ca 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BaseRepositoryBuilder.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BaseRepositoryBuilder.java
@@ -28,6 +28,8 @@ import java.util.Collection;
 import java.util.LinkedList;
 import java.util.List;
 
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.api.errors.InvalidRefNameException;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.internal.JGitText;
@@ -38,6 +40,7 @@ import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.IO;
 import org.eclipse.jgit.util.RawParseUtils;
+import org.eclipse.jgit.util.StringUtils;
 import org.eclipse.jgit.util.SystemReader;
 
 /**
@@ -107,6 +110,8 @@ public class BaseRepositoryBuilder<B extends BaseRepositoryBuilder, R extends Re
 
 	private File workTree;
 
+	private String initialBranch = Constants.MASTER;
+
 	/** Directories limiting the search for a Git repository. */
 	private List<File> ceilingDirectories;
 
@@ -350,6 +355,43 @@ public class BaseRepositoryBuilder<B extends BaseRepositoryBuilder, R extends Re
 	}
 
 	/**
+	 * Set the initial branch of the new repository. If not specified
+	 * ({@code null} or empty), fall back to the default name (currently
+	 * master).
+	 *
+	 * @param branch
+	 *            initial branch name of the new repository. If {@code null} or
+	 *            empty the configured default branch will be used.
+	 * @return {@code this}
+	 * @throws InvalidRefNameException
+	 *             if the branch name is not valid
+	 *
+	 * @since 5.11
+	 */
+	public B setInitialBranch(String branch) throws InvalidRefNameException {
+		if (StringUtils.isEmptyOrNull(branch)) {
+			this.initialBranch = Constants.MASTER;
+		} else {
+			if (!Repository.isValidRefName(Constants.R_HEADS + branch)) {
+				throw new InvalidRefNameException(MessageFormat
+						.format(JGitText.get().branchNameInvalid, branch));
+			}
+			this.initialBranch = branch;
+		}
+		return self();
+	}
+
+	/**
+	 * Get the initial branch of the new repository.
+	 *
+	 * @return the initial branch of the new repository.
+	 * @since 5.11
+	 */
+	public @NonNull String getInitialBranch() {
+		return initialBranch;
+	}
+
+	/**
 	 * Read standard Git environment variables and configure from those.
 	 * <p>
 	 * This method tries to read the standard Git environment variables, such as
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/CommitBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/CommitBuilder.java
index 4f93fda49f..1665f051e9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/CommitBuilder.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/CommitBuilder.java
@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2007, Dave Watson <dwatson@mimvista.com>
- * Copyright (C) 2006-2007, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2006-2007, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2006, 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
+ * Copyright (C) 2006, 2020, Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -16,14 +16,11 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
-import java.text.MessageFormat;
 import java.util.List;
 
-import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.util.References;
 
 /**
@@ -37,7 +34,7 @@ import org.eclipse.jgit.util.References;
  * and obtain a {@link org.eclipse.jgit.revwalk.RevCommit} instance by calling
  * {@link org.eclipse.jgit.revwalk.RevWalk#parseCommit(AnyObjectId)}.
  */
-public class CommitBuilder {
+public class CommitBuilder extends ObjectBuilder {
 	private static final ObjectId[] EMPTY_OBJECTID_LIST = new ObjectId[0];
 
 	private static final byte[] htree = Constants.encodeASCII("tree"); //$NON-NLS-1$
@@ -50,28 +47,17 @@ public class CommitBuilder {
 
 	private static final byte[] hgpgsig = Constants.encodeASCII("gpgsig"); //$NON-NLS-1$
 
-	private static final byte[] hencoding = Constants.encodeASCII("encoding"); //$NON-NLS-1$
-
 	private ObjectId treeId;
 
 	private ObjectId[] parentIds;
 
-	private PersonIdent author;
-
 	private PersonIdent committer;
 
-	private GpgSignature gpgSignature;
-
-	private String message;
-
-	private Charset encoding;
-
 	/**
 	 * Initialize an empty commit.
 	 */
 	public CommitBuilder() {
 		parentIds = EMPTY_OBJECTID_LIST;
-		encoding = UTF_8;
 	}
 
 	/**
@@ -98,8 +84,9 @@ public class CommitBuilder {
 	 *
 	 * @return the author of this commit (who wrote it).
 	 */
+	@Override
 	public PersonIdent getAuthor() {
-		return author;
+		return super.getAuthor();
 	}
 
 	/**
@@ -108,8 +95,9 @@ public class CommitBuilder {
 	 * @param newAuthor
 	 *            the new author. Should not be null.
 	 */
+	@Override
 	public void setAuthor(PersonIdent newAuthor) {
-		author = newAuthor;
+		super.setAuthor(newAuthor);
 	}
 
 	/**
@@ -132,38 +120,6 @@ public class CommitBuilder {
 	}
 
 	/**
-	 * Set the GPG signature of this commit.
-	 * <p>
-	 * Note, the signature set here will change the payload of the commit, i.e.
-	 * the output of {@link #build()} will include the signature. Thus, the
-	 * typical flow will be:
-	 * <ol>
-	 * <li>call {@link #build()} without a signature set to obtain payload</li>
-	 * <li>create {@link GpgSignature} from payload</li>
-	 * <li>set {@link GpgSignature}</li>
-	 * </ol>
-	 * </p>
-	 *
-	 * @param newSignature
-	 *            the signature to set or <code>null</code> to unset
-	 * @since 5.3
-	 */
-	public void setGpgSignature(GpgSignature newSignature) {
-		gpgSignature = newSignature;
-	}
-
-	/**
-	 * Get the GPG signature of this commit.
-	 *
-	 * @return the GPG signature of this commit, maybe <code>null</code> if the
-	 *         commit is not to be signed
-	 * @since 5.3
-	 */
-	public GpgSignature getGpgSignature() {
-		return gpgSignature;
-	}
-
-	/**
 	 * Get the ancestors of this commit.
 	 *
 	 * @return the ancestors of this commit. Never null.
@@ -239,25 +195,6 @@ public class CommitBuilder {
 	}
 
 	/**
-	 * Get the complete commit message.
-	 *
-	 * @return the complete commit message.
-	 */
-	public String getMessage() {
-		return message;
-	}
-
-	/**
-	 * Set the commit message.
-	 *
-	 * @param newMessage
-	 *            the commit message. Should not be null.
-	 */
-	public void setMessage(String newMessage) {
-		message = newMessage;
-	}
-
-	/**
 	 * Set the encoding for the commit information.
 	 *
 	 * @param encodingName
@@ -267,37 +204,10 @@ public class CommitBuilder {
 	 */
 	@Deprecated
 	public void setEncoding(String encodingName) {
-		encoding = Charset.forName(encodingName);
-	}
-
-	/**
-	 * Set the encoding for the commit information.
-	 *
-	 * @param enc
-	 *            the encoding to use.
-	 */
-	public void setEncoding(Charset enc) {
-		encoding = enc;
+		setEncoding(Charset.forName(encodingName));
 	}
 
-	/**
-	 * Get the encoding that should be used for the commit message text.
-	 *
-	 * @return the encoding that should be used for the commit message text.
-	 */
-	public Charset getEncoding() {
-		return encoding;
-	}
-
-	/**
-	 * Format this builder's state as a commit object.
-	 *
-	 * @return this object in the canonical commit format, suitable for storage
-	 *         in a repository.
-	 * @throws java.io.UnsupportedEncodingException
-	 *             the encoding specified by {@link #getEncoding()} is not
-	 *             supported by this Java runtime.
-	 */
+	@Override
 	public byte[] build() throws UnsupportedEncodingException {
 		ByteArrayOutputStream os = new ByteArrayOutputStream();
 		OutputStreamWriter w = new OutputStreamWriter(os, getEncoding());
@@ -326,19 +236,16 @@ public class CommitBuilder {
 			w.flush();
 			os.write('\n');
 
-			if (getGpgSignature() != null) {
+			GpgSignature signature = getGpgSignature();
+			if (signature != null) {
 				os.write(hgpgsig);
 				os.write(' ');
-				writeGpgSignatureString(getGpgSignature().toExternalString(), os);
+				writeMultiLineHeader(signature.toExternalString(), os,
+						true);
 				os.write('\n');
 			}
 
-			if (!References.isSameObject(getEncoding(), UTF_8)) {
-				os.write(hencoding);
-				os.write(' ');
-				os.write(Constants.encodeASCII(getEncoding().name()));
-				os.write('\n');
-			}
+			writeEncoding(getEncoding(), os);
 
 			os.write('\n');
 
@@ -356,58 +263,6 @@ public class CommitBuilder {
 	}
 
 	/**
-	 * Writes signature to output as per <a href=
-	 * "https://github.com/git/git/blob/master/Documentation/technical/signature-format.txt#L66,L89">gpgsig
-	 * header</a>.
-	 * <p>
-	 * CRLF and CR will be sanitized to LF and signature will have a hanging
-	 * indent of one space starting with line two. A trailing line break is
-	 * <em>not</em> written; the caller is supposed to terminate the GPG
-	 * signature header by writing a single newline.
-	 * </p>
-	 *
-	 * @param in
-	 *            signature string with line breaks
-	 * @param out
-	 *            output stream
-	 * @throws IOException
-	 *             thrown by the output stream
-	 * @throws IllegalArgumentException
-	 *             if the signature string contains non 7-bit ASCII chars
-	 */
-	static void writeGpgSignatureString(String in, OutputStream out)
-			throws IOException, IllegalArgumentException {
-		int length = in.length();
-		for (int i = 0; i < length; ++i) {
-			char ch = in.charAt(i);
-			switch (ch) {
-			case '\r':
-				if (i + 1 < length && in.charAt(i + 1) == '\n') {
-					++i;
-				}
-				if (i + 1 < length) {
-					out.write('\n');
-					out.write(' ');
-				}
-				break;
-			case '\n':
-				if (i + 1 < length) {
-					out.write('\n');
-					out.write(' ');
-				}
-				break;
-			default:
-				// sanity check
-				if (ch > 127)
-					throw new IllegalArgumentException(MessageFormat
-							.format(JGitText.get().notASCIIString, in));
-				out.write(ch);
-				break;
-			}
-		}
-	}
-
-	/**
 	 * Format this builder's state as a commit object.
 	 *
 	 * @return this object in the canonical commit format, suitable for storage
@@ -439,7 +294,7 @@ public class CommitBuilder {
 		}
 
 		r.append("author ");
-		r.append(author != null ? author.toString() : "NOT_SET");
+		r.append(getAuthor() != null ? getAuthor().toString() : "NOT_SET");
 		r.append("\n");
 
 		r.append("committer ");
@@ -447,17 +302,20 @@ public class CommitBuilder {
 		r.append("\n");
 
 		r.append("gpgSignature ");
-		r.append(gpgSignature != null ? gpgSignature.toString() : "NOT_SET");
+		GpgSignature signature = getGpgSignature();
+		r.append(signature != null ? signature.toString()
+				: "NOT_SET");
 		r.append("\n");
 
-		if (encoding != null && !References.isSameObject(encoding, UTF_8)) {
+		Charset encoding = getEncoding();
+		if (!References.isSameObject(encoding, UTF_8)) {
 			r.append("encoding ");
 			r.append(encoding.name());
 			r.append("\n");
 		}
 
 		r.append("\n");
-		r.append(message != null ? message : "");
+		r.append(getMessage() != null ? getMessage() : "");
 		r.append("}");
 		return r.toString();
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 4fcf8e2dcd..03c1ef904c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@ -93,13 +93,27 @@ public final class ConfigConstants {
 	public static final String CONFIG_GPG_SECTION = "gpg";
 
 	/**
+	 * The "protocol" section
+	 * @since 5.9
+	 */
+	public static final String CONFIG_PROTOCOL_SECTION = "protocol";
+
+	/**
 	 * The "format" key
 	 * @since 5.2
 	 */
 	public static final String CONFIG_KEY_FORMAT = "format";
 
 	/**
+	 * The "program" key
+	 *
+	 * @since 5.11
+	 */
+	public static final String CONFIG_KEY_PROGRAM = "program";
+
+	/**
 	 * The "signingKey" key
+	 *
 	 * @since 5.2
 	 */
 	public static final String CONFIG_KEY_SIGNINGKEY = "signingKey";
@@ -111,13 +125,29 @@ public final class ConfigConstants {
 	public static final String CONFIG_COMMIT_SECTION = "commit";
 
 	/**
+	 * The "tag" section
+	 *
+	 * @since 5.11
+	 */
+	public static final String CONFIG_TAG_SECTION = "tag";
+
+	/**
 	 * The "gpgSign" key
+	 *
 	 * @since 5.2
 	 */
 	public static final String CONFIG_KEY_GPGSIGN = "gpgSign";
 
 	/**
+	 * The "forceSignAnnotated" key
+	 *
+	 * @since 5.11
+	 */
+	public static final String CONFIG_KEY_FORCE_SIGN_ANNOTATED = "forceSignAnnotated";
+
+	/**
 	 * The "hooksPath" key.
+	 *
 	 * @since 5.6
 	 */
 	public static final String CONFIG_KEY_HOOKS_PATH = "hooksPath";
@@ -532,12 +562,6 @@ public final class ConfigConstants {
 	public static final String CONFIG_REF_STORAGE_REFTABLE = "reftable";
 
 	/**
-	 * The "reftree" refStorage format
-	 * @since 5.7
-	 */
-	public static final String CONFIG_REFSTORAGE_REFTREE = "reftree";
-
-	/**
 	 * The "jmx" section
 	 * @since 5.1.13
 	 */
@@ -685,10 +709,23 @@ public final class ConfigConstants {
 	public static final String CONFIG_INDEX_SECTION = "index";
 
 	/**
-	 * The "index.version" key
+	 * The "version" key
 	 *
 	 * @since 5.9
 	 */
 	public static final String CONFIG_KEY_VERSION = "version";
 
+	/**
+	 * The "init" section
+	 *
+	 * @since 5.11
+	 */
+	public static final String CONFIG_INIT_SECTION = "init";
+
+	/**
+	 * The "defaultBranch" key
+	 *
+	 * @since 5.11
+	 */
+	public static final String CONFIG_KEY_DEFAULT_BRANCH = "defaultbranch";
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgConfig.java
index c1527bc47b..427a235f3b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgConfig.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgConfig.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2018, Salesforce. and others
+ * Copyright (C) 2018, 2021 Salesforce and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -43,16 +43,65 @@ public class GpgConfig {
 		}
 	}
 
-	private final Config config;
+	private final GpgFormat keyFormat;
+
+	private final String signingKey;
+
+	private final String program;
+
+	private final boolean signCommits;
+
+	private final boolean signAllTags;
+
+	private final boolean forceAnnotated;
+
+	/**
+	 * Create a {@link GpgConfig} with the given parameters and default
+	 * {@code true} for signing commits and {@code false} for tags.
+	 *
+	 * @param keySpec
+	 *            to use
+	 * @param format
+	 *            to use
+	 * @param gpgProgram
+	 *            to use
+	 * @since 5.11
+	 */
+	public GpgConfig(String keySpec, GpgFormat format, String gpgProgram) {
+		keyFormat = format;
+		signingKey = keySpec;
+		program = gpgProgram;
+		signCommits = true;
+		signAllTags = false;
+		forceAnnotated = false;
+	}
 
 	/**
-	 * Create a new GPG config, which will read configuration from config.
+	 * Create a new GPG config that reads the configuration from config.
 	 *
 	 * @param config
 	 *            the config to read from
 	 */
 	public GpgConfig(Config config) {
-		this.config = config;
+		keyFormat = config.getEnum(GpgFormat.values(),
+				ConfigConstants.CONFIG_GPG_SECTION, null,
+				ConfigConstants.CONFIG_KEY_FORMAT, GpgFormat.OPENPGP);
+		signingKey = config.getString(ConfigConstants.CONFIG_USER_SECTION, null,
+				ConfigConstants.CONFIG_KEY_SIGNINGKEY);
+
+		String exe = config.getString(ConfigConstants.CONFIG_GPG_SECTION,
+				keyFormat.toConfigValue(), ConfigConstants.CONFIG_KEY_PROGRAM);
+		if (exe == null) {
+			exe = config.getString(ConfigConstants.CONFIG_GPG_SECTION, null,
+					ConfigConstants.CONFIG_KEY_PROGRAM);
+		}
+		program = exe;
+		signCommits = config.getBoolean(ConfigConstants.CONFIG_COMMIT_SECTION,
+				ConfigConstants.CONFIG_KEY_GPGSIGN, false);
+		signAllTags = config.getBoolean(ConfigConstants.CONFIG_TAG_SECTION,
+				ConfigConstants.CONFIG_KEY_GPGSIGN, false);
+		forceAnnotated = config.getBoolean(ConfigConstants.CONFIG_TAG_SECTION,
+				ConfigConstants.CONFIG_KEY_FORCE_SIGN_ANNOTATED, false);
 	}
 
 	/**
@@ -61,9 +110,19 @@ public class GpgConfig {
 	 * @return the {@link org.eclipse.jgit.lib.GpgConfig.GpgFormat}
 	 */
 	public GpgFormat getKeyFormat() {
-		return config.getEnum(GpgFormat.values(),
-				ConfigConstants.CONFIG_GPG_SECTION, null,
-				ConfigConstants.CONFIG_KEY_FORMAT, GpgFormat.OPENPGP);
+		return keyFormat;
+	}
+
+	/**
+	 * Retrieves the value of the configured GPG program to use, as defined by
+	 * gpg.openpgp.program, gpg.x509.program (depending on the defined
+	 * {@link #getKeyFormat() format}), or gpg.program.
+	 *
+	 * @return the program string configured, or {@code null} if none
+	 * @since 5.11
+	 */
+	public String getProgram() {
+		return program;
 	}
 
 	/**
@@ -72,8 +131,7 @@ public class GpgConfig {
 	 * @return the value of user.signingKey (may be <code>null</code>)
 	 */
 	public String getSigningKey() {
-		return config.getString(ConfigConstants.CONFIG_USER_SECTION, null,
-				ConfigConstants.CONFIG_KEY_SIGNINGKEY);
+		return signingKey;
 	}
 
 	/**
@@ -82,7 +140,29 @@ public class GpgConfig {
 	 * @return the value of commit.gpgSign (defaults to <code>false</code>)
 	 */
 	public boolean isSignCommits() {
-		return config.getBoolean(ConfigConstants.CONFIG_COMMIT_SECTION,
-				ConfigConstants.CONFIG_KEY_GPGSIGN, false);
+		return signCommits;
+	}
+
+	/**
+	 * Retrieves the value of git config {@code tag.gpgSign}.
+	 *
+	 * @return the value of {@code tag.gpgSign}; by default {@code false}
+	 *
+	 * @since 5.11
+	 */
+	public boolean isSignAllTags() {
+		return signAllTags;
+	}
+
+	/**
+	 * Retrieves the value of git config {@code tag.forceSignAnnotated}.
+	 *
+	 * @return the value of {@code tag.forceSignAnnotated}; by default
+	 *         {@code false}
+	 *
+	 * @since 5.11
+	 */
+	public boolean isSignAnnotated() {
+		return forceAnnotated;
 	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgObjectSigner.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgObjectSigner.java
new file mode 100644
index 0000000000..074f46567b
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgObjectSigner.java
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2020 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.lib;
+
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.api.errors.CanceledException;
+import org.eclipse.jgit.api.errors.UnsupportedSigningFormatException;
+import org.eclipse.jgit.transport.CredentialsProvider;
+
+/**
+ * Creates GPG signatures for Git objects.
+ *
+ * @since 5.11
+ */
+public interface GpgObjectSigner {
+
+	/**
+	 * Signs the specified object.
+	 *
+	 * <p>
+	 * Implementors should obtain the payload for signing from the specified
+	 * object via {@link ObjectBuilder#build()} and create a proper
+	 * {@link GpgSignature}. The generated signature must be set on the
+	 * specified {@code object} (see
+	 * {@link ObjectBuilder#setGpgSignature(GpgSignature)}).
+	 * </p>
+	 * <p>
+	 * Any existing signature on the object must be discarded prior obtaining
+	 * the payload via {@link ObjectBuilder#build()}.
+	 * </p>
+	 *
+	 * @param object
+	 *            the object to sign (must not be {@code null} and must be
+	 *            complete to allow proper calculation of payload)
+	 * @param gpgSigningKey
+	 *            the signing key to locate (passed as is to the GPG signing
+	 *            tool as is; eg., value of <code>user.signingkey</code>)
+	 * @param committer
+	 *            the signing identity (to help with key lookup in case signing
+	 *            key is not specified)
+	 * @param credentialsProvider
+	 *            provider to use when querying for signing key credentials (eg.
+	 *            passphrase)
+	 * @param config
+	 *            GPG settings from the git config
+	 * @throws CanceledException
+	 *             when signing was canceled (eg., user aborted when entering
+	 *             passphrase)
+	 * @throws UnsupportedSigningFormatException
+	 *             if a config is given and the wanted key format is not
+	 *             supported
+	 */
+	void signObject(@NonNull ObjectBuilder object,
+			@Nullable String gpgSigningKey, @NonNull PersonIdent committer,
+			CredentialsProvider credentialsProvider, GpgConfig config)
+			throws CanceledException, UnsupportedSigningFormatException;
+
+	/**
+	 * Indicates if a signing key is available for the specified committer
+	 * and/or signing key.
+	 *
+	 * @param gpgSigningKey
+	 *            the signing key to locate (passed as is to the GPG signing
+	 *            tool as is; eg., value of <code>user.signingkey</code>)
+	 * @param committer
+	 *            the signing identity (to help with key lookup in case signing
+	 *            key is not specified)
+	 * @param credentialsProvider
+	 *            provider to use when querying for signing key credentials (eg.
+	 *            passphrase)
+	 * @param config
+	 *            GPG settings from the git config
+	 * @return <code>true</code> if a signing key is available,
+	 *         <code>false</code> otherwise
+	 * @throws CanceledException
+	 *             when signing was canceled (eg., user aborted when entering
+	 *             passphrase)
+	 * @throws UnsupportedSigningFormatException
+	 *             if a config is given and the wanted key format is not
+	 *             supported
+	 */
+	public abstract boolean canLocateSigningKey(@Nullable String gpgSigningKey,
+			@NonNull PersonIdent committer,
+			CredentialsProvider credentialsProvider, GpgConfig config)
+			throws CanceledException, UnsupportedSigningFormatException;
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifier.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifier.java
new file mode 100644
index 0000000000..a7a39c998f
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifier.java
@@ -0,0 +1,158 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.lib;
+
+import java.io.IOException;
+import java.util.Date;
+
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.revwalk.RevObject;
+
+/**
+ * A {@code GpgVerifier} can verify GPG signatures on git commits and tags.
+ *
+ * @since 5.11
+ */
+public interface GpgSignatureVerifier {
+
+	/**
+	 * Verifies the signature on a signed commit or tag.
+	 *
+	 * @param object
+	 *            to verify
+	 * @param config
+	 *            the {@link GpgConfig} to use
+	 * @return a {@link SignatureVerification} describing the outcome of the
+	 *         verification, or {@code null} if the object was not signed
+	 * @throws IOException
+	 *             if an error occurs getting a public key
+	 * @throws org.eclipse.jgit.api.errors.JGitInternalException
+	 *             if signature verification fails
+	 */
+	@Nullable
+	SignatureVerification verifySignature(@NonNull RevObject object,
+			@NonNull GpgConfig config) throws IOException;
+
+
+	/**
+	 * Verifies a given signature for given data.
+	 *
+	 * @param data
+	 *            the signature is for
+	 * @param signatureData
+	 *            the ASCII-armored signature
+	 * @return a {@link SignatureVerification} describing the outcome
+	 * @throws IOException
+	 *             if the signature cannot be parsed
+	 * @throws JGitInternalException
+	 *             if signature verification fails
+	 */
+	public SignatureVerification verify(byte[] data, byte[] signatureData)
+			throws IOException;
+
+	/**
+	 * Retrieves the name of this verifier. This should be a short string
+	 * identifying the engine that verified the signature, like "gpg" if GPG is
+	 * used, or "bc" for a BouncyCastle implementation.
+	 *
+	 * @return the name
+	 */
+	@NonNull
+	String getName();
+
+	/**
+	 * A {@link GpgSignatureVerifier} may cache public keys to speed up
+	 * verifying signatures on multiple objects. This clears this cache, if any.
+	 */
+	void clear();
+
+	/**
+	 * A {@code SignatureVerification} returns data about a (positively or
+	 * negatively) verified signature.
+	 */
+	interface SignatureVerification {
+
+		// Data about the signature.
+
+		@NonNull
+		Date getCreationDate();
+
+		// Data from the signature used to find a public key.
+
+		/**
+		 * Obtains the signer as stored in the signature, if known.
+		 *
+		 * @return the signer, or {@code null} if unknown
+		 */
+		String getSigner();
+
+		/**
+		 * Obtains the short or long fingerprint of the public key as stored in
+		 * the signature, if known.
+		 *
+		 * @return the fingerprint, or {@code null} if unknown
+		 */
+		String getKeyFingerprint();
+
+		// Some information about the found public key.
+
+		/**
+		 * Obtains the OpenPGP user ID associated with the key.
+		 *
+		 * @return the user id, or {@code null} if unknown
+		 */
+		String getKeyUser();
+
+		/**
+		 * Tells whether the public key used for this signature verification was
+		 * expired when the signature was created.
+		 *
+		 * @return {@code true} if the key was expired already, {@code false}
+		 *         otherwise
+		 */
+		boolean isExpired();
+
+		/**
+		 * Obtains the trust level of the public key used to verify the
+		 * signature.
+		 *
+		 * @return the trust level
+		 */
+		@NonNull
+		TrustLevel getTrustLevel();
+
+		// The verification result.
+
+		/**
+		 * Tells whether the signature verification was successful.
+		 *
+		 * @return {@code true} if the signature was verified successfully;
+		 *         {@code false} if not.
+		 */
+		boolean getVerified();
+
+		/**
+		 * Obtains a human-readable message giving additional information about
+		 * the outcome of the verification.
+		 *
+		 * @return the message, or {@code null} if none set.
+		 */
+		String getMessage();
+	}
+
+	/**
+	 * The owner's trust in a public key.
+	 */
+	enum TrustLevel {
+		UNKNOWN, NEVER, MARGINAL, FULL, ULTIMATE
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifierFactory.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifierFactory.java
new file mode 100644
index 0000000000..4b1dbedeb1
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSignatureVerifierFactory.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.lib;
+
+import java.util.Iterator;
+import java.util.ServiceConfigurationError;
+import java.util.ServiceLoader;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A {@code GpgSignatureVerifierFactory} creates {@link GpgSignatureVerifier} instances.
+ *
+ * @since 5.11
+ */
+public abstract class GpgSignatureVerifierFactory {
+
+	private static final Logger LOG = LoggerFactory
+			.getLogger(GpgSignatureVerifierFactory.class);
+
+	private static volatile GpgSignatureVerifierFactory defaultFactory = loadDefault();
+
+	private static GpgSignatureVerifierFactory loadDefault() {
+		try {
+			ServiceLoader<GpgSignatureVerifierFactory> loader = ServiceLoader
+					.load(GpgSignatureVerifierFactory.class);
+			Iterator<GpgSignatureVerifierFactory> iter = loader.iterator();
+			if (iter.hasNext()) {
+				return iter.next();
+			}
+		} catch (ServiceConfigurationError e) {
+			LOG.error(e.getMessage(), e);
+		}
+		return null;
+	}
+
+	/**
+	 * Retrieves the default factory.
+	 *
+	 * @return the default factory or {@code null} if none set
+	 */
+	public static GpgSignatureVerifierFactory getDefault() {
+		return defaultFactory;
+	}
+
+	/**
+	 * Sets the default factory.
+	 *
+	 * @param factory
+	 *            the new default factory
+	 */
+	public static void setDefault(GpgSignatureVerifierFactory factory) {
+		defaultFactory = factory;
+	}
+
+	/**
+	 * Creates a new {@link GpgSignatureVerifier}.
+	 *
+	 * @return the new {@link GpgSignatureVerifier}
+	 */
+	public abstract GpgSignatureVerifier getVerifier();
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectBuilder.java
new file mode 100644
index 0000000000..4b7054f72b
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectBuilder.java
@@ -0,0 +1,225 @@
+/*
+ * Copyright (C) 2020, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.lib;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+import java.text.MessageFormat;
+import java.util.Objects;
+
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.util.References;
+
+/**
+ * Common base class for {@link CommitBuilder} and {@link TagBuilder}.
+ *
+ * @since 5.11
+ */
+public abstract class ObjectBuilder {
+
+	/** Byte representation of "encoding". */
+	private static final byte[] hencoding = Constants.encodeASCII("encoding"); //$NON-NLS-1$
+
+	private PersonIdent author;
+
+	private GpgSignature gpgSignature;
+
+	private String message;
+
+	private Charset encoding = StandardCharsets.UTF_8;
+
+	/**
+	 * Retrieves the author of this object.
+	 *
+	 * @return the author of this object, or {@code null} if not set yet
+	 */
+	protected PersonIdent getAuthor() {
+		return author;
+	}
+
+	/**
+	 * Sets the author (name, email address, and date) of this object.
+	 *
+	 * @param newAuthor
+	 *            the new author, must be non-{@code null}
+	 */
+	protected void setAuthor(PersonIdent newAuthor) {
+		author = Objects.requireNonNull(newAuthor);
+	}
+
+	/**
+	 * Sets the GPG signature of this object.
+	 * <p>
+	 * Note, the signature set here will change the payload of the object, i.e.
+	 * the output of {@link #build()} will include the signature. Thus, the
+	 * typical flow will be:
+	 * <ol>
+	 * <li>call {@link #build()} without a signature set to obtain payload</li>
+	 * <li>create {@link GpgSignature} from payload</li>
+	 * <li>set {@link GpgSignature}</li>
+	 * </ol>
+	 * </p>
+	 *
+	 * @param gpgSignature
+	 *            the signature to set or {@code null} to unset
+	 * @since 5.3
+	 */
+	public void setGpgSignature(@Nullable GpgSignature gpgSignature) {
+		this.gpgSignature = gpgSignature;
+	}
+
+	/**
+	 * Retrieves the GPG signature of this object.
+	 *
+	 * @return the GPG signature of this object, or {@code null} if the object
+	 *         is not signed
+	 * @since 5.3
+	 */
+	@Nullable
+	public GpgSignature getGpgSignature() {
+		return gpgSignature;
+	}
+
+	/**
+	 * Retrieves the complete message of the object.
+	 *
+	 * @return the complete message; can be {@code null}.
+	 */
+	@Nullable
+	public String getMessage() {
+		return message;
+	}
+
+	/**
+	 * Sets the message (commit message, or message of an annotated tag).
+	 *
+	 * @param message
+	 *            the message.
+	 */
+	public void setMessage(@Nullable String message) {
+		this.message = message;
+	}
+
+	/**
+	 * Retrieves the encoding that should be used for the message text.
+	 *
+	 * @return the encoding that should be used for the message text.
+	 */
+	@NonNull
+	public Charset getEncoding() {
+		return encoding;
+	}
+
+	/**
+	 * Sets the encoding for the object message.
+	 *
+	 * @param encoding
+	 *            the encoding to use.
+	 */
+	public void setEncoding(@NonNull Charset encoding) {
+		this.encoding = encoding;
+	}
+
+	/**
+	 * Format this builder's state as a git object.
+	 *
+	 * @return this object in the canonical git format, suitable for storage in
+	 *         a repository.
+	 * @throws java.io.UnsupportedEncodingException
+	 *             the encoding specified by {@link #getEncoding()} is not
+	 *             supported by this Java runtime.
+	 */
+	@NonNull
+	public abstract byte[] build() throws UnsupportedEncodingException;
+
+	/**
+	 * Writes signature to output as per <a href=
+	 * "https://github.com/git/git/blob/master/Documentation/technical/signature-format.txt#L66,L89">gpgsig
+	 * header</a>.
+	 * <p>
+	 * CRLF and CR will be sanitized to LF and signature will have a hanging
+	 * indent of one space starting with line two. A trailing line break is
+	 * <em>not</em> written; the caller is supposed to terminate the GPG
+	 * signature header by writing a single newline.
+	 * </p>
+	 *
+	 * @param in
+	 *            signature string with line breaks
+	 * @param out
+	 *            output stream
+	 * @param enforceAscii
+	 *            whether to throw {@link IllegalArgumentException} if non-ASCII
+	 *            characters are encountered
+	 * @throws IOException
+	 *             thrown by the output stream
+	 * @throws IllegalArgumentException
+	 *             if the signature string contains non 7-bit ASCII chars and
+	 *             {@code enforceAscii == true}
+	 */
+	static void writeMultiLineHeader(@NonNull String in,
+			@NonNull OutputStream out, boolean enforceAscii)
+			throws IOException, IllegalArgumentException {
+		int length = in.length();
+		for (int i = 0; i < length; ++i) {
+			char ch = in.charAt(i);
+			switch (ch) {
+			case '\r':
+				if (i + 1 < length && in.charAt(i + 1) == '\n') {
+					++i;
+				}
+				if (i + 1 < length) {
+					out.write('\n');
+					out.write(' ');
+				}
+				break;
+			case '\n':
+				if (i + 1 < length) {
+					out.write('\n');
+					out.write(' ');
+				}
+				break;
+			default:
+				// sanity check
+				if (ch > 127 && enforceAscii)
+					throw new IllegalArgumentException(MessageFormat
+							.format(JGitText.get().notASCIIString, in));
+				out.write(ch);
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Writes an "encoding" header.
+	 *
+	 * @param encoding
+	 *            to write
+	 * @param out
+	 *            to write to
+	 * @throws IOException
+	 *             if writing fails
+	 */
+	static void writeEncoding(@NonNull Charset encoding,
+			@NonNull OutputStream out) throws IOException {
+		if (!References.isSameObject(encoding, UTF_8)) {
+			out.write(hencoding);
+			out.write(' ');
+			out.write(Constants.encodeASCII(encoding.name()));
+			out.write('\n');
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectReader.java
index 6bb6ae590a..718ed89142 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectReader.java
@@ -17,9 +17,18 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 
+import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.internal.revwalk.BitmappedObjectReachabilityChecker;
+import org.eclipse.jgit.internal.revwalk.BitmappedReachabilityChecker;
+import org.eclipse.jgit.internal.revwalk.PedestrianObjectReachabilityChecker;
+import org.eclipse.jgit.internal.revwalk.PedestrianReachabilityChecker;
+import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
+import org.eclipse.jgit.revwalk.ObjectWalk;
+import org.eclipse.jgit.revwalk.ReachabilityChecker;
+import org.eclipse.jgit.revwalk.RevWalk;
 
 /**
  * Reads an {@link org.eclipse.jgit.lib.ObjectDatabase} for a single thread.
@@ -408,6 +417,54 @@ public abstract class ObjectReader implements AutoCloseable {
 	}
 
 	/**
+	 * Create a reachability checker that will use bitmaps if possible.
+	 *
+	 * @param rw
+	 *            revwalk for use by the reachability checker
+	 * @return the most efficient reachability checker for this repository.
+	 * @throws IOException
+	 *             if it cannot open any of the underlying indices.
+	 *
+	 * @since 5.11
+	 */
+	@NonNull
+	public ReachabilityChecker createReachabilityChecker(RevWalk rw)
+			throws IOException {
+		if (getBitmapIndex() != null) {
+			return new BitmappedReachabilityChecker(rw);
+		}
+
+		return new PedestrianReachabilityChecker(true, rw);
+	}
+
+	/**
+	 * Create an object reachability checker that will use bitmaps if possible.
+	 *
+	 * This reachability checker accepts any object as target. For checks
+	 * exclusively between commits, use
+	 * {@link #createReachabilityChecker(RevWalk)}.
+	 *
+	 * @param ow
+	 *            objectwalk for use by the reachability checker
+	 * @return the most efficient object reachability checker for this
+	 *         repository.
+	 *
+	 * @throws IOException
+	 *             if it cannot open any of the underlying indices.
+	 *
+	 * @since 5.11
+	 */
+	@NonNull
+	public ObjectReachabilityChecker createObjectReachabilityChecker(
+			ObjectWalk ow) throws IOException {
+		if (getBitmapIndex() != null) {
+			return new BitmappedObjectReachabilityChecker(ow);
+		}
+
+		return new PedestrianObjectReachabilityChecker(ow);
+	}
+
+	/**
 	 * Get the {@link org.eclipse.jgit.lib.ObjectInserter} from which this
 	 * reader was created using {@code inserter.newReader()}
 	 *
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
index 6832c9cd80..7b7bdebac8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java
@@ -21,6 +21,9 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
 
@@ -414,6 +417,31 @@ public abstract class RefDatabase {
 	}
 
 	/**
+	 * Returns refs whose names start with a given prefix excluding all refs that
+	 * start with one of the given prefixes.
+	 *
+	 * <p>
+	 * The default implementation is not efficient. Implementors of {@link RefDatabase}
+	 * should override this method directly if a better implementation is possible.
+	 * 
+	 * @param include string that names of refs should start with; may be empty.
+	 * @param excludes strings that names of refs can't start with; may be empty.
+	 * @return immutable list of refs whose names start with {@code prefix} and none
+	 *         of the strings in {@code exclude}.
+	 * @throws java.io.IOException the reference space cannot be accessed.
+	 * @since 5.11
+	 */
+	@NonNull
+	public List<Ref> getRefsByPrefixWithExclusions(String include, Set<String> excludes)
+			throws IOException {
+		Stream<Ref> refs = getRefs(include).values().stream();
+		for(String exclude: excludes) {
+			refs = refs.filter(r -> !r.getName().startsWith(exclude));
+		}
+		return Collections.unmodifiableList(refs.collect(Collectors.toList()));
+	}
+
+	/**
 	 * Returns refs whose names start with one of the given prefixes.
 	 * <p>
 	 * The default implementation uses {@link #getRefsByPrefix(String)}.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
index a7a832c1aa..1e8a6c9175 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
@@ -127,6 +127,8 @@ public abstract class Repository implements AutoCloseable {
 	/** If not bare, the index file caching the working file states. */
 	private final File indexFile;
 
+	private final String initialBranch;
+
 	/**
 	 * Initialize a new repository instance.
 	 *
@@ -138,6 +140,7 @@ public abstract class Repository implements AutoCloseable {
 		fs = options.getFS();
 		workTree = options.getWorkTree();
 		indexFile = options.getIndexFile();
+		initialBranch = options.getInitialBranch();
 	}
 
 	/**
@@ -1034,6 +1037,16 @@ public abstract class Repository implements AutoCloseable {
 	}
 
 	/**
+	 * Get the initial branch name of a new repository
+	 *
+	 * @return the initial branch name of a new repository
+	 * @since 5.11
+	 */
+	protected @NonNull String getInitialBranch() {
+		return initialBranch;
+	}
+
+	/**
 	 * Objects known to exist but not expressed by {@link #getAllRefs()}.
 	 * <p>
 	 * When a repository borrows objects from another repository, it can
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
index d36ccd5bea..41f291b57b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
@@ -14,6 +14,7 @@ import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
@@ -193,7 +194,7 @@ public class RepositoryCache {
 		cache.configureEviction(repositoryCacheConfig);
 	}
 
-	private final ConcurrentHashMap<Key, Repository> cacheMap;
+	private final Map<Key, Repository> cacheMap;
 
 	private final Lock[] openLocks;
 
@@ -201,6 +202,8 @@ public class RepositoryCache {
 
 	private volatile long expireAfter;
 
+	private final Object schedulerLock = new Lock();
+
 	private RepositoryCache() {
 		cacheMap = new ConcurrentHashMap<>();
 		openLocks = new Lock[4];
@@ -214,7 +217,7 @@ public class RepositoryCache {
 			RepositoryCacheConfig repositoryCacheConfig) {
 		expireAfter = repositoryCacheConfig.getExpireAfter();
 		ScheduledThreadPoolExecutor scheduler = WorkQueue.getExecutor();
-		synchronized (scheduler) {
+		synchronized (schedulerLock) {
 			if (cleanupTask != null) {
 				cleanupTask.cancel(false);
 			}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/TagBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/TagBuilder.java
index 71f01150c9..facb4a54be 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/TagBuilder.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/TagBuilder.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (C) 2006-2008, Robin Rosenberg <robin.rosenberg@dewire.com>
+ * Copyright (C) 2006, 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
- * Copyright (C) 2010, Chris Aniszczyk <caniszczyk@gmail.com> and others
+ * Copyright (C) 2010, 2020, Chris Aniszczyk <caniszczyk@gmail.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -17,8 +17,13 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStreamWriter;
+import java.io.UnsupportedEncodingException;
+import java.nio.charset.Charset;
 
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.revwalk.RevObject;
+import org.eclipse.jgit.util.References;
 
 /**
  * Mutable builder to construct an annotated tag recording a project state.
@@ -30,17 +35,22 @@ import org.eclipse.jgit.revwalk.RevObject;
  * and obtain a {@link org.eclipse.jgit.revwalk.RevTag} instance by calling
  * {@link org.eclipse.jgit.revwalk.RevWalk#parseTag(AnyObjectId)}.
  */
-public class TagBuilder {
+public class TagBuilder extends ObjectBuilder {
+
+	private static final byte[] hobject = Constants.encodeASCII("object"); //$NON-NLS-1$
+
+	private static final byte[] htype = Constants.encodeASCII("type"); //$NON-NLS-1$
+
+	private static final byte[] htag = Constants.encodeASCII("tag"); //$NON-NLS-1$
+
+	private static final byte[] htagger = Constants.encodeASCII("tagger"); //$NON-NLS-1$
+
 	private ObjectId object;
 
 	private int type = Constants.OBJ_BAD;
 
 	private String tag;
 
-	private PersonIdent tagger;
-
-	private String message;
-
 	/**
 	 * Get the type of object this tag refers to.
 	 *
@@ -109,7 +119,7 @@ public class TagBuilder {
 	 * @return creator of this tag. May be null.
 	 */
 	public PersonIdent getTagger() {
-		return tagger;
+		return getAuthor();
 	}
 
 	/**
@@ -119,26 +129,7 @@ public class TagBuilder {
 	 *            the creator. May be null.
 	 */
 	public void setTagger(PersonIdent taggerIdent) {
-		tagger = taggerIdent;
-	}
-
-	/**
-	 * Get the complete commit message.
-	 *
-	 * @return the complete commit message.
-	 */
-	public String getMessage() {
-		return message;
-	}
-
-	/**
-	 * Set the tag's message.
-	 *
-	 * @param newMessage
-	 *            the tag's message.
-	 */
-	public void setMessage(String newMessage) {
-		message = newMessage;
+		setAuthor(taggerIdent);
 	}
 
 	/**
@@ -147,31 +138,65 @@ public class TagBuilder {
 	 * @return this object in the canonical annotated tag format, suitable for
 	 *         storage in a repository.
 	 */
-	public byte[] build() {
+	@Override
+	public byte[] build() throws UnsupportedEncodingException {
 		ByteArrayOutputStream os = new ByteArrayOutputStream();
 		try (OutputStreamWriter w = new OutputStreamWriter(os,
-				UTF_8)) {
-			w.write("object "); //$NON-NLS-1$
-			getObjectId().copyTo(w);
-			w.write('\n');
+				getEncoding())) {
 
-			w.write("type "); //$NON-NLS-1$
-			w.write(Constants.typeString(getObjectType()));
-			w.write("\n"); //$NON-NLS-1$
+			os.write(hobject);
+			os.write(' ');
+			getObjectId().copyTo(os);
+			os.write('\n');
 
-			w.write("tag "); //$NON-NLS-1$
+			os.write(htype);
+			os.write(' ');
+			os.write(Constants
+					.encodeASCII(Constants.typeString(getObjectType())));
+			os.write('\n');
+
+			os.write(htag);
+			os.write(' ');
 			w.write(getTag());
-			w.write("\n"); //$NON-NLS-1$
+			w.flush();
+			os.write('\n');
 
 			if (getTagger() != null) {
-				w.write("tagger "); //$NON-NLS-1$
+				os.write(htagger);
+				os.write(' ');
 				w.write(getTagger().toExternalString());
-				w.write('\n');
+				w.flush();
+				os.write('\n');
+			}
+
+			writeEncoding(getEncoding(), os);
+
+			os.write('\n');
+			String msg = getMessage();
+			if (msg != null) {
+				w.write(msg);
+				w.flush();
 			}
 
-			w.write('\n');
-			if (getMessage() != null)
-				w.write(getMessage());
+			GpgSignature signature = getGpgSignature();
+			if (signature != null) {
+				if (msg != null && !msg.isEmpty() && !msg.endsWith("\n")) { //$NON-NLS-1$
+					// If signed, the message *must* end with a linefeed
+					// character, otherwise signature verification will fail.
+					// (The signature will have been computed over the payload
+					// containing the message without LF, but will be verified
+					// against a payload with the LF.) The signature must start
+					// on a new line.
+					throw new JGitInternalException(
+							JGitText.get().signedTagMessageNoLf);
+				}
+				String externalForm = signature.toExternalString();
+				w.write(externalForm);
+				w.flush();
+				if (!externalForm.endsWith("\n")) { //$NON-NLS-1$
+					os.write('\n');
+				}
+			}
 		} catch (IOException err) {
 			// This should never occur, the only way to get it above is
 			// for the ByteArrayOutputStream to throw, but it doesn't.
@@ -185,10 +210,17 @@ public class TagBuilder {
 	 * Format this builder's state as an annotated tag object.
 	 *
 	 * @return this object in the canonical annotated tag format, suitable for
-	 *         storage in a repository.
+	 *         storage in a repository, or {@code null} if the tag cannot be
+	 *         encoded
+	 * @deprecated since 5.11; use {@link #build()} instead
 	 */
+	@Deprecated
 	public byte[] toByteArray() {
-		return build();
+		try {
+			return build();
+		} catch (UnsupportedEncodingException e) {
+			return null;
+		}
 	}
 
 	/** {@inheritDoc} */
@@ -211,14 +243,23 @@ public class TagBuilder {
 		r.append(tag != null ? tag : "NOT_SET");
 		r.append("\n");
 
-		if (tagger != null) {
+		if (getTagger() != null) {
 			r.append("tagger ");
-			r.append(tagger);
+			r.append(getTagger());
+			r.append("\n");
+		}
+
+		Charset encoding = getEncoding();
+		if (!References.isSameObject(encoding, UTF_8)) {
+			r.append("encoding ");
+			r.append(encoding.name());
 			r.append("\n");
 		}
 
 		r.append("\n");
-		r.append(message != null ? message : "");
+		r.append(getMessage() != null ? getMessage() : "");
+		GpgSignature signature = getGpgSignature();
+		r.append(signature != null ? signature.toExternalString() : "");
 		r.append("}");
 		return r.toString();
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
index 6c217fdf25..4bfb38d286 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
@@ -703,18 +703,21 @@ public class ResolveMerger extends ThreeWayMerger {
 			// conflict between ours and theirs. file/folder conflicts between
 			// base/index/workingTree and something else are not relevant or
 			// detected later
-			if (nonTree(modeO) && !nonTree(modeT)) {
-				if (nonTree(modeB))
-					add(tw.getRawPath(), base, DirCacheEntry.STAGE_1, EPOCH, 0);
-				add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2, EPOCH, 0);
-				unmergedPaths.add(tw.getPathString());
-				enterSubtree = false;
-				return true;
-			}
-			if (nonTree(modeT) && !nonTree(modeO)) {
+			if (nonTree(modeO) != nonTree(modeT)) {
+				if (ignoreConflicts) {
+					// In case of merge failures, ignore this path instead of reporting unmerged, so
+					// a caller can use virtual commit. This will not result in files with conflict
+					// markers in the index/working tree. The actual diff on the path will be
+					// computed directly on children.
+					enterSubtree = false;
+					return true;
+				}
 				if (nonTree(modeB))
 					add(tw.getRawPath(), base, DirCacheEntry.STAGE_1, EPOCH, 0);
-				add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3, EPOCH, 0);
+				if (nonTree(modeO))
+					add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2, EPOCH, 0);
+				if (nonTree(modeT))
+					add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3, EPOCH, 0);
 				unmergedPaths.add(tw.getPathString());
 				enterSubtree = false;
 				return true;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/nls/NLS.java b/org.eclipse.jgit/src/org/eclipse/jgit/nls/NLS.java
index d7dd3bee52..881873de6f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/nls/NLS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/nls/NLS.java
@@ -11,6 +11,7 @@
 package org.eclipse.jgit.nls;
 
 import java.util.Locale;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.eclipse.jgit.errors.TranslationBundleLoadingException;
@@ -110,7 +111,8 @@ public class NLS {
 	}
 
 	private final Locale locale;
-	private final ConcurrentHashMap<Class, TranslationBundle> map = new ConcurrentHashMap<>();
+
+	private final Map<Class, TranslationBundle> map = new ConcurrentHashMap<>();
 
 	private NLS(Locale locale) {
 		this.locale = locale;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/DateRevQueue.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/DateRevQueue.java
index b875be9270..0cabf07057 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/DateRevQueue.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/DateRevQueue.java
@@ -93,7 +93,7 @@ public class DateRevQueue extends AbstractRevQueue {
 			head = n;
 		} else {
 			Entry p = q.next;
-			while (p != null && p.commit.commitTime > when) {
+			while (p != null && p.commit.commitTime >= when) {
 				q = p;
 				p = q.next;
 			}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/ObjectWalk.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/ObjectWalk.java
index 4c7a6f556e..e6f9580bf7 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/ObjectWalk.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/ObjectWalk.java
@@ -172,14 +172,14 @@ public class ObjectWalk extends RevWalk {
 	 *             when the index fails to load.
 	 *
 	 * @since 5.8
+	 * @deprecated use
+	 *             {@code ObjectReader#createObjectReachabilityChecker(ObjectWalk)}
+	 *             instead.
 	 */
-	public ObjectReachabilityChecker createObjectReachabilityChecker()
+	@Deprecated
+	public final ObjectReachabilityChecker createObjectReachabilityChecker()
 			throws IOException {
-		if (reader.getBitmapIndex() != null) {
-			return new BitmappedObjectReachabilityChecker(this);
-		}
-
-		return new PedestrianObjectReachabilityChecker(this);
+		return reader.createObjectReachabilityChecker(this);
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevTag.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevTag.java
index cac257199f..b9d145008b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevTag.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevTag.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (C) 2008-2009, Google Inc.
+ * Copyright (C) 2008, 2009, Google Inc.
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2021, Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -18,7 +18,9 @@ import java.io.IOException;
 import java.nio.charset.Charset;
 import java.nio.charset.IllegalCharsetNameException;
 import java.nio.charset.UnsupportedCharsetException;
+import java.util.Arrays;
 
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
@@ -35,6 +37,10 @@ import org.eclipse.jgit.util.StringUtils;
  * An annotated tag.
  */
 public class RevTag extends RevObject {
+
+	private static final byte[] hSignature = Constants
+			.encodeASCII("-----BEGIN PGP SIGNATURE-----"); //$NON-NLS-1$
+
 	/**
 	 * Parse an annotated tag from its canonical format.
 	 *
@@ -171,6 +177,71 @@ public class RevTag extends RevObject {
 		return RawParseUtils.parsePersonIdent(raw, nameB);
 	}
 
+	private static int nextStart(byte[] prefix, byte[] buffer, int from) {
+		int stop = buffer.length - prefix.length + 1;
+		int ptr = from;
+		if (ptr > 0) {
+			ptr = RawParseUtils.nextLF(buffer, ptr - 1);
+		}
+		while (ptr < stop) {
+			int lineStart = ptr;
+			boolean found = true;
+			for (byte element : prefix) {
+				if (element != buffer[ptr++]) {
+					found = false;
+					break;
+				}
+			}
+			if (found) {
+				return lineStart;
+			}
+			do {
+				ptr = RawParseUtils.nextLF(buffer, ptr);
+			} while (ptr < stop && buffer[ptr] == '\n');
+		}
+		return -1;
+	}
+
+	private int getSignatureStart() {
+		byte[] raw = buffer;
+		int msgB = RawParseUtils.tagMessage(raw, 0);
+		if (msgB < 0) {
+			return msgB;
+		}
+		// Find the last signature start and return the rest
+		int start = nextStart(hSignature, raw, msgB);
+		if (start < 0) {
+			return start;
+		}
+		int next = RawParseUtils.nextLF(raw, start);
+		while (next < raw.length) {
+			int newStart = nextStart(hSignature, raw, next);
+			if (newStart < 0) {
+				break;
+			}
+			start = newStart;
+			next = RawParseUtils.nextLF(raw, start);
+		}
+		return start;
+	}
+
+	/**
+	 * Parse the GPG signature from the raw buffer.
+	 *
+	 * @return contents of the GPG signature; {@code null} if the tag was not
+	 *         signed.
+	 * @since 5.11
+	 */
+	@Nullable
+	public final byte[] getRawGpgSignature() {
+		byte[] raw = buffer;
+		int start = getSignatureStart();
+		if (start < 0) {
+			return null;
+		}
+		return Arrays.copyOfRange(raw, start, raw.length);
+	}
+
 	/**
 	 * Parse the complete tag message and decode it to a string.
 	 * <p>
@@ -187,7 +258,12 @@ public class RevTag extends RevObject {
 		if (msgB < 0) {
 			return ""; //$NON-NLS-1$
 		}
-		return RawParseUtils.decode(guessEncoding(), raw, msgB, raw.length);
+		int signatureStart = getSignatureStart();
+		int end = signatureStart < 0 ? raw.length : signatureStart;
+		if (end == msgB) {
+			return ""; //$NON-NLS-1$
+		}
+		return RawParseUtils.decode(guessEncoding(), raw, msgB, end);
 	}
 
 	/**
@@ -213,6 +289,16 @@ public class RevTag extends RevObject {
 		}
 
 		int msgE = RawParseUtils.endOfParagraph(raw, msgB);
+		int signatureStart = getSignatureStart();
+		if (signatureStart >= msgB && msgE > signatureStart) {
+			msgE = signatureStart;
+			if (msgE > msgB) {
+				msgE--;
+			}
+			if (msgB == msgE) {
+				return ""; //$NON-NLS-1$
+			}
+		}
 		String str = RawParseUtils.decode(guessEncoding(), raw, msgB, msgE);
 		if (RevCommit.hasLF(raw, msgB, msgE)) {
 			str = StringUtils.replaceLineBreaksWithSpace(str);
@@ -258,6 +344,22 @@ public class RevTag extends RevObject {
 	}
 
 	/**
+	 * Obtain the raw unparsed tag body (<b>NOTE - THIS IS NOT A COPY</b>).
+	 * <p>
+	 * This method is exposed only to provide very fast, efficient access to
+	 * this tag's message buffer. Applications relying on this buffer should be
+	 * very careful to ensure they do not modify its contents during their use
+	 * of it.
+	 *
+	 * @return the raw unparsed tag body. This is <b>NOT A COPY</b>. Do not
+	 *         alter the returned array.
+	 * @since 5.11
+	 */
+	public final byte[] getRawBuffer() {
+		return buffer;
+	}
+
+	/**
 	 * Discard the message buffer to reduce memory usage.
 	 * <p>
 	 * After discarding the memory usage of the {@code RevTag} is reduced to
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java
index 6b62fcdf6d..631d861c0d 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java
@@ -236,13 +236,13 @@ public class RevWalk implements Iterable<RevCommit>, AutoCloseable {
 	 *             if it cannot open any of the underlying indices.
 	 *
 	 * @since 5.4
+	 * @deprecated use {@code ObjectReader#createReachabilityChecker(RevWalk)}
+	 *             instead.
 	 */
-	public ReachabilityChecker createReachabilityChecker() throws IOException {
-		if (reader.getBitmapIndex() != null) {
-			return new BitmappedReachabilityChecker(this);
-		}
-
-		return new PedestrianReachabilityChecker(true, this);
+	@Deprecated
+	public final ReachabilityChecker createReachabilityChecker()
+			throws IOException {
+		return reader.createReachabilityChecker(this);
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackConnection.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackConnection.java
index 3a36398629..3826bf7401 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackConnection.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackConnection.java
@@ -1,8 +1,8 @@
 /*
- * Copyright (C) 2008-2010, Google Inc.
+ * Copyright (C) 2008, 2010 Google Inc.
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -13,7 +13,12 @@
 
 package org.eclipse.jgit.transport;
 
+import static org.eclipse.jgit.transport.GitProtocolConstants.COMMAND_LS_REFS;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;
+import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_PEELED;
+import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_SYMREF_TARGET;
+import static org.eclipse.jgit.transport.GitProtocolConstants.VERSION_1;
+import static org.eclipse.jgit.transport.GitProtocolConstants.VERSION_2;
 
 import java.io.EOFException;
 import java.io.IOException;
@@ -22,23 +27,29 @@ import java.io.OutputStream;
 import java.text.MessageFormat;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 
+import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.errors.InvalidObjectIdException;
 import org.eclipse.jgit.errors.NoRemoteRepositoryException;
 import org.eclipse.jgit.errors.PackProtocolException;
 import org.eclipse.jgit.errors.RemoteRepositoryException;
 import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectIdRef;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.SymbolicRef;
+import org.eclipse.jgit.util.StringUtils;
 import org.eclipse.jgit.util.io.InterruptTimer;
 import org.eclipse.jgit.util.io.TimeoutInputStream;
 import org.eclipse.jgit.util.io.TimeoutOutputStream;
@@ -92,17 +103,27 @@ abstract class BasePackConnection extends BaseConnection {
 	protected boolean statelessRPC;
 
 	/** Capability tokens advertised by the remote side. */
-	private final Set<String> remoteCapablities = new HashSet<>();
+	private final Map<String, String> remoteCapabilities = new HashMap<>();
 
 	/** Extra objects the remote has, but which aren't offered as refs. */
 	protected final Set<ObjectId> additionalHaves = new HashSet<>();
 
+	private TransferConfig.ProtocolVersion protocol = TransferConfig.ProtocolVersion.V0;
+
 	BasePackConnection(PackTransport packTransport) {
 		transport = (Transport) packTransport;
 		local = transport.local;
 		uri = transport.uri;
 	}
 
+	TransferConfig.ProtocolVersion getProtocolVersion() {
+		return protocol;
+	}
+
+	void setProtocolVersion(@NonNull TransferConfig.ProtocolVersion protocol) {
+		this.protocol = protocol;
+	}
+
 	/**
 	 * Configure this connection with the directional pipes.
 	 *
@@ -147,12 +168,15 @@ abstract class BasePackConnection extends BaseConnection {
 	 * {@link #close()} and the exception is wrapped (if necessary) and thrown
 	 * as a {@link org.eclipse.jgit.errors.TransportException}.
 	 *
+	 * @return {@code true} if the refs were read; {@code false} otherwise
+	 *         indicating that {@link #lsRefs} must be called
+	 *
 	 * @throws org.eclipse.jgit.errors.TransportException
 	 *             the reference list could not be scanned.
 	 */
-	protected void readAdvertisedRefs() throws TransportException {
+	protected boolean readAdvertisedRefs() throws TransportException {
 		try {
-			readAdvertisedRefsImpl();
+			return readAdvertisedRefsImpl();
 		} catch (TransportException err) {
 			close();
 			throw err;
@@ -162,35 +186,79 @@ abstract class BasePackConnection extends BaseConnection {
 		}
 	}
 
-	private void readAdvertisedRefsImpl() throws IOException {
-		final LinkedHashMap<String, Ref> avail = new LinkedHashMap<>();
-		for (;;) {
-			String line;
-
-			try {
-				line = pckIn.readString();
-			} catch (EOFException eof) {
-				if (avail.isEmpty())
-					throw noRepository();
-				throw eof;
-			}
-			if (PacketLineIn.isEnd(line))
-				break;
+	private String readLine() throws IOException {
+		String line = pckIn.readString();
+		if (PacketLineIn.isEnd(line)) {
+			return null;
+		}
+		if (line.startsWith("ERR ")) { //$NON-NLS-1$
+			// This is a customized remote service error.
+			// Users should be informed about it.
+			throw new RemoteRepositoryException(uri, line.substring(4));
+		}
+		return line;
+	}
 
-			if (line.startsWith("ERR ")) { //$NON-NLS-1$
-				// This is a customized remote service error.
-				// Users should be informed about it.
-				throw new RemoteRepositoryException(uri, line.substring(4));
-			}
+	private boolean readAdvertisedRefsImpl() throws IOException {
+		final Map<String, Ref> avail = new LinkedHashMap<>();
+		final Map<String, String> symRefs = new LinkedHashMap<>();
+		for (boolean first = true;; first = false) {
+			String line;
 
-			if (avail.isEmpty()) {
+			if (first) {
+				boolean isV1 = false;
+				try {
+					line = readLine();
+				} catch (EOFException e) {
+					TransportException noRepo = noRepository();
+					noRepo.initCause(e);
+					throw noRepo;
+				}
+				if (line != null && VERSION_1.equals(line)) {
+					// Same as V0, except for this extra line. We shouldn't get
+					// it since we never request V1.
+					setProtocolVersion(TransferConfig.ProtocolVersion.V0);
+					isV1 = true;
+					line = readLine();
+				}
+				if (line == null) {
+					break;
+				}
 				final int nul = line.indexOf('\0');
 				if (nul >= 0) {
-					// The first line (if any) may contain "hidden"
-					// capability values after a NUL byte.
-					remoteCapablities.addAll(
-							Arrays.asList(line.substring(nul + 1).split(" "))); //$NON-NLS-1$
+					// Protocol V0: The first line (if any) may contain
+					// "hidden" capability values after a NUL byte.
+					for (String capability : line.substring(nul + 1)
+							.split(" ")) { //$NON-NLS-1$
+						if (capability.startsWith(CAPABILITY_SYMREF_PREFIX)) {
+							String[] parts = capability
+									.substring(
+											CAPABILITY_SYMREF_PREFIX.length())
+									.split(":", 2); //$NON-NLS-1$
+							if (parts.length == 2) {
+								symRefs.put(parts[0], parts[1]);
+							}
+						} else {
+							addCapability(capability);
+						}
+					}
 					line = line.substring(0, nul);
+					setProtocolVersion(TransferConfig.ProtocolVersion.V0);
+				} else if (!isV1 && VERSION_2.equals(line)) {
+					// Protocol V2: remaining lines are capabilities as
+					// key=value pairs
+					setProtocolVersion(TransferConfig.ProtocolVersion.V2);
+					readCapabilitiesV2();
+					// Break out here so that stateless RPC transports get a
+					// chance to set up the output stream.
+					return false;
+				} else {
+					setProtocolVersion(TransferConfig.ProtocolVersion.V0);
+				}
+			} else {
+				line = readLine();
+				if (line == null) {
+					break;
 				}
 			}
 
@@ -199,73 +267,214 @@ abstract class BasePackConnection extends BaseConnection {
 				throw invalidRefAdvertisementLine(line);
 			}
 			String name = line.substring(41, line.length());
-			if (avail.isEmpty() && name.equals("capabilities^{}")) { //$NON-NLS-1$
-				// special line from git-receive-pack to show
+			if (first && name.equals("capabilities^{}")) { //$NON-NLS-1$
+				// special line from git-receive-pack (protocol V0) to show
 				// capabilities when there are no refs to advertise
 				continue;
 			}
 
-			final ObjectId id;
-			try {
-				id  = ObjectId.fromString(line.substring(0, 40));
-			} catch (InvalidObjectIdException e) {
-				PackProtocolException ppe = invalidRefAdvertisementLine(line);
-				ppe.initCause(e);
-				throw ppe;
-			}
+			final ObjectId id = toId(line, line.substring(0, 40));
 			if (name.equals(".have")) { //$NON-NLS-1$
 				additionalHaves.add(id);
-			} else if (name.endsWith("^{}")) { //$NON-NLS-1$
-				name = name.substring(0, name.length() - 3);
-				final Ref prior = avail.get(name);
-				if (prior == null)
-					throw new PackProtocolException(uri, MessageFormat.format(
-							JGitText.get().advertisementCameBefore, name, name));
-
-				if (prior.getPeeledObjectId() != null)
-					throw duplicateAdvertisement(name + "^{}"); //$NON-NLS-1$
-
-				avail.put(name, new ObjectIdRef.PeeledTag(
-						Ref.Storage.NETWORK, name, prior.getObjectId(), id));
 			} else {
-				final Ref prior = avail.put(name, new ObjectIdRef.PeeledNonTag(
-						Ref.Storage.NETWORK, name, id));
-				if (prior != null)
-					throw duplicateAdvertisement(name);
+				processLineV1(name, id, avail);
 			}
 		}
-		updateWithSymRefs(avail, extractSymRefsFromCapabilities(remoteCapablities));
+		updateWithSymRefs(avail, symRefs);
 		available(avail);
+		return true;
 	}
 
 	/**
-	 * Finds values in the given capabilities of the form:
-	 *
-	 * <pre>
-	 * symref=<em>source</em>:<em>target</em>
-	 * </pre>
+	 * Issue a protocol V2 ls-refs command and read its response.
 	 *
-	 * And returns a Map of source->target entries.
-	 *
-	 * @param capabilities
-	 *            the capabilities lines
-	 * @return a Map of the symref entries from capabilities
-	 * @throws NullPointerException
-	 *             if capabilities, or any entry in it, is null
+	 * @param refSpecs
+	 *            to produce ref prefixes from if the server supports git
+	 *            protocol V2
+	 * @param additionalPatterns
+	 *            to use for ref prefixes if the server supports git protocol V2
+	 * @throws TransportException
+	 *             if the command could not be run or its output not be read
 	 */
-	static Map<String, String> extractSymRefsFromCapabilities(Collection<String> capabilities) {
+	protected void lsRefs(Collection<RefSpec> refSpecs,
+			String... additionalPatterns) throws TransportException {
+		try {
+			lsRefsImpl(refSpecs, additionalPatterns);
+		} catch (TransportException err) {
+			close();
+			throw err;
+		} catch (IOException | RuntimeException err) {
+			close();
+			throw new TransportException(err.getMessage(), err);
+		}
+	}
+
+	private void lsRefsImpl(Collection<RefSpec> refSpecs,
+			String... additionalPatterns) throws IOException {
+		pckOut.writeString("command=" + COMMAND_LS_REFS); //$NON-NLS-1$
+		// Add the user-agent
+		String agent = UserAgent.get();
+		if (agent != null && isCapableOf(OPTION_AGENT)) {
+			pckOut.writeString(OPTION_AGENT + '=' + agent);
+		}
+		pckOut.writeDelim();
+		pckOut.writeString("peel"); //$NON-NLS-1$
+		pckOut.writeString("symrefs"); //$NON-NLS-1$
+		for (String refPrefix : getRefPrefixes(refSpecs, additionalPatterns)) {
+			pckOut.writeString("ref-prefix " + refPrefix); //$NON-NLS-1$
+		}
+		pckOut.end();
+		final Map<String, Ref> avail = new LinkedHashMap<>();
 		final Map<String, String> symRefs = new LinkedHashMap<>();
-		for (String option : capabilities) {
-			if (option.startsWith(CAPABILITY_SYMREF_PREFIX)) {
-				String[] symRef = option
-						.substring(CAPABILITY_SYMREF_PREFIX.length())
-						.split(":", 2); //$NON-NLS-1$
-				if (symRef.length == 2) {
-					symRefs.put(symRef[0], symRef[1]);
+		for (;;) {
+			String line = readLine();
+			if (line == null) {
+				break;
+			}
+			// Expecting to get a line in the form "sha1 refname"
+			if (line.length() < 41 || line.charAt(40) != ' ') {
+				throw invalidRefAdvertisementLine(line);
+			}
+			String name = line.substring(41, line.length());
+			final ObjectId id = toId(line, line.substring(0, 40));
+			if (name.equals(".have")) { //$NON-NLS-1$
+				additionalHaves.add(id);
+			} else {
+				processLineV2(line, id, name, avail, symRefs);
+			}
+		}
+		updateWithSymRefs(avail, symRefs);
+		available(avail);
+	}
+
+	private Collection<String> getRefPrefixes(Collection<RefSpec> refSpecs,
+			String... additionalPatterns) {
+		if (refSpecs.isEmpty() && (additionalPatterns == null
+				|| additionalPatterns.length == 0)) {
+			return Collections.emptyList();
+		}
+		Set<String> patterns = new HashSet<>();
+		if (additionalPatterns != null) {
+			Arrays.stream(additionalPatterns).filter(Objects::nonNull)
+					.forEach(patterns::add);
+		}
+		for (RefSpec spec : refSpecs) {
+			// TODO: for now we only do protocol V2 for fetch. For push
+			// RefSpecs, the logic would need to be different. (At the
+			// minimum, take spec.getDestination().)
+			String src = spec.getSource();
+			if (ObjectId.isId(src)) {
+				continue;
+			}
+			if (spec.isWildcard()) {
+				patterns.add(src.substring(0, src.indexOf('*')));
+			} else {
+				patterns.add(src);
+				patterns.add(Constants.R_REFS + src);
+				patterns.add(Constants.R_HEADS + src);
+				patterns.add(Constants.R_TAGS + src);
+			}
+		}
+		return patterns;
+	}
+
+	private void readCapabilitiesV2() throws IOException {
+		// In git protocol V2, capabilities are different. If it's a key-value
+		// pair, the key may be a command name, and the value a space-separated
+		// list of capabilities for that command. We still store it in the same
+		// map as for protocol v0/v1. Protocol v2 code has to account for this.
+		for (;;) {
+			String line = readLine();
+			if (line == null) {
+				break;
+			}
+			addCapability(line);
+		}
+	}
+
+	private void addCapability(String capability) {
+		String parts[] = capability.split("=", 2); //$NON-NLS-1$
+		if (parts.length == 2) {
+			remoteCapabilities.put(parts[0], parts[1]);
+		}
+		remoteCapabilities.put(capability, null);
+	}
+
+	private ObjectId toId(String line, String value)
+			throws PackProtocolException {
+		try {
+			return ObjectId.fromString(value);
+		} catch (InvalidObjectIdException e) {
+			PackProtocolException ppe = invalidRefAdvertisementLine(line);
+			ppe.initCause(e);
+			throw ppe;
+		}
+	}
+
+	private void processLineV1(String name, ObjectId id, Map<String, Ref> avail)
+			throws IOException {
+		if (name.endsWith("^{}")) { //$NON-NLS-1$
+			name = name.substring(0, name.length() - 3);
+			final Ref prior = avail.get(name);
+			if (prior == null) {
+				throw new PackProtocolException(uri, MessageFormat.format(
+						JGitText.get().advertisementCameBefore, name, name));
+			}
+			if (prior.getPeeledObjectId() != null) {
+				throw duplicateAdvertisement(name + "^{}"); //$NON-NLS-1$
+			}
+			avail.put(name, new ObjectIdRef.PeeledTag(Ref.Storage.NETWORK, name,
+					prior.getObjectId(), id));
+		} else {
+			final Ref prior = avail.put(name, new ObjectIdRef.PeeledNonTag(
+					Ref.Storage.NETWORK, name, id));
+			if (prior != null) {
+				throw duplicateAdvertisement(name);
+			}
+		}
+	}
+
+	private void processLineV2(String line, ObjectId id, String rest,
+			Map<String, Ref> avail, Map<String, String> symRefs)
+			throws IOException {
+		String[] parts = rest.split(" "); //$NON-NLS-1$
+		String name = parts[0];
+		// Two attributes possible, symref-target or peeled
+		String symRefTarget = null;
+		String peeled = null;
+		for (int i = 1; i < parts.length; i++) {
+			if (parts[i].startsWith(REF_ATTR_SYMREF_TARGET)) {
+				if (symRefTarget != null) {
+					throw new PackProtocolException(uri, MessageFormat.format(
+							JGitText.get().duplicateRefAttribute, line));
+				}
+				symRefTarget = parts[i]
+						.substring(REF_ATTR_SYMREF_TARGET.length());
+			} else if (parts[i].startsWith(REF_ATTR_PEELED)) {
+				if (peeled != null) {
+					throw new PackProtocolException(uri, MessageFormat.format(
+							JGitText.get().duplicateRefAttribute, line));
 				}
+				peeled = parts[i].substring(REF_ATTR_PEELED.length());
 			}
+			if (peeled != null && symRefTarget != null) {
+				break;
+			}
+		}
+		Ref idRef;
+		if (peeled != null) {
+			idRef = new ObjectIdRef.PeeledTag(Ref.Storage.NETWORK, name, id,
+					toId(line, peeled));
+		} else {
+			idRef = new ObjectIdRef.PeeledNonTag(Ref.Storage.NETWORK, name, id);
+		}
+		Ref prior = avail.put(name, idRef);
+		if (prior != null) {
+			throw duplicateAdvertisement(name);
+		}
+		if (!StringUtils.isEmptyOrNull(symRefTarget)) {
+			symRefs.put(name, symRefTarget);
 		}
-		return symRefs;
 	}
 
 	/**
@@ -334,6 +543,22 @@ abstract class BasePackConnection extends BaseConnection {
 				}
 			}
 		}
+		// If HEAD is still in the symRefs map here, the real ref was not
+		// reported, but we know it must point to the object reported for HEAD.
+		// So fill it in in the refMap.
+		String headRefName = symRefs.get(Constants.HEAD);
+		if (headRefName != null && !refMap.containsKey(headRefName)) {
+			Ref headRef = refMap.get(Constants.HEAD);
+			if (headRef != null) {
+				ObjectId headObj = headRef.getObjectId();
+				headRef = new ObjectIdRef.PeeledNonTag(Ref.Storage.NETWORK,
+						headRefName, headObj);
+				refMap.put(headRefName, headRef);
+				headRef = new SymbolicRef(Constants.HEAD, headRef);
+				refMap.put(Constants.HEAD, headRef);
+				symRefs.remove(Constants.HEAD);
+			}
+		}
 	}
 
 	/**
@@ -357,7 +582,7 @@ abstract class BasePackConnection extends BaseConnection {
 	 * @return whether this option is supported
 	 */
 	protected boolean isCapableOf(String option) {
-		return remoteCapablities.contains(option);
+		return remoteCapabilities.containsKey(option);
 	}
 
 	/**
@@ -378,6 +603,17 @@ abstract class BasePackConnection extends BaseConnection {
 	}
 
 	/**
+	 * Return a capability value.
+	 *
+	 * @param option
+	 *            to get
+	 * @return the value stored, if any.
+	 */
+	protected String getCapability(String option) {
+		return remoteCapabilities.get(option);
+	}
+
+	/**
 	 * Add user agent capability
 	 *
 	 * @param b
@@ -385,7 +621,7 @@ abstract class BasePackConnection extends BaseConnection {
 	 */
 	protected void addUserAgentCapability(StringBuilder b) {
 		String a = UserAgent.get();
-		if (a != null && UserAgent.hasAgent(remoteCapablities)) {
+		if (a != null && remoteCapabilities.get(OPTION_AGENT) != null) {
 			b.append(' ').append(OPTION_AGENT).append('=').append(a);
 		}
 	}
@@ -393,7 +629,8 @@ abstract class BasePackConnection extends BaseConnection {
 	/** {@inheritDoc} */
 	@Override
 	public String getPeerUserAgent() {
-		return UserAgent.getAgent(remoteCapablities, super.getPeerUserAgent());
+		String agent = remoteCapabilities.get(OPTION_AGENT);
+		return agent != null ? agent : super.getPeerUserAgent();
 	}
 
 	private PackProtocolException duplicateAdvertisement(String name) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java
index a2fb51f46d..d344deac26 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (C) 2008-2010, Google Inc.
+ * Copyright (C) 2008, 2010 Google Inc.
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -16,18 +16,21 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.text.MessageFormat;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.Set;
 
 import org.eclipse.jgit.errors.PackProtocolException;
+import org.eclipse.jgit.errors.RemoteRepositoryException;
 import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.file.PackLock;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Config;
-import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.MutableObjectId;
 import org.eclipse.jgit.lib.NullProgressMonitor;
 import org.eclipse.jgit.lib.ObjectId;
@@ -44,6 +47,7 @@ import org.eclipse.jgit.revwalk.filter.CommitTimeRevFilter;
 import org.eclipse.jgit.revwalk.filter.RevFilter;
 import org.eclipse.jgit.transport.GitProtocolConstants.MultiAck;
 import org.eclipse.jgit.transport.PacketLineIn.AckNackResult;
+import org.eclipse.jgit.util.StringUtils;
 import org.eclipse.jgit.util.TemporaryBuffer;
 
 /**
@@ -207,7 +211,10 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 
 	private int maxHaves;
 
-	/** RPC state, if {@link BasePackConnection#statelessRPC} is true. */
+	/**
+	 * RPC state, if {@link BasePackConnection#statelessRPC} is true or protocol
+	 * V2 is used.
+	 */
 	private TemporaryBuffer.Heap state;
 
 	private PacketLineOut pckState;
@@ -321,6 +328,13 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		return Collections.<PackLock> emptyList();
 	}
 
+	private void clearState() {
+		walk.dispose();
+		reachableCommits = null;
+		state = null;
+		pckState = null;
+	}
+
 	/**
 	 * Execute common ancestor negotiation and fetch the objects.
 	 *
@@ -349,18 +363,34 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 			markRefsAdvertised();
 			markReachable(have, maxTimeWanted(want));
 
+			if (TransferConfig.ProtocolVersion.V2
+					.equals(getProtocolVersion())) {
+				// Protocol V2 always is a "stateless" protocol, even over a
+				// bidirectional pipe: the server serves one "fetch" request and
+				// then forgets anything it has learned, so the next fetch
+				// request has to re-send all wants and previously determined
+				// common objects as "have"s again.
+				state = new TemporaryBuffer.Heap(Integer.MAX_VALUE);
+				pckState = new PacketLineOut(state);
+				try {
+					doFetchV2(monitor, want, outputStream);
+				} finally {
+					clearState();
+				}
+				return;
+			}
+			// Protocol V0/1
 			if (statelessRPC) {
 				state = new TemporaryBuffer.Heap(Integer.MAX_VALUE);
 				pckState = new PacketLineOut(state);
 			}
-
-			if (sendWants(want)) {
+			PacketLineOut output = statelessRPC ? pckState : pckOut;
+			if (sendWants(want, output)) {
+				output.end();
+				outNeedsEnd = false;
 				negotiate(monitor);
 
-				walk.dispose();
-				reachableCommits = null;
-				state = null;
-				pckState = null;
+				clearState();
 
 				receivePack(monitor, outputStream);
 			}
@@ -373,6 +403,185 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		}
 	}
 
+	private void doFetchV2(ProgressMonitor monitor, Collection<Ref> want,
+			OutputStream outputStream) throws IOException, CancelledException {
+		sideband = true;
+		negotiateBegin();
+
+		pckState.writeString("command=" + GitProtocolConstants.COMMAND_FETCH); //$NON-NLS-1$
+		// Capabilities are sent as command arguments in protocol V2
+		String agent = UserAgent.get();
+		if (agent != null && isCapableOf(GitProtocolConstants.OPTION_AGENT)) {
+			pckState.writeString(
+					GitProtocolConstants.OPTION_AGENT + '=' + agent);
+		}
+		Set<String> capabilities = new HashSet<>();
+		String advertised = getCapability(GitProtocolConstants.COMMAND_FETCH);
+		if (!StringUtils.isEmptyOrNull(advertised)) {
+			capabilities.addAll(Arrays.asList(advertised.split("\\s+"))); //$NON-NLS-1$
+		}
+		// Arguments
+		pckState.writeDelim();
+		for (String capability : getCapabilitiesV2(capabilities)) {
+			pckState.writeString(capability);
+		}
+		if (!sendWants(want, pckState)) {
+			// We already have everything we wanted.
+			return;
+		}
+		// If we send something, we always close it properly ourselves.
+		outNeedsEnd = false;
+
+		FetchStateV2 fetchState = new FetchStateV2();
+		boolean sentDone = false;
+		for (;;) {
+			// The "state" buffer contains the full fetch request with all
+			// common objects found so far.
+			state.writeTo(out, monitor);
+			sentDone = sendNextHaveBatch(fetchState, pckOut, monitor);
+			if (sentDone) {
+				break;
+			}
+			if (readAcknowledgments(fetchState, pckIn, monitor)) {
+				// We got a "ready": next should be a patch file.
+				break;
+			}
+			// Note: C git reads and requires here (and after a packfile) a
+			// "0002" packet in stateless RPC transports (https). This "response
+			// end" packet is even mentioned in the protocol V2 technical
+			// documentation. However, it is not actually part of the public
+			// protocol; it occurs only in an internal protocol wrapper in the C
+			// git implementation.
+		}
+		clearState();
+		String line = pckIn.readString();
+		// If we sent a done, we may have an error reply here.
+		if (sentDone && line.startsWith("ERR ")) { //$NON-NLS-1$
+			throw new RemoteRepositoryException(uri, line.substring(4));
+		}
+		// "shallow-info", "wanted-refs", and "packfile-uris" would have to be
+		// handled here in that order.
+		if (!GitProtocolConstants.SECTION_PACKFILE.equals(line)) {
+			throw new PackProtocolException(
+					MessageFormat.format(JGitText.get().expectedGot,
+							GitProtocolConstants.SECTION_PACKFILE, line));
+		}
+		receivePack(monitor, outputStream);
+	}
+
+	/**
+	 * Sends the next batch of "have"s and terminates the {@code output}.
+	 *
+	 * @param fetchState
+	 *            is updated with information about the number of items written,
+	 *            and whether to expect a packfile next
+	 * @param output
+	 *            to write to
+	 * @param monitor
+	 *            for progress reporting and cancellation
+	 * @return {@code true} if a "done" was written and we should thus expect a
+	 *         packfile next
+	 * @throws IOException
+	 *             on errors
+	 * @throws CancelledException
+	 *             on cancellation
+	 */
+	private boolean sendNextHaveBatch(FetchStateV2 fetchState,
+			PacketLineOut output, ProgressMonitor monitor)
+			throws IOException, CancelledException {
+		long n = 0;
+		while (n < fetchState.havesToSend) {
+			final RevCommit c = walk.next();
+			if (c == null) {
+				break;
+			}
+			output.writeString("have " + c.getId().name() + '\n'); //$NON-NLS-1$
+			n++;
+			if (n % 10 == 0 && monitor.isCancelled()) {
+				throw new CancelledException();
+			}
+		}
+		fetchState.havesTotal += n;
+		if (n == 0
+				|| (fetchState.hadAcks
+						&& fetchState.havesWithoutAck > MAX_HAVES)
+				|| fetchState.havesTotal > maxHaves) {
+			output.writeString("done\n"); //$NON-NLS-1$
+			output.end();
+			return true;
+		}
+		// Increment only after the test above. Of course we have no ACKs yet
+		// for the newly added "have"s, so it makes no sense to count them
+		// against the MAX_HAVES limit.
+		fetchState.havesWithoutAck += n;
+		output.end();
+		fetchState.incHavesToSend(statelessRPC);
+		return false;
+	}
+
+	/**
+	 * Reads and processes acknowledgments, adding ACKed objects as "have"s to
+	 * the global state {@link TemporaryBuffer}.
+	 *
+	 * @param fetchState
+	 *            to update
+	 * @param input
+	 *            to read from
+	 * @param monitor
+	 *            for progress reporting and cancellation
+	 * @return {@code true} if a "ready" was received and a packfile is expected
+	 *         next
+	 * @throws IOException
+	 *             on errors
+	 * @throws CancelledException
+	 *             on cancellation
+	 */
+	private boolean readAcknowledgments(FetchStateV2 fetchState,
+			PacketLineIn input, ProgressMonitor monitor)
+			throws IOException, CancelledException {
+		String line = input.readString();
+		if (!GitProtocolConstants.SECTION_ACKNOWLEDGMENTS.equals(line)) {
+			throw new PackProtocolException(MessageFormat.format(
+					JGitText.get().expectedGot,
+					GitProtocolConstants.SECTION_ACKNOWLEDGMENTS, line));
+		}
+		MutableObjectId returnedId = new MutableObjectId();
+		line = input.readString();
+		boolean gotReady = false;
+		long n = 0;
+		while (!PacketLineIn.isEnd(line) && !PacketLineIn.isDelimiter(line)) {
+			AckNackResult ack = PacketLineIn.parseACKv2(line, returnedId);
+			// If we got a "ready", we just skip the remaining lines after
+			// having checked them for being valid. (Normally, the "ready"
+			// should be the last line anyway.)
+			if (!gotReady) {
+				if (ack == AckNackResult.ACK_COMMON) {
+					// markCommon appends the object to the "state"
+					markCommon(walk.parseAny(returnedId), ack, true);
+					fetchState.havesWithoutAck = 0;
+					fetchState.hadAcks = true;
+				} else if (ack == AckNackResult.ACK_READY) {
+					gotReady = true;
+				}
+			}
+			n++;
+			if (n % 10 == 0 && monitor.isCancelled()) {
+				throw new CancelledException();
+			}
+			line = input.readString();
+		}
+		if (gotReady) {
+			if (!PacketLineIn.isDelimiter(line)) {
+				throw new PackProtocolException(MessageFormat
+						.format(JGitText.get().expectedGot, "0001", line)); //$NON-NLS-1$
+			}
+		} else if (!PacketLineIn.isEnd(line)) {
+			throw new PackProtocolException(MessageFormat
+					.format(JGitText.get().expectedGot, "0000", line)); //$NON-NLS-1$
+		}
+		return gotReady;
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
@@ -456,8 +665,8 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		}
 	}
 
-	private boolean sendWants(Collection<Ref> want) throws IOException {
-		final PacketLineOut p = statelessRPC ? pckState : pckOut;
+	private boolean sendWants(Collection<Ref> want, PacketLineOut p)
+			throws IOException {
 		boolean first = true;
 		for (Ref r : want) {
 			ObjectId objectId = r.getObjectId();
@@ -479,10 +688,11 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 			final StringBuilder line = new StringBuilder(46);
 			line.append("want "); //$NON-NLS-1$
 			line.append(objectId.name());
-			if (first) {
+			if (first && TransferConfig.ProtocolVersion.V0
+					.equals(getProtocolVersion())) {
 				line.append(enableCapabilities());
-				first = false;
 			}
+			first = false;
 			line.append('\n');
 			p.writeString(line.toString());
 		}
@@ -492,11 +702,34 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		if (!filterSpec.isNoOp()) {
 			p.writeString(filterSpec.filterLine());
 		}
-		p.end();
-		outNeedsEnd = false;
 		return true;
 	}
 
+	private Set<String> getCapabilitiesV2(Set<String> advertisedCapabilities)
+			throws TransportException {
+		Set<String> capabilities = new LinkedHashSet<>();
+		// Protocol V2 is implicitly capable of all these.
+		if (noProgress) {
+			capabilities.add(OPTION_NO_PROGRESS);
+		}
+		if (includeTags) {
+			capabilities.add(OPTION_INCLUDE_TAG);
+		}
+		if (allowOfsDelta) {
+			capabilities.add(OPTION_OFS_DELTA);
+		}
+		if (thinPack) {
+			capabilities.add(OPTION_THIN_PACK);
+		}
+		if (!filterSpec.isNoOp()
+				&& !advertisedCapabilities.contains(OPTION_FILTER)) {
+			throw new PackProtocolException(uri,
+					JGitText.get().filterRequiresCapability);
+		}
+		// The FilterSpec will be added later in sendWants().
+		return capabilities;
+	}
+
 	private String enableCapabilities() throws TransportException {
 		final StringBuilder line = new StringBuilder();
 		if (noProgress)
@@ -622,7 +855,7 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 					// we need to continue to talk about other parts of
 					// our local history.
 					//
-					markCommon(walk.parseAny(ackId), anr);
+					markCommon(walk.parseAny(ackId), anr, statelessRPC);
 					receivedAck = true;
 					receivedContinue = true;
 					havesSinceLastContinue = 0;
@@ -757,16 +990,10 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		}
 	}
 
-	private void markCommon(RevObject obj, AckNackResult anr)
+	private void markCommon(RevObject obj, AckNackResult anr, boolean useState)
 			throws IOException {
-		if (statelessRPC && anr == AckNackResult.ACK_COMMON && !obj.has(STATE)) {
-			StringBuilder s;
-
-			s = new StringBuilder(6 + Constants.OBJECT_ID_STRING_LENGTH);
-			s.append("have "); //$NON-NLS-1$
-			s.append(obj.name());
-			s.append('\n');
-			pckState.writeString(s.toString());
+		if (useState && anr == AckNackResult.ACK_COMMON && !obj.has(STATE)) {
+			pckState.writeString("have " + obj.name() + '\n'); //$NON-NLS-1$
 			obj.add(STATE);
 		}
 		obj.add(COMMON);
@@ -806,4 +1033,31 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 	private static class CancelledException extends Exception {
 		private static final long serialVersionUID = 1L;
 	}
+
+	private static class FetchStateV2 {
+
+		long havesToSend = 32;
+
+		long havesTotal;
+
+		// Set to true if we got at least one ACK in protocol V2.
+		boolean hadAcks;
+
+		// Counts haves without ACK. Use as cutoff for negotiation only once
+		// hadAcks == true.
+		long havesWithoutAck;
+
+		void incHavesToSend(boolean statelessRPC) {
+			if (statelessRPC) {
+				// Increase this quicker since connection setup costs accumulate
+				if (havesToSend < 16384) {
+					havesToSend *= 2;
+				} else {
+					havesToSend = havesToSend * 11 / 10;
+				}
+			} else {
+				havesToSend += 32;
+			}
+		}
+	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java
index 0f1892a97e..34bad6e029 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -48,6 +48,7 @@ import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RefDatabase;
 import org.eclipse.jgit.revwalk.ObjectWalk;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.util.StringUtils;
 
 class FetchProcess {
 	/** Transport we will fetch over. */
@@ -79,7 +80,8 @@ class FetchProcess {
 		toFetch = f;
 	}
 
-	void execute(ProgressMonitor monitor, FetchResult result)
+	void execute(ProgressMonitor monitor, FetchResult result,
+			String initialBranch)
 			throws NotSupportedException, TransportException {
 		askFor.clear();
 		localUpdates.clear();
@@ -87,24 +89,64 @@ class FetchProcess {
 		packLocks.clear();
 		localRefs = null;
 
+		Throwable e1 = null;
 		try {
-			executeImp(monitor, result);
+			executeImp(monitor, result, initialBranch);
+		} catch (NotSupportedException | TransportException err) {
+			e1 = err;
+			throw err;
 		} finally {
 			try {
-			for (PackLock lock : packLocks)
-				lock.unlock();
+				for (PackLock lock : packLocks) {
+					lock.unlock();
+				}
 			} catch (IOException e) {
+				if (e1 != null) {
+					e.addSuppressed(e1);
+				}
 				throw new TransportException(e.getMessage(), e);
 			}
 		}
 	}
 
+	private boolean isInitialBranchMissing(Map<String, Ref> refsMap,
+			String initialBranch) {
+		if (StringUtils.isEmptyOrNull(initialBranch) || refsMap.isEmpty()) {
+			return false;
+		}
+		if (refsMap.containsKey(initialBranch)
+				|| refsMap.containsKey(Constants.R_HEADS + initialBranch)
+				|| refsMap.containsKey(Constants.R_TAGS + initialBranch)) {
+			return false;
+		}
+		return true;
+	}
+
 	private void executeImp(final ProgressMonitor monitor,
-			final FetchResult result) throws NotSupportedException,
-			TransportException {
-		conn = transport.openFetch();
+			final FetchResult result, String initialBranch)
+			throws NotSupportedException, TransportException {
+		final TagOpt tagopt = transport.getTagOpt();
+		String getTags = (tagopt == TagOpt.NO_TAGS) ? null : Constants.R_TAGS;
+		String getHead = null;
+		try {
+			// If we don't have a HEAD yet, we're cloning and need to get the
+			// upstream HEAD, too.
+			Ref head = transport.local.exactRef(Constants.HEAD);
+			ObjectId id = head != null ? head.getObjectId() : null;
+			if (id == null || id.equals(ObjectId.zeroId())) {
+				getHead = Constants.HEAD;
+			}
+		} catch (IOException e) {
+			// Ignore
+		}
+		conn = transport.openFetch(toFetch, getTags, getHead);
 		try {
-			result.setAdvertisedRefs(transport.getURI(), conn.getRefsMap());
+			Map<String, Ref> refsMap = conn.getRefsMap();
+			if (isInitialBranchMissing(refsMap, initialBranch)) {
+				throw new TransportException(MessageFormat.format(
+						JGitText.get().remoteBranchNotFound, initialBranch));
+			}
+			result.setAdvertisedRefs(transport.getURI(), refsMap);
 			result.peerUserAgent = conn.getPeerUserAgent();
 			final Set<Ref> matched = new HashSet<>();
 			for (RefSpec spec : toFetch) {
@@ -119,7 +161,6 @@ class FetchProcess {
 			}
 
 			Collection<Ref> additionalTags = Collections.<Ref> emptyList();
-			final TagOpt tagopt = transport.getTagOpt();
 			if (tagopt == TagOpt.AUTO_FOLLOW)
 				additionalTags = expandAutoFollowTags();
 			else if (tagopt == TagOpt.FETCH_TAGS)
@@ -253,7 +294,17 @@ class FetchProcess {
 		if (conn != null)
 			return;
 
-		conn = transport.openFetch();
+		// Build prefixes
+		Set<String> prefixes = new HashSet<>();
+		for (Ref toGet : askFor.values()) {
+			String src = toGet.getName();
+			prefixes.add(src);
+			prefixes.add(Constants.R_REFS + src);
+			prefixes.add(Constants.R_HEADS + src);
+			prefixes.add(Constants.R_TAGS + src);
+		}
+		conn = transport.openFetch(Collections.emptyList(),
+				prefixes.toArray(new String[0]));
 
 		// Since we opened a new connection we cannot be certain
 		// that the system we connected to has the same exact set
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/GitProtocolConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/GitProtocolConstants.java
index 35e2978bc4..36fce7a3f5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/GitProtocolConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/GitProtocolConstants.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (C) 2008-2013, Google Inc.
+ * Copyright (C) 2008, 2013 Google Inc.
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -247,6 +247,74 @@ public final class GitProtocolConstants {
 	 */
 	public static final String COMMAND_FETCH = "fetch"; //$NON-NLS-1$
 
+	/**
+	 * HTTP header to set by clients to request a specific git protocol version
+	 * in the HTTP transport.
+	 *
+	 * @since 5.11
+	 */
+	public static final String PROTOCOL_HEADER = "Git-Protocol"; //$NON-NLS-1$
+
+	/**
+	 * Environment variable to set by clients to request a specific git protocol
+	 * in the file:// and ssh:// transports.
+	 *
+	 * @since 5.11
+	 */
+	public static final String PROTOCOL_ENVIRONMENT_VARIABLE = "GIT_PROTOCOL"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 ref advertisement attribute containing the peeled object id
+	 * for annotated tags.
+	 *
+	 * @since 5.11
+	 */
+	public static final String REF_ATTR_PEELED = "peeled:"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 ref advertisement attribute containing the name of the ref
+	 * for symbolic refs.
+	 *
+	 * @since 5.11
+	 */
+	public static final String REF_ATTR_SYMREF_TARGET = "symref-target:"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 acknowledgments section header.
+	 *
+	 * @since 5.11
+	 */
+	public static final String SECTION_ACKNOWLEDGMENTS = "acknowledgments"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 packfile section header.
+	 *
+	 * @since 5.11
+	 */
+	public static final String SECTION_PACKFILE = "packfile"; //$NON-NLS-1$
+
+	/**
+	 * Protocol announcement for protocol version 1. This is the same as V0,
+	 * except for this initial line.
+	 *
+	 * @since 5.11
+	 */
+	public static final String VERSION_1 = "version 1"; //$NON-NLS-1$
+
+	/**
+	 * Protocol announcement for protocol version 2.
+	 *
+	 * @since 5.11
+	 */
+	public static final String VERSION_2 = "version 2"; //$NON-NLS-1$
+
+	/**
+	 * Protocol request for protocol version 2.
+	 *
+	 * @since 5.11
+	 */
+	public static final String VERSION_2_REQUEST = "version=2"; //$NON-NLS-1$
+
 	enum MultiAck {
 		OFF, CONTINUE, DETAILED;
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/HttpTransport.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/HttpTransport.java
index 49c8b587d7..febeb3ce9c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/HttpTransport.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/HttpTransport.java
@@ -26,7 +26,7 @@ public abstract class HttpTransport extends Transport {
 	 *
 	 * @since 3.3
 	 */
-	protected static HttpConnectionFactory connectionFactory = new JDKHttpConnectionFactory();
+	protected static volatile HttpConnectionFactory connectionFactory = new JDKHttpConnectionFactory();
 
 	/**
 	 * Get the {@link org.eclipse.jgit.transport.http.HttpConnectionFactory}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
index 350311ecc8..68c5b348ad 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
@@ -103,6 +103,38 @@ public class PacketLineIn {
 		this.limit = limit;
 	}
 
+	/**
+	 * Parses a ACK/NAK line in protocol V2.
+	 *
+	 * @param line
+	 *            to parse
+	 * @param returnedId
+	 *            in case of {@link AckNackResult#ACK_COMMON ACK_COMMON}
+	 * @return one of {@link AckNackResult#NAK NAK},
+	 *         {@link AckNackResult#ACK_COMMON ACK_COMMON}, or
+	 *         {@link AckNackResult#ACK_READY ACK_READY}
+	 * @throws IOException
+	 *             on protocol or transport errors
+	 */
+	static AckNackResult parseACKv2(String line, MutableObjectId returnedId)
+			throws IOException {
+		if ("NAK".equals(line)) { //$NON-NLS-1$
+			return AckNackResult.NAK;
+		}
+		if (line.startsWith("ACK ") && line.length() == 44) { //$NON-NLS-1$
+			returnedId.fromString(line.substring(4, 44));
+			return AckNackResult.ACK_COMMON;
+		}
+		if ("ready".equals(line)) { //$NON-NLS-1$
+			return AckNackResult.ACK_READY;
+		}
+		if (line.startsWith("ERR ")) { //$NON-NLS-1$
+			throw new PackProtocolException(line.substring(4));
+		}
+		throw new PackProtocolException(
+				MessageFormat.format(JGitText.get().expectedACKNAKGot, line));
+	}
+
 	AckNackResult readACK(MutableObjectId returnedId) throws IOException {
 		final String line = readString();
 		if (line.length() == 0)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineOut.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineOut.java
index 6fc2042e1f..77f0a7a516 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineOut.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineOut.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (C) 2008-2010, Google Inc.
- * Copyright (C) 2008-2009, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2010 Google Inc.
+ * Copyright (C) 2008, 2009 Robin Rosenberg <robin.rosenberg@dewire.com>
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -33,12 +33,15 @@ import org.slf4j.LoggerFactory;
  * against the underlying OutputStream.
  */
 public class PacketLineOut {
+
 	private static final Logger log = LoggerFactory.getLogger(PacketLineOut.class);
 
 	private final OutputStream out;
 
 	private final byte[] lenbuffer;
 
+	private final boolean logEnabled;
+
 	private boolean flushOnEnd;
 
 	private boolean usingSideband;
@@ -50,9 +53,24 @@ public class PacketLineOut {
 	 *            stream.
 	 */
 	public PacketLineOut(OutputStream outputStream) {
+		this(outputStream, true);
+	}
+
+	/**
+	 * Create a new packet line writer that potentially doesn't log.
+	 *
+	 * @param outputStream
+	 *            stream.
+	 * @param enableLogging
+	 *            {@code false} to suppress all logging; {@code true} to log
+	 *            normally
+	 * @since 5.11
+	 */
+	public PacketLineOut(OutputStream outputStream, boolean enableLogging) {
 		out = outputStream;
 		lenbuffer = new byte[5];
 		flushOnEnd = true;
+		logEnabled = enableLogging;
 	}
 
 	/**
@@ -139,9 +157,15 @@ public class PacketLineOut {
 			out.write(lenbuffer, 0, 4);
 		}
 		out.write(buf, pos, len);
-		if (log.isDebugEnabled()) {
-			String s = RawParseUtils.decode(UTF_8, buf, pos, len);
-			log.debug("git> " + s); //$NON-NLS-1$
+		if (logEnabled && log.isDebugEnabled()) {
+			// Escape a trailing \n to avoid empty lines in the log.
+			if (len > 0 && buf[pos + len - 1] == '\n') {
+				log.debug(
+						"git> " + RawParseUtils.decode(UTF_8, buf, pos, len - 1) //$NON-NLS-1$
+								+ "\\n"); //$NON-NLS-1$
+			} else {
+				log.debug("git> " + RawParseUtils.decode(UTF_8, buf, pos, len)); //$NON-NLS-1$
+			}
 		}
 	}
 
@@ -156,7 +180,9 @@ public class PacketLineOut {
 	public void writeDelim() throws IOException {
 		formatLength(1);
 		out.write(lenbuffer, 0, 4);
-		log.debug("git> 0001"); //$NON-NLS-1$
+		if (logEnabled && log.isDebugEnabled()) {
+			log.debug("git> 0001"); //$NON-NLS-1$
+		}
 	}
 
 	/**
@@ -175,9 +201,12 @@ public class PacketLineOut {
 	public void end() throws IOException {
 		formatLength(0);
 		out.write(lenbuffer, 0, 4);
-		log.debug("git> 0000"); //$NON-NLS-1$
-		if (flushOnEnd)
+		if (logEnabled && log.isDebugEnabled()) {
+			log.debug("git> 0000"); //$NON-NLS-1$
+		}
+		if (flushOnEnd) {
 			flush();
+		}
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
index 3adebba03c..c525e66848 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2010, Google Inc. and others
+ * Copyright (C) 2008, 2020 Google Inc. and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -13,6 +13,8 @@ package org.eclipse.jgit.transport;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SYMREF;
+import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_PEELED;
+import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_SYMREF_TARGET;
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -287,7 +289,8 @@ public abstract class RefAdvertiser {
 
 			if (useProtocolV2) {
 				String symrefPart = symrefs.containsKey(ref.getName())
-						? (" symref-target:" + symrefs.get(ref.getName())) //$NON-NLS-1$
+						? (' ' + REF_ATTR_SYMREF_TARGET
+								+ symrefs.get(ref.getName()))
 						: ""; //$NON-NLS-1$
 				String peelPart = ""; //$NON-NLS-1$
 				if (derefTags) {
@@ -296,7 +299,8 @@ public abstract class RefAdvertiser {
 					}
 					ObjectId peeledObjectId = ref.getPeeledObjectId();
 					if (peeledObjectId != null) {
-						peelPart = " peeled:" + peeledObjectId.getName(); //$NON-NLS-1$
+						peelPart = ' ' + REF_ATTR_PEELED
+								+ peeledObjectId.getName();
 					}
 				}
 				writeOne(objectId.getName() + " " + ref.getName() + symrefPart //$NON-NLS-1$
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RemoteSession2.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RemoteSession2.java
new file mode 100644
index 0000000000..23f670ae25
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RemoteSession2.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2020, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.transport;
+
+import java.io.IOException;
+import java.util.Map;
+
+/**
+ * A {@link RemoteSession} that supports passing environment variables to
+ * commands.
+ *
+ * @since 5.11
+ */
+public interface RemoteSession2 extends RemoteSession {
+
+	/**
+	 * Creates a new remote {@link Process} to execute the given command. The
+	 * returned process's streams exist and are connected, and execution of the
+	 * process is already started.
+	 *
+	 * @param commandName
+	 *            command to execute
+	 * @param environment
+	 *            environment variables to pass on
+	 * @param timeout
+	 *            timeout value, in seconds, for creating the remote process
+	 * @return a new remote process, already started
+	 * @throws java.io.IOException
+	 *             may be thrown in several cases. For example, on problems
+	 *             opening input or output streams or on problems connecting or
+	 *             communicating with the remote host. For the latter two cases,
+	 *             a TransportException may be thrown (a subclass of
+	 *             java.io.IOException).
+	 */
+	Process exec(String commandName, Map<String, String> environment,
+			int timeout) throws IOException;
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransferConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransferConfig.java
index cc577fa11e..83ffd4123a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransferConfig.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransferConfig.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2009, Google Inc. and others
+ * Copyright (C) 2008, 2020 Google Inc. and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -21,6 +21,7 @@ import java.util.Map;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.internal.storage.file.LazyObjectIdSetFile;
 import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Config.SectionParser;
 import org.eclipse.jgit.lib.ObjectChecker;
 import org.eclipse.jgit.lib.ObjectIdSet;
@@ -60,11 +61,19 @@ public class TransferConfig {
 	}
 
 	/**
-	 * A git configuration variable for which versions of the Git protocol to prefer.
-	 * Used in protocol.version.
+	 * A git configuration variable for which versions of the Git protocol to
+	 * prefer. Used in protocol.version.
+	 *
+	 * @since 5.9
 	 */
-	enum ProtocolVersion {
+	public enum ProtocolVersion {
+		/**
+		 * Git wire protocol version 0 (the default).
+		 */
 		V0("0"), //$NON-NLS-1$
+		/**
+		 * Git wire protocol version 2.
+		 */
 		V2("2"); //$NON-NLS-1$
 
 		final String name;
@@ -73,6 +82,15 @@ public class TransferConfig {
 			this.name = name;
 		}
 
+		/**
+		 * Returns version number
+		 *
+		 * @return string version
+		 */
+		public String version() {
+			return name;
+		}
+
 		@Nullable
 		static ProtocolVersion parse(@Nullable String name) {
 			if (name == null) {
@@ -83,6 +101,9 @@ public class TransferConfig {
 					return v;
 				}
 			}
+			if ("1".equals(name)) { //$NON-NLS-1$
+				return V0;
+			}
 			return null;
 		}
 	}
@@ -177,7 +198,9 @@ public class TransferConfig {
 				"uploadpack", "allowreachablesha1inwant", false);
 		allowFilter = rc.getBoolean(
 				"uploadpack", "allowfilter", false);
-		protocolVersion = ProtocolVersion.parse(rc.getString("protocol", null, "version"));
+		protocolVersion = ProtocolVersion.parse(rc
+				.getString(ConfigConstants.CONFIG_PROTOCOL_SECTION, null,
+						ConfigConstants.CONFIG_KEY_VERSION));
 		hideRefs = rc.getStringList("uploadpack", null, "hiderefs");
 		allowSidebandAll = rc.getBoolean(
 				"uploadpack", "allowsidebandall", false);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/Transport.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/Transport.java
index 2ddd0a6128..5b781ac25f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/Transport.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/Transport.java
@@ -1,8 +1,8 @@
 /*
- * Copyright (C) 2008-2009, Google Inc.
+ * Copyright (C) 2008, 2009 Google Inc.
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -39,6 +39,7 @@ import java.util.Vector;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.api.errors.AbortedByHookException;
 import org.eclipse.jgit.errors.NotSupportedException;
 import org.eclipse.jgit.errors.TransportException;
@@ -774,6 +775,10 @@ public abstract class Transport implements AutoCloseable {
 	private PrintStream hookOutRedirect;
 
 	private PrePushHook prePush;
+
+	@Nullable
+	TransferConfig.ProtocolVersion protocol;
+
 	/**
 	 * Create a new transport instance.
 	 *
@@ -789,6 +794,7 @@ public abstract class Transport implements AutoCloseable {
 		final TransferConfig tc = local.getConfig().get(TransferConfig.KEY);
 		this.local = local;
 		this.uri = uri;
+		this.protocol = tc.protocolVersion;
 		this.objectChecker = tc.newObjectChecker();
 		this.credentialsProvider = CredentialsProvider.getDefault();
 		prePush = Hooks.prePush(local, hookOutRedirect);
@@ -1225,9 +1231,52 @@ public abstract class Transport implements AutoCloseable {
 	 *             the remote connection could not be established or object
 	 *             copying (if necessary) failed or update specification was
 	 *             incorrect.
+	 * @since 5.11
+	 */
+	public FetchResult fetch(final ProgressMonitor monitor,
+			Collection<RefSpec> toFetch)
+			throws NotSupportedException, TransportException {
+		return fetch(monitor, toFetch, null);
+	}
+
+	/**
+	 * Fetch objects and refs from the remote repository to the local one.
+	 * <p>
+	 * This is a utility function providing standard fetch behavior. Local
+	 * tracking refs associated with the remote repository are automatically
+	 * updated if this transport was created from a
+	 * {@link org.eclipse.jgit.transport.RemoteConfig} with fetch RefSpecs
+	 * defined.
+	 *
+	 * @param monitor
+	 *            progress monitor to inform the user about our processing
+	 *            activity. Must not be null. Use
+	 *            {@link org.eclipse.jgit.lib.NullProgressMonitor} if progress
+	 *            updates are not interesting or necessary.
+	 * @param toFetch
+	 *            specification of refs to fetch locally. May be null or the
+	 *            empty collection to use the specifications from the
+	 *            RemoteConfig. Source for each RefSpec can't be null.
+	 * @param branch
+	 *            the initial branch to check out when cloning the repository.
+	 *            Can be specified as ref name (<code>refs/heads/master</code>),
+	 *            branch name (<code>master</code>) or tag name
+	 *            (<code>v1.2.3</code>). The default is to use the branch
+	 *            pointed to by the cloned repository's HEAD and can be
+	 *            requested by passing {@code null} or <code>HEAD</code>.
+	 * @return information describing the tracking refs updated.
+	 * @throws org.eclipse.jgit.errors.NotSupportedException
+	 *             this transport implementation does not support fetching
+	 *             objects.
+	 * @throws org.eclipse.jgit.errors.TransportException
+	 *             the remote connection could not be established or object
+	 *             copying (if necessary) failed or update specification was
+	 *             incorrect.
+	 * @since 5.11
 	 */
 	public FetchResult fetch(final ProgressMonitor monitor,
-			Collection<RefSpec> toFetch) throws NotSupportedException,
+			Collection<RefSpec> toFetch, String branch)
+			throws NotSupportedException,
 			TransportException {
 		if (toFetch == null || toFetch.isEmpty()) {
 			// If the caller did not ask for anything use the defaults.
@@ -1257,7 +1306,7 @@ public abstract class Transport implements AutoCloseable {
 		}
 
 		final FetchResult result = new FetchResult();
-		new FetchProcess(this, toFetch).execute(monitor, result);
+		new FetchProcess(this, toFetch).execute(monitor, result, branch);
 
 		local.autoGC(monitor);
 
@@ -1453,6 +1502,43 @@ public abstract class Transport implements AutoCloseable {
 			TransportException;
 
 	/**
+	 * Begins a new connection for fetching from the remote repository.
+	 * <p>
+	 * If the transport has no local repository, the fetch connection can only
+	 * be used for reading remote refs.
+	 * </p>
+	 * <p>
+	 * If the server supports git protocol V2, the {@link RefSpec}s and the
+	 * additional patterns, if any, are used to restrict the server's ref
+	 * advertisement to matching refs only.
+	 * </p>
+	 * <p>
+	 * Transports that want to support git protocol V2 <em>must</em> override
+	 * this; the default implementation ignores its arguments and calls
+	 * {@link #openFetch()}.
+	 * </p>
+	 *
+	 * @param refSpecs
+	 *            that will be fetched via
+	 *            {@link FetchConnection#fetch(ProgressMonitor, Collection, java.util.Set, OutputStream)} later
+	 * @param additionalPatterns
+	 *            that will be set as ref prefixes if the server supports git
+	 *            protocol V2; {@code null} values are ignored
+	 *
+	 * @return a fresh connection to fetch from the remote repository.
+	 * @throws org.eclipse.jgit.errors.NotSupportedException
+	 *             the implementation does not support fetching.
+	 * @throws org.eclipse.jgit.errors.TransportException
+	 *             the remote connection could not be established.
+	 * @since 5.11
+	 */
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns)
+			throws NotSupportedException, TransportException {
+		return openFetch();
+	}
+
+	/**
 	 * Begins a new connection for pushing into the remote repository.
 	 *
 	 * @return a fresh connection to push into the remote repository.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitAnon.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitAnon.java
index 820ec1a67a..a1914b6182 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitAnon.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitAnon.java
@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -22,6 +22,7 @@ import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.Socket;
 import java.net.UnknownHostException;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.Set;
@@ -94,6 +95,13 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 		return new TcpFetchConnection();
 	}
 
+	@Override
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns)
+			throws NotSupportedException, TransportException {
+		return new TcpFetchConnection(refSpecs, additionalPatterns);
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public PushConnection openPush() throws TransportException {
@@ -113,7 +121,6 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 		final Socket s = new Socket();
 		try {
 			final InetAddress host = InetAddress.getByName(uri.getHost());
-			s.bind(null);
 			s.connect(new InetSocketAddress(host, port), tms);
 		} catch (IOException c) {
 			try {
@@ -130,7 +137,8 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 		return s;
 	}
 
-	void service(String name, PacketLineOut pckOut)
+	void service(String name, PacketLineOut pckOut,
+			TransferConfig.ProtocolVersion gitProtocol)
 			throws IOException {
 		final StringBuilder cmd = new StringBuilder();
 		cmd.append(name);
@@ -144,6 +152,11 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 			cmd.append(uri.getPort());
 		}
 		cmd.append('\0');
+		if (TransferConfig.ProtocolVersion.V2.equals(gitProtocol)) {
+			cmd.append('\0');
+			cmd.append(GitProtocolConstants.VERSION_2_REQUEST);
+			cmd.append('\0');
+		}
 		pckOut.writeString(cmd.toString());
 		pckOut.flush();
 	}
@@ -152,6 +165,11 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 		private Socket sock;
 
 		TcpFetchConnection() throws TransportException {
+			this(Collections.emptyList());
+		}
+
+		TcpFetchConnection(Collection<RefSpec> refSpecs,
+				String... additionalPatterns) throws TransportException {
 			super(TransportGitAnon.this);
 			sock = openConnection();
 			try {
@@ -162,13 +180,19 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 				sOut = new BufferedOutputStream(sOut);
 
 				init(sIn, sOut);
-				service("git-upload-pack", pckOut); //$NON-NLS-1$
+				TransferConfig.ProtocolVersion gitProtocol = protocol;
+				if (gitProtocol == null) {
+					gitProtocol = TransferConfig.ProtocolVersion.V2;
+				}
+				service("git-upload-pack", pckOut, gitProtocol); //$NON-NLS-1$
 			} catch (IOException err) {
 				close();
 				throw new TransportException(uri,
 						JGitText.get().remoteHungUpUnexpectedly, err);
 			}
-			readAdvertisedRefs();
+			if (!readAdvertisedRefs()) {
+				lsRefs(refSpecs, additionalPatterns);
+			}
 		}
 
 		@Override
@@ -201,7 +225,7 @@ class TransportGitAnon extends TcpTransport implements PackTransport {
 				sOut = new BufferedOutputStream(sOut);
 
 				init(sIn, sOut);
-				service("git-receive-pack", pckOut); //$NON-NLS-1$
+				service("git-receive-pack", pckOut, null); //$NON-NLS-1$
 			} catch (IOException err) {
 				close();
 				throw new TransportException(uri,
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitSsh.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitSsh.java
index b9cb2484d8..19ed4fbcc1 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitSsh.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitSsh.java
@@ -1,8 +1,8 @@
 /*
- * Copyright (C) 2008-2010, Google Inc.
+ * Copyright (C) 2008, 2010 Google Inc.
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -19,11 +19,13 @@ import java.io.InputStream;
 import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Set;
 
 import org.eclipse.jgit.errors.NoRemoteRepositoryException;
@@ -144,6 +146,13 @@ public class TransportGitSsh extends SshTransport implements PackTransport {
 		return new SshFetchConnection();
 	}
 
+	@Override
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns)
+			throws NotSupportedException, TransportException {
+		return new SshFetchConnection(refSpecs, additionalPatterns);
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public PushConnection openPush() throws TransportException {
@@ -196,29 +205,38 @@ public class TransportGitSsh extends SshTransport implements PackTransport {
 		return SystemReader.getInstance().getenv("GIT_SSH") != null; //$NON-NLS-1$
 	}
 
-	private class ExtSession implements RemoteSession {
+	private class ExtSession implements RemoteSession2 {
+
 		@Override
 		public Process exec(String command, int timeout)
 				throws TransportException {
+			return exec(command, null, timeout);
+		}
+
+		@Override
+		public Process exec(String command, Map<String, String> environment,
+				int timeout) throws TransportException {
 			String ssh = SystemReader.getInstance().getenv("GIT_SSH"); //$NON-NLS-1$
 			boolean putty = ssh.toLowerCase(Locale.ROOT).contains("plink"); //$NON-NLS-1$
 
 			List<String> args = new ArrayList<>();
 			args.add(ssh);
-			if (putty
-					&& !ssh.toLowerCase(Locale.ROOT).contains("tortoiseplink")) //$NON-NLS-1$
+			if (putty && !ssh.toLowerCase(Locale.ROOT)
+					.contains("tortoiseplink")) {//$NON-NLS-1$
 				args.add("-batch"); //$NON-NLS-1$
+			}
 			if (0 < getURI().getPort()) {
 				args.add(putty ? "-P" : "-p"); //$NON-NLS-1$ //$NON-NLS-2$
 				args.add(String.valueOf(getURI().getPort()));
 			}
-			if (getURI().getUser() != null)
+			if (getURI().getUser() != null) {
 				args.add(getURI().getUser() + "@" + getURI().getHost()); //$NON-NLS-1$
-			else
+			} else {
 				args.add(getURI().getHost());
+			}
 			args.add(command);
 
-			ProcessBuilder pb = createProcess(args);
+			ProcessBuilder pb = createProcess(args, environment);
 			try {
 				return pb.start();
 			} catch (IOException err) {
@@ -226,9 +244,13 @@ public class TransportGitSsh extends SshTransport implements PackTransport {
 			}
 		}
 
-		private ProcessBuilder createProcess(List<String> args) {
+		private ProcessBuilder createProcess(List<String> args,
+				Map<String, String> environment) {
 			ProcessBuilder pb = new ProcessBuilder();
 			pb.command(args);
+			if (environment != null) {
+				pb.environment().putAll(environment);
+			}
 			File directory = local != null ? local.getDirectory() : null;
 			if (directory != null) {
 				pb.environment().put(Constants.GIT_DIR_KEY,
@@ -249,10 +271,31 @@ public class TransportGitSsh extends SshTransport implements PackTransport {
 		private StreamCopyThread errorThread;
 
 		SshFetchConnection() throws TransportException {
+			this(Collections.emptyList());
+		}
+
+		SshFetchConnection(Collection<RefSpec> refSpecs,
+				String... additionalPatterns) throws TransportException {
 			super(TransportGitSsh.this);
 			try {
-				process = getSession().exec(commandFor(getOptionUploadPack()),
-						getTimeout());
+				RemoteSession session = getSession();
+				TransferConfig.ProtocolVersion gitProtocol = protocol;
+				if (gitProtocol == null) {
+					gitProtocol = TransferConfig.ProtocolVersion.V2;
+				}
+				if (session instanceof RemoteSession2
+						&& TransferConfig.ProtocolVersion.V2
+								.equals(gitProtocol)) {
+					process = ((RemoteSession2) session).exec(
+							commandFor(getOptionUploadPack()), Collections
+									.singletonMap(
+											GitProtocolConstants.PROTOCOL_ENVIRONMENT_VARIABLE,
+											GitProtocolConstants.VERSION_2_REQUEST),
+							getTimeout());
+				} else {
+					process = session.exec(commandFor(getOptionUploadPack()),
+							getTimeout());
+				}
 				final MessageWriter msg = new MessageWriter();
 				setMessageWriter(msg);
 
@@ -272,7 +315,9 @@ public class TransportGitSsh extends SshTransport implements PackTransport {
 			}
 
 			try {
-				readAdvertisedRefs();
+				if (!readAdvertisedRefs()) {
+					lsRefs(refSpecs, additionalPatterns);
+				}
 			} catch (NoRemoteRepositoryException notFound) {
 				final String msgs = getMessages();
 				checkExecFailure(process.exitValue(), getOptionUploadPack(),
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java
index 6768387e65..2e5d18dc15 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java
@@ -1,8 +1,8 @@
 /*
- * Copyright (C) 2008-2010, Google Inc.
+ * Copyright (C) 2008, 2010 Google Inc.
  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
  * Copyright (C) 2013, Matthias Sohn <matthias.sohn@sap.com>
- * Copyright (C) 2017, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ * Copyright (C) 2017, 2020 Thomas Wolf <thomas.wolf@paranor.ch> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -33,14 +33,15 @@ import static org.eclipse.jgit.util.HttpSupport.HDR_WWW_AUTHENTICATE;
 import static org.eclipse.jgit.util.HttpSupport.METHOD_GET;
 import static org.eclipse.jgit.util.HttpSupport.METHOD_POST;
 
+import java.io.BufferedInputStream;
 import java.io.BufferedReader;
-import java.io.ByteArrayInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.InterruptedIOException;
 import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
 import java.net.HttpCookie;
 import java.net.MalformedURLException;
 import java.net.Proxy;
@@ -49,10 +50,12 @@ import java.net.SocketException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.security.GeneralSecurityException;
 import java.security.cert.CertPathBuilderException;
 import java.security.cert.CertPathValidatorException;
 import java.security.cert.CertificateException;
@@ -75,6 +78,7 @@ import java.util.zip.GZIPOutputStream;
 
 import javax.net.ssl.SSLHandshakeException;
 
+import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.errors.NoRemoteRepositoryException;
 import org.eclipse.jgit.errors.NotSupportedException;
@@ -95,6 +99,8 @@ import org.eclipse.jgit.lib.SymbolicRef;
 import org.eclipse.jgit.transport.HttpAuthMethod.Type;
 import org.eclipse.jgit.transport.HttpConfig.HttpRedirectMode;
 import org.eclipse.jgit.transport.http.HttpConnection;
+import org.eclipse.jgit.transport.http.HttpConnectionFactory;
+import org.eclipse.jgit.transport.http.HttpConnectionFactory2;
 import org.eclipse.jgit.util.HttpSupport;
 import org.eclipse.jgit.util.IO;
 import org.eclipse.jgit.util.RawParseUtils;
@@ -132,6 +138,9 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	private static final String SVC_RECEIVE_PACK = "git-receive-pack"; //$NON-NLS-1$
 
+	private static final byte[] VERSION = "version" //$NON-NLS-1$
+			.getBytes(StandardCharsets.US_ASCII);
+
 	/**
 	 * Accept-Encoding header in the HTTP request
 	 * (https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html).
@@ -257,6 +266,12 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	private boolean sslFailure = false;
 
+	private HttpConnectionFactory factory;
+
+	private HttpConnectionFactory2.GitSession gitSession;
+
+	private boolean factoryUsed;
+
 	/**
 	 * All stored cookies bound to this repo (independent of the baseUrl)
 	 */
@@ -279,6 +294,7 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		sslVerify = http.isSslVerify();
 		cookieFile = getCookieFileFromConfig(http);
 		relevantCookies = filterCookies(cookieFile, baseUrl);
+		factory = HttpTransport.getConnectionFactory();
 	}
 
 	private URL toURL(URIish urish) throws MalformedURLException {
@@ -321,6 +337,7 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		sslVerify = http.isSslVerify();
 		cookieFile = getCookieFileFromConfig(http);
 		relevantCookies = filterCookies(cookieFile, baseUrl);
+		factory = HttpTransport.getConnectionFactory();
 	}
 
 	/**
@@ -339,11 +356,15 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	@SuppressWarnings("resource") // Closed by caller
 	private FetchConnection getConnection(HttpConnection c, InputStream in,
-			String service) throws IOException {
+			String service, Collection<RefSpec> refSpecs,
+			String... additionalPatterns) throws IOException {
 		BaseConnection f;
 		if (isSmartHttp(c, service)) {
-			readSmartHeaders(in, service);
-			f = new SmartHttpFetchConnection(in);
+			InputStream withMark = in.markSupported() ? in
+					: new BufferedInputStream(in);
+			readSmartHeaders(withMark, service);
+			f = new SmartHttpFetchConnection(withMark, refSpecs,
+					additionalPatterns);
 		} else {
 			// Assume this server doesn't support smart HTTP fetch
 			// and fall back on dumb object walking.
@@ -353,15 +374,98 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		return (FetchConnection) f;
 	}
 
+	/**
+	 * Sets the {@link HttpConnectionFactory} to be used by this
+	 * {@link TransportHttp} instance.
+	 * <p>
+	 * If no factory is set explicitly, the {@link TransportHttp} instance uses
+	 * the {@link HttpTransport#getConnectionFactory() globally defined
+	 * factory}.
+	 * </p>
+	 *
+	 * @param customFactory
+	 *            the {@link HttpConnectionFactory} to use
+	 * @throws IllegalStateException
+	 *             if an HTTP/HTTPS connection has already been opened on this
+	 *             {@link TransportHttp} instance
+	 * @since 5.11
+	 */
+	public void setHttpConnectionFactory(
+			@NonNull HttpConnectionFactory customFactory) {
+		if (factoryUsed) {
+			throw new IllegalStateException(JGitText.get().httpFactoryInUse);
+		}
+		factory = customFactory;
+	}
+
+	/**
+	 * Retrieves the {@link HttpConnectionFactory} used by this
+	 * {@link TransportHttp} instance.
+	 *
+	 * @return the {@link HttpConnectionFactory}
+	 * @since 5.11
+	 */
+	@NonNull
+	public HttpConnectionFactory getHttpConnectionFactory() {
+		return factory;
+	}
+
+	/**
+	 * Sets preemptive Basic HTTP authentication. If the given {@code username}
+	 * or {@code password} is empty or {@code null}, no preemptive
+	 * authentication will be done. If {@code username} and {@code password} are
+	 * set, they will override authority information from the URI
+	 * ("user:password@").
+	 * <p>
+	 * If the connection encounters redirects, the pre-authentication will be
+	 * cleared if the redirect goes to a different host.
+	 * </p>
+	 *
+	 * @param username
+	 *            to use
+	 * @param password
+	 *            to use
+	 * @throws IllegalStateException
+	 *             if an HTTP/HTTPS connection has already been opened on this
+	 *             {@link TransportHttp} instance
+	 * @since 5.11
+	 */
+	public void setPreemptiveBasicAuthentication(String username,
+			String password) {
+		if (factoryUsed) {
+			throw new IllegalStateException(JGitText.get().httpPreAuthTooLate);
+		}
+		if (StringUtils.isEmptyOrNull(username)
+				|| StringUtils.isEmptyOrNull(password)) {
+			authMethod = authFromUri(currentUri);
+		} else {
+			HttpAuthMethod basic = HttpAuthMethod.Type.BASIC.method(null);
+			basic.authorize(username, password);
+			authMethod = basic;
+		}
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public FetchConnection openFetch() throws TransportException,
 			NotSupportedException {
+		return openFetch(Collections.emptyList());
+	}
+
+	@Override
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns)
+			throws NotSupportedException, TransportException {
 		final String service = SVC_UPLOAD_PACK;
 		try {
-			final HttpConnection c = connect(service);
+			TransferConfig.ProtocolVersion gitProtocol = protocol;
+			if (gitProtocol == null) {
+				gitProtocol = TransferConfig.ProtocolVersion.V2;
+			}
+			HttpConnection c = connect(service, gitProtocol);
 			try (InputStream in = openInputStream(c)) {
-				return getConnection(c, in, service);
+				return getConnection(c, in, service, refSpecs,
+						additionalPatterns);
 			}
 		} catch (NotSupportedException | TransportException err) {
 			throw err;
@@ -456,8 +560,9 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	private PushConnection smartPush(String service, HttpConnection c,
 			InputStream in) throws IOException, TransportException {
-		readSmartHeaders(in, service);
-		SmartHttpPushConnection p = new SmartHttpPushConnection(in);
+		BufferedInputStream inBuf = new BufferedInputStream(in);
+		readSmartHeaders(inBuf, service);
+		SmartHttpPushConnection p = new SmartHttpPushConnection(inBuf);
 		p.setPeerUserAgent(c.getHeaderField(HttpSupport.HDR_SERVER));
 		return p;
 	}
@@ -465,7 +570,10 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
-		// No explicit connections are maintained.
+		if (gitSession != null) {
+			gitSession.close();
+			gitSession = null;
+		}
 	}
 
 	/**
@@ -492,9 +600,40 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		return new NoRemoteRepositoryException(u, text);
 	}
 
+	private HttpAuthMethod authFromUri(URIish u) {
+		String user = u.getUser();
+		String pass = u.getPass();
+		if (user != null && pass != null) {
+			try {
+				// User/password are _not_ application/x-www-form-urlencoded. In
+				// particular the "+" sign would be replaced by a space.
+				user = URLDecoder.decode(user.replace("+", "%2B"), //$NON-NLS-1$ //$NON-NLS-2$
+						StandardCharsets.UTF_8.name());
+				pass = URLDecoder.decode(pass.replace("+", "%2B"), //$NON-NLS-1$ //$NON-NLS-2$
+						StandardCharsets.UTF_8.name());
+				HttpAuthMethod basic = HttpAuthMethod.Type.BASIC.method(null);
+				basic.authorize(user, pass);
+				return basic;
+			} catch (IllegalArgumentException
+					| UnsupportedEncodingException e) {
+				LOG.warn(JGitText.get().httpUserInfoDecodeError, u);
+			}
+		}
+		return HttpAuthMethod.Type.NONE.method(null);
+	}
+
 	private HttpConnection connect(String service)
 			throws TransportException, NotSupportedException {
+		return connect(service, null);
+	}
+
+	private HttpConnection connect(String service,
+			TransferConfig.ProtocolVersion protocolVersion)
+			throws TransportException, NotSupportedException {
 		URL u = getServiceURL(service);
+		if (HttpAuthMethod.Type.NONE.equals(authMethod.getType())) {
+			authMethod = authFromUri(currentUri);
+		}
 		int authAttempts = 1;
 		int redirects = 0;
 		Collection<Type> ignoreTypes = null;
@@ -507,6 +646,11 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 				} else {
 					conn.setRequestProperty(HDR_ACCEPT, "*/*"); //$NON-NLS-1$
 				}
+				if (TransferConfig.ProtocolVersion.V2.equals(protocolVersion)) {
+					conn.setRequestProperty(
+							GitProtocolConstants.PROTOCOL_HEADER,
+							GitProtocolConstants.VERSION_2_REQUEST);
+				}
 				final int status = HttpSupport.response(conn);
 				processResponseCookies(conn);
 				switch (status) {
@@ -796,7 +940,13 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		}
 		try {
 			URI redirectTo = new URI(location);
+			// Reset authentication if the redirect has user/password info or
+			// if the host is different.
+			boolean resetAuth = !StringUtils
+					.isEmptyOrNull(redirectTo.getUserInfo());
+			String currentHost = currentUrl.getHost();
 			redirectTo = currentUrl.toURI().resolve(redirectTo);
+			resetAuth = resetAuth || !currentHost.equals(redirectTo.getHost());
 			String redirected = redirectTo.toASCIIString();
 			if (!isValidRedirect(baseUrl, redirected, checkFor)) {
 				throw new TransportException(uri,
@@ -805,6 +955,9 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 			}
 			redirected = redirected.substring(0, redirected.indexOf(checkFor));
 			URIish result = new URIish(redirected);
+			if (resetAuth) {
+				authMethod = HttpAuthMethod.Type.NONE.method(null);
+			}
 			if (LOG.isInfoEnabled()) {
 				LOG.info(MessageFormat.format(JGitText.get().redirectHttp,
 						uri.setPass(null),
@@ -885,9 +1038,20 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		}
 
 		final Proxy proxy = HttpSupport.proxyFor(proxySelector, u);
-		HttpConnection conn = connectionFactory.create(u, proxy);
+		factoryUsed = true;
+		HttpConnection conn = factory.create(u, proxy);
 
-		if (!sslVerify && "https".equals(u.getProtocol())) { //$NON-NLS-1$
+		if (gitSession == null && (factory instanceof HttpConnectionFactory2)) {
+			gitSession = ((HttpConnectionFactory2) factory).newSession();
+		}
+		if (gitSession != null) {
+			try {
+				gitSession.configure(conn, sslVerify);
+			} catch (GeneralSecurityException e) {
+				throw new IOException(e.getMessage(), e);
+			}
+		} else if (!sslVerify && "https".equals(u.getProtocol())) { //$NON-NLS-1$
+			// Backwards compatibility
 			HttpSupport.disableSslVerify(conn);
 		}
 
@@ -1148,20 +1312,37 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	private void readSmartHeaders(InputStream in, String service)
 			throws IOException {
-		// A smart reply will have a '#' after the first 4 bytes, but
-		// a dumb reply cannot contain a '#' until after byte 41. Do a
+		// A smart protocol V0 reply will have a '#' after the first 4 bytes,
+		// but a dumb reply cannot contain a '#' until after byte 41. Do a
 		// quick check to make sure its a smart reply before we parse
 		// as a pkt-line stream.
 		//
-		final byte[] magic = new byte[5];
+		// There appears to be a confusion about this in protocol V2. Github
+		// sends the # service line as a git (not http) header also when
+		// protocol V2 is used. Gitlab also does so. JGit's UploadPack doesn't,
+		// and thus Gerrit also does not.
+		final byte[] magic = new byte[14];
+		if (!in.markSupported()) {
+			throw new TransportException(uri,
+					JGitText.get().inputStreamMustSupportMark);
+		}
+		in.mark(14);
 		IO.readFully(in, magic, 0, magic.length);
+		// Did we get 000dversion 2 or similar? (Canonical is 000eversion 2\n,
+		// but JGit and thus Gerrit omits the \n.)
+		if (Arrays.equals(Arrays.copyOfRange(magic, 4, 11), VERSION)
+				&& magic[12] >= '1' && magic[12] <= '9') {
+			// It's a smart server doing version 1 or greater, but not sending
+			// the # service line header. Don't consume the version line.
+			in.reset();
+			return;
+		}
 		if (magic[4] != '#') {
 			throw new TransportException(uri, MessageFormat.format(
 					JGitText.get().expectedPktLineWithService, RawParseUtils.decode(magic)));
 		}
-
-		final PacketLineIn pckIn = new PacketLineIn(new UnionInputStream(
-				new ByteArrayInputStream(magic), in));
+		in.reset();
+		final PacketLineIn pckIn = new PacketLineIn(in);
 		final String exp = "# service=" + service; //$NON-NLS-1$
 		final String act = pckIn.readString();
 		if (!exp.equals(act)) {
@@ -1327,12 +1508,24 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 		SmartHttpFetchConnection(InputStream advertisement)
 				throws TransportException {
+			this(advertisement, Collections.emptyList());
+		}
+
+		SmartHttpFetchConnection(InputStream advertisement,
+				Collection<RefSpec> refSpecs, String... additionalPatterns)
+				throws TransportException {
 			super(TransportHttp.this);
 			statelessRPC = true;
 
 			init(advertisement, DisabledOutputStream.INSTANCE);
 			outNeedsEnd = false;
-			readAdvertisedRefs();
+			if (!readAdvertisedRefs()) {
+				// Must be protocol V2
+				LongPollService service = new LongPollService(SVC_UPLOAD_PACK,
+						getProtocolVersion());
+				init(service.getInputStream(), service.getOutputStream());
+				lsRefs(refSpecs, additionalPatterns);
+			}
 		}
 
 		@Override
@@ -1340,7 +1533,8 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 				final Collection<Ref> want, final Set<ObjectId> have,
 				final OutputStream outputStream) throws TransportException {
 			try {
-				svc = new MultiRequestService(SVC_UPLOAD_PACK);
+				svc = new MultiRequestService(SVC_UPLOAD_PACK,
+						getProtocolVersion());
 				init(svc.getInputStream(), svc.getOutputStream());
 				super.doFetch(monitor, want, have, outputStream);
 			} finally {
@@ -1369,7 +1563,8 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		protected void doPush(final ProgressMonitor monitor,
 				final Map<String, RemoteRefUpdate> refUpdates,
 				OutputStream outputStream) throws TransportException {
-			final Service svc = new MultiRequestService(SVC_RECEIVE_PACK);
+			final Service svc = new MultiRequestService(SVC_RECEIVE_PACK,
+					getProtocolVersion());
 			init(svc.getInputStream(), svc.getOutputStream());
 			super.doPush(monitor, refUpdates, outputStream);
 		}
@@ -1389,10 +1584,14 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 		protected final HttpExecuteStream execute;
 
+		protected final TransferConfig.ProtocolVersion protocolVersion;
+
 		final UnionInputStream in;
 
-		Service(String serviceName) {
+		Service(String serviceName,
+				TransferConfig.ProtocolVersion protocolVersion) {
 			this.serviceName = serviceName;
+			this.protocolVersion = protocolVersion;
 			this.requestType = "application/x-" + serviceName + "-request"; //$NON-NLS-1$ //$NON-NLS-2$
 			this.responseType = "application/x-" + serviceName + "-result"; //$NON-NLS-1$ //$NON-NLS-2$
 
@@ -1408,6 +1607,10 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 			conn.setDoOutput(true);
 			conn.setRequestProperty(HDR_CONTENT_TYPE, requestType);
 			conn.setRequestProperty(HDR_ACCEPT, responseType);
+			if (TransferConfig.ProtocolVersion.V2.equals(protocolVersion)) {
+				conn.setRequestProperty(GitProtocolConstants.PROTOCOL_HEADER,
+						GitProtocolConstants.VERSION_2_REQUEST);
+			}
 		}
 
 		void sendRequest() throws IOException {
@@ -1663,8 +1866,9 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 	class MultiRequestService extends Service {
 		boolean finalRequest;
 
-		MultiRequestService(String serviceName) {
-			super(serviceName);
+		MultiRequestService(String serviceName,
+				TransferConfig.ProtocolVersion protocolVersion) {
+			super(serviceName, protocolVersion);
 		}
 
 		/** Keep opening send-receive pairs to the given URI. */
@@ -1701,11 +1905,10 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	/** Service for maintaining a single long-poll connection. */
 	class LongPollService extends Service {
-		/**
-		 * @param serviceName
-		 */
-		LongPollService(String serviceName) {
-			super(serviceName);
+
+		LongPollService(String serviceName,
+				TransferConfig.ProtocolVersion protocolVersion) {
+			super(serviceName, protocolVersion);
 		}
 
 		/** Only open one send-receive request. */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportLocal.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportLocal.java
index 403f98d869..77d1419ea2 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportLocal.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportLocal.java
@@ -1,9 +1,9 @@
 /*
  * Copyright (C) 2007, Dave Watson <dwatson@mimvista.com>
- * Copyright (C) 2008-2010, Google Inc.
+ * Copyright (C) 2008, 2010 Google Inc.
  * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
  * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -20,6 +20,7 @@ import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.Map;
 import java.util.Set;
@@ -153,11 +154,17 @@ class TransportLocal extends Transport implements PackTransport {
 	/** {@inheritDoc} */
 	@Override
 	public FetchConnection openFetch() throws TransportException {
+		return openFetch(Collections.emptyList());
+	}
+
+	@Override
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns) throws TransportException {
 		final String up = getOptionUploadPack();
 		if (!"git-upload-pack".equals(up) //$NON-NLS-1$
-				&& !"git upload-pack".equals(up)) //$NON-NLS-1$
-			return new ForkLocalFetchConnection();
-
+				&& !"git upload-pack".equals(up)) {//$NON-NLS-1$
+			return new ForkLocalFetchConnection(refSpecs, additionalPatterns);
+		}
 		UploadPackFactory<Void> upf = (Void req,
 				Repository db) -> createUploadPack(db);
 		return new InternalFetchConnection<>(this, upf, null, openRepo());
@@ -193,6 +200,23 @@ class TransportLocal extends Transport implements PackTransport {
 	 */
 	protected Process spawn(String cmd)
 			throws TransportException {
+		return spawn(cmd, null);
+	}
+
+	/**
+	 * Spawn process
+	 *
+	 * @param cmd
+	 *            command
+	 * @param protocolVersion
+	 *            to use
+	 * @return a {@link java.lang.Process} object.
+	 * @throws org.eclipse.jgit.errors.TransportException
+	 *             if any.
+	 */
+	private Process spawn(String cmd,
+			TransferConfig.ProtocolVersion protocolVersion)
+			throws TransportException {
 		try {
 			String[] args = { "." }; //$NON-NLS-1$
 			ProcessBuilder proc = local.getFS().runInShell(cmd, args);
@@ -208,7 +232,10 @@ class TransportLocal extends Transport implements PackTransport {
 			env.remove("GIT_GRAFT_FILE"); //$NON-NLS-1$
 			env.remove("GIT_INDEX_FILE"); //$NON-NLS-1$
 			env.remove("GIT_NO_REPLACE_OBJECTS"); //$NON-NLS-1$
-
+			if (TransferConfig.ProtocolVersion.V2.equals(protocolVersion)) {
+				env.put(GitProtocolConstants.PROTOCOL_ENVIRONMENT_VARIABLE,
+						GitProtocolConstants.VERSION_2_REQUEST);
+			}
 			return proc.start();
 		} catch (IOException err) {
 			throw new TransportException(uri, err.getMessage(), err);
@@ -221,12 +248,21 @@ class TransportLocal extends Transport implements PackTransport {
 		private Thread errorReaderThread;
 
 		ForkLocalFetchConnection() throws TransportException {
+			this(Collections.emptyList());
+		}
+
+		ForkLocalFetchConnection(Collection<RefSpec> refSpecs,
+				String... additionalPatterns) throws TransportException {
 			super(TransportLocal.this);
 
 			final MessageWriter msg = new MessageWriter();
 			setMessageWriter(msg);
 
-			uploadPack = spawn(getOptionUploadPack());
+			TransferConfig.ProtocolVersion gitProtocol = protocol;
+			if (gitProtocol == null) {
+				gitProtocol = TransferConfig.ProtocolVersion.V2;
+			}
+			uploadPack = spawn(getOptionUploadPack(), gitProtocol);
 
 			final InputStream upErr = uploadPack.getErrorStream();
 			errorReaderThread = new StreamCopyThread(upErr, msg.getRawStream());
@@ -239,7 +275,9 @@ class TransportLocal extends Transport implements PackTransport {
 			upOut = new BufferedOutputStream(upOut);
 
 			init(upIn, upOut);
-			readAdvertisedRefs();
+			if (!readAdvertisedRefs()) {
+				lsRefs(refSpecs, additionalPatterns);
+			}
 		}
 
 		@Override
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
index 1242ef1b4a..7f1ddaab2e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2010, Google Inc. and others
+ * Copyright (C) 2008, 2020 Google Inc. and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -33,6 +33,7 @@ import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SIDEBAND_AL
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SIDE_BAND;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SIDE_BAND_64K;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_THIN_PACK;
+import static org.eclipse.jgit.transport.GitProtocolConstants.VERSION_2_REQUEST;
 import static org.eclipse.jgit.util.RefMap.toRefMap;
 
 import java.io.ByteArrayOutputStream;
@@ -709,7 +710,7 @@ public class UploadPack {
 	 * @since 5.0
 	 */
 	public void setExtraParameters(Collection<String> params) {
-		this.clientRequestedV2 = params.contains("version=2"); //$NON-NLS-1$
+		this.clientRequestedV2 = params.contains(VERSION_2_REQUEST);
 	}
 
 	/**
@@ -722,7 +723,8 @@ public class UploadPack {
 	}
 
 	private boolean useProtocolV2() {
-		return ProtocolVersion.V2.equals(transferConfig.protocolVersion)
+		return (transferConfig.protocolVersion == null
+			|| ProtocolVersion.V2.equals(transferConfig.protocolVersion))
 				&& clientRequestedV2;
 	}
 
@@ -1191,17 +1193,18 @@ public class UploadPack {
 
 		if (req.wasDoneReceived()) {
 			processHaveLines(req.getPeerHas(), ObjectId.zeroId(),
-					new PacketLineOut(NullOutputStream.INSTANCE),
+					new PacketLineOut(NullOutputStream.INSTANCE, false),
 					accumulator);
 		} else {
-			pckOut.writeString("acknowledgments\n"); //$NON-NLS-1$
+			pckOut.writeString(
+					GitProtocolConstants.SECTION_ACKNOWLEDGMENTS + '\n');
 			for (ObjectId id : req.getPeerHas()) {
 				if (walk.getObjectReader().has(id)) {
 					pckOut.writeString("ACK " + id.getName() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
 				}
 			}
 			processHaveLines(req.getPeerHas(), ObjectId.zeroId(),
-					new PacketLineOut(NullOutputStream.INSTANCE),
+					new PacketLineOut(NullOutputStream.INSTANCE, false),
 					accumulator);
 			if (okToGiveUp()) {
 				pckOut.writeString("ready\n"); //$NON-NLS-1$
@@ -1243,7 +1246,8 @@ public class UploadPack {
 			if (!pckOut.isUsingSideband()) {
 				// sendPack will write "packfile\n" for us if sideband-all is used.
 				// But sideband-all is not used, so we have to write it ourselves.
-				pckOut.writeString("packfile\n"); //$NON-NLS-1$
+				pckOut.writeString(
+						GitProtocolConstants.SECTION_PACKFILE + '\n');
 			}
 
 			accumulator.timeNegotiating = Duration
@@ -1955,8 +1959,8 @@ public class UploadPack {
 							.map(objId -> objectIdToRevObject(objWalk, objId))
 							.filter(Objects::nonNull); // Ignore missing tips
 
-					ObjectReachabilityChecker reachabilityChecker = objWalk
-							.createObjectReachabilityChecker();
+					ObjectReachabilityChecker reachabilityChecker = reader
+							.createObjectReachabilityChecker(objWalk);
 					Optional<RevObject> unreachable = reachabilityChecker
 							.areAllReachable(wantsAsObjs, startersAsObjs);
 					if (unreachable.isPresent()) {
@@ -1967,8 +1971,8 @@ public class UploadPack {
 			}
 
 			// All wants are commits, we can use ReachabilityChecker
-			ReachabilityChecker reachabilityChecker = walk
-					.createReachabilityChecker();
+			ReachabilityChecker reachabilityChecker = reader
+					.createReachabilityChecker(walk);
 
 			Stream<RevCommit> reachableCommits = importantRefsFirst(visibleRefs)
 					.map(UploadPack::refToObjectId)
@@ -2327,7 +2331,8 @@ public class UploadPack {
 					// for us if provided a PackfileUriConfig. In this case, we
 					// are not providing a PackfileUriConfig, so we have to
 					// write this line ourselves.
-					pckOut.writeString("packfile\n"); //$NON-NLS-1$
+					pckOut.writeString(
+							GitProtocolConstants.SECTION_PACKFILE + '\n');
 				}
 			}
 			pw.writePack(pm, NullProgressMonitor.INSTANCE, packOut);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/WalkFetchConnection.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/WalkFetchConnection.java
index c44838ab89..a6b20451dd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/WalkFetchConnection.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/WalkFetchConnection.java
@@ -510,6 +510,7 @@ class WalkFetchConnection extends BaseFetchConnection {
 			// and attach it to the local repository so we can use
 			// all of the contained objects.
 			//
+			Throwable e1 = null;
 			try {
 				pack.downloadPack(monitor);
 			} catch (IOException err) {
@@ -519,6 +520,7 @@ class WalkFetchConnection extends BaseFetchConnection {
 				// an alternate.
 				//
 				recordError(id, err);
+				e1 = err;
 				continue;
 			} finally {
 				// If the pack was good its in the local repository
@@ -531,6 +533,9 @@ class WalkFetchConnection extends BaseFetchConnection {
 					if (pack.tmpIdx != null)
 						FileUtils.delete(pack.tmpIdx);
 				} catch (IOException e) {
+					if (e1 != null) {
+						e.addSuppressed(e1);
+					}
 					throw new TransportException(e.getMessage(), e);
 				}
 				packItr.remove();
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/HttpConnectionFactory2.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/HttpConnectionFactory2.java
new file mode 100644
index 0000000000..88abc60162
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/HttpConnectionFactory2.java
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2020 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.transport.http;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+
+import org.eclipse.jgit.annotations.NonNull;
+
+/**
+ * A {@link HttpConnectionFactory} that supports client-side sessions that can
+ * maintain state and configure connections.
+ *
+ * @since 5.11
+ */
+public interface HttpConnectionFactory2 extends HttpConnectionFactory {
+
+	/**
+	 * Creates a new {@link GitSession} instance that can be used with
+	 * connections created by this {@link HttpConnectionFactory} instance.
+	 *
+	 * @return a new {@link GitSession}
+	 */
+	@NonNull
+	GitSession newSession();
+
+	/**
+	 * A {@code GitSession} groups the multiple HTTP connections
+	 * {@link org.eclipse.jgit.transport.TransportHttp TransportHttp} uses for
+	 * the requests it makes during a git fetch or push. A {@code GitSession}
+	 * can maintain client-side HTTPS state and can configure individual
+	 * connections.
+	 */
+	interface GitSession {
+
+		/**
+		 * Configure a just created {@link HttpConnection}.
+		 *
+		 * @param connection
+		 *            to configure; created by the same
+		 *            {@link HttpConnectionFactory} instance
+		 * @param sslVerify
+		 *            whether SSL is to be verified
+		 * @return the configured {@connection}
+		 * @throws IOException
+		 *             if the connection cannot be configured
+		 * @throws GeneralSecurityException
+		 *             if the connection cannot be configured
+		 */
+		@NonNull
+		HttpConnection configure(@NonNull HttpConnection connection,
+				boolean sslVerify) throws IOException, GeneralSecurityException;
+
+		/**
+		 * Closes the {@link GitSession}, releasing any internal state.
+		 */
+		void close();
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/JDKHttpConnectionFactory.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/JDKHttpConnectionFactory.java
index b39f1579be..1b5d1b3c43 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/JDKHttpConnectionFactory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/JDKHttpConnectionFactory.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2013 Christian Halstrick <christian.halstrick@sap.com> and others
+ * Copyright (C) 2013, 2020 Christian Halstrick <christian.halstrick@sap.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -12,6 +12,18 @@ package org.eclipse.jgit.transport.http;
 import java.io.IOException;
 import java.net.Proxy;
 import java.net.URL;
+import java.security.GeneralSecurityException;
+import java.text.MessageFormat;
+
+import javax.net.ssl.HttpsURLConnection;
+import javax.net.ssl.SSLContext;
+import javax.net.ssl.SSLSocket;
+import javax.net.ssl.SSLSocketFactory;
+import javax.net.ssl.TrustManager;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.internal.transport.http.DelegatingSSLSocketFactory;
+import org.eclipse.jgit.util.HttpSupport;
 
 /**
  * A factory returning instances of
@@ -19,17 +31,70 @@ import java.net.URL;
  *
  * @since 3.3
  */
-public class JDKHttpConnectionFactory implements HttpConnectionFactory {
-	/** {@inheritDoc} */
+public class JDKHttpConnectionFactory implements HttpConnectionFactory2 {
+
 	@Override
 	public HttpConnection create(URL url) throws IOException {
 		return new JDKHttpConnection(url);
 	}
 
-	/** {@inheritDoc} */
 	@Override
 	public HttpConnection create(URL url, Proxy proxy)
 			throws IOException {
 		return new JDKHttpConnection(url, proxy);
 	}
+
+	@Override
+	public GitSession newSession() {
+		return new JdkConnectionSession();
+	}
+
+	private static class JdkConnectionSession implements GitSession {
+
+		private SSLContext securityContext;
+
+		private SSLSocketFactory socketFactory;
+
+		@Override
+		public JDKHttpConnection configure(HttpConnection connection,
+				boolean sslVerify) throws GeneralSecurityException {
+			if (!(connection instanceof JDKHttpConnection)) {
+				throw new IllegalArgumentException(MessageFormat.format(
+						JGitText.get().httpWrongConnectionType,
+						JDKHttpConnection.class.getName(),
+						connection.getClass().getName()));
+			}
+			JDKHttpConnection conn = (JDKHttpConnection) connection;
+			String scheme = conn.getURL().getProtocol();
+			if (!"https".equals(scheme) || sslVerify) { //$NON-NLS-1$
+				// sslVerify == true: use the JDK defaults
+				return conn;
+			}
+			if (securityContext == null) {
+				securityContext = SSLContext.getInstance("TLS"); //$NON-NLS-1$
+				TrustManager[] trustAllCerts = {
+						new NoCheckX509TrustManager() };
+				securityContext.init(null, trustAllCerts, null);
+				socketFactory = new DelegatingSSLSocketFactory(
+						securityContext.getSocketFactory()) {
+
+					@Override
+					protected void configure(SSLSocket socket) {
+						HttpSupport.configureTLS(socket);
+					}
+				};
+			}
+			conn.setHostnameVerifier((name, session) -> true);
+			((HttpsURLConnection) conn.wrappedUrlConnection)
+					.setSSLSocketFactory(socketFactory);
+			return conn;
+		}
+
+		@Override
+		public void close() {
+			securityContext = null;
+			socketFactory = null;
+		}
+	}
+
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/NoCheckX509TrustManager.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/NoCheckX509TrustManager.java
new file mode 100644
index 0000000000..5cd4fb4c82
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/http/NoCheckX509TrustManager.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2016, 2020 JGit contributors
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Contributors:
+ *    Saša Živkov 2016 - initial API
+ *    Thomas Wolf 2020 - extracted from HttpSupport
+ */
+package org.eclipse.jgit.transport.http;
+
+import java.security.cert.X509Certificate;
+
+import javax.net.ssl.X509TrustManager;
+
+/**
+ * A {@link X509TrustManager} that doesn't verify anything. Can be used for
+ * skipping SSL checks.
+ *
+ * @since 5.11
+ */
+public class NoCheckX509TrustManager implements X509TrustManager {
+
+	@Override
+	public X509Certificate[] getAcceptedIssuers() {
+		return null;
+	}
+
+	@Override
+	public void checkClientTrusted(X509Certificate[] certs,
+			String authType) {
+		// no check
+	}
+
+	@Override
+	public void checkServerTrusted(X509Certificate[] certs,
+			String authType) {
+		// no check
+	}
+}
\ No newline at end of file
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
index 72278dc9c3..55b7d6279a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
@@ -2,7 +2,7 @@
  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
  * Copyright (C) 2010, Christian Halstrick <christian.halstrick@sap.com>
  * Copyright (C) 2010, Matthias Sohn <matthias.sohn@sap.com>
- * Copyright (C) 2012-2020, Robin Rosenberg and others
+ * Copyright (C) 2012-2021, Robin Rosenberg and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -63,6 +63,7 @@ import org.eclipse.jgit.submodule.SubmoduleWalk;
 import org.eclipse.jgit.treewalk.TreeWalk.OperationType;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.FS.ExecutionResult;
+import org.eclipse.jgit.util.FileUtils;
 import org.eclipse.jgit.util.Holder;
 import org.eclipse.jgit.util.IO;
 import org.eclipse.jgit.util.Paths;
@@ -799,7 +800,10 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 			if (Constants.DOT_GIT.equals(name))
 				continue;
 			if (Constants.DOT_GIT_IGNORE.equals(name))
-				ignoreNode = new PerDirectoryIgnoreNode(e);
+				ignoreNode = new PerDirectoryIgnoreNode(
+						TreeWalk.pathOf(path, 0, pathOffset)
+								+ Constants.DOT_GIT_IGNORE,
+						e);
 			if (Constants.DOT_GIT_ATTRIBUTES.equals(name))
 				attributesNode = new PerDirectoryAttributesNode(e);
 			if (i != o)
@@ -983,8 +987,9 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 					return true;
 				} else if (ObjectId.zeroId().compareTo(idBuffer,
 						idOffset) == 0) {
-					return new File(repository.getWorkTree(),
-							entry.getPathString()).list().length > 0;
+					Path p = repository.getWorkTree().toPath()
+							.resolve(entry.getPathString());
+					return FileUtils.hasFiles(p);
 				}
 				return false;
 			} else if (mode == FileMode.SYMLINK.getBits())
@@ -1272,17 +1277,20 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 
 	/** Magic type indicating we know rules exist, but they aren't loaded. */
 	private static class PerDirectoryIgnoreNode extends IgnoreNode {
-		final Entry entry;
+		protected final Entry entry;
+
+		private final String name;
 
-		PerDirectoryIgnoreNode(Entry entry) {
+		PerDirectoryIgnoreNode(String name, Entry entry) {
 			super(Collections.<FastIgnoreRule> emptyList());
+			this.name = name;
 			this.entry = entry;
 		}
 
 		IgnoreNode load() throws IOException {
 			IgnoreNode r = new IgnoreNode();
 			try (InputStream in = entry.openInputStream()) {
-				r.parse(in);
+				r.parse(name, in);
 			}
 			return r.getRules().isEmpty() ? null : r;
 		}
@@ -1293,7 +1301,7 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		final Repository repository;
 
 		RootIgnoreNode(Entry entry, Repository repository) {
-			super(entry);
+			super(entry != null ? entry.getName() : null, entry);
 			this.repository = repository;
 		}
 
@@ -1327,7 +1335,7 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 				throws FileNotFoundException, IOException {
 			if (FS.DETECTED.exists(exclude)) {
 				try (FileInputStream in = new FileInputStream(exclude)) {
-					r.parse(in);
+					r.parse(exclude.getAbsolutePath(), in);
 				}
 			}
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
index d8cab358e7..0946f645fb 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
@@ -22,7 +22,6 @@ import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
-import java.io.PrintStream;
 import java.io.Writer;
 import java.nio.charset.Charset;
 import java.nio.file.AccessDeniedException;
@@ -337,6 +336,9 @@ public abstract class FS {
 			try {
 				path = path.toAbsolutePath();
 				Path dir = Files.isDirectory(path) ? path : path.getParent();
+				if (dir == null) {
+					return FALLBACK_FILESTORE_ATTRIBUTES;
+				}
 				FileStoreAttributes cached = attrCacheByPath.get(dir);
 				if (cached != null) {
 					return cached;
@@ -511,7 +513,10 @@ public abstract class FS {
 		}
 
 		private static void write(Path p, String body) throws IOException {
-			FileUtils.mkdirs(p.getParent().toFile(), true);
+			Path parent = p.getParent();
+			if (parent != null) {
+				FileUtils.mkdirs(parent.toFile(), true);
+			}
 			try (Writer w = new OutputStreamWriter(Files.newOutputStream(p),
 					UTF_8)) {
 				w.write(body);
@@ -1867,18 +1872,18 @@ public abstract class FS {
 	 * @throws org.eclipse.jgit.api.errors.JGitInternalException
 	 *             if we fail to run the hook somehow. Causes may include an
 	 *             interrupted process or I/O errors.
-	 * @since 4.0
+	 * @since 5.11
 	 */
 	public ProcessResult runHookIfPresent(Repository repository,
 			final String hookName,
-			String[] args, PrintStream outRedirect, PrintStream errRedirect,
+			String[] args, OutputStream outRedirect, OutputStream errRedirect,
 			String stdinArgs) throws JGitInternalException {
 		return new ProcessResult(Status.NOT_SUPPORTED);
 	}
 
 	/**
 	 * See
-	 * {@link #runHookIfPresent(Repository, String, String[], PrintStream, PrintStream, String)}
+	 * {@link #runHookIfPresent(Repository, String, String[], OutputStream, OutputStream, String)}
 	 * . Should only be called by FS supporting shell scripts execution.
 	 *
 	 * @param repository
@@ -1903,11 +1908,11 @@ public abstract class FS {
 	 * @throws org.eclipse.jgit.api.errors.JGitInternalException
 	 *             if we fail to run the hook somehow. Causes may include an
 	 *             interrupted process or I/O errors.
-	 * @since 4.0
+	 * @since 5.11
 	 */
 	protected ProcessResult internalRunHookIfPresent(Repository repository,
-			final String hookName, String[] args, PrintStream outRedirect,
-			PrintStream errRedirect, String stdinArgs)
+			final String hookName, String[] args, OutputStream outRedirect,
+			OutputStream errRedirect, String stdinArgs)
 			throws JGitInternalException {
 		File hookFile = findHook(repository, hookName);
 		if (hookFile == null || hookName == null) {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
index fb63dc02bb..946d81c73a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
@@ -16,7 +16,7 @@ import java.io.BufferedReader;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
-import java.io.PrintStream;
+import java.io.OutputStream;
 import java.nio.charset.Charset;
 import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.FileStore;
@@ -268,7 +268,7 @@ public class FS_POSIX extends FS {
 	/** {@inheritDoc} */
 	@Override
 	public ProcessResult runHookIfPresent(Repository repository, String hookName,
-			String[] args, PrintStream outRedirect, PrintStream errRedirect,
+			String[] args, OutputStream outRedirect, OutputStream errRedirect,
 			String stdinArgs) throws JGitInternalException {
 		return internalRunHookIfPresent(repository, hookName, args, outRedirect,
 				errRedirect, stdinArgs);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32_Cygwin.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32_Cygwin.java
index d53bff78ea..add5498175 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32_Cygwin.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32_Cygwin.java
@@ -13,7 +13,7 @@ package org.eclipse.jgit.util;
 import static java.nio.charset.StandardCharsets.UTF_8;
 
 import java.io.File;
-import java.io.PrintStream;
+import java.io.OutputStream;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.util.ArrayList;
@@ -139,7 +139,7 @@ public class FS_Win32_Cygwin extends FS_Win32 {
 	/** {@inheritDoc} */
 	@Override
 	public ProcessResult runHookIfPresent(Repository repository, String hookName,
-			String[] args, PrintStream outRedirect, PrintStream errRedirect,
+			String[] args, OutputStream outRedirect, OutputStream errRedirect,
 			String stdinArgs) throws JGitInternalException {
 		return internalRunHookIfPresent(repository, hookName, args, outRedirect,
 				errRedirect, stdinArgs);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
index aa39a44642..b9dd9baa61 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
@@ -43,6 +43,7 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Random;
 import java.util.regex.Pattern;
+import java.util.stream.Stream;
 
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.Constants;
@@ -802,6 +803,23 @@ public class FileUtils {
 	}
 
 	/**
+	 * Whether the path is a directory with files in it.
+	 *
+	 * @param dir
+	 *            directory path
+	 * @return {@code true} if the given directory path contains files
+	 * @throws IOException
+	 *             on any I/O errors accessing the path
+	 *
+	 * @since 5.11
+	 */
+	public static boolean hasFiles(Path dir) throws IOException {
+		try (Stream<Path> stream = Files.list(dir)) {
+			return stream.findAny().isPresent();
+		}
+	}
+
+	/**
 	 * Whether the given file can be executed.
 	 *
 	 * @param file
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/HttpSupport.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/HttpSupport.java
index 04b3eab504..23a73faf8c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/HttpSupport.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/HttpSupport.java
@@ -24,21 +24,18 @@ import java.net.URL;
 import java.net.URLEncoder;
 import java.security.KeyManagementException;
 import java.security.NoSuchAlgorithmException;
-import java.security.cert.X509Certificate;
 import java.text.MessageFormat;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
-import javax.net.ssl.HostnameVerifier;
-import javax.net.ssl.SSLSession;
 import javax.net.ssl.SSLSocket;
 import javax.net.ssl.TrustManager;
-import javax.net.ssl.X509TrustManager;
 
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.transport.http.HttpConnection;
+import org.eclipse.jgit.transport.http.NoCheckX509TrustManager;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -301,40 +298,13 @@ public class HttpSupport {
 	 */
 	public static void disableSslVerify(HttpConnection conn)
 			throws IOException {
-		final TrustManager[] trustAllCerts = new TrustManager[] {
-				new DummyX509TrustManager() };
+		TrustManager[] trustAllCerts = {
+				new NoCheckX509TrustManager() };
 		try {
 			conn.configure(null, trustAllCerts, null);
-			conn.setHostnameVerifier(new DummyHostnameVerifier());
+			conn.setHostnameVerifier((name, session) -> true);
 		} catch (KeyManagementException | NoSuchAlgorithmException e) {
-			throw new IOException(e.getMessage());
-		}
-	}
-
-	private static class DummyX509TrustManager implements X509TrustManager {
-		@Override
-		public X509Certificate[] getAcceptedIssuers() {
-			return null;
-		}
-
-		@Override
-		public void checkClientTrusted(X509Certificate[] certs,
-				String authType) {
-			// no check
-		}
-
-		@Override
-		public void checkServerTrusted(X509Certificate[] certs,
-				String authType) {
-			// no check
-		}
-	}
-
-	private static class DummyHostnameVerifier implements HostnameVerifier {
-		@Override
-		public boolean verify(String hostname, SSLSession session) {
-			// always accept
-			return true;
+			throw new IOException(e.getMessage(), e);
 		}
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/IO.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/IO.java
index 680d90392d..6d5694e435 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/IO.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/IO.java
@@ -246,7 +246,7 @@ public class IO {
 	 *            buffer that must be fully populated, [off, off+len).
 	 * @param off
 	 *            position within the buffer to start writing to.
-	 * @return number of bytes in buffer or stream, whichever is shortest
+	 * @return number of bytes read
 	 * @throws java.io.IOException
 	 *             there was an error reading from the stream.
 	 */
@@ -254,8 +254,8 @@ public class IO {
 			throws IOException {
 		int r;
 		int len = 0;
-		while ((r = fd.read(dst, off, dst.length - off)) >= 0
-				&& len < dst.length) {
+		while (off < dst.length
+				&& (r = fd.read(dst, off, dst.length - off)) >= 0) {
 			off += r;
 			len += r;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/SignatureUtils.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/SignatureUtils.java
new file mode 100644
index 0000000000..cf06172c17
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/SignatureUtils.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2021, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.util;
+
+import java.text.MessageFormat;
+import java.util.Locale;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.GpgSignatureVerifier.SignatureVerification;
+import org.eclipse.jgit.lib.GpgSignatureVerifier.TrustLevel;
+import org.eclipse.jgit.lib.PersonIdent;
+
+/**
+ * Utilities for signature verification.
+ *
+ * @since 5.11
+ */
+public final class SignatureUtils {
+
+	private SignatureUtils() {
+		// No instantiation
+	}
+
+	/**
+	 * Writes information about a signature verification to a string.
+	 *
+	 * @param verification
+	 *            to show
+	 * @param creator
+	 *            of the object verified; used for time zone information
+	 * @param formatter
+	 *            to use for dates
+	 * @return a textual representation of the {@link SignatureVerification},
+	 *         using LF as line separator
+	 */
+	public static String toString(SignatureVerification verification,
+			PersonIdent creator, GitDateFormatter formatter) {
+		StringBuilder result = new StringBuilder();
+		// Use the creator's timezone for the signature date
+		PersonIdent dateId = new PersonIdent(creator,
+				verification.getCreationDate());
+		result.append(MessageFormat.format(JGitText.get().verifySignatureMade,
+				formatter.formatDate(dateId)));
+		result.append('\n');
+		result.append(MessageFormat.format(
+				JGitText.get().verifySignatureKey,
+				verification.getKeyFingerprint().toUpperCase(Locale.ROOT)));
+		result.append('\n');
+		if (!StringUtils.isEmptyOrNull(verification.getSigner())) {
+			result.append(
+					MessageFormat.format(JGitText.get().verifySignatureIssuer,
+							verification.getSigner()));
+			result.append('\n');
+		}
+		String msg;
+		if (verification.getVerified()) {
+			if (verification.isExpired()) {
+				msg = JGitText.get().verifySignatureExpired;
+			} else {
+				msg = JGitText.get().verifySignatureGood;
+			}
+		} else {
+			msg = JGitText.get().verifySignatureBad;
+		}
+		result.append(MessageFormat.format(msg, verification.getKeyUser()));
+		if (!TrustLevel.UNKNOWN.equals(verification.getTrustLevel())) {
+			result.append(' ' + MessageFormat
+					.format(JGitText.get().verifySignatureTrust, verification
+							.getTrustLevel().name().toLowerCase(Locale.ROOT)));
+		}
+		result.append('\n');
+		msg = verification.getMessage();
+		if (!StringUtils.isEmptyOrNull(msg)) {
+			result.append(msg);
+			result.append('\n');
+		}
+		return result.toString();
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
index 447f417e7e..54fd539f67 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
@@ -56,9 +56,9 @@ public abstract class SystemReader {
 
 	private static final SystemReader DEFAULT;
 
-	private static Boolean isMacOS;
+	private static volatile Boolean isMacOS;
 
-	private static Boolean isWindows;
+	private static volatile Boolean isWindows;
 
 	static {
 		SystemReader r = new Default();
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/TemporaryBuffer.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/TemporaryBuffer.java
index 1f0fedda6b..562eb05dd9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/TemporaryBuffer.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/TemporaryBuffer.java
@@ -230,11 +230,16 @@ public abstract class TemporaryBuffer extends OutputStream {
 		if (Integer.MAX_VALUE < len)
 			throw new OutOfMemoryError(
 					JGitText.get().lengthExceedsMaximumArraySize);
-		final byte[] out = new byte[(int) len];
+		int length = (int) len;
+		final byte[] out = new byte[length];
 		int outPtr = 0;
 		for (Block b : blocks) {
-			System.arraycopy(b.buffer, 0, out, outPtr, b.count);
-			outPtr += b.count;
+			int toCopy = Math.min(length - outPtr, b.count);
+			System.arraycopy(b.buffer, 0, out, outPtr, toCopy);
+			outPtr += toCopy;
+			if (outPtr == length) {
+				break;
+			}
 		}
 		return out;
 	}
@@ -461,6 +466,30 @@ public abstract class TemporaryBuffer extends OutputStream {
 		}
 
 		@Override
+		public byte[] toByteArray(int limit) throws IOException {
+			if (onDiskFile == null) {
+				return super.toByteArray(limit);
+			}
+			final long len = Math.min(length(), limit);
+			if (Integer.MAX_VALUE < len) {
+				throw new OutOfMemoryError(
+						JGitText.get().lengthExceedsMaximumArraySize);
+			}
+			final byte[] out = new byte[(int) len];
+			try (FileInputStream in = new FileInputStream(onDiskFile)) {
+				int read = 0;
+				int chunk;
+				while ((chunk = in.read(out, read, out.length - read)) >= 0) {
+					read += chunk;
+					if (read == out.length) {
+						break;
+					}
+				}
+			}
+			return out;
+		}
+
+		@Override
 		public void writeTo(OutputStream os, ProgressMonitor pm)
 				throws IOException {
 			if (onDiskFile == null) {