Client-side protocol V2 support for fetching

Make all transports request protocol V2 when fetching. Depending on
the transport, set the GIT_PROTOCOL environment variable (file and
ssh), pass the Git-Protocol header (http), or set the hidden
"\0version=2\0" (git anon). We'll fall back to V0 if the server
doesn't reply with a version 2 answer.

A user can control which protocol the client requests via the git
config protocol.version; if not set, JGit requests protocol V2 for
fetching. Pushing always uses protocol V0 still.

In the API, there is only a new Transport.openFetch() version that
takes a collection of RefSpecs plus additional patterns to construct
the Ref prefixes for the "ls-refs" command in protocol V2. If none
are given, the server will still advertise all refs, even in protocol
V2.

BasePackConnection.readAdvertisedRefs() handles falling back to
protocol V0. It newly returns true if V0 was used and the advertised
refs were read, and false if V2 is used and an explicit "ls-refs" is
needed. (This can't be done transparently inside readAdvertisedRefs()
because a "stateless RPC" transport like TransportHttp may need to
open a new connection for writing.)

BasePackFetchConnection implements the changes needed for the protocol
V2 "fetch" command (simplified ACK handling, delimiters, section
headers).

In TransportHttp, change readSmartHeaders() to also recognize the
"version 2" packet line as a valid smart server indication.

Adapt tests, and run all the HTTP tests not only with both HTTP
connection factories (JDK and Apache HttpClient) but also with both
protocol V0 and V2. Do the same for the SSH transport tests.

Bug: 553083
Change-Id: Ice9866aa78020f5ca8f397cde84dc224bf5d41b4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/AllProtocolsHttpTestCase.java

@@ -0,0 +1,99 @@
+/*
+ * 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.http.test;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+import org.eclipse.jgit.junit.http.HttpTestCase;
+import org.eclipse.jgit.transport.HttpTransport;
+import org.eclipse.jgit.transport.http.HttpConnectionFactory;
+import org.eclipse.jgit.transport.http.JDKHttpConnectionFactory;
+import org.eclipse.jgit.transport.http.apache.HttpClientConnectionFactory;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Ignore;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+/**
+ * Abstract test base class for running HTTP-related tests with all connection
+ * factories provided in JGit and with both protocol V0 and V2.
+ */
+@Ignore
+@RunWith(Parameterized.class)
+public abstract class AllProtocolsHttpTestCase extends HttpTestCase {
+
+	protected static class TestParameters {
+
+		public final HttpConnectionFactory factory;
+
+		public final boolean enableProtocolV2;
+
+		public TestParameters(HttpConnectionFactory factory,
+				boolean enableProtocolV2) {
+			this.factory = factory;
+			this.enableProtocolV2 = enableProtocolV2;
+		}
+
+		@Override
+		public String toString() {
+			return factory.toString() + " protocol "
+					+ (enableProtocolV2 ? "V2" : "V0");
+		}
+	}
+
+	@Parameters(name = "{0}")
+	public static Collection<TestParameters> data() {
+		// run all tests with both connection factories we have
+		HttpConnectionFactory[] factories = new HttpConnectionFactory[] {
+				new JDKHttpConnectionFactory() {
+
+					@Override
+					public String toString() {
+						return this.getClass().getSuperclass().getName();
+					}
+				}, new HttpClientConnectionFactory() {
+
+					@Override
+					public String toString() {
+						return this.getClass().getSuperclass().getName();
+					}
+				} };
+		List<TestParameters> result = new ArrayList<>();
+		for (HttpConnectionFactory factory : factories) {
+			result.add(new TestParameters(factory, false));
+			result.add(new TestParameters(factory, true));
+		}
+		return result;
+	}
+
+	protected final boolean enableProtocolV2;
+
+	protected AllProtocolsHttpTestCase(TestParameters params) {
+		HttpTransport.setConnectionFactory(params.factory);
+		enableProtocolV2 = params.enableProtocolV2;
+	}
+
+	private static HttpConnectionFactory originalFactory;
+
+	@BeforeClass
+	public static void saveConnectionFactory() {
+		originalFactory = HttpTransport.getConnectionFactory();
+	}
+
+	@AfterClass
+	public static void restoreConnectionFactory() {
+		HttpTransport.setConnectionFactory(originalFactory);
+	}
+
+}

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/DumbClientDumbServerTest.java

@@ -42,11 +42,10 @@ import org.eclipse.jgit.transport.HttpTransport;
 import org.eclipse.jgit.transport.Transport;
 import org.eclipse.jgit.transport.TransportHttp;
 import org.eclipse.jgit.transport.URIish;
-import org.eclipse.jgit.transport.http.HttpConnectionFactory;
 import org.junit.Before;
 import org.junit.Test;
 
-public class DumbClientDumbServerTest extends AllFactoriesHttpTestCase {
+public class DumbClientDumbServerTest extends AllProtocolsHttpTestCase {
 	private Repository remoteRepository;
 
 	private URIish remoteURI;
@@ -55,8 +54,8 @@ public class DumbClientDumbServerTest extends AllFactoriesHttpTestCase {
 
 	private RevCommit A, B;
 
-	public DumbClientDumbServerTest(HttpConnectionFactory cf) {
-		super(cf);
+	public DumbClientDumbServerTest(TestParameters params) {
+		super(params);
 	}
 
 	@Override
@@ -77,6 +76,9 @@ public class DumbClientDumbServerTest extends AllFactoriesHttpTestCase {
 
 		remoteRepository = src.getRepository();
 		remoteURI = toURIish(app, srcGit.getName());
+		if (enableProtocolV2) {
+			remoteRepository.getConfig().setInt("protocol", null, "version", 2);
+		}
 
 		A_txt = src.blob("A");
 		A = src.commit().add("A_txt", A_txt).create();

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/DumbClientSmartServerTest.java

@@ -42,11 +42,10 @@ import org.eclipse.jgit.transport.HttpTransport;
 import org.eclipse.jgit.transport.Transport;
 import org.eclipse.jgit.transport.TransportHttp;
 import org.eclipse.jgit.transport.URIish;
-import org.eclipse.jgit.transport.http.HttpConnectionFactory;
 import org.junit.Before;
 import org.junit.Test;
 
-public class DumbClientSmartServerTest extends AllFactoriesHttpTestCase {
+public class DumbClientSmartServerTest extends AllProtocolsHttpTestCase {
 	private Repository remoteRepository;
 
 	private URIish remoteURI;
@@ -55,8 +54,8 @@ public class DumbClientSmartServerTest extends AllFactoriesHttpTestCase {
 
 	private RevCommit A, B;
 
-	public DumbClientSmartServerTest(HttpConnectionFactory cf) {
-		super(cf);
+	public DumbClientSmartServerTest(TestParameters params) {
+		super(params);
 	}
 
 	@Override
@@ -76,6 +75,9 @@ public class DumbClientSmartServerTest extends AllFactoriesHttpTestCase {
 
 		remoteRepository = src.getRepository();
 		remoteURI = toURIish(app, srcName);
+		if (enableProtocolV2) {
+			remoteRepository.getConfig().setInt("protocol", null, "version", 2);
+		}
 
 		A_txt = src.blob("A");
 		A = src.commit().add("A_txt", A_txt).create();

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerSslTest.java

@@ -1,5 +1,5 @@
 /*
- * 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
@@ -48,7 +48,6 @@ import org.eclipse.jgit.transport.CredentialsProvider;
 import org.eclipse.jgit.transport.Transport;
 import org.eclipse.jgit.transport.URIish;
 import org.eclipse.jgit.transport.UsernamePasswordCredentialsProvider;
-import org.eclipse.jgit.transport.http.HttpConnectionFactory;
 import org.eclipse.jgit.util.HttpSupport;
 import org.junit.Before;
 import org.junit.Test;
@@ -56,7 +55,7 @@ import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
 @RunWith(Parameterized.class)
-public class SmartClientSmartServerSslTest extends AllFactoriesHttpTestCase {
+public class SmartClientSmartServerSslTest extends AllProtocolsHttpTestCase {
 
 	// We run these tests with a server on localhost with a self-signed
 	// certificate. We don't do authentication tests here, so there's no need
@@ -112,8 +111,8 @@ public class SmartClientSmartServerSslTest extends AllFactoriesHttpTestCase {
 
 	private RevCommit A, B;
 
-	public SmartClientSmartServerSslTest(HttpConnectionFactory cf) {
-		super(cf);
+	public SmartClientSmartServerSslTest(TestParameters params) {
+		super(params);
 	}
 
 	@Override
@@ -132,6 +131,10 @@ public class SmartClientSmartServerSslTest extends AllFactoriesHttpTestCase {
 				.getConfig()
 				.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
 						ConfigConstants.CONFIG_KEY_LOGALLREFUPDATES, true);
+		if (enableProtocolV2) {
+			src.getRepository().getConfig().setInt("protocol", null, "version",
+					2);
+		}
 
 		GitServlet gs = new GitServlet();
 
@@ -238,7 +241,7 @@ public class SmartClientSmartServerSslTest extends AllFactoriesHttpTestCase {
 		fsck(dst, B);
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(2, requests.size());
+		assertEquals(enableProtocolV2 ? 3 : 2, requests.size());
 	}
 
 	@Test
@@ -256,7 +259,7 @@ public class SmartClientSmartServerSslTest extends AllFactoriesHttpTestCase {
 		fsck(dst, B);
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(3, requests.size());
+		assertEquals(enableProtocolV2 ? 4 : 3, requests.size());
 	}
 
 	@Test

org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, 2017 Google Inc. and others
+ * Copyright (C) 2010, 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
@@ -86,13 +86,12 @@ import org.eclipse.jgit.transport.TransportHttp;
 import org.eclipse.jgit.transport.URIish;
 import org.eclipse.jgit.transport.UploadPack;
 import org.eclipse.jgit.transport.UsernamePasswordCredentialsProvider;
-import org.eclipse.jgit.transport.http.HttpConnectionFactory;
 import org.eclipse.jgit.util.HttpSupport;
 import org.eclipse.jgit.util.SystemReader;
 import org.junit.Before;
 import org.junit.Test;
 
-public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
+public class SmartClientSmartServerTest extends AllProtocolsHttpTestCase {
 	private static final String HDR_TRANSFER_ENCODING = "Transfer-Encoding";
 
 	private AdvertiseRefsHook advertiseRefsHook;
@@ -120,8 +119,8 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 
 	private RevCommit A, B, unreachableCommit;
 
-	public SmartClientSmartServerTest(HttpConnectionFactory cf) {
-		super(cf);
+	public SmartClientSmartServerTest(TestParameters params) {
+		super(params);
 	}
 
 	@Override
@@ -132,9 +131,12 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		final TestRepository<Repository> src = createTestRepository();
 		final String srcName = src.getRepository().getDirectory().getName();
 		src.getRepository()
-				.getConfig()
-				.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
-						ConfigConstants.CONFIG_KEY_LOGALLREFUPDATES, true);
+				.getConfig().setBoolean(ConfigConstants.CONFIG_CORE_SECTION,
+						null, ConfigConstants.CONFIG_KEY_LOGALLREFUPDATES,
+						true);
+		if (enableProtocolV2) {
+			src.getRepository().getConfig().setInt("protocol", null, "version", 2);
+		}
 
 		GitServlet gs = new GitServlet();
 		gs.setUploadPackFactory((HttpServletRequest req, Repository db) -> {
@@ -448,7 +450,7 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(B, map.get(Constants.HEAD).getObjectId());
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(1, requests.size());
+		assertEquals(enableProtocolV2 ? 2 : 1, requests.size());
 
 		AccessEvent info = requests.get(0);
 		assertEquals("GET", info.getMethod());
@@ -458,7 +460,22 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement", info
 				.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		} else {
+			AccessEvent lsRefs = requests.get(1);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 	}
 
 	@Test
@@ -576,9 +593,10 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(2, requests.size());
+		assertEquals(enableProtocolV2 ? 3 : 2, requests.size());
 
-		AccessEvent info = requests.get(0);
+		int requestNumber = 0;
+		AccessEvent info = requests.get(requestNumber++);
 		assertEquals("GET", info.getMethod());
 		assertEquals(join(remoteURI, "info/refs"), info.getPath());
 		assertEquals(1, info.getParameters().size());
@@ -586,9 +604,24 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement", info
 				.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		} else {
+			AccessEvent lsRefs = requests.get(requestNumber++);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 
-		AccessEvent service = requests.get(1);
+		AccessEvent service = requests.get(requestNumber);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
 		assertEquals(0, service.getParameters().size());
@@ -628,7 +661,8 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(2 + nofRedirects, requests.size());
+		assertEquals((enableProtocolV2 ? 3 : 2) + nofRedirects,
+				requests.size());
 
 		int n = 0;
 		while (n < nofRedirects) {
@@ -644,7 +678,22 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		} else {
+			AccessEvent lsRefs = requests.get(n++);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 
 		AccessEvent service = requests.get(n++);
 		assertEquals("POST", service.getMethod());
@@ -756,7 +805,7 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(3, requests.size());
+		assertEquals(enableProtocolV2 ? 4 : 3, requests.size());
 
 		AccessEvent info = requests.get(0);
 		assertEquals("GET", info.getMethod());
@@ -766,24 +815,27 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		}
 
 		AccessEvent redirect = requests.get(1);
 		assertEquals("POST", redirect.getMethod());
 		assertEquals(301, redirect.getStatus());
 
-		AccessEvent service = requests.get(2);
-		assertEquals("POST", service.getMethod());
-		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
-		assertEquals(0, service.getParameters().size());
-		assertNotNull("has content-length",
-				service.getRequestHeader(HDR_CONTENT_LENGTH));
-		assertNull("not chunked",
-				service.getRequestHeader(HDR_TRANSFER_ENCODING));
-
-		assertEquals(200, service.getStatus());
-		assertEquals("application/x-git-upload-pack-result",
-				service.getResponseHeader(HDR_CONTENT_TYPE));
+		for (int i = 2; i < requests.size(); i++) {
+			AccessEvent service = requests.get(i);
+			assertEquals("POST", service.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
+			assertEquals(0, service.getParameters().size());
+			assertNotNull("has content-length",
+					service.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					service.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals(200, service.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					service.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 	}
 
 	@Test
@@ -830,7 +882,7 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(3, requests.size());
+		assertEquals(enableProtocolV2 ? 4 : 3, requests.size());
 
 		AccessEvent info = requests.get(0);
 		assertEquals("GET", info.getMethod());
@@ -844,20 +896,24 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
-
-		AccessEvent service = requests.get(2);
-		assertEquals("POST", service.getMethod());
-		assertEquals(join(authURI, "git-upload-pack"), service.getPath());
-		assertEquals(0, service.getParameters().size());
-		assertNotNull("has content-length",
-				service.getRequestHeader(HDR_CONTENT_LENGTH));
-		assertNull("not chunked",
-				service.getRequestHeader(HDR_TRANSFER_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		}
 
-		assertEquals(200, service.getStatus());
-		assertEquals("application/x-git-upload-pack-result",
-				service.getResponseHeader(HDR_CONTENT_TYPE));
+		for (int i = 2; i < requests.size(); i++) {
+			AccessEvent service = requests.get(i);
+			assertEquals("POST", service.getMethod());
+			assertEquals(join(authURI, "git-upload-pack"), service.getPath());
+			assertEquals(0, service.getParameters().size());
+			assertNotNull("has content-length",
+					service.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					service.getRequestHeader(HDR_TRANSFER_ENCODING));
+
+			assertEquals(200, service.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					service.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 	}
 
 	@Test
@@ -937,19 +993,20 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(4, requests.size());
+		assertEquals(enableProtocolV2 ? 5 : 4, requests.size());
 
-		AccessEvent redirect = requests.get(0);
+		int requestNumber = 0;
+		AccessEvent redirect = requests.get(requestNumber++);
 		assertEquals("GET", redirect.getMethod());
 		assertEquals(join(cloneFrom, "info/refs"), redirect.getPath());
 		assertEquals(301, redirect.getStatus());
 
-		AccessEvent info = requests.get(1);
+		AccessEvent info = requests.get(requestNumber++);
 		assertEquals("GET", info.getMethod());
 		assertEquals(join(authURI, "info/refs"), info.getPath());
 		assertEquals(401, info.getStatus());
 
-		info = requests.get(2);
+		info = requests.get(requestNumber++);
 		assertEquals("GET", info.getMethod());
 		assertEquals(join(authURI, "info/refs"), info.getPath());
 		assertEquals(1, info.getParameters().size());
@@ -957,9 +1014,24 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		} else {
+			AccessEvent lsRefs = requests.get(requestNumber++);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(authURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 
-		AccessEvent service = requests.get(3);
+		AccessEvent service = requests.get(requestNumber);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(authURI, "git-upload-pack"), service.getPath());
 		assertEquals(0, service.getParameters().size());
@@ -987,7 +1059,7 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		}
 
 		List<AccessEvent> requests = getRequests();
-		assertEquals(3, requests.size());
+		assertEquals(enableProtocolV2 ? 4 : 3, requests.size());
 
 		AccessEvent info = requests.get(0);
 		assertEquals("GET", info.getMethod());
@@ -997,25 +1069,30 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals(200, info.getStatus());
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
-		assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		if (!enableProtocolV2) {
+			assertEquals("gzip", info.getResponseHeader(HDR_CONTENT_ENCODING));
+		}
 
 		AccessEvent service = requests.get(1);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(authOnPostURI, "git-upload-pack"), service.getPath());
 		assertEquals(401, service.getStatus());
 
-		service = requests.get(2);
-		assertEquals("POST", service.getMethod());
-		assertEquals(join(authOnPostURI, "git-upload-pack"), service.getPath());
-		assertEquals(0, service.getParameters().size());
-		assertNotNull("has content-length",
-				service.getRequestHeader(HDR_CONTENT_LENGTH));
-		assertNull("not chunked",
-				service.getRequestHeader(HDR_TRANSFER_ENCODING));
-
-		assertEquals(200, service.getStatus());
-		assertEquals("application/x-git-upload-pack-result",
-				service.getResponseHeader(HDR_CONTENT_TYPE));
+		for (int i = 2; i < requests.size(); i++) {
+			service = requests.get(i);
+			assertEquals("POST", service.getMethod());
+			assertEquals(join(authOnPostURI, "git-upload-pack"),
+					service.getPath());
+			assertEquals(0, service.getParameters().size());
+			assertNotNull("has content-length",
+					service.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					service.getRequestHeader(HDR_TRANSFER_ENCODING));
+
+			assertEquals(200, service.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					service.getResponseHeader(HDR_CONTENT_TYPE));
+		}
 	}
 
 	@Test
@@ -1052,9 +1129,11 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 
 		List<AccessEvent> requests = getRequests();
 		requests.removeAll(cloneRequests);
-		assertEquals(2, requests.size());
 
-		AccessEvent info = requests.get(0);
+		assertEquals(enableProtocolV2 ? 3 : 2, requests.size());
+
+		int requestNumber = 0;
+		AccessEvent info = requests.get(requestNumber++);
 		assertEquals("GET", info.getMethod());
 		assertEquals(join(remoteURI, "info/refs"), info.getPath());
 		assertEquals(1, info.getParameters().size());
@@ -1063,9 +1142,24 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals("application/x-git-upload-pack-advertisement",
 				info.getResponseHeader(HDR_CONTENT_TYPE));
 
+		if (enableProtocolV2) {
+			AccessEvent lsRefs = requests.get(requestNumber++);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
+
 		// We should have needed one request to perform the fetch.
 		//
-		AccessEvent service = requests.get(1);
+		AccessEvent service = requests.get(requestNumber);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
 		assertEquals(0, service.getParameters().size());
@@ -1116,9 +1210,10 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 
 		List<AccessEvent> requests = getRequests();
 		requests.removeAll(cloneRequests);
-		assertEquals(3, requests.size());
+		assertEquals(enableProtocolV2 ? 4 : 3, requests.size());
 
-		AccessEvent info = requests.get(0);
+		int requestNumber = 0;
+		AccessEvent info = requests.get(requestNumber++);
 		assertEquals("GET", info.getMethod());
 		assertEquals(join(remoteURI, "info/refs"), info.getPath());
 		assertEquals(1, info.getParameters().size());
@@ -1127,10 +1222,25 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals("application/x-git-upload-pack-advertisement", info
 				.getResponseHeader(HDR_CONTENT_TYPE));
 
+		if (enableProtocolV2) {
+			AccessEvent lsRefs = requests.get(requestNumber++);
+			assertEquals("POST", lsRefs.getMethod());
+			assertEquals(join(remoteURI, "git-upload-pack"), lsRefs.getPath());
+			assertEquals(0, lsRefs.getParameters().size());
+			assertNotNull("has content-length",
+					lsRefs.getRequestHeader(HDR_CONTENT_LENGTH));
+			assertNull("not chunked",
+					lsRefs.getRequestHeader(HDR_TRANSFER_ENCODING));
+			assertEquals("version=2", lsRefs.getRequestHeader("Git-Protocol"));
+			assertEquals(200, lsRefs.getStatus());
+			assertEquals("application/x-git-upload-pack-result",
+					lsRefs.getResponseHeader(HDR_CONTENT_TYPE));
+		}
+
 		// We should have needed two requests to perform the fetch
 		// due to the high number of local unknown commits.
 		//
-		AccessEvent service = requests.get(1);
+		AccessEvent service = requests.get(requestNumber++);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
 		assertEquals(0, service.getParameters().size());
@@ -1143,7 +1253,7 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		assertEquals("application/x-git-upload-pack-result", service
 				.getResponseHeader(HDR_CONTENT_TYPE));
 
-		service = requests.get(2);
+		service = requests.get(requestNumber);
 		assertEquals("POST", service.getMethod());
 		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
 		assertEquals(0, service.getParameters().size());
@@ -1429,5 +1539,4 @@ public class SmartClientSmartServerTest extends AllFactoriesHttpTestCase {
 		cfg.setBoolean("http", null, "receivepack", true);
 		cfg.save();
 	}
-
 }

org.eclipse.jgit.ssh.apache.test/tst/org/eclipse/jgit/transport/sshd/ApacheSshProtocol2Test.java

@@ -0,0 +1,24 @@
+/*
+ * 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.sshd;
+
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.lib.StoredConfig;
+
+public class ApacheSshProtocol2Test extends ApacheSshTest {
+
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		StoredConfig config = ((Repository) db).getConfig();
+		config.setInt("protocol", null, "version", 2);
+		config.save();
+	}
+}

org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSession.java

@@ -24,6 +24,7 @@ import java.util.Collections;
 import java.util.EnumSet;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
@@ -53,7 +54,7 @@ import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.internal.transport.sshd.JGitSshClient;
 import org.eclipse.jgit.internal.transport.sshd.SshdText;
 import org.eclipse.jgit.transport.FtpChannel;
-import org.eclipse.jgit.transport.RemoteSession;
+import org.eclipse.jgit.transport.RemoteSession2;
 import org.eclipse.jgit.transport.SshConstants;
 import org.eclipse.jgit.transport.URIish;
 import org.eclipse.jgit.util.StringUtils;
@@ -61,11 +62,12 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * An implementation of {@link RemoteSession} based on Apache MINA sshd.
+ * An implementation of {@link org.eclipse.jgit.transport.RemoteSession
+ * RemoteSession} based on Apache MINA sshd.
  *
  * @since 5.2
  */
-public class SshdSession implements RemoteSession {
+public class SshdSession implements RemoteSession2 {
 
 	private static final Logger LOG = LoggerFactory
 			.getLogger(SshdSession.class);
@@ -290,8 +292,15 @@ public class SshdSession implements RemoteSession {
 
 	@Override
 	public Process exec(String commandName, int timeout) throws IOException {
+		return exec(commandName, Collections.emptyMap(), timeout);
+	}
+
+	@Override
+	public Process exec(String commandName, Map<String, String> environment,
+			int timeout) throws IOException {
 		@SuppressWarnings("resource")
-		ChannelExec exec = session.createExecChannel(commandName);
+		ChannelExec exec = session.createExecChannel(commandName, null,
+				environment);
 		if (timeout <= 0) {
 			try {
 				exec.open().verify();

org.eclipse.jgit.ssh.jsch.test/tst/org/eclipse/jgit/transport/JSchSshProtocol2Test.java

@@ -0,0 +1,26 @@
+/*
+ * 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
+ */
+
+//TODO(ms): move to org.eclipse.jgit.ssh.jsch in 6.0
+package org.eclipse.jgit.transport;
+
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.lib.StoredConfig;
+
+public class JSchSshProtocol2Test extends JSchSshTest {
+
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		StoredConfig config = ((Repository) db).getConfig();
+		config.setInt("protocol", null, "version", 2);
+		config.save();
+	}
+}

org.eclipse.jgit.ssh.jsch/src/org/eclipse/jgit/transport/JschSession.java

@@ -22,7 +22,9 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.concurrent.TimeUnit;
 
@@ -44,7 +46,7 @@ import com.jcraft.jsch.SftpException;
  * {@link org.eclipse.jgit.transport.JschConfigSessionFactory} is used to create
  * the actual session passed to the constructor.
  */
-public class JschSession implements RemoteSession {
+public class JschSession implements RemoteSession2 {
 	final Session sock;
 	final URIish uri;
 
@@ -65,7 +67,14 @@ public class JschSession implements RemoteSession {
 	/** {@inheritDoc} */
 	@Override
 	public Process exec(String command, int timeout) throws IOException {
-		return new JschProcess(command, timeout);
+		return exec(command, Collections.emptyMap(), timeout);
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public Process exec(String command, Map<String, String> environment,
+			int timeout) throws IOException {
+		return new JschProcess(command, environment, timeout);
 	}
 
 	/** {@inheritDoc} */
@@ -124,6 +133,8 @@ public class JschSession implements RemoteSession {
 		 *
 		 * @param commandName
 		 *            the command to execute
+		 * @param environment
+		 *            environment variables to pass on
 		 * @param tms
 		 *            the timeout value, in seconds, for the command.
 		 * @throws TransportException
@@ -132,11 +143,17 @@ public class JschSession implements RemoteSession {
 		 * @throws IOException
 		 *             on problems opening streams
 		 */
-		JschProcess(String commandName, int tms)
-				throws TransportException, IOException {
+		JschProcess(String commandName, Map<String, String> environment,
+				int tms) throws TransportException, IOException {
 			timeout = tms;
 			try {
 				channel = (ChannelExec) sock.openChannel("exec"); //$NON-NLS-1$
+				if (environment != null) {
+					for (Map.Entry<String, String> envVar : environment
+							.entrySet()) {
+						channel.setEnv(envVar.getKey(), envVar.getValue());
+					}
+				}
 				channel.setCommand(commandName);
 				setupStreams();
 				channel.connect(timeout > 0 ? timeout * 1000 : 0);

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -232,6 +232,7 @@ 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.

org.eclipse.jgit/src/org/eclipse/jgit/api/LsRemoteCommand.java

@@ -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)

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

@@ -260,6 +260,7 @@ 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;

org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackConnection.java

@@ -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;
@@ -21,20 +26,28 @@ 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.HashMap;
 import java.util.HashSet;
 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.util.TemporaryBuffer;
 import org.eclipse.jgit.util.io.InterruptTimer;
 import org.eclipse.jgit.util.io.TimeoutInputStream;
 import org.eclipse.jgit.util.io.TimeoutOutputStream;
@@ -86,17 +99,27 @@ 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.
 	 *
@@ -141,12 +164,15 @@ 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;
@@ -156,35 +182,66 @@ abstract class BasePackConnection extends BaseConnection {
 		}
 	}
 
-	private void readAdvertisedRefsImpl() throws IOException {
+	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;
+	}
+
+	private boolean readAdvertisedRefsImpl() throws IOException {
 		final LinkedHashMap<String, Ref> avail = new LinkedHashMap<>();
-		for (;;) {
+		for (boolean first = true;; first = false) {
 			String line;
 
-			try {
-				line = pckIn.readString();
-			} catch (EOFException eof) {
-				if (avail.isEmpty())
+			if (first) {
+				boolean isV1 = false;
+				try {
+					line = readLine();
+				} catch (EOFException e) {
 					throw noRepository();
-				throw eof;
-			}
-			if (PacketLineIn.isEnd(line))
-				break;
-
-			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));
-			}
-
-			if (avail.isEmpty()) {
+				}
+				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(" ")) { //$NON-NLS-1$
+						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;
 				}
 			}
 
@@ -193,44 +250,230 @@ 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
+				// TODO: throw error if protocol version is >= V2?
 				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));
+			} else {
+				processLineV1(name, id, avail);
+			}
+		}
+		available(avail);
+		return true;
+	}
 
-				if (prior.getPeeledObjectId() != null)
-					throw duplicateAdvertisement(name + "^{}"); //$NON-NLS-1$
+	/**
+	 * Issue a protocol V2 ls-refs command and read its response.
+	 *
+	 * @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
+	 */
+	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);
+		}
+	}
 
-				avail.put(name, new ObjectIdRef.PeeledTag(
-						Ref.Storage.NETWORK, name, prior.getObjectId(), id));
+	private void lsRefsImpl(Collection<RefSpec> refSpecs,
+			String... additionalPatterns) throws IOException {
+		TemporaryBuffer state = null;
+		PacketLineOut pckState = null;
+		PacketLineOut output = pckOut;
+		if (statelessRPC) {
+			state = new TemporaryBuffer.Heap(Integer.MAX_VALUE);
+			pckState = new PacketLineOut(state);
+			output = pckState;
+		}
+		output.writeString("command=" + COMMAND_LS_REFS); //$NON-NLS-1$
+		// Add the user-agent
+		String agent = UserAgent.get();
+		if (agent != null && isCapableOf(OPTION_AGENT)) {
+			output.writeString(OPTION_AGENT + '=' + agent);
+		}
+		output.writeDelim();
+		output.writeString("peel"); //$NON-NLS-1$
+		for (String refPrefix : getRefPrefixes(refSpecs, additionalPatterns)) {
+			output.writeString("ref-prefix " + refPrefix); //$NON-NLS-1$
+		}
+		output.end();
+		output.flush();
+		if (state != null) {
+			state.writeTo(out, null);
+			out.flush();
+			state = null;
+			pckState = null;
+		}
+		final LinkedHashMap<String, Ref> avail = new LinkedHashMap<>();
+		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 {
-				final Ref prior = avail.put(name, new ObjectIdRef.PeeledNonTag(
-						Ref.Storage.NETWORK, name, id));
-				if (prior != null)
-					throw duplicateAdvertisement(name);
+				processLineV2(line, id, name, avail);
 			}
 		}
 		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) 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 (symRefTarget != null) {
+			// What do we have to do with this information? In protocol V0, this
+			// info comes in the capability advertisement, but OPTION_SYMREF is
+			// used only in RefAdvertiser. JGit's client side doesn't make use
+			// of this information, and actually never requests it.
+		}
+	}
+
 	/**
 	 * Create an exception to indicate problems finding a remote repository. The
 	 * caller is expected to throw the returned exception.
@@ -252,7 +495,7 @@ abstract class BasePackConnection extends BaseConnection {
 	 * @return whether this option is supported
 	 */
 	protected boolean isCapableOf(String option) {
-		return remoteCapablities.contains(option);
+		return remoteCapabilities.containsKey(option);
 	}
 
 	/**
@@ -272,6 +515,17 @@ abstract class BasePackConnection extends BaseConnection {
 		return true;
 	}
 
+	/**
+	 * 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
 	 *
@@ -280,7 +534,7 @@ 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);
 		}
 	}
@@ -288,7 +542,8 @@ 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) {

org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java

@@ -16,9 +16,12 @@ 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;
@@ -212,6 +215,8 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 
 	private PacketLineOut pckState;
 
+	private Set<String> fetchCapabilities = new HashSet<>();
+
 	/**
 	 * Either FilterSpec.NO_FILTER for a filter that doesn't filter
 	 * anything, or a filter that indicates what and what not to send to the
@@ -354,6 +359,28 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 				pckState = new PacketLineOut(state);
 			}
 
+			if (TransferConfig.ProtocolVersion.V2
+					.equals(getProtocolVersion())) {
+				sideband = true;
+				noDone = true;
+				multiAck = MultiAck.DETAILED;
+				setFetchOptions();
+				PacketLineOut output = statelessRPC ? pckState : pckOut;
+				output.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)) {
+					output.writeString(
+							GitProtocolConstants.OPTION_AGENT + '=' + agent);
+				}
+				output.writeDelim();
+				// Arguments
+				for (String capability : getCapabilitiesV2()) {
+					output.writeString(capability);
+				}
+			}
 			if (sendWants(want)) {
 				negotiate(monitor);
 
@@ -362,6 +389,25 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 				state = null;
 				pckState = null;
 
+				if (TransferConfig.ProtocolVersion.V2
+						.equals(getProtocolVersion())) {
+					String header = pckIn.readString();
+					if (PacketLineIn.isEnd(header)) {
+						// No packfile following.
+						return;
+					}
+
+					if (header.startsWith("ERR ")) { //$NON-NLS-1$
+						// Protocol V2 may give us an error here (for instance,
+						// invalid want)
+						throw new PackProtocolException(header.substring(4));
+					}
+					if (!GitProtocolConstants.SECTION_PACKFILE.equals(header)) {
+						throw new PackProtocolException(MessageFormat.format(
+								JGitText.get().expectedGot,
+								GitProtocolConstants.SECTION_PACKFILE, header));
+					}
+				}
 				receivePack(monitor, outputStream);
 			}
 		} catch (CancelledException ce) {
@@ -381,6 +427,14 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		super.close();
 	}
 
+	private void setFetchOptions() {
+		String advertised = getCapability(GitProtocolConstants.COMMAND_FETCH);
+		if (advertised == null) {
+			return;
+		}
+		fetchCapabilities.addAll(Arrays.asList(advertised.split(" "))); //$NON-NLS-1$
+	}
+
 	FetchConfig getFetchConfig() {
 		return local.getConfig().get(FetchConfig::new);
 	}
@@ -479,10 +533,11 @@ 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 +547,35 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		if (!filterSpec.isNoOp()) {
 			p.writeString(filterSpec.filterLine());
 		}
-		p.end();
-		outNeedsEnd = false;
+		if (TransferConfig.ProtocolVersion.V0.equals(getProtocolVersion())) {
+			p.end();
+			outNeedsEnd = false;
+		}
 		return true;
 	}
 
+	private Set<String> getCapabilitiesV2() throws TransportException {
+		Set<String> capabilities = new LinkedHashSet<>();
+		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()
+				&& !fetchCapabilities.contains(OPTION_FILTER)) {
+			throw new PackProtocolException(uri,
+					JGitText.get().filterRequiresCapability);
+		}
+		return capabilities;
+	}
+
 	private String enableCapabilities() throws TransportException {
 		final StringBuilder line = new StringBuilder();
 		if (noProgress)
@@ -550,6 +629,7 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 		boolean receivedContinue = false;
 		boolean receivedAck = false;
 		boolean receivedReady = false;
+		boolean needsAcknowledgementV2 = true;
 
 		if (statelessRPC) {
 			state.writeTo(out, null);
@@ -563,7 +643,7 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 			}
 
 			ObjectId o = c.getId();
-			pckOut.writeString("have " + o.name() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
+			pckOut.writeString("have " + o.name() + '\n'); //$NON-NLS-1$
 			havesSent++;
 			havesSinceLastContinue++;
 
@@ -580,6 +660,7 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 			}
 
 			pckOut.end();
+			outNeedsEnd = false;
 			resultsPending++; // Each end will cause a result to come back.
 
 			if (havesSent == 32 && !statelessRPC) {
@@ -591,9 +672,32 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 				continue;
 			}
 
+			// Read the section header
+			if (needsAcknowledgementV2 && TransferConfig.ProtocolVersion.V2
+					.equals(getProtocolVersion())) {
+				String header = pckIn.readString();
+				if (!GitProtocolConstants.SECTION_ACKNOWLEDGMENTS
+						.equals(header)) {
+					throw new PackProtocolException(MessageFormat.format(
+							JGitText.get().expectedGot,
+							GitProtocolConstants.SECTION_ACKNOWLEDGMENTS,
+							header));
+				}
+				needsAcknowledgementV2 = false;
+			}
 			READ_RESULT: for (;;) {
-				final AckNackResult anr = pckIn.readACK(ackId);
+				AckNackResult anr = pckIn.readACKorEOF(ackId);
 				switch (anr) {
+				case ACK_EOF:
+					if (TransferConfig.ProtocolVersion.V0
+							.equals(getProtocolVersion())) {
+						throw new PackProtocolException(
+								JGitText.get().expectedACKNAKFoundEOF);
+					}
+					// More lines needed
+					resultsPending--;
+					break READ_RESULT;
+
 				case NAK:
 					// More have lines are necessary to compute the
 					// pack on the remote side. Keep doing that.
@@ -602,17 +706,24 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 					break READ_RESULT;
 
 				case ACK:
-					// The remote side is happy and knows exactly what
-					// to send us. There is no further negotiation and
-					// we can break out immediately.
-					//
-					multiAck = MultiAck.OFF;
-					resultsPending = 0;
-					receivedAck = true;
-					if (statelessRPC) {
-						state.writeTo(out, null);
+					if (TransferConfig.ProtocolVersion.V0
+							.equals(getProtocolVersion())) {
+						// The remote side is happy and knows exactly what
+						// to send us. There is no further negotiation and
+						// we can break out immediately.
+						//
+						multiAck = MultiAck.OFF;
+						resultsPending = 0;
+						receivedAck = true;
+						if (statelessRPC) {
+							state.writeTo(out, null);
+						}
+						break SEND_HAVES;
 					}
-					break SEND_HAVES;
+					// Keep on reading ACKs until we get the ACK_READY
+					markCommon(walk.parseAny(ackId), AckNackResult.ACK_COMMON);
+					receivedAck = true;
+					break;
 
 				case ACK_CONTINUE:
 				case ACK_COMMON:
@@ -628,6 +739,12 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 					havesSinceLastContinue = 0;
 					if (anr == AckNackResult.ACK_READY) {
 						receivedReady = true;
+						if (TransferConfig.ProtocolVersion.V2
+								.equals(getProtocolVersion())) {
+							multiAck = MultiAck.OFF;
+							resultsPending = 0;
+							break SEND_HAVES;
+						}
 					}
 					break;
 				}
@@ -661,15 +778,36 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 			throw new CancelledException();
 		}
 
+		if (receivedReady && TransferConfig.ProtocolVersion.V2
+				.equals(getProtocolVersion())) {
+			// We'll get the packfile right away. Skip the delimiter.
+			String delim = pckIn.readString();
+			if (!PacketLineIn.isDelimiter(delim)) {
+				throw new PackProtocolException(MessageFormat
+						.format(JGitText.get().expectedGot, "0001", delim)); //$NON-NLS-1$
+			}
+			return;
+		}
 		if (!receivedReady || !noDone) {
 			// When statelessRPC is true we should always leave SEND_HAVES
 			// loop above while in the middle of a request. This allows us
 			// to just write done immediately.
 			//
 			pckOut.writeString("done\n"); //$NON-NLS-1$
+			if (TransferConfig.ProtocolVersion.V2
+					.equals(getProtocolVersion())) {
+				pckOut.end();
+				outNeedsEnd = false;
+				pckOut.flush();
+				// Protocol V2 will skip acknowledgments completely if we send
+				// a done.
+				return;
+			}
 			pckOut.flush();
 		}
 
+		// Below is protocol V0 only.
+
 		if (!receivedAck) {
 			// Apparently if we have never received an ACK earlier
 			// there is one more result expected from the done we
@@ -689,6 +827,14 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 				//
 				break;
 
+			case ACK_EOF:
+				if (TransferConfig.ProtocolVersion.V0
+						.equals(getProtocolVersion())) {
+					throw new PackProtocolException(
+							JGitText.get().expectedACKNAKFoundEOF);
+				}
+				break READ_RESULT;
+
 			case ACK:
 				// A solitary ACK at this point means the remote won't
 				// speak anymore, but is going to send us a pack now.
@@ -697,7 +843,16 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 
 			case ACK_CONTINUE:
 			case ACK_COMMON:
+				// We will expect a normal ACK to break out of the loop.
+				//
+				multiAck = MultiAck.CONTINUE;
+				break;
+
 			case ACK_READY:
+				if (TransferConfig.ProtocolVersion.V2
+						.equals(getProtocolVersion())) {
+					break READ_RESULT;
+				}
 				// We will expect a normal ACK to break out of the loop.
 				//
 				multiAck = MultiAck.CONTINUE;

org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java

@@ -102,7 +102,21 @@ class FetchProcess {
 	private void executeImp(final ProgressMonitor monitor,
 			final FetchResult result) throws NotSupportedException,
 			TransportException {
-		conn = transport.openFetch();
+		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());
 			result.peerUserAgent = conn.getPeerUserAgent();
@@ -119,7 +133,6 @@ 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 +266,17 @@ 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

org.eclipse.jgit/src/org/eclipse/jgit/transport/GitProtocolConstants.java

@@ -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 5.10
+	 */
+	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 5.10
+	 */
+	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 5.10
+	 */
+	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 5.10
+	 */
+	public static final String REF_ATTR_SYMREF_TARGET = "symref-target:"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 acknowledgments section header.
+	 *
+	 * @since 5.10
+	 */
+	public static final String SECTION_ACKNOWLEDGMENTS = "acknowledgments"; //$NON-NLS-1$
+
+	/**
+	 * Protocol V2 packfile section header.
+	 *
+	 * @since 5.10
+	 */
+	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 5.10
+	 */
+	public static final String VERSION_1 = "version 1"; //$NON-NLS-1$
+
+	/**
+	 * Protocol announcement for protocol version 2.
+	 *
+	 * @since 5.10
+	 */
+	public static final String VERSION_2 = "version 2"; //$NON-NLS-1$
+
+	/**
+	 * Protocol request for protocol version 2.
+	 *
+	 * @since 5.10
+	 */
+	public static final String VERSION_2_REQUEST = "version=2"; //$NON-NLS-1$
+
 	enum MultiAck {
 		OFF, CONTINUE, DETAILED;
 	}

org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java

@@ -72,7 +72,9 @@ public class PacketLineIn {
 		/** ACK + common */
 		ACK_COMMON,
 		/** ACK + ready */
-		ACK_READY;
+		ACK_READY,
+		/** EOF (0000) recieved in protocol V2 when expecting an ACK/NAK */
+		ACK_EOF;
 	}
 
 	private final byte[] lineBuffer = new byte[SideBandOutputStream.SMALL_BUF];
@@ -103,12 +105,26 @@ public class PacketLineIn {
 		this.limit = limit;
 	}
 
+
 	AckNackResult readACK(MutableObjectId returnedId) throws IOException {
+		AckNackResult result = readACKorEOF(returnedId);
+		if (result == AckNackResult.ACK_EOF) {
+			throw new PackProtocolException(
+					JGitText.get().expectedACKNAKFoundEOF);
+		}
+		return result;
+	}
+
+	AckNackResult readACKorEOF(MutableObjectId returnedId) throws IOException {
 		final String line = readString();
 		if (line.length() == 0)
-			throw new PackProtocolException(JGitText.get().expectedACKNAKFoundEOF);
+			return AckNackResult.ACK_EOF;
 		if ("NAK".equals(line)) //$NON-NLS-1$
 			return AckNackResult.NAK;
+		if ("ready".equals(line)) { //$NON-NLS-1$
+			// Protocol V2
+			return AckNackResult.ACK_READY;
+		}
 		if (line.startsWith("ACK ")) { //$NON-NLS-1$
 			returnedId.fromString(line.substring(4, 44));
 			if (line.length() == 44)

org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java

@@ -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 //$NON-NLS-1$

org.eclipse.jgit/src/org/eclipse/jgit/transport/RemoteSession2.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2020, Thomas Wolf <thoams.wolf@paranor.ch>
+ *
+ * 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 5.10
+ */
+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;
+}

org.eclipse.jgit/src/org/eclipse/jgit/transport/Transport.java

@@ -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);
@@ -1452,6 +1458,43 @@ public abstract class Transport implements AutoCloseable {
 	public abstract FetchConnection openFetch() throws NotSupportedException,
 			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 5.10
+	 */
+	public FetchConnection openFetch(Collection<RefSpec> refSpecs,
+			String... additionalPatterns)
+			throws NotSupportedException, TransportException {
+		return openFetch();
+	}
+
 	/**
 	 * Begins a new connection for pushing into the remote repository.
 	 *

org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitAnon.java

@@ -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 {
@@ -130,7 +138,8 @@ 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 +153,11 @@ 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 +166,11 @@ 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 +181,19 @@ 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 +226,7 @@ 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,

org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportGitSsh.java

@@ -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(),

org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java

@@ -33,8 +33,8 @@ 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;
@@ -339,11 +339,15 @@ 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.
@@ -357,11 +361,23 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 	@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 +472,9 @@ 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;
 	}
@@ -494,6 +511,12 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 
 	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);
 		int authAttempts = 1;
 		int redirects = 0;
@@ -507,6 +530,11 @@ 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) {
@@ -1148,20 +1176,37 @@ 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".getBytes()) && magic[12] >= '1' && magic[12] <= '9') { //$NON-NLS-1$
+			// 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 +1372,24 @@ 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 +1397,8 @@ 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 +1427,8 @@ 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 +1448,14 @@ 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 +1471,10 @@ 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 +1730,9 @@ 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 +1769,10 @@ 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. */

org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportLocal.java

@@ -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

org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

@@ -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);
 	}
 
 	/**
@@ -1194,7 +1195,8 @@ public class UploadPack {
 					new PacketLineOut(NullOutputStream.INSTANCE),
 					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"); //$NON-NLS-1$ //$NON-NLS-2$
@@ -1243,7 +1245,8 @@ 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
@@ -2327,7 +2330,8 @@ 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);