Introduce ProtocolV2Hook

In Git protocol v2, UploadPack and ReceivePack have the same
capabilities and can process any protocol v2 request. For example, a
client can sent a "fetch" command to the "/git-receive-pack" endpoint.

This makes it difficult for existing hook interfaces. For example,
PreUploadHook takes UploadPack, but a "fetch" command may be received by
ReceivePack.

To resolve this skew, this change introduce a different hook interface
for the protocol v2. The hook takes a request that is independent to the
handlers (UploadPack, ReceivePack). Also this makes it clear what
parameters the hook is counting on, instead of keep track of the hook
using getters from UploadPack / ReceivePack.

Bug: 534847
Change-Id: I71f3266584483db1e2b2edfc1a72d0bdf1bb6041
Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>

5 files changed, 375 insertions, 32 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java
index 9c43c0b0a4..79d3d87e2d 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java
@@ -3,20 +3,22 @@ package org.eclipse.jgit.transport;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.hasItems;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.theInstance;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Map;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.StringWriter;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
 import org.eclipse.jgit.errors.PackProtocolException;
 import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.internal.storage.dfs.DfsGarbageCollector;
@@ -31,8 +33,8 @@ import org.eclipse.jgit.lib.Sets;
 import org.eclipse.jgit.lib.TextProgressMonitor;
 import org.eclipse.jgit.revwalk.RevBlob;
 import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.RevTag;
+import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.transport.UploadPack.RequestPolicy;
 import org.eclipse.jgit.transport.resolver.ServiceNotAuthorizedException;
 import org.eclipse.jgit.transport.resolver.ServiceNotEnabledException;
@@ -421,7 +423,8 @@ public class UploadPackTest {
 	 * and returns UploadPack's output stream.
 	 */
 	private ByteArrayInputStream uploadPackV2Setup(RequestPolicy requestPolicy,
-			RefFilter refFilter, String... inputLines) throws Exception {
+			RefFilter refFilter, ProtocolV2Hook hook, String... inputLines)
+			throws Exception {
 
 		ByteArrayOutputStream send = new ByteArrayOutputStream();
 		PacketLineOut pckOut = new PacketLineOut(send);
@@ -442,6 +445,9 @@ public class UploadPackTest {
 		if (refFilter != null)
 			up.setRefFilter(refFilter);
 		up.setExtraParameters(Sets.of("version=2"));
+		if (hook != null) {
+			up.setProtocolV2Hook(hook);
+		}
 
 		ByteArrayOutputStream recv = new ByteArrayOutputStream();
 		up.upload(new ByteArrayInputStream(send.toByteArray()), recv, null);
@@ -455,9 +461,10 @@ public class UploadPackTest {
 	 * advertisement by the server.
 	 */
 	private ByteArrayInputStream uploadPackV2(RequestPolicy requestPolicy,
-			RefFilter refFilter, String... inputLines) throws Exception {
+			RefFilter refFilter, ProtocolV2Hook hook, String... inputLines)
+			throws Exception {
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(requestPolicy, refFilter, inputLines);
+				uploadPackV2Setup(requestPolicy, refFilter, hook, inputLines);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
 		// drain capabilities
@@ -468,15 +475,33 @@ public class UploadPackTest {
 	}
 
 	private ByteArrayInputStream uploadPackV2(String... inputLines) throws Exception {
-		return uploadPackV2(null, null, inputLines);
+		return uploadPackV2(null, null, null, inputLines);
+	}
+
+	private static class TestV2Hook implements ProtocolV2Hook {
+		private CapabilitiesV2Request capabilitiesRequest;
+
+		private LsRefsV2Request lsRefsRequest;
+
+		@Override
+		public void onCapabilities(CapabilitiesV2Request req) {
+			capabilitiesRequest = req;
+		}
+
+		@Override
+		public void onLsRefs(LsRefsV2Request req) {
+			lsRefsRequest = req;
+		}
 	}
 
 	@Test
 	public void testV2Capabilities() throws Exception {
+		TestV2Hook hook = new TestV2Hook();
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(null, null, PacketLineIn.END);
+				uploadPackV2Setup(null, null, hook, PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
+		assertThat(hook.capabilitiesRequest, notNullValue());
 		assertThat(pckIn.readString(), is("version 2"));
 		assertThat(
 			Arrays.asList(pckIn.readString(), pckIn.readString()),
@@ -494,7 +519,7 @@ public class UploadPackTest {
 	public void testV2CapabilitiesAllowFilter() throws Exception {
 		server.getConfig().setBoolean("uploadpack", null, "allowfilter", true);
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(null, null, PacketLineIn.END);
+				uploadPackV2Setup(null, null, null, PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
 		assertThat(pckIn.readString(), is("version 2"));
@@ -510,7 +535,7 @@ public class UploadPackTest {
 	public void testV2CapabilitiesRefInWant() throws Exception {
 		server.getConfig().setBoolean("uploadpack", null, "allowrefinwant", true);
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(null, null, PacketLineIn.END);
+				uploadPackV2Setup(null, null, null, PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
 		assertThat(pckIn.readString(), is("version 2"));
@@ -526,7 +551,7 @@ public class UploadPackTest {
 	public void testV2CapabilitiesRefInWantNotAdvertisedIfUnallowed() throws Exception {
 		server.getConfig().setBoolean("uploadpack", null, "allowrefinwant", false);
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(null, null, PacketLineIn.END);
+				uploadPackV2Setup(null, null, null, PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
 		assertThat(pckIn.readString(), is("version 2"));
@@ -541,7 +566,7 @@ public class UploadPackTest {
 		server.getConfig().setBoolean("uploadpack", null, "allowrefinwant", true);
 		server.getConfig().setBoolean("uploadpack", null, "advertiserefinwant", false);
 		ByteArrayInputStream recvStream =
-			uploadPackV2Setup(null, null, PacketLineIn.END);
+				uploadPackV2Setup(null, null, null, PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
 		assertThat(pckIn.readString(), is("version 2"));
@@ -568,9 +593,12 @@ public class UploadPackTest {
 		RevTag tag = remote.tag("tag", tip);
 		remote.update("refs/tags/tag", tag);
 
-		ByteArrayInputStream recvStream = uploadPackV2("command=ls-refs\n", PacketLineIn.END);
+		TestV2Hook hook = new TestV2Hook();
+		ByteArrayInputStream recvStream = uploadPackV2(null, null, hook,
+				"command=ls-refs\n", PacketLineIn.END);
 		PacketLineIn pckIn = new PacketLineIn(recvStream);
 
+		assertThat(hook.lsRefsRequest, notNullValue());
 		assertThat(pckIn.readString(), is(tip.toObjectId().getName() + " HEAD"));
 		assertThat(pckIn.readString(), is(tip.toObjectId().getName() + " refs/heads/master"));
 		assertThat(pckIn.readString(), is(tag.toObjectId().getName() + " refs/tags/tag"));
@@ -722,6 +750,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.ADVERTISED,
 			null,
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + advertized.name() + "\n",
@@ -734,6 +763,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.ADVERTISED,
 			null,
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + unadvertized.name() + "\n",
@@ -751,6 +781,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.REACHABLE_COMMIT,
 			null,
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + reachable.name() + "\n",
@@ -763,6 +794,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.REACHABLE_COMMIT,
 			null,
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + unreachable.name() + "\n",
@@ -779,6 +811,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.TIP,
 			new RejectAllRefFilter(),
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + tip.name() + "\n",
@@ -791,6 +824,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.TIP,
 			new RejectAllRefFilter(),
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + parentOfTip.name() + "\n",
@@ -808,6 +842,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.REACHABLE_COMMIT_TIP,
 			new RejectAllRefFilter(),
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + parentOfTip.name() + "\n",
@@ -820,6 +855,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.REACHABLE_COMMIT_TIP,
 			new RejectAllRefFilter(),
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + unreachable.name() + "\n",
@@ -834,6 +870,7 @@ public class UploadPackTest {
 		uploadPackV2(
 			RequestPolicy.ANY,
 			null,
+			null,
 			"command=fetch\n",
 			PacketLineIn.DELIM,
 			"want " + unreachable.name() + "\n",
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/CapabilitiesV2Request.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/CapabilitiesV2Request.java
new file mode 100644
index 0000000000..b133ab579a
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/CapabilitiesV2Request.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2018, Google LLC.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.transport;
+
+/**
+ * Capabilities protocol v2 request.
+ *
+ * <p>
+ * This is used as an input to {@link ProtocolV2Hook}.
+ *
+ * @since 5.1
+ */
+public final class CapabilitiesV2Request {
+	private CapabilitiesV2Request() {
+	}
+
+	/** @return A builder of {@link CapabilitiesV2Request}. */
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	/** A builder for {@link CapabilitiesV2Request}. */
+	public static final class Builder {
+		private Builder() {
+		}
+
+		/** @return CapabilitiesV2Request */
+		public CapabilitiesV2Request build() {
+			return new CapabilitiesV2Request();
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/LsRefsV2Request.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/LsRefsV2Request.java
new file mode 100644
index 0000000000..3aff584a00
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/LsRefsV2Request.java
@@ -0,0 +1,134 @@
+/*
+ * Copyright (C) 2018, Google LLC.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.transport;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * ls-refs protocol v2 request.
+ *
+ * <p>
+ * This is used as an input to {@link ProtocolV2Hook}.
+ *
+ * @since 5.1
+ */
+public final class LsRefsV2Request {
+	private final List<String> refPrefixes;
+
+	private final boolean symrefs;
+
+	private final boolean peel;
+
+	private LsRefsV2Request(List<String> refPrefixes, boolean symrefs,
+			boolean peel) {
+		this.refPrefixes = refPrefixes;
+		this.symrefs = symrefs;
+		this.peel = peel;
+	}
+
+	/** @return ref prefixes that the client requested. */
+	public List<String> getRefPrefixes() {
+		return refPrefixes;
+	}
+
+	/** @return true if the client requests symbolic references. */
+	public boolean getSymrefs() {
+		return symrefs;
+	}
+
+	/** @return true if the client requests tags to be peeled. */
+	public boolean getPeel() {
+		return peel;
+	}
+
+	/** @return A builder of {@link LsRefsV2Request}. */
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	/** A builder for {@link LsRefsV2Request}. */
+	public static final class Builder {
+		private List<String> refPrefixes = Collections.emptyList();
+
+		private boolean symrefs;
+
+		private boolean peel;
+
+		private Builder() {
+		}
+
+		/**
+		 * @param value
+		 * @return the Builder
+		 */
+		public Builder setRefPrefixes(List<String> value) {
+			refPrefixes = value;
+			return this;
+		}
+
+		/**
+		 * @param value
+		 * @return the Builder
+		 */
+		public Builder setSymrefs(boolean value) {
+			symrefs = value;
+			return this;
+		}
+
+		/**
+		 * @param value
+		 * @return the Builder
+		 */
+		public Builder setPeel(boolean value) {
+			peel = value;
+			return this;
+		}
+
+		/** @return LsRefsV2Request */
+		public LsRefsV2Request build() {
+			return new LsRefsV2Request(
+					Collections.unmodifiableList(refPrefixes), symrefs, peel);
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/ProtocolV2Hook.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/ProtocolV2Hook.java
new file mode 100644
index 0000000000..02760fdde4
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/ProtocolV2Hook.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2018, Google LLC.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.transport;
+
+/**
+ * Hook to allow callers to be notified on Git protocol v2 requests.
+ *
+ * @see UploadPack#setProtocolV2Hook(ProtocolV2Hook)
+ * @since 5.1
+ */
+public interface ProtocolV2Hook {
+	/**
+	 * The default hook implementation that does nothing.
+	 */
+	static ProtocolV2Hook DEFAULT = new ProtocolV2Hook() {
+		// No override.
+	};
+
+	/**
+	 * @param req
+	 *            the capabilities request
+	 * @throws ServiceMayNotContinueException
+	 *             abort; the message will be sent to the user
+	 * @since 5.1
+	 */
+	default void onCapabilities(CapabilitiesV2Request req)
+			throws ServiceMayNotContinueException {
+		// Do nothing by default.
+	}
+
+	/**
+	 * @param req
+	 *            the ls-refs request
+	 * @throws ServiceMayNotContinueException
+	 *             abort; the message will be sent to the user
+	 * @since 5.1
+	 */
+	default void onLsRefs(LsRefsV2Request req)
+			throws ServiceMayNotContinueException {
+		// Do nothing by default.
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
index 3ad350d0db..de7be6dec5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
@@ -267,6 +267,9 @@ public class UploadPack {
 	/** The refs we advertised as existing at the start of the connection. */
 	private Map<String, Ref> refs;
 
+	/** Hook used while processing Git protocol v2 requests. */
+	private ProtocolV2Hook protocolV2Hook = ProtocolV2Hook.DEFAULT;
+
 	/** Hook used while advertising the refs to the client. */
 	private AdvertiseRefsHook advertiseRefsHook = AdvertiseRefsHook.DEFAULT;
 
@@ -579,6 +582,16 @@ public class UploadPack {
 	}
 
 	/**
+	 * Set the protocol V2 hook.
+	 *
+	 * @param hook
+	 * @since 5.1
+	 */
+	public void setProtocolV2Hook(ProtocolV2Hook hook) {
+		this.protocolV2Hook = hook;
+	}
+
+	/**
 	 * Set the filter used while advertising the refs to the client.
 	 * <p>
 	 * Only refs allowed by this filter will be sent to the client. The filter
@@ -880,25 +893,19 @@ public class UploadPack {
 	}
 
 	private void lsRefsV2() throws IOException {
-		PacketLineOutRefAdvertiser adv = new PacketLineOutRefAdvertiser(pckOut);
-		String line;
-		ArrayList<String> refPrefixes = new ArrayList<>();
-		boolean needToFindSymrefs = false;
-
-		adv.setUseProtocolV2(true);
-
-		line = pckIn.readString();
-
+		LsRefsV2Request.Builder builder = LsRefsV2Request.builder();
+		List<String> prefixes = new ArrayList<>();
+		String line = pckIn.readString();
 		// Currently, we do not support any capabilities, so the next
 		// line is DELIM if there are arguments or END if not.
 		if (line == PacketLineIn.DELIM) {
 			while ((line = pckIn.readString()) != PacketLineIn.END) {
 				if (line.equals("peel")) { //$NON-NLS-1$
-					adv.setDerefTags(true);
+					builder.setPeel(true);
 				} else if (line.equals("symrefs")) { //$NON-NLS-1$
-					needToFindSymrefs = true;
+					builder.setSymrefs(true);
 				} else if (line.startsWith("ref-prefix ")) { //$NON-NLS-1$
-					refPrefixes.add(line.substring("ref-prefix ".length())); //$NON-NLS-1$
+					prefixes.add(line.substring("ref-prefix ".length())); //$NON-NLS-1$
 				} else {
 					throw new PackProtocolException(MessageFormat
 							.format(JGitText.get().unexpectedPacketLine, line));
@@ -908,21 +915,28 @@ public class UploadPack {
 			throw new PackProtocolException(MessageFormat
 					.format(JGitText.get().unexpectedPacketLine, line));
 		}
-		rawOut.stopBuffering();
+		LsRefsV2Request req = builder.setRefPrefixes(prefixes).build();
+
+		protocolV2Hook.onLsRefs(req);
 
+		rawOut.stopBuffering();
+		PacketLineOutRefAdvertiser adv = new PacketLineOutRefAdvertiser(pckOut);
+		adv.setUseProtocolV2(true);
+		if (req.getPeel()) {
+			adv.setDerefTags(true);
+		}
 		Map<String, Ref> refsToSend;
-		if (refPrefixes.isEmpty()) {
+		if (req.getRefPrefixes().isEmpty()) {
 			refsToSend = getAdvertisedOrDefaultRefs();
 		} else {
 			refsToSend = new HashMap<>();
-			for (String refPrefix : refPrefixes) {
+			for (String refPrefix : req.getRefPrefixes()) {
 				for (Ref ref : db.getRefDatabase().getRefsByPrefix(refPrefix)) {
 					refsToSend.put(ref.getName(), ref);
 				}
 			}
 		}
-
-		if (needToFindSymrefs) {
+		if (req.getSymrefs()) {
 			findSymrefs(adv, refsToSend);
 		}
 
@@ -1174,6 +1188,8 @@ public class UploadPack {
 			// is sent only if this is a bidirectional pipe. (If
 			// not, the client is expected to call
 			// sendAdvertisedRefs() on its own.)
+			protocolV2Hook
+					.onCapabilities(CapabilitiesV2Request.builder().build());
 			for (String s : getV2CapabilityAdvertisement()) {
 				pckOut.writeString(s + "\n"); //$NON-NLS-1$
 			}
@@ -1338,6 +1354,8 @@ public class UploadPack {
 		if (useProtocolV2()) {
 			// The equivalent in v2 is only the capabilities
 			// advertisement.
+			protocolV2Hook
+					.onCapabilities(CapabilitiesV2Request.builder().build());
 			for (String s : getV2CapabilityAdvertisement()) {
 				adv.writeOne(s);
 			}