Add extension point to register JGit PostReceiveHooks

Plugins may want to get notified when a pack file is received.
For example, the quota plugin may want to cache the repository
size in the file system and update it every time a new pack is
received.

Change-Id: I0212eab6e4867819ebe7ecc7fc5532c26bb82282

Documentation/dev-plugins.txt

@@ -424,6 +424,14 @@ by Gerrit just before a ReceivePack instance will be used. Usually,
 plugins will make use of the setXXX methods on the ReceivePack to
 set additional properties on it.
 
+[[post-receive-hook]]
+== Post Receive-Pack Hooks
+
+Plugins may register PostReceiveHook instances in order to get
+notified when JGit successfully receives a pack. This may be useful
+for those plugins which would like to monitor changes in Git
+repositories.
+
 [[ssh]]
 == SSH Commands
 

gerrit-httpd/src/main/java/com/google/gerrit/httpd/GitOverHttpServlet.java

@@ -15,6 +15,7 @@
 package com.google.gerrit.httpd;
 
 import com.google.common.cache.Cache;
+import com.google.common.collect.Lists;
 import com.google.gerrit.common.data.Capable;
 import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.reviewdb.client.Project;
@@ -48,6 +49,8 @@ import org.eclipse.jgit.http.server.ServletUtils;
 import org.eclipse.jgit.http.server.resolver.AsIsFileService;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.transport.PostReceiveHook;
+import org.eclipse.jgit.transport.PostReceiveHookChain;
 import org.eclipse.jgit.transport.ReceivePack;
 import org.eclipse.jgit.transport.UploadPack;
 import org.eclipse.jgit.transport.resolver.ReceivePackFactory;
@@ -247,13 +250,16 @@ public class GitOverHttpServlet extends GitServlet {
     private final AsyncReceiveCommits.Factory factory;
     private final TransferConfig config;
     private DynamicSet<ReceivePackInitializer> receivePackInitializers;
+    private DynamicSet<PostReceiveHook> postReceiveHooks;
 
     @Inject
     ReceiveFactory(AsyncReceiveCommits.Factory factory, TransferConfig config,
-        DynamicSet<ReceivePackInitializer> receivePackInitializers) {
+        DynamicSet<ReceivePackInitializer> receivePackInitializers,
+        DynamicSet<PostReceiveHook> postReceiveHooks) {
       this.factory = factory;
       this.config = config;
       this.receivePackInitializers = receivePackInitializers;
+      this.postReceiveHooks = postReceiveHooks;
     }
 
     @Override
@@ -273,6 +279,8 @@ public class GitOverHttpServlet extends GitServlet {
       rp.setTimeout(config.getTimeout());
       rp.setMaxObjectSizeLimit(config.getMaxObjectSizeLimit());
       init(pc.getProject().getNameKey(), rp);
+      rp.setPostReceiveHook(PostReceiveHookChain.newChain(
+          Lists.newArrayList(postReceiveHooks)));
       req.setAttribute(ATT_RC, rc);
       return rp;
     }

gerrit-server/src/main/java/com/google/gerrit/server/config/GerritGlobalModule.java

@@ -126,6 +126,7 @@ import com.google.inject.TypeLiteral;
 import com.google.inject.internal.UniqueAnnotations;
 
 import org.apache.velocity.runtime.RuntimeInstance;
+import org.eclipse.jgit.transport.PostReceiveHook;
 
 import java.util.List;
 import java.util.Set;
@@ -245,6 +246,7 @@ public class GerritGlobalModule extends FactoryModule {
     DynamicMap.mapOf(binder(), CapabilityDefinition.class);
     DynamicSet.setOf(binder(), GitReferenceUpdatedListener.class);
     DynamicSet.setOf(binder(), ReceivePackInitializer.class);
+    DynamicSet.setOf(binder(), PostReceiveHook.class);
     DynamicSet.setOf(binder(), NewProjectCreatedListener.class);
     DynamicSet.setOf(binder(), ProjectDeletedListener.class);
     DynamicSet.setOf(binder(), HeadUpdatedListener.class);

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/Receive.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.sshd.commands;
 
+import com.google.common.collect.Lists;
 import com.google.gerrit.common.data.Capable;
 import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.reviewdb.client.Account;
@@ -32,6 +33,8 @@ import org.eclipse.jgit.errors.UnpackException;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RefDatabase;
 import org.eclipse.jgit.transport.AdvertiseRefsHook;
+import org.eclipse.jgit.transport.PostReceiveHook;
+import org.eclipse.jgit.transport.PostReceiveHookChain;
 import org.eclipse.jgit.transport.ReceivePack;
 import org.kohsuke.args4j.Option;
 import org.slf4j.Logger;
@@ -64,6 +67,9 @@ final class Receive extends AbstractGitCommand {
   @Inject
   private DynamicSet<ReceivePackInitializer> receivePackInitializers;
 
+  @Inject
+  private DynamicSet<PostReceiveHook> postReceiveHooks;
+
   private final Set<Account.Id> reviewerId = new HashSet<Account.Id>();
   private final Set<Account.Id> ccId = new HashSet<Account.Id>();
 
@@ -103,6 +109,8 @@ final class Receive extends AbstractGitCommand {
     rp.setMaxObjectSizeLimit(config.getEffectiveMaxObjectSizeLimit(
         projectControl.getProjectState()));
     init(rp);
+    rp.setPostReceiveHook(PostReceiveHookChain.newChain(
+        Lists.newArrayList(postReceiveHooks)));
     try {
       rp.receive(in, out, err);
     } catch (UnpackException badStream) {