Add an event for the update of a project's HEAD

When the HEAD of a project is updated Gerrit now informs about this by
sending an event. Plugins can implement a listener to be notified
about this event. Having this new event enables the replication plugin
to replicate HEAD updates.

Change-Id: I4dd7969020880190668190e8345197a23dbc92f1
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/dev-plugins.txt

@@ -364,6 +364,10 @@ Project creation
 +
 Project deletion
 
+* `com.google.gerrit.extensions.events.HeadUpdatedListener`:
++
+Update of HEAD on a project
+
 [[stream-events]]
 Sending Events to the Events Stream
 -----------------------------------

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/events/HeadUpdatedListener.java

@@ -0,0 +1,29 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.extensions.events;
+
+import com.google.gerrit.extensions.annotations.ExtensionPoint;
+
+/** Notified whenever the HEAD of a project is updated. */
+@ExtensionPoint
+public interface HeadUpdatedListener {
+  public interface Event {
+    String getProjectName();
+    String getOldHeadName();
+    String getNewHeadName();
+  }
+
+  void onHeadUpdated(Event event);
+}

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

@@ -23,6 +23,7 @@ import com.google.gerrit.extensions.config.CapabilityDefinition;
 import com.google.gerrit.extensions.config.DownloadCommand;
 import com.google.gerrit.extensions.config.DownloadScheme;
 import com.google.gerrit.extensions.events.GitReferenceUpdatedListener;
+import com.google.gerrit.extensions.events.HeadUpdatedListener;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.extensions.events.NewProjectCreatedListener;
 import com.google.gerrit.extensions.events.ProjectDeletedListener;
@@ -241,6 +242,7 @@ public class GerritGlobalModule extends FactoryModule {
     DynamicSet.setOf(binder(), GitReferenceUpdatedListener.class);
     DynamicSet.setOf(binder(), NewProjectCreatedListener.class);
     DynamicSet.setOf(binder(), ProjectDeletedListener.class);
+    DynamicSet.setOf(binder(), HeadUpdatedListener.class);
     DynamicSet.bind(binder(), GitReferenceUpdatedListener.class).to(ChangeCache.class);
     DynamicSet.setOf(binder(), ChangeListener.class);
     DynamicSet.setOf(binder(), CommitValidationListener.class);

gerrit-server/src/main/java/com/google/gerrit/server/project/SetHead.java

@@ -15,6 +15,8 @@
 package com.google.gerrit.server.project;
 
 import com.google.common.base.Strings;
+import com.google.gerrit.extensions.events.HeadUpdatedListener;
+import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.DefaultInput;
 import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
@@ -31,10 +33,14 @@ import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.Repository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 
 public class SetHead implements RestModifyView<ProjectResource, Input> {
+  private static final Logger log = LoggerFactory.getLogger(SetHead.class);
+
   static class Input {
     @DefaultInput
     String ref;
@@ -42,15 +48,19 @@ public class SetHead implements RestModifyView<ProjectResource, Input> {
 
   private final GitRepositoryManager repoManager;
   private final Provider<IdentifiedUser> identifiedUser;
+  private final DynamicSet<HeadUpdatedListener> headUpdatedListener;
 
   @Inject
-  SetHead(GitRepositoryManager repoManager, Provider<IdentifiedUser> identifiedUser) {
+  SetHead(GitRepositoryManager repoManager,
+      Provider<IdentifiedUser> identifiedUser,
+      DynamicSet<HeadUpdatedListener> headUpdatedListener) {
     this.repoManager = repoManager;
     this.identifiedUser = identifiedUser;
+    this.headUpdatedListener = headUpdatedListener;
   }
 
   @Override
-  public String apply(ProjectResource rsrc, Input input) throws AuthException,
+  public String apply(final ProjectResource rsrc, Input input) throws AuthException,
       ResourceNotFoundException, BadRequestException,
       UnprocessableEntityException, IOException {
     if (!rsrc.getControl().isOwner()) {
@@ -72,10 +82,12 @@ public class SetHead implements RestModifyView<ProjectResource, Input> {
             "Ref Not Found: %s", ref));
       }
 
-      if (!repo.getRef(Constants.HEAD).getTarget().getName().equals(ref)) {
+      final String oldHead = repo.getRef(Constants.HEAD).getTarget().getName();
+      final String newHead = ref;
+      if (!oldHead.equals(newHead)) {
         final RefUpdate u = repo.updateRef(Constants.HEAD, true);
         u.setRefLogIdent(identifiedUser.get().newRefLogIdent());
-        RefUpdate.Result res = u.link(ref);
+        RefUpdate.Result res = u.link(newHead);
         switch(res) {
           case NO_CHANGE:
           case RENAMED:
@@ -85,6 +97,30 @@ public class SetHead implements RestModifyView<ProjectResource, Input> {
           default:
             throw new IOException("Setting HEAD failed with " + res);
         }
+
+        HeadUpdatedListener.Event event = new HeadUpdatedListener.Event() {
+          @Override
+          public String getProjectName() {
+            return rsrc.getNameKey().get();
+          }
+
+          @Override
+          public String getOldHeadName() {
+            return oldHead;
+          }
+
+          @Override
+          public String getNewHeadName() {
+            return newHead;
+          }
+        };
+        for (HeadUpdatedListener l : headUpdatedListener) {
+          try {
+            l.onHeadUpdated(event);
+          } catch (RuntimeException e) {
+            log.warn("Failure in HeadUpdatedListener", e);
+          }
+        }
       }
       return ref;
     } catch (RepositoryNotFoundException e) {