Add REST endpoint to get one change message

Change-Id: I816623bc2e610e377280c2f705f3258f56f4e890

Documentation/rest-api-changes.txt

@@ -2453,6 +2453,38 @@ As response a list of link:#change-message-info[ChangeMessageInfo] entities is r
   ]
 ----
 
+[[get-change-message]]
+=== Get Change Message
+
+Retrieves a change message including link:#detailed-accounts[detailed account information].
+
+--
+'GET /changes/link:#change-id[\{change-id\}]/message/link:#change-message-id[\{change-message-id\}'
+--
+
+As response a link:#change-message-info[ChangeMessageInfo] entity is returned.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json; charset=UTF-8
+
+  )]}'
+  {
+    "id": "aaee04dcb46bafc8be24d8aa70b3b1beb7df5780",
+    "author": {
+      "_account_id": 1000096,
+      "name": "John Doe",
+      "email": "john.doe@example.com",
+      "username": "jdoe"
+     },
+     "date": "2013-03-23 21:34:02.419000000",
+     "message": "Change message removed by: Administrator; Reason: spam",
+     "_revision_number": 1
+  }
+----
+
 [[edit-endpoints]]
 == Change Edit Endpoints
 
@@ -5415,6 +5447,10 @@ If you need more time to migrate off of old change IDs, please see
 link:config-gerrit.html#change.api.allowedIdentifier[change.api.allowedIdentifier]
 for more information on how to enable the use of deprecated identifiers.
 
+[[change-message-id]]
+=== \{change-message-id\}
+ID of a change message returned in a link:#change-message-info[ChangeMessageInfo].
+
 [[comment-id]]
 === \{comment-id\}
 UUID of a published comment.

java/com/google/gerrit/extensions/api/changes/ChangeApi.java

@@ -292,6 +292,17 @@ public interface ChangeApi {
    */
   List<ChangeMessageInfo> messages() throws RestApiException;
 
+  /**
+   * Look up a change message of a change by its id.
+   *
+   * @param id the id of the change message. Note that in NoteDb, this id is the {@code ObjectId} of
+   *     a commit on the change meta branch. In ReviewDb, it's a UUID generated randomly. That means
+   *     a change message id could be different between NoteDb and ReviewDb.
+   * @return API for accessing a change message.
+   * @throws RestApiException if the id is invalid.
+   */
+  ChangeMessageApi message(String id) throws RestApiException;
+
   abstract class SuggestedReviewersRequest {
     private String query;
     private int limit;
@@ -604,5 +615,10 @@ public interface ChangeApi {
     public List<ChangeMessageInfo> messages() throws RestApiException {
       throw new NotImplementedException();
     }
+
+    @Override
+    public ChangeMessageApi message(String id) throws RestApiException {
+      throw new NotImplementedException();
+    }
   }
 }

java/com/google/gerrit/extensions/api/changes/ChangeMessageApi.java

@@ -0,0 +1,36 @@
+// Copyright (C) 2018 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.api.changes;
+
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.restapi.NotImplementedException;
+import com.google.gerrit.extensions.restapi.RestApiException;
+
+/** Interface for change message APIs. */
+public interface ChangeMessageApi {
+  /** Gets one change message. */
+  ChangeMessageInfo get() throws RestApiException;
+
+  /**
+   * A default implementation which allows source compatibility when adding new methods to the
+   * interface.
+   */
+  class NotImplemented implements ChangeMessageApi {
+    @Override
+    public ChangeMessageInfo get() throws RestApiException {
+      throw new NotImplementedException();
+    }
+  }
+}

java/com/google/gerrit/server/api/changes/ChangeApiImpl.java

@@ -23,6 +23,7 @@ import com.google.gerrit.extensions.api.changes.AddReviewerResult;
 import com.google.gerrit.extensions.api.changes.AssigneeInput;
 import com.google.gerrit.extensions.api.changes.ChangeApi;
 import com.google.gerrit.extensions.api.changes.ChangeEditApi;
+import com.google.gerrit.extensions.api.changes.ChangeMessageApi;
 import com.google.gerrit.extensions.api.changes.Changes;
 import com.google.gerrit.extensions.api.changes.FixInput;
 import com.google.gerrit.extensions.api.changes.HashtagsInput;
@@ -54,6 +55,7 @@ import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.server.StarredChangesUtil;
 import com.google.gerrit.server.StarredChangesUtil.IllegalLabelException;
 import com.google.gerrit.server.change.ChangeJson;
+import com.google.gerrit.server.change.ChangeMessageResource;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.change.PureRevert;
 import com.google.gerrit.server.change.WorkInProgressOp;
@@ -113,6 +115,7 @@ class ChangeApiImpl implements ChangeApi {
   private final Revisions revisions;
   private final ReviewerApiImpl.Factory reviewerApi;
   private final RevisionApiImpl.Factory revisionApi;
+  private final ChangeMessageApiImpl.Factory changeMessageApi;
   private final ChangeMessages changeMessages;
   private final SuggestChangeReviewers suggestReviewers;
   private final ChangeResource change;
@@ -160,6 +163,7 @@ class ChangeApiImpl implements ChangeApi {
       Revisions revisions,
       ReviewerApiImpl.Factory reviewerApi,
       RevisionApiImpl.Factory revisionApi,
+      ChangeMessageApiImpl.Factory changeMessageApi,
       ChangeMessages changeMessages,
       SuggestChangeReviewers suggestReviewers,
       Abandon abandon,
@@ -205,6 +209,7 @@ class ChangeApiImpl implements ChangeApi {
     this.revisions = revisions;
     this.reviewerApi = reviewerApi;
     this.revisionApi = revisionApi;
+    this.changeMessageApi = changeMessageApi;
     this.changeMessages = changeMessages;
     this.suggestReviewers = suggestReviewers;
     this.abandon = abandon;
@@ -723,4 +728,14 @@ class ChangeApiImpl implements ChangeApi {
       throw asRestApiException("Cannot list change messages", e);
     }
   }
+
+  @Override
+  public ChangeMessageApi message(String id) throws RestApiException {
+    try {
+      ChangeMessageResource resource = changeMessages.parse(change, IdString.fromDecoded(id));
+      return changeMessageApi.create(resource);
+    } catch (Exception e) {
+      throw asRestApiException("Cannot parse change message " + id, e);
+    }
+  }
 }

java/com/google/gerrit/server/api/changes/ChangeMessageApiImpl.java

@@ -0,0 +1,50 @@
+// Copyright (C) 2018 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.server.api.changes;
+
+import static com.google.gerrit.server.api.ApiUtil.asRestApiException;
+
+import com.google.gerrit.extensions.api.changes.ChangeMessageApi;
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.server.change.ChangeMessageResource;
+import com.google.gerrit.server.restapi.change.GetChangeMessage;
+import com.google.inject.Inject;
+import com.google.inject.assistedinject.Assisted;
+
+class ChangeMessageApiImpl implements ChangeMessageApi {
+  interface Factory {
+    ChangeMessageApiImpl create(ChangeMessageResource changeMessageResource);
+  }
+
+  private final GetChangeMessage getChangeMessage;
+  private final ChangeMessageResource changeMessageResource;
+
+  @Inject
+  ChangeMessageApiImpl(
+      GetChangeMessage getChangeMessage, @Assisted ChangeMessageResource changeMessageResource) {
+    this.getChangeMessage = getChangeMessage;
+    this.changeMessageResource = changeMessageResource;
+  }
+
+  @Override
+  public ChangeMessageInfo get() throws RestApiException {
+    try {
+      return getChangeMessage.apply(changeMessageResource);
+    } catch (Exception e) {
+      throw asRestApiException("Cannot retrieve change message", e);
+    }
+  }
+}

java/com/google/gerrit/server/api/changes/Module.java

@@ -31,5 +31,6 @@ public class Module extends FactoryModule {
     factory(ReviewerApiImpl.Factory.class);
     factory(RevisionReviewerApiImpl.Factory.class);
     factory(ChangeEditApiImpl.Factory.class);
+    factory(ChangeMessageApiImpl.Factory.class);
   }
 }

java/com/google/gerrit/server/restapi/change/GetChangeMessage.java

@@ -0,0 +1,29 @@
+// Copyright (C) 2018 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.server.restapi.change;
+
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.restapi.RestReadView;
+import com.google.gerrit.server.change.ChangeMessageResource;
+import com.google.inject.Singleton;
+
+/** Gets one change message. */
+@Singleton
+public class GetChangeMessage implements RestReadView<ChangeMessageResource> {
+  @Override
+  public ChangeMessageInfo apply(ChangeMessageResource resource) {
+    return resource.getChangeMessage();
+  }
+}

java/com/google/gerrit/server/restapi/change/Module.java

@@ -177,6 +177,7 @@ public class Module extends RestApiModule {
     post(COMMIT_KIND, "cherrypick").to(CherryPickCommit.class);
 
     child(CHANGE_KIND, "messages").to(ChangeMessages.class);
+    get(CHANGE_MESSAGE_KIND).to(GetChangeMessage.class);
 
     factory(AccountLoader.Factory.class);
     factory(ChangeEdits.Create.Factory.class);

javatests/com/google/gerrit/acceptance/rest/change/ChangeMessagesIT.java

@@ -110,9 +110,18 @@ public class ChangeMessagesIT extends AbstractDaemonTest {
     assertThat(messages1).containsExactlyElementsIn(messages2).inOrder();
   }
 
-  private int createOneChangeWithMultipleChangeMessagesInHistory() throws Exception {
+  @Test
-    // Creates the following commit history on the meta branch of the test change.
+  public void getOneChangeMessage() throws Exception {
+    int changeNum = createOneChangeWithMultipleChangeMessagesInHistory();
+    List<ChangeMessageInfo> messages = new ArrayList<>(gApi.changes().id(changeNum).get().messages);
 
+    for (ChangeMessageInfo messageInfo : messages) {
+      String id = messageInfo.id;
+      assertThat(gApi.changes().id(changeNum).message(id).get()).isEqualTo(messageInfo);
+    }
+  }
+
+  private int createOneChangeWithMultipleChangeMessagesInHistory() throws Exception {
     setApiUser(user);
     // Commit 1: create a change.
     PushOneCommit.Result result = createChange();