Merge changes from topic "change-messages-rest-api"

* changes:
  Add REST endpoint to get one change message
  Add REST endpoint for listing change messages

Documentation/rest-api-changes.txt

@@ -2403,6 +2403,87 @@ As response the change's hashtags are returned as a list of strings.
   ]
 ----
 
+[[list-change-messages]]
+=== List Change Messages
+--
+'GET /changes/link:#change-id[\{change-id\}]/messages'
+--
+
+Lists all the messages of a change including link:#detailed-accounts[detailed account information].
+
+.Request
+----
+  GET /changes/myProject~master~I8473b95934b5732ac55d26311a706c9c2bde9940/messages
+----
+
+As response a list of link:#change-message-info[ChangeMessageInfo] entities is returned.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json; charset=UTF-8
+
+  )]}'
+  [
+    {
+      "id": "YH-egE",
+      "author": {
+      "_account_id": 1000096,
+      "name": "John Doe",
+      "email": "john.doe@example.com",
+      "username": "jdoe"
+      },
+      "date": "2013-03-23 21:34:02.419000000",
+      "message": "Patch Set 1:\n\nThis is the first message.",
+      "_revision_number": 1
+    },
+    {
+      "id": "WEEdhU",
+      "author": {
+      "_account_id": 1000097,
+      "name": "Jane Roe",
+      "email": "jane.roe@example.com",
+      "username": "jroe"
+      },
+      "date": "2013-03-23 21:36:52.332000000",
+      "message": "Patch Set 1:\n\nThis is the second message.\n\nWith a line break.",
+      "_revision_number": 1
+    }
+  ]
+----
+
+[[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
@@ -5366,6 +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

@@ -19,6 +19,7 @@ import com.google.gerrit.common.Nullable;
 import com.google.gerrit.extensions.client.ListChangesOption;
 import com.google.gerrit.extensions.common.AccountInfo;
 import com.google.gerrit.extensions.common.ChangeInfo;
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
 import com.google.gerrit.extensions.common.CommentInfo;
 import com.google.gerrit.extensions.common.CommitMessageInput;
 import com.google.gerrit.extensions.common.EditInfo;
@@ -283,6 +284,25 @@ public interface ChangeApi {
   /** Check if this change is a pure revert of claimedOriginal (SHA1 in 40 digit hex). */
   PureRevertInfo pureRevert(String claimedOriginal) throws RestApiException;
 
+  /**
+   * Get all messages of a change with detailed account info.
+   *
+   * @return a list of messages sorted by their creation time.
+   * @throws RestApiException
+   */
+  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;
@@ -590,5 +610,15 @@ public interface ChangeApi {
     public PureRevertInfo pureRevert(String claimedOriginal) throws RestApiException {
       throw new NotImplementedException();
     }
+
+    @Override
+    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/extensions/common/ChangeMessageInfo.java

@@ -15,6 +15,7 @@
 package com.google.gerrit.extensions.common;
 
 import java.sql.Timestamp;
+import java.util.Objects;
 
 public class ChangeMessageInfo {
   public String id;
@@ -24,4 +25,24 @@ public class ChangeMessageInfo {
   public Timestamp date;
   public String message;
   public Integer _revisionNumber;
+
+  @Override
+  public boolean equals(Object o) {
+    if (o instanceof ChangeMessageInfo) {
+      ChangeMessageInfo cmi = (ChangeMessageInfo) o;
+      return Objects.equals(id, cmi.id)
+          && Objects.equals(tag, cmi.tag)
+          && Objects.equals(author, cmi.author)
+          && Objects.equals(realAuthor, cmi.realAuthor)
+          && Objects.equals(date, cmi.date)
+          && Objects.equals(message, cmi.message)
+          && Objects.equals(_revisionNumber, cmi._revisionNumber);
+    }
+    return false;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(id, tag, author, realAuthor, date, message, _revisionNumber);
+  }
 }

java/com/google/gerrit/server/ChangeMessagesUtil.java

@@ -19,10 +19,12 @@ import static com.google.common.base.Preconditions.checkState;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.gerrit.common.Nullable;
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.ChangeMessage;
 import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.account.AccountLoader;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.notedb.ChangeUpdate;
 import com.google.gerrit.server.notedb.NotesMigration;
@@ -141,4 +143,21 @@ public class ChangeMessagesUtil {
   public static boolean isAutogenerated(@Nullable String tag) {
     return tag != null && tag.startsWith(AUTOGENERATED_TAG_PREFIX);
   }
+
+  public static ChangeMessageInfo createChangeMessageInfo(
+      ChangeMessage message, AccountLoader accountLoader) {
+    PatchSet.Id patchNum = message.getPatchSetId();
+    ChangeMessageInfo cmi = new ChangeMessageInfo();
+    cmi.id = message.getKey().get();
+    cmi.author = accountLoader.get(message.getAuthor());
+    cmi.date = message.getWrittenOn();
+    cmi.message = message.getMessage();
+    cmi.tag = message.getTag();
+    cmi._revisionNumber = patchNum != null ? patchNum.get() : null;
+    Account.Id realAuthor = message.getRealAuthor();
+    if (realAuthor != null) {
+      cmi.realAuthor = accountLoader.get(realAuthor);
+    }
+    return cmi;
+  }
 }

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;
@@ -39,6 +40,7 @@ import com.google.gerrit.extensions.api.changes.TopicInput;
 import com.google.gerrit.extensions.client.ListChangesOption;
 import com.google.gerrit.extensions.common.AccountInfo;
 import com.google.gerrit.extensions.common.ChangeInfo;
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
 import com.google.gerrit.extensions.common.CommentInfo;
 import com.google.gerrit.extensions.common.CommitMessageInput;
 import com.google.gerrit.extensions.common.EditInfo;
@@ -53,11 +55,13 @@ 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;
 import com.google.gerrit.server.restapi.change.Abandon;
 import com.google.gerrit.server.restapi.change.ChangeIncludedIn;
+import com.google.gerrit.server.restapi.change.ChangeMessages;
 import com.google.gerrit.server.restapi.change.Check;
 import com.google.gerrit.server.restapi.change.CreateMergePatchSet;
 import com.google.gerrit.server.restapi.change.DeleteAssignee;
@@ -111,6 +115,8 @@ 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;
   private final Abandon abandon;
@@ -157,6 +163,8 @@ class ChangeApiImpl implements ChangeApi {
       Revisions revisions,
       ReviewerApiImpl.Factory reviewerApi,
       RevisionApiImpl.Factory revisionApi,
+      ChangeMessageApiImpl.Factory changeMessageApi,
+      ChangeMessages changeMessages,
       SuggestChangeReviewers suggestReviewers,
       Abandon abandon,
       Revert revert,
@@ -201,6 +209,8 @@ 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;
     this.restore = restore;
@@ -709,4 +719,23 @@ class ChangeApiImpl implements ChangeApi {
       throw asRestApiException("Cannot compute pure revert", e);
     }
   }
+
+  @Override
+  public List<ChangeMessageInfo> messages() throws RestApiException {
+    try {
+      return changeMessages.list().apply(change);
+    } catch (Exception e) {
+      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/change/ChangeJson.java

@@ -37,6 +37,7 @@ import static com.google.gerrit.extensions.client.ListChangesOption.SKIP_MERGEAB
 import static com.google.gerrit.extensions.client.ListChangesOption.SUBMITTABLE;
 import static com.google.gerrit.extensions.client.ListChangesOption.TRACKING_IDS;
 import static com.google.gerrit.extensions.client.ListChangesOption.WEB_LINKS;
+import static com.google.gerrit.server.ChangeMessagesUtil.createChangeMessageInfo;
 import static com.google.gerrit.server.CommonConverters.toGitPerson;
 import static java.util.stream.Collectors.toList;
 
@@ -1189,19 +1190,7 @@ public class ChangeJson {
 
     List<ChangeMessageInfo> result = Lists.newArrayListWithCapacity(messages.size());
     for (ChangeMessage message : messages) {
-      PatchSet.Id patchNum = message.getPatchSetId();
-      ChangeMessageInfo cmi = new ChangeMessageInfo();
-      cmi.id = message.getKey().get();
-      cmi.author = accountLoader.get(message.getAuthor());
-      cmi.date = message.getWrittenOn();
-      cmi.message = message.getMessage();
-      cmi.tag = message.getTag();
-      cmi._revisionNumber = patchNum != null ? patchNum.get() : null;
-      Account.Id realAuthor = message.getRealAuthor();
-      if (realAuthor != null) {
-        cmi.realAuthor = accountLoader.get(realAuthor);
-      }
-      result.add(cmi);
+      result.add(createChangeMessageInfo(message, accountLoader));
     }
     return result;
   }

java/com/google/gerrit/server/change/ChangeMessageResource.java

@@ -0,0 +1,63 @@
+// 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.change;
+
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.restapi.RestResource;
+import com.google.gerrit.extensions.restapi.RestView;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.inject.TypeLiteral;
+
+/** A change message resource. */
+public class ChangeMessageResource implements RestResource {
+  public static final TypeLiteral<RestView<ChangeMessageResource>> CHANGE_MESSAGE_KIND =
+      new TypeLiteral<RestView<ChangeMessageResource>>() {};
+
+  private final ChangeResource changeResource;
+  private final ChangeMessageInfo changeMessage;
+  private final int changeMessageIndex;
+
+  public ChangeMessageResource(
+      ChangeResource changeResource, ChangeMessageInfo changeMessage, int changeMessageIndex) {
+    this.changeResource = changeResource;
+    this.changeMessage = changeMessage;
+    this.changeMessageIndex = changeMessageIndex;
+  }
+
+  public ChangeResource getChangeResource() {
+    return changeResource;
+  }
+
+  public ChangeMessageInfo getChangeMessage() {
+    return changeMessage;
+  }
+
+  public Change.Id getChangeId() {
+    return changeResource.getId();
+  }
+
+  public String getChangeMessageId() {
+    return changeMessage.id;
+  }
+
+  /**
+   * Gets the index of the change message among all messages of the change sorted by creation time.
+   *
+   * @return the index of the change message.
+   */
+  public int getChangeMessageIndex() {
+    return changeMessageIndex;
+  }
+}

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

@@ -0,0 +1,73 @@
+// 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.registration.DynamicMap;
+import com.google.gerrit.extensions.restapi.ChildCollection;
+import com.google.gerrit.extensions.restapi.IdString;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestView;
+import com.google.gerrit.server.change.ChangeMessageResource;
+import com.google.gerrit.server.change.ChangeResource;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+import java.util.List;
+
+@Singleton
+public class ChangeMessages implements ChildCollection<ChangeResource, ChangeMessageResource> {
+  private final DynamicMap<RestView<ChangeMessageResource>> views;
+  private final ListChangeMessages listChangeMessages;
+
+  @Inject
+  ChangeMessages(
+      DynamicMap<RestView<ChangeMessageResource>> views, ListChangeMessages listChangeMessages) {
+    this.views = views;
+    this.listChangeMessages = listChangeMessages;
+  }
+
+  @Override
+  public DynamicMap<RestView<ChangeMessageResource>> views() {
+    return views;
+  }
+
+  @Override
+  public ListChangeMessages list() {
+    return listChangeMessages;
+  }
+
+  @Override
+  public ChangeMessageResource parse(ChangeResource parent, IdString id)
+      throws OrmException, ResourceNotFoundException {
+    String uuid = id.get();
+
+    List<ChangeMessageInfo> changeMessages = listChangeMessages.apply(parent);
+    int index = -1;
+    for (int i = 0; i < changeMessages.size(); ++i) {
+      ChangeMessageInfo changeMessage = changeMessages.get(i);
+      if (changeMessage.id.equals(uuid)) {
+        index = i;
+        break;
+      }
+    }
+
+    if (index < 0) {
+      throw new ResourceNotFoundException(String.format("change message %s not found", uuid));
+    }
+
+    return new ChangeMessageResource(parent, changeMessages.get(index), index);
+  }
+}

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/ListChangeMessages.java

@@ -0,0 +1,61 @@
+// 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 static com.google.gerrit.server.ChangeMessagesUtil.createChangeMessageInfo;
+
+import com.google.gerrit.extensions.common.ChangeMessageInfo;
+import com.google.gerrit.extensions.restapi.RestReadView;
+import com.google.gerrit.reviewdb.client.ChangeMessage;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.ChangeMessagesUtil;
+import com.google.gerrit.server.account.AccountLoader;
+import com.google.gerrit.server.change.ChangeResource;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import java.util.List;
+import java.util.stream.Collectors;
+
+@Singleton
+public class ListChangeMessages implements RestReadView<ChangeResource> {
+  private final Provider<ReviewDb> dbProvider;
+  private final ChangeMessagesUtil changeMessagesUtil;
+  private final AccountLoader accountLoader;
+
+  @Inject
+  public ListChangeMessages(
+      Provider<ReviewDb> dbProvider,
+      ChangeMessagesUtil changeMessagesUtil,
+      AccountLoader.Factory accountLoaderFactory) {
+    this.dbProvider = dbProvider;
+    this.changeMessagesUtil = changeMessagesUtil;
+    this.accountLoader = accountLoaderFactory.create(true);
+  }
+
+  @Override
+  public List<ChangeMessageInfo> apply(ChangeResource resource) throws OrmException {
+    List<ChangeMessage> messages =
+        changeMessagesUtil.byChange(dbProvider.get(), resource.getNotes());
+    List<ChangeMessageInfo> messageInfos =
+        messages
+            .stream()
+            .map(m -> createChangeMessageInfo(m, accountLoader))
+            .collect(Collectors.toList());
+    accountLoader.fill();
+    return messageInfos;
+  }
+}

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

@@ -15,6 +15,7 @@
 package com.google.gerrit.server.restapi.change;
 
 import static com.google.gerrit.server.change.ChangeEditResource.CHANGE_EDIT_KIND;
+import static com.google.gerrit.server.change.ChangeMessageResource.CHANGE_MESSAGE_KIND;
 import static com.google.gerrit.server.change.ChangeResource.CHANGE_KIND;
 import static com.google.gerrit.server.change.CommentResource.COMMENT_KIND;
 import static com.google.gerrit.server.change.DraftCommentResource.DRAFT_COMMENT_KIND;
@@ -65,6 +66,7 @@ public class Module extends RestApiModule {
     DynamicMap.mapOf(binder(), REVISION_KIND);
     DynamicMap.mapOf(binder(), CHANGE_EDIT_KIND);
     DynamicMap.mapOf(binder(), VOTE_KIND);
+    DynamicMap.mapOf(binder(), CHANGE_MESSAGE_KIND);
 
     get(CHANGE_KIND).to(GetChange.class);
     post(CHANGE_KIND, "merge").to(CreateMergePatchSet.class);
@@ -174,6 +176,9 @@ public class Module extends RestApiModule {
     get(CHANGE_EDIT_KIND, "meta").to(ChangeEdits.GetMeta.class);
     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);
     factory(ChangeEdits.DeleteFile.Factory.class);

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

@@ -15,16 +15,22 @@
 package com.google.gerrit.acceptance.rest.change;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.gerrit.acceptance.PushOneCommit.FILE_NAME;
 import static com.google.gerrit.extensions.client.ListChangesOption.MESSAGES;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Lists;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
 import com.google.gerrit.extensions.common.ChangeInfo;
 import com.google.gerrit.extensions.common.ChangeMessageInfo;
 import com.google.gerrit.testing.ConfigSuite;
 import com.google.gerrit.testing.TestTimeUtil;
+import java.util.ArrayList;
 import java.util.Iterator;
+import java.util.List;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -95,7 +101,64 @@ public class ChangeMessagesIT extends AbstractDaemonTest {
     assertThat(actual.tag).isEqualTo(tag);
   }
 
-  private void assertMessage(String expected, String actual) {
+  @Test
+  public void listChangeMessages() throws Exception {
+    int changeNum = createOneChangeWithMultipleChangeMessagesInHistory();
+    List<ChangeMessageInfo> messages1 = gApi.changes().id(changeNum).messages();
+    List<ChangeMessageInfo> messages2 =
+        new ArrayList<>(gApi.changes().id(changeNum).get().messages);
+    assertThat(messages1).containsExactlyElementsIn(messages2).inOrder();
+  }
+
+  @Test
+  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();
+    String changeId = result.getChangeId();
+    // Commit 2: post a review with message "message 1".
+    setApiUser(admin);
+    addOneReview(changeId, "message 1");
+    // Commit 3: amend a new patch set.
+    setApiUser(user);
+    amendChange(changeId);
+    // Commit 4: post a review with message "message 2".
+    addOneReview(changeId, "message 2");
+    // Commit 5: amend a new patch set.
+    amendChange(changeId);
+    // Commit 6: approve the change.
+    setApiUser(admin);
+    gApi.changes().id(changeId).current().review(ReviewInput.approve());
+    // commit 7: submit the change.
+    gApi.changes().id(changeId).current().submit();
+
+    return result.getChange().getId().get();
+  }
+
+  private void addOneReview(String changeId, String changeMessage) throws Exception {
+    ReviewInput.CommentInput c = new ReviewInput.CommentInput();
+    c.line = 1;
+    c.message = "comment 1";
+    c.path = FILE_NAME;
+
+    ReviewInput reviewInput = new ReviewInput().label("Code-Review", 1);
+    reviewInput.comments = ImmutableMap.of(c.path, Lists.newArrayList(c));
+    reviewInput.message = changeMessage;
+
+    gApi.changes().id(changeId).current().review(reviewInput);
+  }
+
+  private static void assertMessage(String expected, String actual) {
     assertThat(actual).isEqualTo("Patch Set 1:\n\n" + expected);
   }