Support to get/set the HEAD of a project via REST

Change-Id: I84e0c5f91a97f984baab6ef353ef181066e2082e
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-projects.txt

@@ -318,6 +318,62 @@ As response the new parent project name is returned.
   "Public-Plugins"
 ----
 
+[[get-head]]
+Get HEAD
+~~~~~~~~
+[verse]
+'GET /projects/link:#project-name[\{project-name\}]/HEAD'
+
+Retrieves for a project the name of the branch to which `HEAD` points.
+
+.Request
+----
+  GET /projects/plugins%2Freplication/HEAD HTTP/1.0
+----
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  "refs/heads/master"
+----
+
+[[set-head]]
+Set HEAD
+~~~~~~~~
+[verse]
+'PUT /projects/link:#project-name[\{project-name\}]/HEAD'
+
+Sets `HEAD` for a project.
+
+The new ref to which `HEAD` should point must be provided in the
+request body inside a link:#head-input[HeadInput] entity.
+
+.Request
+----
+  PUT /projects/plugins%2Freplication/HEAD HTTP/1.0
+  Content-Type: application/json;charset=UTF-8
+
+  {
+    "ref": "refs/heads/stable"
+  }
+----
+
+As response the new ref to which `HEAD` points is returned.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  "refs/heads/stable"
+----
+
 [[dashboard-endpoints]]
 Dashboard Endpoints
 -------------------
@@ -632,6 +688,20 @@ in a dashboard.
 Tokens such as `${project}` are not resolved.
 |===========================
 
+[[head-input]]
+HeadInput
+~~~~~~~~~
+The `HeadInput` entity contains information for setting `HEAD` for a
+project.
+
+[options="header",width="50%",cols="1,6"]
+|============================
+|Field Name      |Description
+|`ref`           |
+The ref to which `HEAD` should be set, the `refs/heads` prefix can be
+omitted.
+|============================
+
 [[project-description-input]]
 ProjectDescriptionInput
 ~~~~~~~~~~~~~~~~~~~~~~~

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

@@ -0,0 +1,69 @@
+// 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.server.project;
+
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestReadView;
+import com.google.gerrit.server.auth.AuthException;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.inject.Inject;
+
+import org.eclipse.jgit.errors.RepositoryNotFoundException;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+
+import java.io.IOException;
+
+public class GetHead implements RestReadView<ProjectResource> {
+
+  private GitRepositoryManager repoManager;
+
+  @Inject
+  GetHead(GitRepositoryManager repoManager) {
+    this.repoManager = repoManager;
+  }
+
+  @Override
+  public String apply(ProjectResource rsrc) throws AuthException,
+      ResourceNotFoundException, IOException {
+    Repository repo = null;
+    try {
+      repo = repoManager.openRepository(rsrc.getNameKey());
+      Ref head = repo.getRef(Constants.HEAD);
+      if (head == null) {
+        throw new ResourceNotFoundException(Constants.HEAD);
+      } else if (head.isSymbolic()) {
+        String n = head.getTarget().getName();
+        if (rsrc.getControl().controlForRef(n).isVisible()) {
+          return n;
+        }
+        throw new AuthException();
+      } else if (head.getObjectId() != null) {
+        if (rsrc.getControl().isOwner()) {
+          return head.getObjectId().name();
+        }
+        throw new AuthException();
+      }
+      throw new ResourceNotFoundException(Constants.HEAD);
+    } catch (RepositoryNotFoundException e) {
+      throw new ResourceNotFoundException(rsrc.getName());
+    } finally {
+      if (repo != null) {
+        repo.close();
+      }
+    }
+  }
+}

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

@@ -40,6 +40,9 @@ public class Module extends RestApiModule {
     get(PROJECT_KIND, "parent").to(GetParent.class);
     put(PROJECT_KIND, "parent").to(SetParent.class);
 
+    get(PROJECT_KIND, "HEAD").to(GetHead.class);
+    put(PROJECT_KIND, "HEAD").to(SetHead.class);
+
     child(PROJECT_KIND, "dashboards").to(DashboardsCollection.class);
     get(DASHBOARD_KIND).to(GetDashboard.class);
     put(DASHBOARD_KIND).to(SetDashboard.class);

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

@@ -0,0 +1,97 @@
+// 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.server.project;
+
+import com.google.common.base.Strings;
+import com.google.gerrit.extensions.restapi.BadRequestException;
+import com.google.gerrit.extensions.restapi.DefaultInput;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestModifyView;
+import com.google.gerrit.extensions.restapi.UnprocessableEntityException;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.auth.AuthException;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.project.SetHead.Input;
+import com.google.inject.Inject;
+
+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 java.io.IOException;
+
+public class SetHead implements RestModifyView<ProjectResource, Input> {
+  static class Input {
+    @DefaultInput
+    String ref;
+  }
+
+  private final GitRepositoryManager repoManager;
+  private final IdentifiedUser identifiedUser;
+
+  @Inject
+  SetHead(GitRepositoryManager repoManager, IdentifiedUser identifiedUser) {
+    this.repoManager = repoManager;
+    this.identifiedUser = identifiedUser;
+  }
+
+  @Override
+  public String apply(ProjectResource rsrc, Input input) throws AuthException,
+      ResourceNotFoundException, BadRequestException,
+      UnprocessableEntityException, IOException {
+    if (!rsrc.getControl().isOwner()) {
+      throw new AuthException("restricted to project owner");
+    }
+    if (input == null || Strings.isNullOrEmpty(input.ref)) {
+      throw new BadRequestException("ref required");
+    }
+    String ref = input.ref;
+    if (!ref.startsWith(Constants.R_REFS)) {
+      ref = Constants.R_HEADS + ref;
+    }
+
+    Repository repo = null;
+    try {
+      repo = repoManager.openRepository(rsrc.getNameKey());
+      if (repo.getRef(ref) == null) {
+        throw new UnprocessableEntityException(String.format(
+            "Ref Not Found: %s", ref));
+      }
+
+      if (!repo.getRef(Constants.HEAD).getTarget().getName().equals(ref)) {
+        final RefUpdate u = repo.updateRef(Constants.HEAD, true);
+        u.setRefLogIdent(identifiedUser.newRefLogIdent());
+        RefUpdate.Result res = u.link(ref);
+        switch(res) {
+          case NO_CHANGE:
+          case RENAMED:
+          case FORCED:
+          case NEW:
+            break;
+          default:
+            throw new IOException("Setting HEAD failed with " + res);
+        }
+      }
+      return ref;
+    } catch (RepositoryNotFoundException e) {
+      throw new ResourceNotFoundException(rsrc.getName());
+    } finally {
+      if (repo != null) {
+        repo.close();
+      }
+    }
+  }
+}