Support to retrieve a branch via REST

GET on /projects/<project-name>/branches/<branch-id> retrieves a
branch.

Change-Id: I1c2c81dcc5292d644d8048436c142039a4274e32
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-projects.txt

@@ -531,6 +531,35 @@ returned.
   ]
 ----
 
+[[get-branch]]
+Get Branch
+~~~~~~~~~~
+[verse]
+'GET /projects/link:#project-name[\{project-name\}]/branches/link:#branch-id[\{branch-id\}]'
+
+Retrieves a branch of a project.
+
+.Request
+----
+  GET /projects/work%2Fmy-project/branches/master HTTP/1.0
+----
+
+As response a link:#branch-info[BranchInfo] entity is returned that
+describes the branch.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  {
+    "ref": "refs/heads/master",
+    "revision": "67ebf73496383c6777035e374d2d664009e2aa5c"
+  }
+----
+
 [[child-project-endpoints]]
 Child Project Endpoints
 -----------------------
@@ -901,6 +930,12 @@ requests.
 IDs
 ---
 
+[[branch-id]]
+\{branch-id\}
+~~~~~~~~~~~~~
+The name of a branch or `HEAD`. The prefix `refs/heads/` can be
+omitted.
+
 [[dashboard-id]]
 \{dashboard-id\}
 ~~~~~~~~~~~~~~~~

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

@@ -15,21 +15,21 @@
 package com.google.gerrit.server.project;
 
 import com.google.gerrit.extensions.restapi.RestView;
-import com.google.gerrit.reviewdb.client.Branch;
+import com.google.gerrit.server.project.ListBranches.BranchInfo;
 import com.google.inject.TypeLiteral;
 
 public class BranchResource extends ProjectResource {
   public static final TypeLiteral<RestView<BranchResource>> BRANCH_KIND =
       new TypeLiteral<RestView<BranchResource>>() {};
 
-  private final Branch.NameKey branch;
+  private final BranchInfo branchInfo;
 
-  public BranchResource(ProjectControl control, Branch.NameKey branch) {
+  public BranchResource(ProjectControl control, BranchInfo branchInfo) {
     super(control);
-    this.branch = branch;
+    this.branchInfo = branchInfo;
   }
 
-  public Branch.NameKey getBranch() {
+  public BranchInfo getBranchInfo() {
-    return branch;
+    return branchInfo;
   }
 }

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

@@ -19,9 +19,15 @@ 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.project.ListBranches.BranchInfo;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 
+import org.eclipse.jgit.lib.Constants;
+
+import java.io.IOException;
+import java.util.List;
+
 public class BranchesCollection implements
     ChildCollection<ProjectResource, BranchResource> {
   private final DynamicMap<RestView<BranchResource>> views;
@@ -41,8 +47,19 @@ public class BranchesCollection implements
 
   @Override
   public BranchResource parse(ProjectResource parent, IdString id)
-      throws ResourceNotFoundException {
+      throws ResourceNotFoundException, IOException {
-    throw new ResourceNotFoundException(id);
+    String branchName = id.get();
+    if (!branchName.startsWith(Constants.R_REFS)
+        && !branchName.equals(Constants.HEAD)) {
+      branchName = Constants.R_HEADS + branchName;
+    }
+    List<BranchInfo> branches = list.get().apply(parent);
+    for (BranchInfo b : branches) {
+      if (branchName.equals(b.ref)) {
+        return new BranchResource(parent.getControl(), b);
+      }
+    }
+    throw new ResourceNotFoundException();
   }
 
   @Override

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

@@ -0,0 +1,26 @@
+// 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.RestReadView;
+import com.google.gerrit.server.project.ListBranches.BranchInfo;
+
+public class GetBranch implements RestReadView<BranchResource> {
+
+  @Override
+  public BranchInfo apply(BranchResource rsrc) {
+    return rsrc.getBranchInfo();
+  }
+}

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

@@ -53,6 +53,7 @@ public class Module extends RestApiModule {
     post(PROJECT_KIND, "gc").to(GarbageCollect.class);
 
     child(PROJECT_KIND, "branches").to(BranchesCollection.class);
+    get(BRANCH_KIND).to(GetBranch.class);
 
     child(PROJECT_KIND, "dashboards").to(DashboardsCollection.class);
     get(DASHBOARD_KIND).to(GetDashboard.class);