Support retrieving the server version via REST

The Gerrit server version can now be retrieved by GET on
/config/server/version.

Change-Id: Id784ff9af13c2327100acefe2d737a0243483204
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-config.txt

@@ -9,6 +9,28 @@ link:rest-api.html[REST API].
 Config Endpoints
 ---------------
 
+[[get-version]]
+Get Version
+~~~~~~~~~~~
+[verse]
+'GET /config/server/version'
+
+Returns the version of the Gerrit server.
+
+.Request
+----
+  GET /config/server/version HTTP/1.0
+----
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  "2.7"
+----
+
 [[list-capabilities]]
 List Capabilities
 ~~~~~~~~~~~~~~~~~

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

@@ -0,0 +1,30 @@
+// 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.config;
+
+import com.google.gerrit.common.Version;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestReadView;
+
+public class GetVersion implements RestReadView<ConfigResource> {
+  @Override
+  public String apply(ConfigResource resource) throws ResourceNotFoundException {
+    String version = Version.getVersion();
+    if (version == null) {
+      throw new ResourceNotFoundException();
+    }
+    return version;
+  }
+}

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

@@ -26,5 +26,6 @@ public class Module extends RestApiModule {
     DynamicMap.mapOf(binder(), CONFIG_KIND);
     DynamicMap.mapOf(binder(), CAPABILITY_KIND);
     child(CONFIG_KIND, "capabilities").to(CapabilitiesCollection.class);
+    get(CONFIG_KIND, "version").to(GetVersion.class);
   }
 }