Support to retrieve the username of an account via REST

By GET on /accounts/<account-id>/username it is now possible to
retrieve the username of an account.

Change-Id: I061dbc2f59920edb7421c6341854a42b36c782ca
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-accounts.txt

@@ -161,6 +161,31 @@ Deletes the name of an account.
   HTTP/1.1 204 No Content
 ----
 
+[[get-username]]
+Get Username
+~~~~~~~~~~~~
+[verse]
+'GET /accounts/link:#account-id[\{account-id\}]/username'
+
+Retrieves the username of an account.
+
+.Request
+----
+  GET /accounts/self/username HTTP/1.0
+----
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  "john.doe"
+----
+
+If the account does not have a username the response is `404 Not Found`.
+
 [[get-active]]
 Get Active
 ~~~~~~~~~~

gerrit-server/src/main/java/com/google/gerrit/server/account/GetUsername.java

@@ -0,0 +1,46 @@
+// 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.account;
+
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestReadView;
+import com.google.gerrit.server.CurrentUser;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+
+public class GetUsername implements RestReadView<AccountResource> {
+
+  private final Provider<CurrentUser> self;
+
+  @Inject
+  GetUsername(Provider<CurrentUser> self) {
+    this.self = self;
+  }
+
+  @Override
+  public String apply(AccountResource rsrc) throws AuthException,
+      ResourceNotFoundException {
+    if (self.get() != rsrc.getUser()
+        && !self.get().getCapabilities().canAdministrateServer()) {
+      throw new AuthException("not allowed to get username");
+    }
+    String username = rsrc.getUser().getAccount().getUserName();
+    if (username == null) {
+      throw new ResourceNotFoundException();
+    }
+    return username;
+  }
+}

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

@@ -39,6 +39,7 @@ public class Module extends RestApiModule {
     get(ACCOUNT_KIND, "name").to(GetName.class);
     put(ACCOUNT_KIND, "name").to(PutName.class);
     delete(ACCOUNT_KIND, "name").to(PutName.class);
+    get(ACCOUNT_KIND, "username").to(GetUsername.class);
     get(ACCOUNT_KIND, "active").to(GetActive.class);
     put(ACCOUNT_KIND, "active").to(PutActive.class);
     delete(ACCOUNT_KIND, "active").to(DeleteActive.class);