Accept POST on supported REST collections

POST on /groups/ should create a new resource whose id is
determined from the input body. The AcceptsCreate interface
does not work here as there was no id in the path remaining.
Build a new interface AcceptsPost that handles POST calls on
a collection using the collection itself to construct the view.
This is primarily meant for TopLevelResource collections.

Change-Id: I0086ffc69cf42905db8c98198a809bfa755b52dd

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/restapi/AcceptsPost.java

@@ -0,0 +1,36 @@
+// Copyright (C) 2012 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.restapi;
+
+/**
+ * Optional interface for {@link RestCollection}.
+ * <p>
+ * Collections that implement this interface can accept a {@code POST} directly
+ * on the collection itself when no id was given in the path. This interface is
+ * intended to be used with TopLevelResource collections. Nested collections
+ * often bind POST on the parent collection to the view implementation handling
+ * the insertion of a new member.
+ */
+public interface AcceptsPost<P extends RestResource> {
+  /**
+   * Handle creation of a child resource by POST on the collection.
+   *
+   * @param parent parent collection handle.
+   * @return a view to perform the creation. The id of the newly created
+   *         resource should be determined from the input body.
+   * @throws RestApiException the view cannot be constructed.
+   */
+  <I> RestModifyView<P, I> post(P parent) throws RestApiException;
+}