Add a hook for custom rest endpoints

Let the user specify custom modules which can be used for implementing extra
endpoints.

synapse/http/additional_resource.py

@@ -0,0 +1,55 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 New Vector Ltd
+#
+# 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.
+
+from synapse.http.server import wrap_request_handler
+from twisted.web.resource import Resource
+from twisted.web.server import NOT_DONE_YET
+
+
+class AdditionalResource(Resource):
+    """Resource wrapper for additional_resources
+
+    If the user has configured additional_resources, we need to wrap the
+    handler class with a Resource so that we can map it into the resource tree.
+
+    This class is also where we wrap the request handler with logging, metrics,
+    and exception handling.
+    """
+    def __init__(self, hs, handler):
+        """Initialise AdditionalResource
+
+        The ``handler`` should return a deferred which completes when it has
+        done handling the request. It should write a response with
+        ``request.write()``, and call ``request.finish()``.
+
+        Args:
+            hs (synapse.server.HomeServer): homeserver
+            handler ((twisted.web.server.Request) -> twisted.internet.defer.Deferred):
+                function to be called to handle the request.
+        """
+        Resource.__init__(self)
+        self._handler = handler
+
+        # these are required by the request_handler wrapper
+        self.version_string = hs.version_string
+        self.clock = hs.get_clock()
+
+    def render(self, request):
+        self._async_render(request)
+        return NOT_DONE_YET
+
+    @wrap_request_handler
+    def _async_render(self, request):
+        return self._handler(request)