From fcdfc911eef966ad6b1e0cbe9a4af5b1679d66bd Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Thu, 2 Nov 2017 14:18:24 +0000
Subject: [PATCH] Add a hook for custom rest endpoints

Let the user specify custom modules which can be used for implementing extra
endpoints.
---
 synapse/app/homeserver.py           | 12 +++++++
 synapse/config/server.py            |  7 ++++
 synapse/http/additional_resource.py | 55 +++++++++++++++++++++++++++++
 3 files changed, 74 insertions(+)
 create mode 100644 synapse/http/additional_resource.py

diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index 3adf72e14..8f2e08506 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -30,6 +30,8 @@ from synapse.config._base import ConfigError
 from synapse.config.homeserver import HomeServerConfig
 from synapse.crypto import context_factory
 from synapse.federation.transport.server import TransportLayerServer
+from synapse.module_api import ModuleApi
+from synapse.http.additional_resource import AdditionalResource
 from synapse.http.server import RootRedirect
 from synapse.http.site import SynapseSite
 from synapse.metrics import register_memory_metrics
@@ -49,6 +51,7 @@ from synapse.storage.prepare_database import UpgradeDatabaseException, prepare_d
 from synapse.util.httpresourcetree import create_resource_tree
 from synapse.util.logcontext import LoggingContext
 from synapse.util.manhole import manhole
+from synapse.util.module_loader import load_module
 from synapse.util.rlimit import change_resource_limit
 from synapse.util.versionstring import get_version_string
 from twisted.application import service
@@ -154,6 +157,15 @@ class SynapseHomeServer(HomeServer):
                 if name == "metrics" and self.get_config().enable_metrics:
                     resources[METRICS_PREFIX] = MetricsResource(self)
 
+        additional_resources = listener_config.get("additional_resources", {})
+        logger.debug("Configuring additional resources: %r",
+                     additional_resources)
+        module_api = ModuleApi(self, self.get_auth_handler())
+        for path, resmodule in additional_resources.items():
+            handler_cls, config = load_module(resmodule)
+            handler = handler_cls(config, module_api)
+            resources[path] = AdditionalResource(self, handler.handle_request)
+
         if WEB_CLIENT_PREFIX in resources:
             root_resource = RootRedirect(WEB_CLIENT_PREFIX)
         else:
diff --git a/synapse/config/server.py b/synapse/config/server.py
index b66993dab..4d9193536 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -247,6 +247,13 @@ class ServerConfig(Config):
               - names: [federation]  # Federation APIs
                 compress: false
 
+            # optional list of additional endpoints which can be loaded via
+            # dynamic modules
+            # additional_resources:
+            #   "/_matrix/my/custom/endpoint":
+            #     module: my_module.CustomRequestHandler
+            #     config: {}
+
           # Unsecure HTTP listener,
           # For when matrix traffic passes through loadbalancer that unwraps TLS.
           - port: %(unsecure_port)s
diff --git a/synapse/http/additional_resource.py b/synapse/http/additional_resource.py
new file mode 100644
index 000000000..343e932cb
--- /dev/null
+++ b/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)