Allow additional_resources to implement Resource directly (#6686)

AdditionalResource really doesn't add any value, and it gets in the way for
resources which want to support child resources or the like. So, if the
resource object already implements the IResource interface, don't bother
wrapping it.

changelog.d/6686.misc

@@ -0,0 +1 @@
+Allow additional_resources to implement IResource directly.

synapse/app/homeserver.py

@@ -31,7 +31,7 @@ from prometheus_client import Gauge
 from twisted.application import service
 from twisted.internet import defer, reactor
 from twisted.python.failure import Failure
-from twisted.web.resource import EncodingResourceWrapper, NoResource
+from twisted.web.resource import EncodingResourceWrapper, IResource, NoResource
 from twisted.web.server import GzipEncoderFactory
 from twisted.web.static import File
 
@@ -109,7 +109,16 @@ class SynapseHomeServer(HomeServer):
         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 IResource.providedBy(handler):
+                resource = handler
+            elif hasattr(handler, "handle_request"):
+                resource = AdditionalResource(self, handler.handle_request)
+            else:
+                raise ConfigError(
+                    "additional_resource %s does not implement a known interface"
+                    % (resmodule["module"],)
+                )
+            resources[path] = resource
 
         # try to find something useful to redirect '/' to
         if WEB_CLIENT_PREFIX in resources: