Merge tag 'v1.3.0'

Synapse 1.3.0 (2019-08-15)
==========================

Bugfixes
--------

- Fix 500 Internal Server Error on `publicRooms` when the public room list was
  cached. ([\#5851](https://github.com/matrix-org/synapse/issues/5851))

Synapse 1.3.0rc1 (2019-08-13)
==========================

Features
--------

- Use `M_USER_DEACTIVATED` instead of `M_UNKNOWN` for errcode when a deactivated user attempts to login. ([\#5686](https://github.com/matrix-org/synapse/issues/5686))
- Add sd_notify hooks to ease systemd integration and allows usage of Type=Notify. ([\#5732](https://github.com/matrix-org/synapse/issues/5732))
- Synapse will no longer serve any media repo admin endpoints when `enable_media_repo` is set to False in the configuration. If a media repo worker is used, the admin APIs relating to the media repo will be served from it instead. ([\#5754](https://github.com/matrix-org/synapse/issues/5754), [\#5848](https://github.com/matrix-org/synapse/issues/5848))
- Synapse can now be configured to not join remote rooms of a given "complexity" (currently, state events) over federation. This option can be used to prevent adverse performance on resource-constrained homeservers. ([\#5783](https://github.com/matrix-org/synapse/issues/5783))
- Allow defining HTML templates to serve the user on account renewal attempt when using the account validity feature. ([\#5807](https://github.com/matrix-org/synapse/issues/5807))

Bugfixes
--------

- Fix UISIs during homeserver outage. ([\#5693](https://github.com/matrix-org/synapse/issues/5693), [\#5789](https://github.com/matrix-org/synapse/issues/5789))
- Fix stack overflow in server key lookup code. ([\#5724](https://github.com/matrix-org/synapse/issues/5724))
- start.sh no longer uses deprecated cli option. ([\#5725](https://github.com/matrix-org/synapse/issues/5725))
- Log when we receive an event receipt from an unexpected origin. ([\#5743](https://github.com/matrix-org/synapse/issues/5743))
- Fix debian packaging scripts to correctly build sid packages. ([\#5775](https://github.com/matrix-org/synapse/issues/5775))
- Correctly handle redactions of redactions. ([\#5788](https://github.com/matrix-org/synapse/issues/5788))
- Return 404 instead of 403 when accessing /rooms/{roomId}/event/{eventId} for an event without the appropriate permissions. ([\#5798](https://github.com/matrix-org/synapse/issues/5798))
- Fix check that tombstone is a state event in push rules. ([\#5804](https://github.com/matrix-org/synapse/issues/5804))
- Fix error when trying to login as a deactivated user when using a worker to handle login. ([\#5806](https://github.com/matrix-org/synapse/issues/5806))
- Fix bug where user `/sync` stream could get wedged in rare circumstances. ([\#5825](https://github.com/matrix-org/synapse/issues/5825))
- The purge_remote_media.sh script was fixed. ([\#5839](https://github.com/matrix-org/synapse/issues/5839))

Deprecations and Removals
-------------------------

- Synapse now no longer accepts the `-v`/`--verbose`, `-f`/`--log-file`, or `--log-config` command line flags, and removes the deprecated `verbose` and `log_file` configuration file options. Users of these options should migrate their options into the dedicated log configuration. ([\#5678](https://github.com/matrix-org/synapse/issues/5678), [\#5729](https://github.com/matrix-org/synapse/issues/5729))
- Remove non-functional 'expire_access_token' setting. ([\#5782](https://github.com/matrix-org/synapse/issues/5782))

Internal Changes
----------------

- Make Jaeger fully configurable. ([\#5694](https://github.com/matrix-org/synapse/issues/5694))
- Add precautionary measures to prevent future abuse of `window.opener` in default welcome page. ([\#5695](https://github.com/matrix-org/synapse/issues/5695))
- Reduce database IO usage by optimising queries for current membership. ([\#5706](https://github.com/matrix-org/synapse/issues/5706), [\#5738](https://github.com/matrix-org/synapse/issues/5738), [\#5746](https://github.com/matrix-org/synapse/issues/5746), [\#5752](https://github.com/matrix-org/synapse/issues/5752), [\#5770](https://github.com/matrix-org/synapse/issues/5770), [\#5774](https://github.com/matrix-org/synapse/issues/5774), [\#5792](https://github.com/matrix-org/synapse/issues/5792), [\#5793](https://github.com/matrix-org/synapse/issues/5793))
- Improve caching when fetching `get_filtered_current_state_ids`. ([\#5713](https://github.com/matrix-org/synapse/issues/5713))
- Don't accept opentracing data from clients. ([\#5715](https://github.com/matrix-org/synapse/issues/5715))
- Speed up PostgreSQL unit tests in CI. ([\#5717](https://github.com/matrix-org/synapse/issues/5717))
- Update the coding style document. ([\#5719](https://github.com/matrix-org/synapse/issues/5719))
- Improve database query performance when recording retry intervals for remote hosts. ([\#5720](https://github.com/matrix-org/synapse/issues/5720))
- Add a set of opentracing utils. ([\#5722](https://github.com/matrix-org/synapse/issues/5722))
- Cache result of get_version_string to reduce overhead of `/version` federation requests. ([\#5730](https://github.com/matrix-org/synapse/issues/5730))
- Return 'user_type' in admin API user endpoints results. ([\#5731](https://github.com/matrix-org/synapse/issues/5731))
- Don't package the sytest test blacklist file. ([\#5733](https://github.com/matrix-org/synapse/issues/5733))
- Replace uses of returnValue with plain return, as returnValue is not needed on Python 3. ([\#5736](https://github.com/matrix-org/synapse/issues/5736))
- Blacklist some flakey tests in worker mode. ([\#5740](https://github.com/matrix-org/synapse/issues/5740))
- Fix some error cases in the caching layer. ([\#5749](https://github.com/matrix-org/synapse/issues/5749))
- Add a prometheus metric for pending cache lookups. ([\#5750](https://github.com/matrix-org/synapse/issues/5750))
- Stop trying to fetch events with event_id=None. ([\#5753](https://github.com/matrix-org/synapse/issues/5753))
- Convert RedactionTestCase to modern test style. ([\#5768](https://github.com/matrix-org/synapse/issues/5768))
- Allow looping calls to be given arguments. ([\#5780](https://github.com/matrix-org/synapse/issues/5780))
- Set the logs emitted when checking typing and presence timeouts to DEBUG level, not INFO. ([\#5785](https://github.com/matrix-org/synapse/issues/5785))
- Remove DelayedCall debugging from the test suite, as it is no longer required in the vast majority of Synapse's tests. ([\#5787](https://github.com/matrix-org/synapse/issues/5787))
- Remove some spurious exceptions from the logs where we failed to talk to a remote server. ([\#5790](https://github.com/matrix-org/synapse/issues/5790))
- Improve performance when making `.well-known` requests by sharing the SSL options between requests. ([\#5794](https://github.com/matrix-org/synapse/issues/5794))
- Disable codecov GitHub comments on PRs. ([\#5796](https://github.com/matrix-org/synapse/issues/5796))
- Don't allow clients to send tombstone events that reference the room it's sent in. ([\#5801](https://github.com/matrix-org/synapse/issues/5801))
- Deny redactions of events sent in a different room. ([\#5802](https://github.com/matrix-org/synapse/issues/5802))
- Deny sending well known state types as non-state events. ([\#5805](https://github.com/matrix-org/synapse/issues/5805))
- Handle incorrectly encoded query params correctly by returning a 400. ([\#5808](https://github.com/matrix-org/synapse/issues/5808))
- Handle pusher being deleted during processing rather than logging an exception. ([\#5809](https://github.com/matrix-org/synapse/issues/5809))
- Return 502 not 500 when failing to reach any remote server. ([\#5810](https://github.com/matrix-org/synapse/issues/5810))
- Reduce global pauses in the events stream caused by expensive state resolution during persistence. ([\#5826](https://github.com/matrix-org/synapse/issues/5826))
- Add a lower bound to well-known lookup cache time to avoid repeated lookups. ([\#5836](https://github.com/matrix-org/synapse/issues/5836))
- Whitelist history visbility sytests in worker mode tests. ([\#5843](https://github.com/matrix-org/synapse/issues/5843))

7 files changed, 146 insertions, 103 deletions

diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index f7bb806ae7..5a1e23a145 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -106,7 +106,7 @@ class FederationBase(object):
                     "Failed to find copy of %s with valid signature", pdu.event_id
                 )
 
-            defer.returnValue(res)
+            return res
 
         handle = preserve_fn(handle_check_result)
         deferreds2 = [handle(pdu, deferred) for pdu, deferred in zip(pdus, deferreds)]
@@ -116,9 +116,9 @@ class FederationBase(object):
         ).addErrback(unwrapFirstError)
 
         if include_none:
-            defer.returnValue(valid_pdus)
+            return valid_pdus
         else:
-            defer.returnValue([p for p in valid_pdus if p])
+            return [p for p in valid_pdus if p]
 
     def _check_sigs_and_hash(self, room_version, pdu):
         return make_deferred_yieldable(
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 3cb4b94420..bec3080895 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -213,7 +213,7 @@ class FederationClient(FederationBase):
             ).addErrback(unwrapFirstError)
         )
 
-        defer.returnValue(pdus)
+        return pdus
 
     @defer.inlineCallbacks
     @log_function
@@ -245,7 +245,7 @@ class FederationClient(FederationBase):
 
         ev = self._get_pdu_cache.get(event_id)
         if ev:
-            defer.returnValue(ev)
+            return ev
 
         pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
 
@@ -307,7 +307,7 @@ class FederationClient(FederationBase):
         if signed_pdu:
             self._get_pdu_cache[event_id] = signed_pdu
 
-        defer.returnValue(signed_pdu)
+        return signed_pdu
 
     @defer.inlineCallbacks
     @log_function
@@ -355,7 +355,7 @@ class FederationClient(FederationBase):
 
             auth_chain.sort(key=lambda e: e.depth)
 
-            defer.returnValue((pdus, auth_chain))
+            return (pdus, auth_chain)
         except HttpResponseException as e:
             if e.code == 400 or e.code == 404:
                 logger.info("Failed to use get_room_state_ids API, falling back")
@@ -404,7 +404,7 @@ class FederationClient(FederationBase):
 
         signed_auth.sort(key=lambda e: e.depth)
 
-        defer.returnValue((signed_pdus, signed_auth))
+        return (signed_pdus, signed_auth)
 
     @defer.inlineCallbacks
     def get_events_from_store_or_dest(self, destination, room_id, event_ids):
@@ -429,7 +429,7 @@ class FederationClient(FederationBase):
             missing_events.discard(k)
 
         if not missing_events:
-            defer.returnValue((signed_events, failed_to_fetch))
+            return (signed_events, failed_to_fetch)
 
         logger.debug(
             "Fetching unknown state/auth events %s for room %s",
@@ -465,7 +465,7 @@ class FederationClient(FederationBase):
             # We removed all events we successfully fetched from `batch`
             failed_to_fetch.update(batch)
 
-        defer.returnValue((signed_events, failed_to_fetch))
+        return (signed_events, failed_to_fetch)
 
     @defer.inlineCallbacks
     @log_function
@@ -485,7 +485,7 @@ class FederationClient(FederationBase):
 
         signed_auth.sort(key=lambda e: e.depth)
 
-        defer.returnValue(signed_auth)
+        return signed_auth
 
     @defer.inlineCallbacks
     def _try_destination_list(self, description, destinations, callback):
@@ -511,9 +511,8 @@ class FederationClient(FederationBase):
             The [Deferred] result of callback, if it succeeds
 
         Raises:
-            SynapseError if the chosen remote server returns a 300/400 code.
-
-            RuntimeError if no servers were reachable.
+            SynapseError if the chosen remote server returns a 300/400 code, or
+            no servers were reachable.
         """
         for destination in destinations:
             if destination == self.server_name:
@@ -521,7 +520,7 @@ class FederationClient(FederationBase):
 
             try:
                 res = yield callback(destination)
-                defer.returnValue(res)
+                return res
             except InvalidResponseError as e:
                 logger.warn("Failed to %s via %s: %s", description, destination, e)
             except HttpResponseException as e:
@@ -538,7 +537,7 @@ class FederationClient(FederationBase):
             except Exception:
                 logger.warn("Failed to %s via %s", description, destination, exc_info=1)
 
-        raise RuntimeError("Failed to %s via any server" % (description,))
+        raise SynapseError(502, "Failed to %s via any server" % (description,))
 
     def make_membership_event(
         self, destinations, room_id, user_id, membership, content, params
@@ -615,7 +614,7 @@ class FederationClient(FederationBase):
                 event_dict=pdu_dict,
             )
 
-            defer.returnValue((destination, ev, event_format))
+            return (destination, ev, event_format)
 
         return self._try_destination_list(
             "make_" + membership, destinations, send_request
@@ -728,13 +727,11 @@ class FederationClient(FederationBase):
 
             check_authchain_validity(signed_auth)
 
-            defer.returnValue(
-                {
-                    "state": signed_state,
-                    "auth_chain": signed_auth,
-                    "origin": destination,
-                }
-            )
+            return {
+                "state": signed_state,
+                "auth_chain": signed_auth,
+                "origin": destination,
+            }
 
         return self._try_destination_list("send_join", destinations, send_request)
 
@@ -758,7 +755,7 @@ class FederationClient(FederationBase):
 
         # FIXME: We should handle signature failures more gracefully.
 
-        defer.returnValue(pdu)
+        return pdu
 
     @defer.inlineCallbacks
     def _do_send_invite(self, destination, pdu, room_version):
@@ -786,7 +783,7 @@ class FederationClient(FederationBase):
                     "invite_room_state": pdu.unsigned.get("invite_room_state", []),
                 },
             )
-            defer.returnValue(content)
+            return content
         except HttpResponseException as e:
             if e.code in [400, 404]:
                 err = e.to_synapse_error()
@@ -821,7 +818,7 @@ class FederationClient(FederationBase):
             event_id=pdu.event_id,
             content=pdu.get_pdu_json(time_now),
         )
-        defer.returnValue(content)
+        return content
 
     def send_leave(self, destinations, pdu):
         """Sends a leave event to one of a list of homeservers.
@@ -856,7 +853,7 @@ class FederationClient(FederationBase):
             )
 
             logger.debug("Got content: %s", content)
-            defer.returnValue(None)
+            return None
 
         return self._try_destination_list("send_leave", destinations, send_request)
 
@@ -917,7 +914,7 @@ class FederationClient(FederationBase):
             "missing": content.get("missing", []),
         }
 
-        defer.returnValue(ret)
+        return ret
 
     @defer.inlineCallbacks
     def get_missing_events(
@@ -974,7 +971,7 @@ class FederationClient(FederationBase):
             # get_missing_events
             signed_events = []
 
-        defer.returnValue(signed_events)
+        return signed_events
 
     @defer.inlineCallbacks
     def forward_third_party_invite(self, destinations, room_id, event_dict):
@@ -986,7 +983,7 @@ class FederationClient(FederationBase):
                 yield self.transport_layer.exchange_third_party_invite(
                     destination=destination, room_id=room_id, event_dict=event_dict
                 )
-                defer.returnValue(None)
+                return None
             except CodeMessageException:
                 raise
             except Exception as e:
@@ -995,3 +992,39 @@ class FederationClient(FederationBase):
                 )
 
         raise RuntimeError("Failed to send to any server.")
+
+    @defer.inlineCallbacks
+    def get_room_complexity(self, destination, room_id):
+        """
+        Fetch the complexity of a remote room from another server.
+
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+
+        Returns:
+            Deferred[dict] or Deferred[None]: Dict contains the complexity
+            metric versions, while None means we could not fetch the complexity.
+        """
+        try:
+            complexity = yield self.transport_layer.get_room_complexity(
+                destination=destination, room_id=room_id
+            )
+            defer.returnValue(complexity)
+        except CodeMessageException as e:
+            # We didn't manage to get it -- probably a 404. We are okay if other
+            # servers don't give it to us.
+            logger.debug(
+                "Failed to fetch room complexity via %s for %s, got a %d",
+                destination,
+                room_id,
+                e.code,
+            )
+        except Exception:
+            logger.exception(
+                "Failed to fetch room complexity via %s for %s", destination, room_id
+            )
+
+        # If we don't manage to find it, return None. It's not an error if a
+        # server doesn't give it to us.
+        defer.returnValue(None)
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index ed2b6d5eef..d216c46dfe 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -99,7 +99,7 @@ class FederationServer(FederationBase):
 
             res = self._transaction_from_pdus(pdus).get_dict()
 
-        defer.returnValue((200, res))
+        return (200, res)
 
     @defer.inlineCallbacks
     @log_function
@@ -126,7 +126,7 @@ class FederationServer(FederationBase):
                 origin, transaction, request_time
             )
 
-        defer.returnValue(result)
+        return result
 
     @defer.inlineCallbacks
     def _handle_incoming_transaction(self, origin, transaction, request_time):
@@ -147,8 +147,7 @@ class FederationServer(FederationBase):
                 "[%s] We've already responded to this request",
                 transaction.transaction_id,
             )
-            defer.returnValue(response)
-            return
+            return response
 
         logger.debug("[%s] Transaction is new", transaction.transaction_id)
 
@@ -163,7 +162,7 @@ class FederationServer(FederationBase):
             yield self.transaction_actions.set_response(
                 origin, transaction, 400, response
             )
-            defer.returnValue((400, response))
+            return (400, response)
 
         received_pdus_counter.inc(len(transaction.pdus))
 
@@ -265,7 +264,7 @@ class FederationServer(FederationBase):
         logger.debug("Returning: %s", str(response))
 
         yield self.transaction_actions.set_response(origin, transaction, 200, response)
-        defer.returnValue((200, response))
+        return (200, response)
 
     @defer.inlineCallbacks
     def received_edu(self, origin, edu_type, content):
@@ -298,7 +297,7 @@ class FederationServer(FederationBase):
                 event_id,
             )
 
-        defer.returnValue((200, resp))
+        return (200, resp)
 
     @defer.inlineCallbacks
     def on_state_ids_request(self, origin, room_id, event_id):
@@ -315,9 +314,7 @@ class FederationServer(FederationBase):
         state_ids = yield self.handler.get_state_ids_for_pdu(room_id, event_id)
         auth_chain_ids = yield self.store.get_auth_chain_ids(state_ids)
 
-        defer.returnValue(
-            (200, {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids})
-        )
+        return (200, {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids})
 
     @defer.inlineCallbacks
     def _on_context_state_request_compute(self, room_id, event_id):
@@ -336,12 +333,10 @@ class FederationServer(FederationBase):
                     )
                 )
 
-        defer.returnValue(
-            {
-                "pdus": [pdu.get_pdu_json() for pdu in pdus],
-                "auth_chain": [pdu.get_pdu_json() for pdu in auth_chain],
-            }
-        )
+        return {
+            "pdus": [pdu.get_pdu_json() for pdu in pdus],
+            "auth_chain": [pdu.get_pdu_json() for pdu in auth_chain],
+        }
 
     @defer.inlineCallbacks
     @log_function
@@ -349,15 +344,15 @@ class FederationServer(FederationBase):
         pdu = yield self.handler.get_persisted_pdu(origin, event_id)
 
         if pdu:
-            defer.returnValue((200, self._transaction_from_pdus([pdu]).get_dict()))
+            return (200, self._transaction_from_pdus([pdu]).get_dict())
         else:
-            defer.returnValue((404, ""))
+            return (404, "")
 
     @defer.inlineCallbacks
     def on_query_request(self, query_type, args):
         received_queries_counter.labels(query_type).inc()
         resp = yield self.registry.on_query(query_type, args)
-        defer.returnValue((200, resp))
+        return (200, resp)
 
     @defer.inlineCallbacks
     def on_make_join_request(self, origin, room_id, user_id, supported_versions):
@@ -371,9 +366,7 @@ class FederationServer(FederationBase):
 
         pdu = yield self.handler.on_make_join_request(origin, room_id, user_id)
         time_now = self._clock.time_msec()
-        defer.returnValue(
-            {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
-        )
+        return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
 
     @defer.inlineCallbacks
     def on_invite_request(self, origin, content, room_version):
@@ -391,7 +384,7 @@ class FederationServer(FederationBase):
         yield self.check_server_matches_acl(origin_host, pdu.room_id)
         ret_pdu = yield self.handler.on_invite_request(origin, pdu)
         time_now = self._clock.time_msec()
-        defer.returnValue({"event": ret_pdu.get_pdu_json(time_now)})
+        return {"event": ret_pdu.get_pdu_json(time_now)}
 
     @defer.inlineCallbacks
     def on_send_join_request(self, origin, content, room_id):
@@ -407,16 +400,14 @@ class FederationServer(FederationBase):
         logger.debug("on_send_join_request: pdu sigs: %s", pdu.signatures)
         res_pdus = yield self.handler.on_send_join_request(origin, pdu)
         time_now = self._clock.time_msec()
-        defer.returnValue(
-            (
-                200,
-                {
-                    "state": [p.get_pdu_json(time_now) for p in res_pdus["state"]],
-                    "auth_chain": [
-                        p.get_pdu_json(time_now) for p in res_pdus["auth_chain"]
-                    ],
-                },
-            )
+        return (
+            200,
+            {
+                "state": [p.get_pdu_json(time_now) for p in res_pdus["state"]],
+                "auth_chain": [
+                    p.get_pdu_json(time_now) for p in res_pdus["auth_chain"]
+                ],
+            },
         )
 
     @defer.inlineCallbacks
@@ -428,9 +419,7 @@ class FederationServer(FederationBase):
         room_version = yield self.store.get_room_version(room_id)
 
         time_now = self._clock.time_msec()
-        defer.returnValue(
-            {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
-        )
+        return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
 
     @defer.inlineCallbacks
     def on_send_leave_request(self, origin, content, room_id):
@@ -445,7 +434,7 @@ class FederationServer(FederationBase):
 
         logger.debug("on_send_leave_request: pdu sigs: %s", pdu.signatures)
         yield self.handler.on_send_leave_request(origin, pdu)
-        defer.returnValue((200, {}))
+        return (200, {})
 
     @defer.inlineCallbacks
     def on_event_auth(self, origin, room_id, event_id):
@@ -456,7 +445,7 @@ class FederationServer(FederationBase):
             time_now = self._clock.time_msec()
             auth_pdus = yield self.handler.on_event_auth(event_id)
             res = {"auth_chain": [a.get_pdu_json(time_now) for a in auth_pdus]}
-        defer.returnValue((200, res))
+        return (200, res)
 
     @defer.inlineCallbacks
     def on_query_auth_request(self, origin, content, room_id, event_id):
@@ -509,7 +498,7 @@ class FederationServer(FederationBase):
                 "missing": ret.get("missing", []),
             }
 
-        defer.returnValue((200, send_content))
+        return (200, send_content)
 
     @log_function
     def on_query_client_keys(self, origin, content):
@@ -548,7 +537,7 @@ class FederationServer(FederationBase):
             ),
         )
 
-        defer.returnValue({"one_time_keys": json_result})
+        return {"one_time_keys": json_result}
 
     @defer.inlineCallbacks
     @log_function
@@ -580,9 +569,7 @@ class FederationServer(FederationBase):
 
             time_now = self._clock.time_msec()
 
-        defer.returnValue(
-            {"events": [ev.get_pdu_json(time_now) for ev in missing_events]}
-        )
+        return {"events": [ev.get_pdu_json(time_now) for ev in missing_events]}
 
     @log_function
     def on_openid_userinfo(self, token):
@@ -676,14 +663,14 @@ class FederationServer(FederationBase):
         ret = yield self.handler.exchange_third_party_invite(
             sender_user_id, target_user_id, room_id, signed
         )
-        defer.returnValue(ret)
+        return ret
 
     @defer.inlineCallbacks
     def on_exchange_third_party_invite_request(self, origin, room_id, event_dict):
         ret = yield self.handler.on_exchange_third_party_invite_request(
             origin, room_id, event_dict
         )
-        defer.returnValue(ret)
+        return ret
 
     @defer.inlineCallbacks
     def check_server_matches_acl(self, server_name, room_id):
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index 9aab12c0d3..fad980b893 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -374,7 +374,7 @@ class PerDestinationQueue(object):
 
         assert len(edus) <= limit, "get_devices_by_remote returned too many EDUs"
 
-        defer.returnValue((edus, now_stream_id))
+        return (edus, now_stream_id)
 
     @defer.inlineCallbacks
     def _get_to_device_message_edus(self, limit):
@@ -393,4 +393,4 @@ class PerDestinationQueue(object):
             for content in contents
         ]
 
-        defer.returnValue((edus, stream_id))
+        return (edus, stream_id)
diff --git a/synapse/federation/sender/transaction_manager.py b/synapse/federation/sender/transaction_manager.py
index 0460a8c4ac..52706302f2 100644
--- a/synapse/federation/sender/transaction_manager.py
+++ b/synapse/federation/sender/transaction_manager.py
@@ -133,4 +133,4 @@ class TransactionManager(object):
                 )
             success = False
 
-        defer.returnValue(success)
+        return success
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 1aae9ec9e7..0cea0d2a10 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -21,7 +21,11 @@ from six.moves import urllib
 from twisted.internet import defer
 
 from synapse.api.constants import Membership
-from synapse.api.urls import FEDERATION_V1_PREFIX, FEDERATION_V2_PREFIX
+from synapse.api.urls import (
+    FEDERATION_UNSTABLE_PREFIX,
+    FEDERATION_V1_PREFIX,
+    FEDERATION_V2_PREFIX,
+)
 from synapse.logging.utils import log_function
 
 logger = logging.getLogger(__name__)
@@ -183,7 +187,7 @@ class TransportLayerClient(object):
             try_trailing_slash_on_400=True,
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -201,7 +205,7 @@ class TransportLayerClient(object):
             ignore_backoff=ignore_backoff,
         )
 
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -259,7 +263,7 @@ class TransportLayerClient(object):
             ignore_backoff=ignore_backoff,
         )
 
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -270,7 +274,7 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -288,7 +292,7 @@ class TransportLayerClient(object):
             ignore_backoff=True,
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -299,7 +303,7 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -310,7 +314,7 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -339,7 +343,7 @@ class TransportLayerClient(object):
             destination=remote_server, path=path, args=args, ignore_backoff=True
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -350,7 +354,7 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=event_dict
         )
 
-        defer.returnValue(response)
+        return response
 
     @defer.inlineCallbacks
     @log_function
@@ -359,7 +363,7 @@ class TransportLayerClient(object):
 
         content = yield self.client.get_json(destination=destination, path=path)
 
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -370,7 +374,7 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content
         )
 
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -402,7 +406,7 @@ class TransportLayerClient(object):
         content = yield self.client.post_json(
             destination=destination, path=path, data=query_content, timeout=timeout
         )
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -426,7 +430,7 @@ class TransportLayerClient(object):
         content = yield self.client.get_json(
             destination=destination, path=path, timeout=timeout
         )
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -460,7 +464,7 @@ class TransportLayerClient(object):
         content = yield self.client.post_json(
             destination=destination, path=path, data=query_content, timeout=timeout
         )
-        defer.returnValue(content)
+        return content
 
     @defer.inlineCallbacks
     @log_function
@@ -488,7 +492,7 @@ class TransportLayerClient(object):
             timeout=timeout,
         )
 
-        defer.returnValue(content)
+        return content
 
     @log_function
     def get_group_profile(self, destination, group_id, requester_user_id):
@@ -935,6 +939,23 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
+    def get_room_complexity(self, destination, room_id):
+        """
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+        """
+        path = _create_path(FEDERATION_UNSTABLE_PREFIX, "/rooms/%s/complexity", room_id)
+
+        return self.client.get_json(destination=destination, path=path)
+
+
+def _create_path(federation_prefix, path, *args):
+    """
+    Ensures that all args are url encoded.
+    """
+    return federation_prefix + path % tuple(urllib.parse.quote(arg, "") for arg in args)
+
 
 def _create_v1_path(path, *args):
     """Creates a path against V1 federation API from the path template and
@@ -951,9 +972,7 @@ def _create_v1_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V1_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V1_PREFIX, path, *args)
 
 
 def _create_v2_path(path, *args):
@@ -971,6 +990,4 @@ def _create_v2_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V2_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V2_PREFIX, path, *args)
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index ea4e1b6d0f..9a86bd0263 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -19,6 +19,8 @@ import functools
 import logging
 import re
 
+from twisted.internet.defer import maybeDeferred
+
 import synapse
 import synapse.logging.opentracing as opentracing
 from synapse.api.errors import Codes, FederationDeniedError, SynapseError
@@ -745,8 +747,12 @@ class PublicRoomList(BaseFederationServlet):
         else:
             network_tuple = ThirdPartyInstanceID(None, None)
 
-        data = await self.handler.get_local_public_room_list(
-            limit, since_token, network_tuple=network_tuple, from_federation=True
+        data = await maybeDeferred(
+            self.handler.get_local_public_room_list,
+            limit,
+            since_token,
+            network_tuple=network_tuple,
+            from_federation=True,
         )
         return 200, data