Room Complexity Client Implementation (#5783)

2 files changed, 105 insertions, 4 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 89b37dbc1c..10160bfe86 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2796,3 +2796,28 @@ class FederationHandler(BaseHandler):
             )
         else:
             return user_joined_room(self.distributor, user, room_id)
+
+    @defer.inlineCallbacks
+    def get_room_complexity(self, remote_room_hosts, room_id):
+        """
+        Fetch the complexity of a remote room over federation.
+
+        Args:
+            remote_room_hosts (list[str]): The remote servers to ask.
+            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.
+        """
+
+        for host in remote_room_hosts:
+            res = yield self.federation_client.get_room_complexity(host, room_id)
+
+            # We got a result, return it.
+            if res:
+                defer.returnValue(res)
+
+        # We fell off the bottom, couldn't get the complexity from anyone. Oh
+        # well.
+        defer.returnValue(None)
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index baea08ddd0..249a6d9c5d 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -26,8 +26,7 @@ from unpaddedbase64 import decode_base64
 
 from twisted.internet import defer
 
-import synapse.server
-import synapse.types
+from synapse import types
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import AuthError, Codes, HttpResponseException, SynapseError
 from synapse.types import RoomID, UserID
@@ -543,7 +542,7 @@ class RoomMemberHandler(object):
             ), "Sender (%s) must be same as requester (%s)" % (sender, requester.user)
             assert self.hs.is_mine(sender), "Sender must be our own: %s" % (sender,)
         else:
-            requester = synapse.types.create_requester(target_user)
+            requester = types.create_requester(target_user)
 
         prev_event = yield self.event_creation_handler.deduplicate_state_event(
             event, context
@@ -946,13 +945,53 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         self.distributor.declare("user_left_room")
 
     @defer.inlineCallbacks
+    def _is_remote_room_too_complex(self, room_id, remote_room_hosts):
+        """
+        Check if complexity of a remote room is too great.
+
+        Args:
+            room_id (str)
+            remote_room_hosts (list[str])
+
+        Returns: bool of whether the complexity is too great, or None
+            if unable to be fetched
+        """
+        max_complexity = self.hs.config.limit_remote_rooms.complexity
+        complexity = yield self.federation_handler.get_room_complexity(
+            remote_room_hosts, room_id
+        )
+
+        if complexity:
+            if complexity["v1"] > max_complexity:
+                return True
+            return False
+        return None
+
+    @defer.inlineCallbacks
+    def _is_local_room_too_complex(self, room_id):
+        """
+        Check if the complexity of a local room is too great.
+
+        Args:
+            room_id (str)
+
+        Returns: bool
+        """
+        max_complexity = self.hs.config.limit_remote_rooms.complexity
+        complexity = yield self.store.get_room_complexity(room_id)
+
+        if complexity["v1"] > max_complexity:
+            return True
+
+        return False
+
+    @defer.inlineCallbacks
     def _remote_join(self, requester, remote_room_hosts, room_id, user, content):
         """Implements RoomMemberHandler._remote_join
         """
         # filter ourselves out of remote_room_hosts: do_invite_join ignores it
         # and if it is the only entry we'd like to return a 404 rather than a
         # 500.
-
         remote_room_hosts = [
             host for host in remote_room_hosts if host != self.hs.hostname
         ]
@@ -960,6 +999,18 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         if len(remote_room_hosts) == 0:
             raise SynapseError(404, "No known servers")
 
+        if self.hs.config.limit_remote_rooms.enabled:
+            # Fetch the room complexity
+            too_complex = yield self._is_remote_room_too_complex(
+                room_id, remote_room_hosts
+            )
+            if too_complex is True:
+                raise SynapseError(
+                    code=400,
+                    msg=self.hs.config.limit_remote_rooms.complexity_error,
+                    errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+                )
+
         # We don't do an auth check if we are doing an invite
         # join dance for now, since we're kinda implicitly checking
         # that we are allowed to join when we decide whether or not we
@@ -969,6 +1020,31 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         )
         yield self._user_joined_room(user, room_id)
 
+        # Check the room we just joined wasn't too large, if we didn't fetch the
+        # complexity of it before.
+        if self.hs.config.limit_remote_rooms.enabled:
+            if too_complex is False:
+                # We checked, and we're under the limit.
+                return
+
+            # Check again, but with the local state events
+            too_complex = yield self._is_local_room_too_complex(room_id)
+
+            if too_complex is False:
+                # We're under the limit.
+                return
+
+            # The room is too large. Leave.
+            requester = types.create_requester(user, None, False, None)
+            yield self.update_membership(
+                requester=requester, target=user, room_id=room_id, action="leave"
+            )
+            raise SynapseError(
+                code=400,
+                msg=self.hs.config.limit_remote_rooms.complexity_error,
+                errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+            )
+
     @defer.inlineCallbacks
     def _remote_reject_invite(self, requester, remote_room_hosts, room_id, target):
         """Implements RoomMemberHandler._remote_reject_invite