Directly lookup local membership instead of getting all members in a room first (`get_users_in_room` mis-use) (#13608)

See https://github.com/matrix-org/synapse/pull/13575#discussion_r953023755

1 files changed, 8 insertions, 2 deletions

diff --git a/synapse/server_notices/server_notices_manager.py b/synapse/server_notices/server_notices_manager.py
index 70d054a8f4..564e3705c2 100644
--- a/synapse/server_notices/server_notices_manager.py
+++ b/synapse/server_notices/server_notices_manager.py
@@ -102,6 +102,10 @@ class ServerNoticesManager:
         Returns:
             The room's ID, or None if no room could be found.
         """
+        # If there is no server notices MXID, then there is no server notices room
+        if self.server_notices_mxid is None:
+            return None
+
         rooms = await self._store.get_rooms_for_local_user_where_membership_is(
             user_id, [Membership.INVITE, Membership.JOIN]
         )
@@ -111,8 +115,10 @@ class ServerNoticesManager:
             # be joined. This is kinda deliberate, in that if somebody somehow
             # manages to invite the system user to a room, that doesn't make it
             # the server notices room.
-            user_ids = await self._store.get_users_in_room(room.room_id)
-            if len(user_ids) <= 2 and self.server_notices_mxid in user_ids:
+            is_server_notices_room = await self._store.check_local_user_in_room(
+                user_id=self.server_notices_mxid, room_id=room.room_id
+            )
+            if is_server_notices_room:
                 # we found a room which our user shares with the system notice
                 # user
                 return room.room_id