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

synapse/handlers/events.py

@@ -151,7 +151,7 @@ class EventHandler:
         """Retrieve a single specified event.
 
         Args:
-            user: The user requesting the event
+            user: The local user requesting the event
             room_id: The expected room id. We'll return None if the
                 event's room does not match.
             event_id: The event ID to obtain.
@@ -173,8 +173,11 @@ class EventHandler:
         if not event:
             return None
 
-        users = await self.store.get_users_in_room(event.room_id)
-        is_peeking = user.to_string() not in users
+        is_user_in_room = await self.store.check_local_user_in_room(
+            user_id=user.to_string(), room_id=event.room_id
+        )
+        # The user is peeking if they aren't in the room already
+        is_peeking = not is_user_in_room
 
         filtered = await filter_events_for_client(
             self._storage_controllers, user.to_string(), [event], is_peeking=is_peeking

synapse/handlers/message.py

@@ -761,8 +761,10 @@ class EventCreationHandler:
     async def _is_server_notices_room(self, room_id: str) -> bool:
         if self.config.servernotices.server_notices_mxid is None:
             return False
-        user_ids = await self.store.get_users_in_room(room_id)
-        return self.config.servernotices.server_notices_mxid in user_ids
+        is_server_notices_room = await self.store.check_local_user_in_room(
+            user_id=self.config.servernotices.server_notices_mxid, room_id=room_id
+        )
+        return is_server_notices_room
 
     async def assert_accepted_privacy_policy(self, requester: Requester) -> None:
         """Check if a user has accepted the privacy policy

synapse/handlers/room.py

@@ -1284,8 +1284,11 @@ class RoomContextHandler:
         before_limit = math.floor(limit / 2.0)
         after_limit = limit - before_limit
 
-        users = await self.store.get_users_in_room(room_id)
-        is_peeking = user.to_string() not in users
+        is_user_in_room = await self.store.check_local_user_in_room(
+            user_id=user.to_string(), room_id=room_id
+        )
+        # The user is peeking if they aren't in the room already
+        is_peeking = not is_user_in_room
 
         async def filter_evts(events: List[EventBase]) -> List[EventBase]:
             if use_admin_priviledge:

synapse/handlers/room_member.py

@@ -1620,8 +1620,10 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
     async def _is_server_notice_room(self, room_id: str) -> bool:
         if self._server_notices_mxid is None:
             return False
-        user_ids = await self.store.get_users_in_room(room_id)
-        return 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_id
+        )
+        return is_server_notices_room
 
 
 class RoomMemberMasterHandler(RoomMemberHandler):