Add a do_users_share_a_room method and use that in the presence handler.

synapse/handlers/presence.py

@@ -159,12 +159,11 @@ class PresenceHandler(BaseHandler):
         if allowed_by_subscription:
             defer.returnValue(True)
 
-        rm_handler = self.homeserver.get_handlers().room_member_handler
-        for room_id in (yield rm_handler.get_rooms_for_user(observer_user)):
-            if observed_user in (yield rm_handler.get_room_members(room_id)):
-                defer.returnValue(True)
+        share_room = yield self.store.do_users_share_a_room(
+            [observer_user, observed_user]
+        )
 
-        defer.returnValue(False)
+        defer.returnValue(share_room)
 
     @defer.inlineCallbacks
     def get_state(self, target_user, auth_user):

synapse/storage/roommember.py

@@ -150,3 +150,24 @@ class RoomMemberStore(SQLBaseStore):
 
         results = [self._parse_event_from_row(r) for r in rows]
         defer.returnValue(results)
+
+    @defer.inlineCallbacks
+    def do_users_share_a_room(self, user_list):
+        """ Checks whether a list of users share a room.
+        """
+        user_list_clause = " OR ".join(["m.user_id = ?"] * len(user_list))
+        sql = (
+            "SELECT m.room_id FROM room_memberships as m "
+            "INNER JOIN current_state_events as c "
+            "ON m.event_id = c.event_id "
+            "WHERE m.membership = 'join' "
+            "AND (%(clause)s) "
+            "GROUP BY m.room_id HAVING COUNT(m.room_id) = ?"
+        ) % {"clause": user_list_clause}
+
+        args = user_list
+        args.append(len(user_list))
+
+        rows = yield self._execute(None, sql, *args)
+
+        defer.returnValue(len(rows) > 0)