'Check if an application service knows this room alias exists.
Args:
room_alias(RoomAlias): The room alias to query.
Returns:
namedtuple: with keys "room_id" and "servers" or None if no
association can be found.'

@defer.inlineCallbacks
def query_room_alias_exists(self, room_alias):

    room_alias_str = room_alias.to_string()
    services = self.store.get_app_services()
    alias_query_services = [s for s in services if s.is_interested_in_alias(room_alias_str)]
    for alias_service in alias_query_services:
        is_known_alias = (yield self.appservice_api.query_alias(alias_service, room_alias_str))
        if is_known_alias:
            result = (yield self.store.get_association_from_room_alias(room_alias))
            defer.returnValue(result)
