code: def __recv_cb(self, msg):
          
          try:
              self.__msg_callback(msg)
          except:
              logger.exception("AmqpLink.__recv_cb exception calling msg_callback")
          finally:
              # only works if all messages handled in series
              self.__last_id = msg.delivery_tag
              self.__unacked += 1
docs: Calls user-provided callback and marks message for Ack regardless of success