code: def _transport_interceptor(self, callback):
          
  
          def add_item_to_queue(header, message):
              queue_item = (
                  Priority.TRANSPORT,
                  next(
                      self._transport_interceptor_counter
                  ),  # insertion sequence to keep messages in order
                  (callback, header, message),
              )
              self.__queue.put(
                  queue_item
              )  # Block incoming transport until insertion completes
  
          return add_item_to_queue
docs: Takes a callback function and returns a function that takes headers and
          messages and places them on the main service queue.