docs: def register_transport_ready_event(self, user_cb, user_arg):
          """
          Register for transport ready events.  The `transport ready`
          event is raised via a user callback.  If the endpoint
          is configured as a source, then the user may then
          call :py:meth:`write_transport` in order to send data to
          the associated sink.
          Otherwise, if the endpoint is configured as a sink, then
          the user may call :py:meth:`read_transport` to read
          from the associated source instead.
  
          :param func user_cb: User defined callback function.  It
              must take one parameter which is the user's callback
              argument.
          :param user_arg: User defined callback argument.
          :return:
  
          See also: :py:meth:`unregister_transport_ready_event`
          """
          self.user_cb = user_cb
          self.user_arg = user_arg