docs: def _recvbuf_pop(self):
          """
          Internal helper to pop a message off the receive buffer.  If
          the message is an Exception, that exception will be raised;
          otherwise, a tuple of command and payload will be returned.
          """
  
          # Pop a message off the recv buffer and return (or raise) it
          msg = self._recvbuf.pop(0)
          if isinstance(msg, Exception):
              raise msg
          return msg['cmd'], msg['payload']