code: def stuff(packet):
      
  
      if is_framed(packet):
          raise ValueError('packet contains leading DLE and trailing DLE/ETX')
      else:
          return packet.replace(CHR_DLE, CHR_DLE + CHR_DLE)
docs: Add byte stuffing to TSIP packet.
      :param packet: TSIP packet with byte stuffing. The packet must already
          have been stripped or `ValueError` will be raised.
      :type packet: Binary string.
      :return: Packet with byte stuffing.