docs: def __pack_message(operation, data):
      """Takes message data and adds a message header based on the operation.
  
      Returns the resultant message string.
      """
      request_id = _randint()
      message = struct.pack("<i", 16 + len(data))
      message += struct.pack("<i", request_id)
      message += _ZERO_32  # responseTo
      message += struct.pack("<i", operation)
      return (request_id, message + data)