'Associate a buffer header and payload with this message.
Args:
buf_header (JSON) : a buffer header
buf_payload (JSON or bytes) : a buffer payload
Returns:
None
Raises:
MessageError'

def add_buffer(self, buf_header, buf_payload):

    if ('num_buffers' in self._header):
        self._header['num_buffers'] += 1
    else:
        self._header['num_buffers'] = 1
    self._header_json = None
    self._buffers.add((buf_header, buf_payload))
