'Unread a single line of data into the readahead buffer.
This method can be used to unread a single pkt-line into a fixed
readahead buffer.
:param data: The data to unread, without the length prefix.
:raise ValueError: If more than one pkt-line is unread.'

def unread_pkt_line(self, data):

    if (self._readahead is not None):
        raise ValueError('Attempted    to    unread    multiple    pkt-lines.')
    self._readahead = BytesIO(pkt_line(data))
