def _makeHeaderIPv6(sig=V2_SIGNATURE, verCom=b'\x21', famProto=b'\x21',
                    addrLength=b'\x00\x24',
                    addrs=((b'\x00' * 15) + b'\x01') * 2,
                    ports=b'\x1F\x90\x22\xB8'):
    """
    Construct a version 2 IPv6 header with custom bytes.

    @param sig: The protocol signature; defaults to valid L{V2_SIGNATURE}.
    @type sig: L{bytes}

    @param verCom: Protocol version and command.  Defaults to V2 PROXY.
    @type verCom: L{bytes}

    @param famProto: Address family and protocol.  Defaults to AF_INET6/STREAM.
    @type famProto: L{bytes}

    @param addrLength: Network-endian byte length of payload.  Defaults to
        description of default addrs/ports.
    @type addrLength: L{bytes}

    @param addrs: Address payload.  Defaults to C{::1} for source and
        destination.
    @type addrs: L{bytes}

    @param ports: Source and destination ports.  Defaults to 8080 for source
        8888 for destination.
    @type ports: L{bytes}

    @return: A packet with header, addresses, and ports.
    @rtype: L{bytes}
    """
    return sig + verCom + famProto + addrLength + addrs + ports

    Construct a version 2 IPv6 header with custom bytes.

    @param sig: The protocol signature; defaults to valid L{V2_SIGNATURE}.
    @type sig: L{bytes}

    @param verCom: Protocol version and command.  Defaults to V2 PROXY.
    @type verCom: L{bytes}

    @param famProto: Address family and protocol.  Defaults to AF_INET6/STREAM.
    @type famProto: L{bytes}

    @param addrLength: Network-endian byte length of payload.  Defaults to
        description of default addrs/ports.
    @type addrLength: L{bytes}

    @param addrs: Address payload.  Defaults to C{::1} for source and
        destination.
    @type addrs: L{bytes}

    @param ports: Source and destination ports.  Defaults to 8080 for source
        8888 for destination.
    @type ports: L{bytes}

    @return: A packet with header, addresses, and ports.
    @rtype: L{bytes}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/protocols/haproxy/test/test_v2parser.py