gistfile1.py

#!/usr/bin/env python

import random
import struct
import sys

RR_TYPE_A = 1
RR_TYPE_NS = 2
RR_TYPE_CNAME = 5
RR_TYPE_SOA = 6
RR_TYPE_PTR = 12
RR_TYPE_MX = 15
RR_TYPE_TXT = 16

RR_CLASS_IN = 1


def gen_header(ident, flags, qcount, acount, nscount, arcount):
    return struct.pack("!HHHHHH",
        ident, flags,
        qcount, acount,
        nscount, arcount)


def gen_name(name):
    buffer = b""
    for part in name.split('.'):
        label = part.encode("ascii")
        buffer += bytes([len(label)]) + label

    return buffer + b'\0'


def gen_rr(name, typ, clas, ttl, rd):
    buffer = gen_name(name)
    buffer += struct.pack("!HHIH", typ, clas, ttl, len(rd))
    buffer += rd
    return buffer


sys.stdout.buffer.write(gen_header(random.getrandbits(16), 0x0001, 0, 2, 0, 0))
sys.stdout.buffer.write(gen_rr('', RR_TYPE_TXT, RR_CLASS_IN, 0xabcd, b'b'))
sys.stdout.buffer.write(gen_rr('', RR_TYPE_TXT, RR_CLASS_IN, 0xabcd, b'g'))