Python DNS server with Redis backend

redisdns.py

#!/usr/bin/env python

# A naive dns server with a Redis backend
# Set keys in Redis you want to be authoritative for (set google.com. 127.0.0.1)
# Tip: Use Redis's ttl functions to have temporary names
# Currently only does A records, feel free to fix that
# 
# Licensed under the PSF License
# Thanks to: http://code.activestate.com/recipes/491264-mini-fake-dns-server/
# Author: @Kaerast <alice@kaerast.info>

import socket
import redis # https://github.com/andymccurdy/redis-py

PORT = 5053                     # requires root if < 1024

class DNSQuery(object):
  def __init__(self, data):
    self.data=data
    self.dominio=''

    tipo = (ord(data[2]) >> 3) & 15   # Opcode bits
    if tipo == 0:                     # Standard query
      ini=12
      lon=ord(data[ini])
      while lon != 0:
        self.dominio+=data[ini+1:ini+lon+1]+'.'
        ini+=lon+1
        lon=ord(data[ini])

  def respuesta(self, ip):
    packet = []
    if self.dominio and ip is not None:
      packet = [
        self.data[:2], "\x81\x80",
        self.data[4:6], self.data[4:6], '\x00\x00\x00\x00',   # Questions and Answers Counts
        self.data[12:],                                         # Original Domain Name Question
        '\xc0\x0c',                                             # Pointer to domain name
        '\x00\x01\x00\x01\x00\x00\x00\x3c\x00\x04',             # Response type, ttl and resource data length -> 4 bytes
        socket.inet_aton(ip),   # 4bytes of IP
        ]
    elif ip is None:
      packet = [
        self.data[:2], "\x81\x80",
        self.data[4:6], "\x00\x00", '\x00\x00\x00\x00',   # Questions and Answers Counts
        self.data[12:],                                         # Original Domain Name Question
        '\xc0\x0c',                                             # Pointer to domain name
        ]
    return ''.join(packet)

if __name__ == '__main__':
  r = redis.StrictRedis(host='localhost', port=6379, db=0, password='mypassword')
  print 'pyDNS:: dom.query. 60 IN A IP; port {0}'.format(PORT)
  
  udps = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  udps.bind(('',PORT))
  
  try:
    while 1:
      data, addr = udps.recvfrom(1024)
      p=DNSQuery(data)
      ip=r.get(p.dominio)
      print 'Respuesta: %s -> %s' % (p.dominio, ip)
      udps.sendto(p.respuesta(ip), addr)
  except KeyboardInterrupt:
    print 'Finalizando'
    udps.close()