pyminifakeDNS.py

#source http://code.activestate.com/recipes/491264/
#edited by Guangming Li

import socket


class DNSQuery:
    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:
            packet += self.data[:2] + "\x81\x80"
            packet += self.data[4:6] + '\x00\x01\x00\x00\x00\x00'            # Questions and Answers Counts
            pos = self.data.find('\x00', 12) + 5
            packet += self.data[12:pos]                                       # Original Domain Name Question
            packet += '\xc0\x0c'                                             # Pointer to domain name
            packet += '\x00\x01\x00\x01\x00\x00\x00\x00\x00\x04'             # Response type, ttl and resource data length -> 4 bytes
            packet += str.join('', map(lambda x: chr(int(x)), ip.split('.')))  # 4bytes of IP
        return packet


if __name__ == '__main__':
    ip = '192.168.1.1'
    print 'pyminifakeDNS:: dom.query. 60 IN A %s' % ip
    udps = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    udps.bind(('', 5300))

    try:
        while 1:
            data, addr = udps.recvfrom(1024)
            p = DNSQuery(data)
            udps.sendto(p.respuesta(ip), addr)
            print 'Respuesta: %s -> %s' % (p.dominio, ip)
    except KeyboardInterrupt:
        print 'Finalizando'
        udps.close()