Python DNS File Transfer

# -*- coding: utf-8 -*-

from __future__ import print_function

from dnslib import RR,QTYPE,RCODE,TXT,parse_time
from dnslib.label import DNSLabel
from dnslib.server import DNSServer,DNSHandler,BaseResolver,DNSLogger

class ShellResolver(BaseResolver):
    def __init__(self,ttl,ans):
        self.ttl = parse_time(ttl)
        self.ans = ans

    def resolve(self,request,handler):
        reply = request.reply()
        qname = request.q.qname
        label = str(qname)
	counter = label[0:label.index(".")]

        try:
            counter = int(counter)
            if counter >= len(ans):
		reply.add_answer(RR(qname,QTYPE.TXT,ttl=self.ttl,
                       	            rdata=TXT("x00x00x00x00x00")))
            else:
	        reply.add_answer(RR(qname,QTYPE.TXT,ttl=self.ttl,
                                    rdata=TXT(ans[counter])))
        except ValueError:
	        reply.add_answer(RR(qname,QTYPE.TXT,ttl=self.ttl,
                       	            rdata=TXT("x00x00x00x00x00")))

        return reply

if __name__ == '__main__':

    import argparse,sys,time

    p = argparse.ArgumentParser(description="Shell DNS Resolver")
    p.add_argument("--ttl","-t",default="60s",
                    metavar="<ttl>",
                    help="Response TTL (default: 60s)")
    p.add_argument("--port","-p",type=int,default=53,
                    metavar="<port>",
                    help="Server port (default:53)")
    p.add_argument("--address","-a",default="",
                    metavar="<address>",
                    help="Listen address (default:all)")
    p.add_argument("--file",required=True,
                    help="Filename to send")
    args = p.parse_args()

    ans = []
    with open(args.file) as f:
        while True:
            chars = f.read(254)
            if not chars:
                break
            ans.append(chars)

    print(ans)

    resolver = ShellResolver(args.ttl, ans)
    logger = DNSLogger("request,reply,truncated,error",False)

    udp_server = DNSServer(resolver,
                           port=args.port,
                           address=args.address,
                           logger=logger)
    udp_server.start_thread()

    while udp_server.isAlive():
        time.sleep(1)