#!/usr/bin/env python

"""

DNS Server Example

A simple little DNS Server example using

`dnslib <https://pypi.python.org/pypi/dnslib>`_

to handle the DNS protocol parsing and packet

construction (*a really nice library btw with

great integration into circuits*).

Answers ``A 127.0.0.1`` for any query of any type!

To run this example::

pip install dnslib

./dnsserver.py

Usage (*using dig*)::

dig @localhost -p 1053 test.com

"""

import sys

from dnslib import QTYPE, RR, A, DNSHeader, DNSRecord

from circuits import Component, Debugger, Event

from circuits.net.events import write

from circuits.net.sockets import UDPServer

class query(Event):

"""query Event"""

class DNS(Component):

"""DNS Protocol Handling"""

def read(self, peer, data):

self.fire(query(peer, DNSRecord.parse(data)))

class Dummy(Component):

"""

A Dummy DNS Handler

This just returns an A record response

of 127.0.0.1 for any query of any type!

"""

def query(self, peer, request):

id = request.header.id

qname = request.q.qname

print(

f'DNS Request for qname({qname!s:s})',

file=sys.stderr,

)

reply = DNSRecord(

DNSHeader(id=id, qr=1, aa=1, ra=1),

q=request.q,

)

# Add A Record

reply.add_answer(RR(qname, QTYPE.A, rdata=A('127.0.0.1')))

# Send To Client

self.fire(write(peer, reply.pack()))

class DNSServer(Component):

"""

DNS Server

This ties everything together in a nice

configurable way with protocol, transport

and dummy handler as well as optional debugger.

"""

def init(self, bind=None, verbose=False):

self.bind = bind or ('0.0.0.0', 53)

if verbose:

Debugger().register(self)

self.transport = UDPServer(self.bind).register(self)

self.protocol = DNS().register(self)

self.dummy = Dummy().register(self)

def started(self, manager):

print('DNS Server Started!', file=sys.stderr)

def ready(self, server, bind):

print('Ready! Listening on {:s}:{:d}'.format(*bind), file=sys.stderr)

DNSServer(('0.0.0.0', 1053), verbose=True).run()