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#!/usr/bin/env python
"""
DNS Client Example
A simple little DNS Client example using
`dnslib <https://pypi.python.org/pypi/dnslib>`_
to handle the DNS protocol parsing and packet
deconstruction (*a really nice library btw with
great integration into circuits*).
Specify the server, port, and query as arguments
to perform a lookup against a server using UDP.
To run this example::
pip install dnslib
./dnsclient.py 8.8.8.8 53 google.com
"""
import sys
from dnslib import DNSQuestion, DNSRecord
from circuits import Component, Debugger, Event
from circuits.net.events import write
from circuits.net.sockets import UDPClient
class reply(Event):
"""reply Event"""
class DNS(Component):
"""DNS Protocol Handling"""
def read(self, peer, data):
self.fire(reply(peer, DNSRecord.parse(data)))
class Dummy(Component):
"""
A Dummy DNS Handler
This just parses the reply packet and
prints any RR records it finds.
"""
def reply(self, peer, response):
id = response.header.id
qname = response.q.qname
print(
f'DNS Response from {peer[0]:s}:{peer[1]:d} id={id:d} qname={str(qname):s}',
file=sys.stderr,
)
for rr in response.rr:
print(f' {rr!s:s}')
raise SystemExit(0)
class DNSClient(Component):
"""
DNS Client
This ties everything together in a nice
configurable way with protocol, transport,
and dummy handler as well as optional debugger.
"""
def init(self, server, port, query, verbose=False):
self.server = server
self.port = int(port)
self.query = query
if verbose:
Debugger().register(self)
self.transport = UDPClient(0).register(self)
self.protocol = DNS().register(self)
self.dummy = Dummy().register(self)
def started(self, manager):
print('DNS Client Started!', file=sys.stderr)
def ready(self, client, bind):
print('Ready! Bound to {:s}:{:d}'.format(*bind), file=sys.stderr)
request = DNSRecord(q=DNSQuestion(self.query))
self.fire(write((self.server, self.port), request.pack()))
DNSClient(*sys.argv[1:], verbose=True).run()
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