Mock DNS server using twisted

### SERVER ###
from twisted.internet import defer, reactor
from twisted.names import dns, error, server, common

class MockDNSResolver(common.ResolverBase):
    def _lookup(self, name, cls, type, timeout):
        print("Incoming query for:", name)
        record = dns.Record_A(address=b"127.0.0.5")
        answer = dns.RRHeader(name=name, payload=record)
        return defer.succeed(([answer], [], []))

if __name__ == "__main__":
    clients = [MockDNSResolver()]
    factory = server.DNSServerFactory(clients=clients)
    protocol = dns.DNSDatagramProtocol(controller=factory)
    reactor.listenUDP(10053, protocol)
    reactor.listenTCP(10053, factory)
    reactor.run()

### CLIENT ###
from twisted.internet import reactor

from twisted.names import client
resolver = client.createResolver(servers=[('127.0.0.1', 10053)])
d = resolver.getHostByName('does.not.exist')

def callback(result):
    print('Result:', result)

d.addBoth(callback)

reactor.callLater(4, reactor.stop)
reactor.run()