Python Twisted Custom DNS

Question

I am new to the Twisted framework for python. I am playing around with a customer DNS server and I want to know how to located the SRC_IP of the DNS Request.

I am using the following script: http://twisted.readthedocs.org/en/latest/names/howto/custom-server.html

Specifically the one that dynamically resolves and want to know how I can located the source IP of the Request. Thanks

Answer 1

Not being overly familiar with twisted, I don't know if this is the best way. I suspect that what I propose below is not because operating directly on the sockets doesn't feel right, but here it goes.

Subclass server.DNSServerFactory and override the handleQuery() method, for example:

import socket
from twisted.internet.address import IPv4Address

class MyDNSServerFactory(server.DNSServerFactory):

    def handleQuery(self, message, protocol, address):
        if protocol.transport.socket.type == socket.SOCK_STREAM:
            self.peer_address = protocol.transport.getPeer()
        elif protocol.transport.socket.type == socket.SOCK_DGRAM:
            self.peer_address = IPv4Address('UDP', *address)
        else:
            print "Unexpected socket type %r" % protocol.transport.socket.type

        print "Got message from : %r" % self.peer_address
        return server.DNSServerFactory.handleQuery(self, message, protocol, address)
.
.
.

factory = MyDNSServerFactory(
    clients=[DynamicResolver(), client.Resolver(resolv='/etc/resolv.conf')]
)

Things to worry about:

1. IPV6 addresses
2. Direct use of socket seems underhanded.
3. Does socket.SOCK_STREAM always imply a TCP connection?

There are other ways to do it, e.g. subclass dns.DNSDatagramProtocol and override datagramReceived(self, data, addr) to get the client UDP address. TCP client addresses would be gotten by subclassing and overriding server.DNSServerFactory.connectionMade(self, protocol) and getting the peer's address with protocol.transport.getPeer().

---

Updated answer to make peer address available in DynamicResolver

Modify MyDNSServerFactory.handleQuery() to set peer_address for resolvers that have a peer_address attribute:

class MyDNSServerFactory(server.DNSServerFactory):

    def handleQuery(self, message, protocol, address):
        if protocol.transport.socket.type == socket.SOCK_STREAM:
            self.peer_address = protocol.transport.getPeer()
        elif protocol.transport.socket.type == socket.SOCK_DGRAM:
            self.peer_address = IPv4Address('UDP', *address)
        else:
            print "Unexpected socket type %r" % protocol.transport.socket.type

        print "Got message from : %r" % self.peer_address

        # Make peer_address available to resolvers that support that attribute
        for resolver in self.resolver.resolvers:
            if hasattr(resolver, 'peer_address'):
                resolver.peer_address = self.peer_address

        return server.DNSServerFactory.handleQuery(self, message, protocol, address)

Add the following peer_address property to class DynamicResolver:

    def __init__(self):
        self._peer_address = None

    @property
    def peer_address(self):
        return self._peer_address

    @peer_address.setter
    def peer_address(self, value):
        self._peer_address = value

Now you can access peer_address in DynamicResolver.query(), e.g.

    def query(self, query, timeout=None):
        print "In DynamicResolver.query(): self.peer_address = %r" % self.peer_address
        if self._dynamicResponseRequired(query):
            return defer.succeed(self._doDynamicResponse(query))
        else:
            return defer.fail(error.DomainError())