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# -*- coding: utf-8 -*-
"""
DNS server framework - intended to simplify creation of custom resolvers.
Comprises the following components:
DNSServer - socketserver wrapper (in most cases you should just
need to pass this an appropriate resolver instance
and start in either foreground/background)
DNSHandler - handler instantiated by DNSServer to handle requests
The 'handle' method deals with the sending/receiving
packets (handling TCP length prefix) and delegates
the protocol handling to 'get_reply'. This decodes
packet, hands off a DNSRecord to the Resolver instance,
and encodes the returned DNSRecord.
In most cases you dont need to change DNSHandler unless
you need to get hold of the raw protocol data in the
Resolver
DNSLogger - The class provides a default set of logging functions for
the various stages of the request handled by a DNSServer
instance which are enabled/disabled by flags in the 'log'
class variable.
Resolver - Instance implementing a 'resolve' method that receives
the decodes request packet and returns a response.
To implement a custom resolver in most cases all you need
is to implement this interface.
Note that there is only a single instance of the Resolver
so need to be careful about thread-safety and blocking
The following examples use the server framework:
fixedresolver.py - Simple resolver which will respond to all
requests with a fixed response
zoneresolver.py - Resolver which will take a standard zone
file input
shellresolver.py - Example of a dynamic resolver
proxy.py - DNS proxy
intercept.py - Intercepting DNS proxy
>>> resolver = BaseResolver()
>>> logger = DNSLogger(prefix=False)
>>> server = DNSServer(resolver,port=8053,address="localhost",logger=logger)
>>> server.start_thread()
>>> q = DNSRecord.question("abc.def")
>>> a = q.send("localhost",8053)
Request: [...] (udp) / 'abc.def.' (A)
Reply: [...] (udp) / 'abc.def.' (A) / NXDOMAIN
>>> print(DNSRecord.parse(a))
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.def. IN A
>>> server.stop()
>>> class TestResolver:
... def resolve(self,request,handler):
... reply = request.reply()
... reply.add_answer(*RR.fromZone("abc.def. 60 A 1.2.3.4"))
... return reply
>>> resolver = TestResolver()
>>> server = DNSServer(resolver,port=8053,address="localhost",logger=logger,tcp=True)
>>> server.start_thread()
>>> a = q.send("localhost",8053,tcp=True)
Request: [...] (tcp) / 'abc.def.' (A)
Reply: [...] (tcp) / 'abc.def.' (A) / RRs: A
>>> print(DNSRecord.parse(a))
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.def. IN A
;; ANSWER SECTION:
abc.def. 60 IN A 1.2.3.4
>>> server.stop()
"""
from __future__ import print_function
import binascii,socket,struct,threading,time
try:
import socketserver
except ImportError:
import SocketServer as socketserver
from dnslib import DNSRecord,DNSError,QTYPE,RCODE,RR
class BaseResolver(object):
"""
Base resolver implementation. Provides 'resolve' method which is
called by DNSHandler with the decode request (DNSRecord instance)
and returns a DNSRecord instance as reply.
In most cases you should be able to create a custom resolver by
just replacing the resolve method with appropriate resolver code for
application (see fixedresolver/zoneresolver/shellresolver for
examples)
Note that a single instance is used by all DNSHandler instances so
need to consider blocking & thread safety.
"""
def resolve(self,request,handler):
"""
Example resolver - respond to all requests with NXDOMAIN
"""
reply = request.reply()
reply.header.rcode = getattr(RCODE,'NXDOMAIN')
return reply
class DNSHandler(socketserver.BaseRequestHandler):
"""
Handler for socketserver. Transparently handles both TCP/UDP requests
(TCP requests have length prepended) and hands off lookup to resolver
instance specified in <SocketServer>.resolver
"""
udplen = 0 # Max udp packet length (0 = ignore)
def handle(self):
if self.server.socket_type == socket.SOCK_STREAM:
self.protocol = 'tcp'
data = self.request.recv(8192)
length = struct.unpack("!H",bytes(data[:2]))[0]
while len(data) - 2 < length:
new_data = self.request.recv(8192)
if not new_data:
break
data += new_data
data = data[2:]
else:
self.protocol = 'udp'
data,connection = self.request
self.server.logger.log_recv(self,data)
try:
rdata = self.get_reply(data)
self.server.logger.log_send(self,rdata)
if self.protocol == 'tcp':
rdata = struct.pack("!H",len(rdata)) + rdata
self.request.sendall(rdata)
else:
connection.sendto(rdata,self.client_address)
except DNSError as e:
self.server.logger.log_error(self,e)
def get_reply(self,data):
request = DNSRecord.parse(data)
self.server.logger.log_request(self,request)
resolver = self.server.resolver
reply = resolver.resolve(request,self)
self.server.logger.log_reply(self,reply)
if self.protocol == 'udp':
rdata = reply.pack()
if self.udplen and len(rdata) > self.udplen:
truncated_reply = reply.truncate()
rdata = truncated_reply.pack()
self.server.logger.log_truncated(self,truncated_reply)
else:
rdata = reply.pack()
return rdata
class DNSLogger:
"""
The class provides a default set of logging functions for the various
stages of the request handled by a DNSServer instance which are
enabled/disabled by flags in the 'log' class variable.
To customise logging create an object which implements the DNSLogger
interface and pass instance to DNSServer.
The methods which the logger instance must implement are:
log_recv - Raw packet received
log_send - Raw packet sent
log_request - DNS Request
log_reply - DNS Response
log_truncated - Truncated
log_error - Decoding error
log_data - Dump full request/response
"""
def __init__(self,log="",prefix=True):
"""
Selectively enable log hooks depending on log argument
(comma separated list of hooks to enable/disable)
- If empty enable default log hooks
- If entry starts with '+' (eg. +send,+recv) enable hook
- If entry starts with '-' (eg. -data) disable hook
- If entry doesn't start with +/- replace defaults
Prefix argument enables/disables log prefix
"""
default = ["request","reply","truncated","error"]
log = log.split(",") if log else []
enabled = set([ s for s in log if s[0] not in '+-'] or default)
[ enabled.add(l[1:]) for l in log if l.startswith('+') ]
[ enabled.discard(l[1:]) for l in log if l.startswith('-') ]
for l in ['log_recv','log_send','log_request','log_reply',
'log_truncated','log_error','log_data']:
if l[4:] not in enabled:
setattr(self,l,self.log_pass)
self.prefix = prefix
def log_pass(self,*args):
pass
def log_prefix(self,handler):
if self.prefix:
return "%s [%s:%s] " % (time.strftime("%Y-%m-%d %X"),
handler.__class__.__name__,
handler.server.resolver.__class__.__name__)
else:
return ""
def log_recv(self,handler,data):
print("%sReceived: [%s:%d] (%s) <%d> : %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
len(data),
binascii.hexlify(data)))
def log_send(self,handler,data):
print("%sSent: [%s:%d] (%s) <%d> : %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
len(data),
binascii.hexlify(data)))
def log_request(self,handler,request):
print("%sRequest: [%s:%d] (%s) / '%s' (%s)" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
request.q.qname,
QTYPE[request.q.qtype]))
self.log_data(request)
def log_reply(self,handler,reply):
if reply.header.rcode == RCODE.NOERROR:
print("%sReply: [%s:%d] (%s) / '%s' (%s) / RRs: %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
reply.q.qname,
QTYPE[reply.q.qtype],
",".join([QTYPE[a.rtype] for a in reply.rr])))
else:
print("%sReply: [%s:%d] (%s) / '%s' (%s) / %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
reply.q.qname,
QTYPE[reply.q.qtype],
RCODE[reply.header.rcode]))
self.log_data(reply)
def log_truncated(self,handler,reply):
print("%sTruncated Reply: [%s:%d] (%s) / '%s' (%s) / RRs: %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
reply.q.qname,
QTYPE[reply.q.qtype],
",".join([QTYPE[a.rtype] for a in reply.rr])))
self.log_data(reply)
def log_error(self,handler,e):
print("%sInvalid Request: [%s:%d] (%s) :: %s" % (
self.log_prefix(handler),
handler.client_address[0],
handler.client_address[1],
handler.protocol,
e))
def log_data(self,dnsobj):
print("\n",dnsobj.toZone(" "),"\n",sep="")
class UDPServer(socketserver.ThreadingMixIn,socketserver.UDPServer):
allow_reuse_address = True
class TCPServer(socketserver.ThreadingMixIn,socketserver.TCPServer):
allow_reuse_address = True
class DNSServer(object):
"""
Convenience wrapper for socketserver instance allowing
either UDP/TCP server to be started in blocking more
or as a background thread.
Processing is delegated to custom resolver (instance) and
optionally custom logger (instance), handler (class), and
server (class)
In most cases only a custom resolver instance is required
(and possibly logger)
"""
def __init__(self,resolver,
address="",
port=53,
tcp=False,
logger=None,
handler=DNSHandler,
server=None):
"""
resolver: resolver instance
address: listen address (default: "")
port: listen port (default: 53)
tcp: UDP (false) / TCP (true) (default: False)
logger: logger instance (default: DNSLogger)
handler: handler class (default: DNSHandler)
server: socketserver class (default: UDPServer/TCPServer)
"""
if not server:
if tcp:
server = TCPServer
else:
server = UDPServer
self.server = server((address,port),handler)
self.server.resolver = resolver
self.server.logger = logger or DNSLogger()
def start(self):
self.server.serve_forever()
def start_thread(self):
self.thread = threading.Thread(target=self.server.serve_forever)
self.thread.daemon = True
self.thread.start()
def stop(self):
self.server.shutdown()
def isAlive(self):
return self.thread.isAlive()
if __name__ == "__main__":
import doctest
doctest.testmod(optionflags=doctest.ELLIPSIS)
|
