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requires python 3.5+ and dnslib, see https://github.com/samuelcolvin/dnserver for full/better implementation
from datetime import datetime
from time import sleep
from dnslib import DNSLabel, QTYPE, RD, RR
from dnslib import A, AAAA, CNAME, MX, NS, SOA, TXT
from dnslib.server import DNSServer
EPOCH = datetime(1970, 1, 1)
SERIAL = int((datetime.utcnow() - EPOCH).total_seconds())
TYPE_LOOKUP = {
A: QTYPE.A,
AAAA: QTYPE.AAAA,
CNAME: QTYPE.CNAME,
MX: QTYPE.MX,
NS: QTYPE.NS,
SOA: QTYPE.SOA,
TXT: QTYPE.TXT,
}
class Record:
def __init__(self, rdata_type, *args, rtype=None, rname=None, ttl=None, **kwargs):
if isinstance(rdata_type, RD):
# actually an instance, not a type
self._rtype = TYPE_LOOKUP[rdata_type.__class__]
rdata = rdata_type
else:
self._rtype = TYPE_LOOKUP[rdata_type]
if rdata_type == SOA and len(args) == 2:
# add sensible times to SOA
args += ((
SERIAL, # serial number
60 * 60 * 1, # refresh
60 * 60 * 3, # retry
60 * 60 * 24, # expire
60 * 60 * 1, # minimum
),)
rdata = rdata_type(*args)
if rtype:
self._rtype = rtype
self._rname = rname
self.kwargs = dict(
rdata=rdata,
ttl=self.sensible_ttl() if ttl is None else ttl,
**kwargs,
)
def try_rr(self, q):
if q.qtype == QTYPE.ANY or q.qtype == self._rtype:
return self.as_rr(q.qname)
def as_rr(self, alt_rname):
return RR(rname=self._rname or alt_rname, rtype=self._rtype, **self.kwargs)
def sensible_ttl(self):
if self._rtype in (QTYPE.NS, QTYPE.SOA):
return 60 * 60 * 24
else:
return 300
@property
def is_soa(self):
return self._rtype == QTYPE.SOA
def __str__(self):
return '{} {}'.format(QTYPE[self._rtype], self.kwargs)
ZONES = {
'example.com': [
Record(A, '1.2.3.4'),
Record(CNAME, 'whever.com'),
Record(MX, 'whatever.com.', 5),
Record(MX, 'mx2.whatever.com.', 10),
Record(MX, 'mx3.whatever.com.', 20),
Record(NS, 'mx2.whatever.com.'),
Record(NS, 'mx3.whatever.com.'),
Record(TXT, 'hello this is some text'),
Record(SOA, 'ns1.example.com', 'dns.example.com'),
]
}
class Resolver:
def __init__(self):
self.zones = {DNSLabel(k): v for k, v in ZONES.items()}
def resolve(self, request, handler):
reply = request.reply()
zone = self.zones.get(request.q.qname)
if zone is not None:
for zone_records in zone:
rr = zone_records.try_rr(request.q)
rr and reply.add_answer(rr)
else:
# no direct zone so look for an SOA record for a higher level zone
for zone_label, zone_records in self.zones.items():
if request.q.qname.matchSuffix(zone_label):
try:
soa_record = next(r for r in zone_records if r.is_soa)
except StopIteration:
continue
else:
reply.add_answer(soa_record.as_rr(zone_label))
break
return reply
resolver = Resolver()
servers = [
DNSServer(resolver, port=5053, address='localhost', tcp=True),
DNSServer(resolver, port=5053, address='localhost', tcp=False),
]
if __name__ == '__main__':
for s in servers:
s.start_thread()
try:
while 1:
sleep(0.1)
except KeyboardInterrupt:
pass
finally:
for s in servers:
s.stop()
@Torxed

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@Torxed Torxed commented Jan 14, 2018

In all fairness, to whomever ends up here. Record(A, '1.2.3.4') defaults to all responses because it appends the domain from the request. Now, this becomes a slight issue of readability and user friendliness when you try to do Record(A, 'www.example.com', '1.2.3.4'). If you assume this, this code will break. I'm pretty sure that's confusing unless you know what's going on in dnslib or how to adapt this code.

Also doing rr and reply.add_answer(rr) is an odd reading, especially if you're used to actually using if blocks the way they were meant to be used. Just as I'm sure someone who's been in the game long enough and comes from another language background will figure that out pretty quick. But there are some things here that makes this code work, but not necessarily easy to understand or adapt.

Anyone ending up here, actually use the sticky link at the top.

@DEEP7696

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@DEEP7696 DEEP7696 commented Jul 30, 2019

could you please help me with SRV record.

@rhashemian

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@rhashemian rhashemian commented Oct 23, 2020

nicely done.

for whoever interested, if you want the server to return the same records as example.com for non-existent zones change line 92 to:
zone = self.zones.get(request.q.qname,self.zones[DNSLabel('example.com')])

then the server will always return an answer.

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