/usr/share/pyshared/Milter/dns.py is in python-milter 1.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 | ## @package Milter.dns
# Provide a higher level interface to pydns.
import DNS
from DNS import DNSError
MAX_CNAME = 10
## Lookup DNS records by label and RR type.
# The response can include records of other types that the DNS
# server thinks we might need.
# @param name the DNS label to lookup
# @param qtype the name of the DNS RR type to lookup
# @return a list of ((name,type),data) tuples
def DNSLookup(name, qtype):
try:
# To be thread safe, we create a fresh DnsRequest with
# each call. It would be more efficient to reuse
# a req object stored in a Session.
req = DNS.DnsRequest(name, qtype=qtype)
resp = req.req()
#resp.show()
# key k: ('wayforward.net', 'A'), value v
# FIXME: pydns returns AAAA RR as 16 byte binary string, but
# A RR as dotted quad. For consistency, this driver should
# return both as binary string.
return [((a['name'], a['typename']), a['data']) for a in resp.answers]
except IOError, x:
raise DNSError, str(x)
class Session(object):
"""A Session object has a simple cache with no TTL that is valid
for a single "session", for example an SMTP conversation."""
def __init__(self):
self.cache = {}
## Additional DNS RRs we can safely cache.
# We have to be careful which additional DNS RRs we cache. For
# instance, PTR records are controlled by the connecting IP, and they
# could poison our local cache with bogus A and MX records.
# Each entry is a tuple of (query_type,rr_type). So for instance,
# the entry ('MX','A') says it is safe (for milter purposes) to cache
# any 'A' RRs found in an 'MX' query.
SAFE2CACHE = frozenset((
('MX','MX'), ('MX','A'),
('CNAME','CNAME'), ('CNAME','A'),
('A','A'),
('AAAA','AAAA'),
('PTR','PTR'),
('NS','NS'), ('NS','A'),
('TXT','TXT'),
('SPF','SPF')
))
## Cached DNS lookup.
# @param name the DNS label to query
# @param qtype the query type, e.g. 'A'
# @param cnames tracks CNAMES already followed in recursive calls
def dns(self, name, qtype, cnames=None):
"""DNS query.
If the result is in cache, return that. Otherwise pull the
result from DNS, and cache ALL answers, so additional info
is available for further queries later.
CNAMEs are followed.
If there is no data, [] is returned.
pre: qtype in ['A', 'AAAA', 'MX', 'PTR', 'TXT', 'SPF']
post: isinstance(__return__, types.ListType)
"""
if name.endswith('.'): name = name[:-1]
if not reduce(lambda x,y:x and 0 < len(y) < 64, name.split('.'),True):
return [] # invalid DNS name (too long or empty)
result = self.cache.get( (name, qtype) )
cname = None
if result: return result
cnamek = (name,'CNAME')
cname = self.cache.get( cnamek )
if cname:
cname = cname[0]
else:
safe2cache = Session.SAFE2CACHE
for k, v in DNSLookup(name, qtype):
if k == cnamek:
cname = v
if k[1] == 'CNAME' or (qtype,k[1]) in safe2cache:
self.cache.setdefault(k, []).append(v)
result = self.cache.get( (name, qtype), [])
if not result and cname:
if not cnames:
cnames = {}
elif len(cnames) >= MAX_CNAME:
#return result # if too many == NX_DOMAIN
raise DNSError('Length of CNAME chain exceeds %d' % MAX_CNAME)
cnames[name] = cname
if cname in cnames:
raise DNSError('CNAME loop')
result = self.dns(cname, qtype, cnames=cnames)
if result:
self.cache[(name,qtype)] = result
return result
def dns_txt(self, domainname, enc='ascii'):
"Get a list of TXT records for a domain name."
if domainname:
try:
return [''.join(s.decode(enc) for s in a)
for a in self.dns(domainname, 'TXT')]
except UnicodeEncodeError:
raise DNSError('Non-ascii character in SPF TXT record.')
return []
DNS.DiscoverNameServers()
if __name__ == '__main__':
import sys
s = Session()
for n,t in zip(*[iter(sys.argv[1:])]*2):
print n,t
print s.dns(n,t)
|