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#
# (C) Copyright 2003-2010 Jacek Konieczny <jajcus@jajcus.net>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License Version
# 2.1 as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
"""DNS resolever with SRV record support.
Normative reference:
- `RFC 1035 <http://www.ietf.org/rfc/rfc1035.txt>`__
- `RFC 2782 <http://www.ietf.org/rfc/rfc2782.txt>`__
"""
__revision__="$Id$"
__docformat__="restructuredtext en"
import re
import socket
from socket import AF_UNSPEC, AF_INET, AF_INET6
import dns.resolver
import dns.name
import dns.exception
import random
from encodings import idna
service_aliases={"xmpp-server": ("jabber-server","jabber")}
# should match all valid IP addresses, but can pass some false-positives,
# which are not valid domain names
ipv4_re=re.compile(r"^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
ipv6_re=re.compile(r"^[0-9a-f]{0,4}:[0-9a-f:]{0,29}:([0-9a-f]{0,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})$")
def shuffle_srv(records):
"""Randomly reorder SRV records using their weights.
:Parameters:
- `records`: SRV records to shuffle.
:Types:
- `records`: sequence of `dns.rdtypes.IN.SRV`
:return: reordered records.
:returntype: `list` of `dns.rdtypes.IN.SRV`"""
if not records:
return []
ret=[]
while len(records)>1:
weight_sum=0
for rr in records:
weight_sum+=rr.weight+0.1
thres=random.random()*weight_sum
weight_sum=0
for rr in records:
weight_sum+=rr.weight+0.1
if thres<weight_sum:
records.remove(rr)
ret.append(rr)
break
ret.append(records[0])
return ret
def reorder_srv(records):
"""Reorder SRV records using their priorities and weights.
:Parameters:
- `records`: SRV records to shuffle.
:Types:
- `records`: `list` of `dns.rdtypes.IN.SRV`
:return: reordered records.
:returntype: `list` of `dns.rdtypes.IN.SRV`"""
records=list(records)
records.sort()
ret=[]
tmp=[]
for rr in records:
if not tmp or rr.priority==tmp[0].priority:
tmp.append(rr)
continue
ret+=shuffle_srv(tmp)
if tmp:
ret+=shuffle_srv(tmp)
return ret
def resolve_srv(domain,service, proto="tcp"):
"""Resolve service domain to server name and port number using SRV records.
A built-in service alias table will be used to lookup also some obsolete
record names.
:Parameters:
- `domain`: domain name.
- `service`: service name.
- `proto`: protocol name.
:Types:
- `domain`: `unicode` or `str`
- `service`: `unicode` or `str`
- `proto`: `str`
:return: host names and port numbers for the service or None.
:returntype: `list` of (`str`,`int`)"""
names_to_try=[u"_%s._%s.%s" % (service,proto,domain)]
if service_aliases.has_key(service):
for a in service_aliases[service]:
names_to_try.append(u"_%s._%s.%s" % (a,proto,domain))
for name in names_to_try:
name=idna.ToASCII(name)
try:
r=dns.resolver.query(name, 'SRV')
except dns.exception.DNSException:
continue
if not r:
continue
return [(rr.target.to_text(),rr.port) for rr in reorder_srv(r)]
return None
def getaddrinfo(host, port, family= AF_UNSPEC,
socktype = socket.SOCK_STREAM, proto = 0, allow_cname = True):
"""Resolve host and port into addrinfo struct.
Does the same thing as socket.getaddrinfo, but using `dns.resolver`.
:Parameters:
- `host`: service domain name.
- `port`: service port number or name.
- `family`: address family (`AF_INET` for IPv4,
`AF_INET6` for IPv6 or `AF_UNSPEC` for either).
- `socktype`: socket type.
- `proto`: protocol number or name.
- `allow_cname`: when False CNAME responses are not allowed.
:Types:
- `host`: `unicode` or `str`
- `port`: `int` or `str`
- `family`: `int`
- `socktype`: `int`
- `proto`: `int` or `str`
- `allow_cname`: `bool`
:return: list of (family, socktype, proto, canonname, sockaddr).
:returntype: `list` of (`int`, `int`, `int`, `str`, (`str`, `int`))"""
ret=[]
if proto==0:
proto=socket.getprotobyname("tcp")
elif type(proto)!=int:
proto=socket.getprotobyname(proto)
if type(port)!=int:
port=socket.getservbyname(port,proto)
if family not in (AF_UNSPEC, AF_INET, AF_INET6):
raise NotImplementedError, "Unsupported protocol family."
if ipv4_re.match(host) and family in (AF_UNSPEC, AF_INET):
return [(AF_INET, socktype, proto, host, (host, port))]
if ipv6_re.match(host) and family in (AF_UNSPEC, AF_INET6):
return [(AF_INET6, socktype, proto, host, (host, port))]
host=idna.ToASCII(host)
rtypes = []
if family in (AF_UNSPEC, AF_INET6):
rtypes.append(("AAAA", AF_INET6))
if family in (AF_UNSPEC, AF_INET):
rtypes.append(("A", AF_INET))
exception = None
for rtype, rfamily in rtypes:
try:
try:
r=dns.resolver.query(host, rtype)
except dns.exception.DNSException:
r=dns.resolver.query(host+".", rtype)
except dns.exception.DNSException, err:
exception = err
continue
if not allow_cname and r.rrset.name!=dns.name.from_text(host):
raise ValueError,"Unexpected CNAME record found for %s" % (host,)
if r:
for rr in r:
ret.append((rfamily, socktype, proto, r.rrset.name,
(rr.to_text(),port)))
if not ret and exception:
raise exception
return ret
# vi: sts=4 et sw=4
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