# Copyright (C) 2003-2007, 2009, 2010 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
"""DNS stub resolver.
@var default_resolver: The default resolver object
@type default_resolver: dns.resolver.Resolver object"""
import socket
import sys
import time
import dns.exception
import dns.message
import dns.name
import dns.query
import dns.rcode
import dns.rdataclass
import dns.rdatatype
if sys.platform == 'win32':
import _winreg
class NXDOMAIN(dns.exception.DNSException):
"""The query name does not exist."""
pass
# The definition of the Timeout exception has moved from here to the
# dns.exception module. We keep dns.resolver.Timeout defined for
# backwards compatibility.
Timeout = dns.exception.Timeout
class NoAnswer(dns.exception.DNSException):
"""The response did not contain an answer to the question."""
pass
class NoNameservers(dns.exception.DNSException):
"""No non-broken nameservers are available to answer the query."""
pass
class NotAbsolute(dns.exception.DNSException):
"""Raised if an absolute domain name is required but a relative name
was provided."""
pass
class NoRootSOA(dns.exception.DNSException):
"""Raised if for some reason there is no SOA at the root name.
This should never happen!"""
pass
class Answer(object):
"""DNS stub resolver answer
Instances of this class bundle up the result of a successful DNS
resolution.
For convenience, the answer object implements much of the sequence
protocol, forwarding to its rrset. E.g. "for a in answer" is
equivalent to "for a in answer.rrset", "answer[i]" is equivalent
to "answer.rrset[i]", and "answer[i:j]" is equivalent to
"answer.rrset[i:j]".
Note that CNAMEs or DNAMEs in the response may mean that answer
node's name might not be the query name.
@ivar qname: The query name
@type qname: dns.name.Name object
@ivar rdtype: The query type
@type rdtype: int
@ivar rdclass: The query class
@type rdclass: int
@ivar response: The response message
@type response: dns.message.Message object
@ivar rrset: The answer
@type rrset: dns.rrset.RRset object
@ivar expiration: The time when the answer expires
@type expiration: float (seconds since the epoch)
"""
def __init__(self, qname, rdtype, rdclass, response):
self.qname = qname
self.rdtype = rdtype
self.rdclass = rdclass
self.response = response
min_ttl = -1
rrset = None
for count in xrange(0, 15):
try:
rrset = response.find_rrset(response.answer, qname,
rdclass, rdtype)
if min_ttl == -1 or rrset.ttl < min_ttl:
min_ttl = rrset.ttl
break
except KeyError:
if rdtype != dns.rdatatype.CNAME:
try:
crrset = response.find_rrset(response.answer,
qname,
rdclass,
dns.rdatatype.CNAME)
if min_ttl == -1 or crrset.ttl < min_ttl:
min_ttl = crrset.ttl
for rd in crrset:
qname = rd.target
break
continue
except KeyError:
raise NoAnswer
raise NoAnswer
if rrset is None:
raise NoAnswer
self.rrset = rrset
self.expiration = time.time() + min_ttl
def __getattr__(self, attr):
if attr == 'name':
return self.rrset.name
elif attr == 'ttl':
return self.rrset.ttl
elif attr == 'covers':
return self.rrset.covers
elif attr == 'rdclass':
return self.rrset.rdclass
elif attr == 'rdtype':
return self.rrset.rdtype
else:
raise AttributeError(attr)
def __len__(self):
return len(self.rrset)
def __iter__(self):
return iter(self.rrset)
def __getitem__(self, i):
return self.rrset[i]
def __delitem__(self, i):
del self.rrset[i]
def __getslice__(self, i, j):
return self.rrset[i:j]
def __delslice__(self, i, j):
del self.rrset[i:j]
class Cache(object):
"""Simple DNS answer cache.
@ivar data: A dictionary of cached data
@type data: dict
@ivar cleaning_interval: The number of seconds between cleanings. The
default is 300 (5 minutes).
@type cleaning_interval: float
@ivar next_cleaning: The time the cache should next be cleaned (in seconds
since the epoch.)
@type next_cleaning: float
"""
def __init__(self, cleaning_interval=300.0):
"""Initialize a DNS cache.
@param cleaning_interval: the number of seconds between periodic
cleanings. The default is 300.0
@type cleaning_interval: float.
"""
self.data = {}
self.cleaning_interval = cleaning_interval
self.next_cleaning = time.time() + self.cleaning_interval
def maybe_clean(self):
"""Clean the cache if it's time to do so."""
now = time.time()
if self.next_cleaning <= now:
keys_to_delete = []
for (k, v) in self.data.iteritems():
if v.expiration <= now:
keys_to_delete.append(k)
for k in keys_to_delete:
del self.data[k]
now = time.time()
self.next_cleaning = now + self.cleaning_interval
def get(self, key):
"""Get the answer associated with I{key}. Returns None if
no answer is cached for the key.
@param key: the key
@type key: (dns.name.Name, int, int) tuple whose values are the
query name, rdtype, and rdclass.
@rtype: dns.resolver.Answer object or None
"""
self.maybe_clean()
v = self.data.get(key)
if v is None or v.expiration <= time.time():
return None
return v
def put(self, key, value):
"""Associate key and value in the cache.
@param key: the key
@type key: (dns.name.Name, int, int) tuple whose values are the
query name, rdtype, and rdclass.
@param value: The answer being cached
@type value: dns.resolver.Answer object
"""
self.maybe_clean()
self.data[key] = value
def flush(self, key=None):
"""Flush the cache.
If I{key} is specified, only that item is flushed. Otherwise
the entire cache is flushed.
@param key: the key to flush
@type key: (dns.name.Name, int, int) tuple or None
"""
if not key is None:
if self.data.has_key(key):
del self.data[key]
else:
self.data = {}
self.next_cleaning = time.time() + self.cleaning_interval
class Resolver(object):
"""DNS stub resolver
@ivar domain: The domain of this host
@type domain: dns.name.Name object
@ivar nameservers: A list of nameservers to query. Each nameserver is
a string which contains the IP address of a nameserver.
@type nameservers: list of strings
@ivar search: The search list. If the query name is a relative name,
the resolver will construct an absolute query name by appending the search
names one by one to the query name.
@type search: list of dns.name.Name objects
@ivar port: The port to which to send queries. The default is 53.
@type port: int
@ivar timeout: The number of seconds to wait for a response from a
server, before timing out.
@type timeout: float
@ivar lifetime: The total number of seconds to spend trying to get an
answer to the question. If the lifetime expires, a Timeout exception
will occur.
@type lifetime: float
@ivar keyring: The TSIG keyring to use. The default is None.
@type keyring: dict
@ivar keyname: The TSIG keyname to use. The default is None.
@type keyname: dns.name.Name object
@ivar keyalgorithm: The TSIG key algorithm to use. The default is
dns.tsig.default_algorithm.
@type keyalgorithm: string
@ivar edns: The EDNS level to use. The default is -1, no Edns.
@type edns: int
@ivar ednsflags: The EDNS flags
@type ednsflags: int
@ivar payload: The EDNS payload size. The default is 0.
@type payload: int
@ivar cache: The cache to use. The default is None.
@type cache: dns.resolver.Cache object
"""
def __init__(self, filename='/etc/resolv.conf', configure=True):
"""Initialize a resolver instance.
@param filename: The filename of a configuration file in
standard /etc/resolv.conf format. This parameter is meaningful
only when I{configure} is true and the platform is POSIX.
@type filename: string or file object
@param configure: If True (the default), the resolver instance
is configured in the normal fashion for the operating system
the resolver is running on. (I.e. a /etc/resolv.conf file on
POSIX systems and from the registry on Windows systems.)
@type configure: bool"""
self.reset()
if configure:
if sys.platform == 'win32':
self.read_registry()
elif filename:
self.read_resolv_conf(filename)
def reset(self):
"""Reset all resolver configuration to the defaults."""
self.domain = \
dns.name.Name(dns.name.from_text(socket.gethostname())[1:])
if len(self.domain) == 0:
self.domain = dns.name.root
self.nameservers = []
self.search = []
self.port = 53
self.timeout = 2.0
self.lifetime = 30.0
self.keyring = None
self.keyname = None
self.keyalgorithm = dns.tsig.default_algorithm
self.edns = -1
self.ednsflags = 0
self.payload = 0
self.cache = None
def read_resolv_conf(self, f):
"""Process f as a file in the /etc/resolv.conf format. If f is
a string, it is used as the name of the file to open; otherwise it
is treated as the file itself."""
if isinstance(f, str) or isinstance(f, unicode):
try:
f = open(f, 'r')
except IOError:
# /etc/resolv.conf doesn't exist, can't be read, etc.
# We'll just use the default resolver configuration.
self.nameservers = ['127.0.0.1']
return
want_close = True
else:
want_close = False
try:
for l in f:
if len(l) == 0 or l[0] == '#' or l[0] == ';':
continue
tokens = l.split()
if len(tokens) == 0:
continue
if tokens[0] == 'nameserver':
self.nameservers.append(tokens[1])
elif tokens[0] == 'domain':
self.domain = dns.name.from_text(tokens[1])
elif tokens[0] == 'search':
for suffix in tokens[1:]:
self.search.append(dns.name.from_text(suffix))
finally:
if want_close:
f.close()
if len(self.nameservers) == 0:
self.nameservers.append('127.0.0.1')
def _determine_split_char(self, entry):
#
# The windows registry irritatingly changes the list element
# delimiter in between ' ' and ',' (and vice-versa) in various
# versions of windows.
#
if entry.find(' ') >= 0:
split_char = ' '
elif entry.find(',') >= 0:
split_char = ','
else:
# probably a singleton; treat as a space-separated list.
split_char = ' '
return split_char
def _config_win32_nameservers(self, nameservers):
"""Configure a NameServer registry entry."""
# we call str() on nameservers to convert it from unicode to ascii
nameservers = str(nameservers)
split_char = self._determine_split_char(nameservers)
ns_list = nameservers.split(split_char)
for ns in ns_list:
if not ns in self.nameservers:
self.nameservers.append(ns)
def _config_win32_domain(self, domain):
"""Configure a Domain registry entry."""
# we call str() on domain to convert it from unicode to ascii
self.domain = dns.name.from_text(str(domain))
def _config_win32_search(self, search):
"""Configure a Search registry entry."""
# we call str() on search to convert it from unicode to ascii
search = str(search)
split_char = self._determine_split_char(search)
search_list = search.split(split_char)
for s in search_list:
if not s in self.search:
self.search.append(dns.name.from_text(s))
def _config_win32_fromkey(self, key):
"""Extract DNS info from a registry key."""
try:
servers, rtype = _winreg.QueryValueEx(key, 'NameServer')
except WindowsError:
servers = None
if servers:
self._config_win32_nameservers(servers)
try:
dom, rtype = _winreg.QueryValueEx(key, 'Domain')
if dom:
self._config_win32_domain(dom)
except WindowsError:
pass
else:
try:
servers, rtype = _winreg.QueryValueEx(key, 'DhcpNameServer')
except WindowsError:
servers = None
if servers:
self._config_win32_nameservers(servers)
try:
dom, rtype = _winreg.QueryValueEx(key, 'DhcpDomain')
if dom:
self._config_win32_domain(dom)
except WindowsError:
pass
try:
search, rtype = _winreg.QueryValueEx(key, 'SearchList')
except WindowsError:
search = None
if search:
self._config_win32_search(search)
def read_registry(self):
"""Extract resolver configuration from the Windows registry."""
lm = _winreg.ConnectRegistry(None, _winreg.HKEY_LOCAL_MACHINE)
want_scan = False
try:
try:
# XP, 2000
tcp_params = _winreg.OpenKey(lm,
r'SYSTEM\CurrentControlSet'
r'\Services\Tcpip\Parameters')
want_scan = True
except EnvironmentError:
# ME
tcp_params = _winreg.OpenKey(lm,
r'SYSTEM\CurrentControlSet'
r'\Services\VxD\MSTCP')
try:
self._config_win32_fromkey(tcp_params)
finally:
tcp_params.Close()
if want_scan:
interfaces = _winreg.OpenKey(lm,
r'SYSTEM\CurrentControlSet'
r'\Services\Tcpip\Parameters'
r'\Interfaces')
try:
i = 0
while True:
try:
guid = _winreg.EnumKey(interfaces, i)
i += 1
key = _winreg.OpenKey(interfaces, guid)
if not self._win32_is_nic_enabled(lm, guid, key):
continue
try:
self._config_win32_fromkey(key)
finally:
key.Close()
except EnvironmentError:
break
finally:
interfaces.Close()
finally:
lm.Close()
def _win32_is_nic_enabled(self, lm, guid, interface_key):
# Look in the Windows Registry to determine whether the network
# interface corresponding to the given guid is enabled.
#
# (Code contributed by Paul Marks, thanks!)
#
try:
# This hard-coded location seems to be consistent, at least
# from Windows 2000 through Vista.
connection_key = _winreg.OpenKey(
lm,
r'SYSTEM\CurrentControlSet\Control\Network'
r'\{4D36E972-E325-11CE-BFC1-08002BE10318}'
r'\%s\Connection' % guid)
try:
# The PnpInstanceID points to a key inside Enum
(pnp_id, ttype) = _winreg.QueryValueEx(
connection_key, 'PnpInstanceID')
if ttype != _winreg.REG_SZ:
raise ValueError
device_key = _winreg.OpenKey(
lm, r'SYSTEM\CurrentControlSet\Enum\%s' % pnp_id)
try:
# Get ConfigFlags for this device
(flags, ttype) = _winreg.QueryValueEx(
device_key, 'ConfigFlags')
if ttype != _winreg.REG_DWORD:
raise ValueError
# Based on experimentation, bit 0x1 indicates that the
# device is disabled.
return not (flags & 0x1)
finally:
device_key.Close()
finally:
connection_key.Close()
except (EnvironmentError, ValueError):
# Pre-vista, enabled interfaces seem to have a non-empty
# NTEContextList; this was how dnspython detected enabled
# nics before the code above was contributed. We've retained
# the old method since we don't know if the code above works
# on Windows 95/98/ME.
try:
(nte, ttype) = _winreg.QueryValueEx(interface_key,
'NTEContextList')
return nte is not None
except WindowsError:
return False
def _compute_timeout(self, start):
now = time.time()
if now < start:
if start - now > 1:
# Time going backwards is bad. Just give up.
raise Timeout
else:
# Time went backwards, but only a little. This can
# happen, e.g. under vmware with older linux kernels.
# Pretend it didn't happen.
now = start
duration = now - start
if duration >= self.lifetime:
raise Timeout
return min(self.lifetime - duration, self.timeout)
def query(self, qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
tcp=False, source=None):
"""Query nameservers to find the answer to the question.
The I{qname}, I{rdtype}, and I{rdclass} parameters may be objects
of the appropriate type, or strings that can be converted into objects
of the appropriate type. E.g. For I{rdtype} the integer 2 and the
the string 'NS' both mean to query for records with DNS rdata type NS.
@param qname: the query name
@type qname: dns.name.Name object or string
@param rdtype: the query type
@type rdtype: int or string
@param rdclass: the query class
@type rdclass: int or string
@param tcp: use TCP to make the query (default is False).
@type tcp: bool
@param source: bind to this IP address (defaults to machine default IP).
@type source: IP address in dotted quad notation
@rtype: dns.resolver.Answer instance
@raises Timeout: no answers could be found in the specified lifetime
@raises NXDOMAIN: the query name does not exist
@raises NoAnswer: the response did not contain an answer
@raises NoNameservers: no non-broken nameservers are available to
answer the question."""
if isinstance(qname, (str, unicode)):
qname = dns.name.from_text(qname, None)
if isinstance(rdtype, str):
rdtype = dns.rdatatype.from_text(rdtype)
if isinstance(rdclass, str):
rdclass = dns.rdataclass.from_text(rdclass)
qnames_to_try = []
if qname.is_absolute():
qnames_to_try.append(qname)
else:
if len(qname) > 1:
qnames_to_try.append(qname.concatenate(dns.name.root))
if self.search:
for suffix in self.search:
qnames_to_try.append(qname.concatenate(suffix))
else:
qnames_to_try.append(qname.concatenate(self.domain))
all_nxdomain = True
start = time.time()
for qname in qnames_to_try:
if self.cache:
answer = self.cache.get((qname, rdtype, rdclass))
if answer:
return answer
request = dns.message.make_query(qname, rdtype, rdclass)
if not self.keyname is None:
request.use_tsig(self.keyring, self.keyname, self.keyalgorithm)
request.use_edns(self.edns, self.ednsflags, self.payload)
response = None
#
# make a copy of the servers list so we can alter it later.
#
nameservers = self.nameservers[:]
backoff = 0.10
while response is None:
if len(nameservers) == 0:
raise NoNameservers
for nameserver in nameservers[:]:
timeout = self._compute_timeout(start)
try:
if tcp:
response = dns.query.tcp(request, nameserver,
timeout, self.port,
source=source)
else:
response = dns.query.udp(request, nameserver,
timeout, self.port,
source=source)
except (socket.error, dns.exception.Timeout):
#
# Communication failure or timeout. Go to the
# next server
#
response = None
continue
except dns.query.UnexpectedSource:
#
# Who knows? Keep going.
#
response = None
continue
except dns.exception.FormError:
#
# We don't understand what this server is
# saying. Take it out of the mix and
# continue.
#
nameservers.remove(nameserver)
response = None
continue
rcode = response.rcode()
if rcode == dns.rcode.NOERROR or \
rcode == dns.rcode.NXDOMAIN:
break
#
# We got a response, but we're not happy with the
# rcode in it. Remove the server from the mix if
# the rcode isn't SERVFAIL.
#
if rcode != dns.rcode.SERVFAIL:
nameservers.remove(nameserver)
response = None
if not response is None:
break
#
# All nameservers failed!
#
if len(nameservers) > 0:
#
# But we still have servers to try. Sleep a bit
# so we don't pound them!
#
timeout = self._compute_timeout(start)
sleep_time = min(timeout, backoff)
backoff *= 2
time.sleep(sleep_time)
if response.rcode() == dns.rcode.NXDOMAIN:
continue
all_nxdomain = False
break
if all_nxdomain:
raise NXDOMAIN
answer = Answer(qname, rdtype, rdclass, response)
if self.cache:
self.cache.put((qname, rdtype, rdclass), answer)
return answer
def use_tsig(self, keyring, keyname=None,
algorithm=dns.tsig.default_algorithm):
"""Add a TSIG signature to the query.
@param keyring: The TSIG keyring to use; defaults to None.
@type keyring: dict
@param keyname: The name of the TSIG key to use; defaults to None.
The key must be defined in the keyring. If a keyring is specified
but a keyname is not, then the key used will be the first key in the
keyring. Note that the order of keys in a dictionary is not defined,
so applications should supply a keyname when a keyring is used, unless
they know the keyring contains only one key.
@param algorithm: The TSIG key algorithm to use. The default
is dns.tsig.default_algorithm.
@type algorithm: string"""
self.keyring = keyring
if keyname is None:
self.keyname = self.keyring.keys()[0]
else:
self.keyname = keyname
self.keyalgorithm = algorithm
def use_edns(self, edns, ednsflags, payload):
"""Configure Edns.
@param edns: The EDNS level to use. The default is -1, no Edns.
@type edns: int
@param ednsflags: The EDNS flags
@type ednsflags: int
@param payload: The EDNS payload size. The default is 0.
@type payload: int"""
if edns is None:
edns = -1
self.edns = edns
self.ednsflags = ednsflags
self.payload = payload
default_resolver = None
def get_default_resolver():
"""Get the default resolver, initializing it if necessary."""
global default_resolver
if default_resolver is None:
default_resolver = Resolver()
return default_resolver
def query(qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
tcp=False, source=None):
"""Query nameservers to find the answer to the question.
This is a convenience function that uses the default resolver
object to make the query.
@see: L{dns.resolver.Resolver.query} for more information on the
parameters."""
return get_default_resolver().query(qname, rdtype, rdclass, tcp, source)
def zone_for_name(name, rdclass=dns.rdataclass.IN, tcp=False, resolver=None):
"""Find the name of the zone which contains the specified name.
@param name: the query name
@type name: absolute dns.name.Name object or string
@param rdclass: The query class
@type rdclass: int
@param tcp: use TCP to make the query (default is False).
@type tcp: bool
@param resolver: the resolver to use
@type resolver: dns.resolver.Resolver object or None
@rtype: dns.name.Name"""
if isinstance(name, (str, unicode)):
name = dns.name.from_text(name, dns.name.root)
if resolver is None:
resolver = get_default_resolver()
if not name.is_absolute():
raise NotAbsolute(name)
while 1:
try:
answer = resolver.query(name, dns.rdatatype.SOA, rdclass, tcp)
return name
except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
try:
name = name.parent()
except dns.name.NoParent:
raise NoRootSOA