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# -*- test-case-name: twisted.names.test.test_names -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Asynchronous client DNS
The functions exposed in this module can be used for asynchronous name
resolution and dns queries.
If you need to create a resolver with specific requirements, such as needing to
do queries against a particular host, the L{createResolver} function will
return an C{IResolver}.
Future plans: Proper nameserver acquisition on Windows/MacOS,
better caching, respect timeouts
"""
import errno
import os
import warnings
from zope.interface import moduleProvides
from twisted.internet import defer, error, interfaces, protocol
from twisted.internet.abstract import isIPv6Address
from twisted.names import cache, common, dns, hosts as hostsModule, resolve, root
from twisted.python import failure, log
# Twisted imports
from twisted.python.compat import nativeString
from twisted.python.filepath import FilePath
from twisted.python.runtime import platform
moduleProvides(interfaces.IResolver)
class Resolver(common.ResolverBase):
"""
@ivar _waiting: A C{dict} mapping tuple keys of query name/type/class to
Deferreds which will be called back with the result of those queries.
This is used to avoid issuing the same query more than once in
parallel. This is more efficient on the network and helps avoid a
"birthday paradox" attack by keeping the number of outstanding requests
for a particular query fixed at one instead of allowing the attacker to
raise it to an arbitrary number.
@ivar _reactor: A provider of L{IReactorTCP}, L{IReactorUDP}, and
L{IReactorTime} which will be used to set up network resources and
track timeouts.
"""
index = 0
timeout = None
factory = None
servers = None
dynServers = ()
pending = None
connections = None
resolv = None
_lastResolvTime = None
_resolvReadInterval = 60
def __init__(self, resolv=None, servers=None, timeout=(1, 3, 11, 45), reactor=None):
"""
Construct a resolver which will query domain name servers listed in
the C{resolv.conf(5)}-format file given by C{resolv} as well as
those in the given C{servers} list. Servers are queried in a
round-robin fashion. If given, C{resolv} is periodically checked
for modification and re-parsed if it is noticed to have changed.
@type servers: C{list} of C{(str, int)} or L{None}
@param servers: If not None, interpreted as a list of (host, port)
pairs specifying addresses of domain name servers to attempt to use
for this lookup. Host addresses should be in IPv4 dotted-quad
form. If specified, overrides C{resolv}.
@type resolv: C{str}
@param resolv: Filename to read and parse as a resolver(5)
configuration file.
@type timeout: Sequence of C{int}
@param timeout: Default number of seconds after which to reissue the
query. When the last timeout expires, the query is considered
failed.
@param reactor: A provider of L{IReactorTime}, L{IReactorUDP}, and
L{IReactorTCP} which will be used to establish connections, listen
for DNS datagrams, and enforce timeouts. If not provided, the
global reactor will be used.
@raise ValueError: Raised if no nameserver addresses can be found.
"""
common.ResolverBase.__init__(self)
if reactor is None:
from twisted.internet import reactor
self._reactor = reactor
self.timeout = timeout
if servers is None:
self.servers = []
else:
self.servers = servers
self.resolv = resolv
if not len(self.servers) and not resolv:
raise ValueError("No nameservers specified")
self.factory = DNSClientFactory(self, timeout)
self.factory.noisy = 0 # Be quiet by default
self.connections = []
self.pending = []
self._waiting = {}
self.maybeParseConfig()
def __getstate__(self):
d = self.__dict__.copy()
d["connections"] = []
d["_parseCall"] = None
return d
def __setstate__(self, state):
self.__dict__.update(state)
self.maybeParseConfig()
def _openFile(self, path):
"""
Wrapper used for opening files in the class, exists primarily for unit
testing purposes.
"""
return FilePath(path).open()
def maybeParseConfig(self):
if self.resolv is None:
# Don't try to parse it, don't set up a call loop
return
try:
resolvConf = self._openFile(self.resolv)
except OSError as e:
if e.errno == errno.ENOENT:
# Missing resolv.conf is treated the same as an empty resolv.conf
self.parseConfig(())
else:
raise
else:
with resolvConf:
mtime = os.fstat(resolvConf.fileno()).st_mtime
if mtime != self._lastResolvTime:
log.msg(f"{self.resolv} changed, reparsing")
self._lastResolvTime = mtime
self.parseConfig(resolvConf)
# Check again in a little while
self._parseCall = self._reactor.callLater(
self._resolvReadInterval, self.maybeParseConfig
)
def parseConfig(self, resolvConf):
servers = []
for L in resolvConf:
L = L.strip()
if L.startswith(b"nameserver"):
resolver = (nativeString(L.split()[1]), dns.PORT)
servers.append(resolver)
log.msg(f"Resolver added {resolver!r} to server list")
elif L.startswith(b"domain"):
try:
self.domain = L.split()[1]
except IndexError:
self.domain = b""
self.search = None
elif L.startswith(b"search"):
self.search = L.split()[1:]
self.domain = None
if not servers:
servers.append(("127.0.0.1", dns.PORT))
self.dynServers = servers
def pickServer(self):
"""
Return the address of a nameserver.
TODO: Weight servers for response time so faster ones can be
preferred.
"""
if not self.servers and not self.dynServers:
return None
serverL = len(self.servers)
dynL = len(self.dynServers)
self.index += 1
self.index %= serverL + dynL
if self.index < serverL:
return self.servers[self.index]
else:
return self.dynServers[self.index - serverL]
def _connectedProtocol(self, interface=""):
"""
Return a new L{DNSDatagramProtocol} bound to a randomly selected port
number.
"""
failures = 0
proto = dns.DNSDatagramProtocol(self, reactor=self._reactor)
while True:
try:
self._reactor.listenUDP(dns.randomSource(), proto, interface=interface)
except error.CannotListenError as e:
failures += 1
if (
hasattr(e.socketError, "errno")
and e.socketError.errno == errno.EMFILE
):
# We've run out of file descriptors. Stop trying.
raise
if failures >= 1000:
# We've tried a thousand times and haven't found a port.
# This is almost impossible, and likely means something
# else weird is going on. Raise, as to not infinite loop.
raise
else:
return proto
def connectionMade(self, protocol):
"""
Called by associated L{dns.DNSProtocol} instances when they connect.
"""
self.connections.append(protocol)
for (d, q, t) in self.pending:
self.queryTCP(q, t).chainDeferred(d)
del self.pending[:]
def connectionLost(self, protocol):
"""
Called by associated L{dns.DNSProtocol} instances when they disconnect.
"""
if protocol in self.connections:
self.connections.remove(protocol)
def messageReceived(self, message, protocol, address=None):
log.msg("Unexpected message (%d) received from %r" % (message.id, address))
def _query(self, *args):
"""
Get a new L{DNSDatagramProtocol} instance from L{_connectedProtocol},
issue a query to it using C{*args}, and arrange for it to be
disconnected from its transport after the query completes.
@param args: Positional arguments to be passed to
L{DNSDatagramProtocol.query}.
@return: A L{Deferred} which will be called back with the result of the
query.
"""
if isIPv6Address(args[0][0]):
protocol = self._connectedProtocol(interface="::")
else:
protocol = self._connectedProtocol()
d = protocol.query(*args)
def cbQueried(result):
protocol.transport.stopListening()
return result
d.addBoth(cbQueried)
return d
def queryUDP(self, queries, timeout=None):
"""
Make a number of DNS queries via UDP.
@type queries: A C{list} of C{dns.Query} instances
@param queries: The queries to make.
@type timeout: Sequence of C{int}
@param timeout: Number of seconds after which to reissue the query.
When the last timeout expires, the query is considered failed.
@rtype: C{Deferred}
@raise C{twisted.internet.defer.TimeoutError}: When the query times
out.
"""
if timeout is None:
timeout = self.timeout
addresses = self.servers + list(self.dynServers)
if not addresses:
return defer.fail(IOError("No domain name servers available"))
# Make sure we go through servers in the list in the order they were
# specified.
addresses.reverse()
used = addresses.pop()
d = self._query(used, queries, timeout[0])
d.addErrback(self._reissue, addresses, [used], queries, timeout)
return d
def _reissue(self, reason, addressesLeft, addressesUsed, query, timeout):
reason.trap(dns.DNSQueryTimeoutError)
# If there are no servers left to be tried, adjust the timeout
# to the next longest timeout period and move all the
# "used" addresses back to the list of addresses to try.
if not addressesLeft:
addressesLeft = addressesUsed
addressesLeft.reverse()
addressesUsed = []
timeout = timeout[1:]
# If all timeout values have been used this query has failed. Tell the
# protocol we're giving up on it and return a terminal timeout failure
# to our caller.
if not timeout:
return failure.Failure(defer.TimeoutError(query))
# Get an address to try. Take it out of the list of addresses
# to try and put it ino the list of already tried addresses.
address = addressesLeft.pop()
addressesUsed.append(address)
# Issue a query to a server. Use the current timeout. Add this
# function as a timeout errback in case another retry is required.
d = self._query(address, query, timeout[0], reason.value.id)
d.addErrback(self._reissue, addressesLeft, addressesUsed, query, timeout)
return d
def queryTCP(self, queries, timeout=10):
"""
Make a number of DNS queries via TCP.
@type queries: Any non-zero number of C{dns.Query} instances
@param queries: The queries to make.
@type timeout: C{int}
@param timeout: The number of seconds after which to fail.
@rtype: C{Deferred}
"""
if not len(self.connections):
address = self.pickServer()
if address is None:
return defer.fail(IOError("No domain name servers available"))
host, port = address
self._reactor.connectTCP(host, port, self.factory)
self.pending.append((defer.Deferred(), queries, timeout))
return self.pending[-1][0]
else:
return self.connections[0].query(queries, timeout)
def filterAnswers(self, message):
"""
Extract results from the given message.
If the message was truncated, re-attempt the query over TCP and return
a Deferred which will fire with the results of that query.
If the message's result code is not C{twisted.names.dns.OK}, return a
Failure indicating the type of error which occurred.
Otherwise, return a three-tuple of lists containing the results from
the answers section, the authority section, and the additional section.
"""
if message.trunc:
return self.queryTCP(message.queries).addCallback(self.filterAnswers)
if message.rCode != dns.OK:
return failure.Failure(self.exceptionForCode(message.rCode)(message))
return (message.answers, message.authority, message.additional)
def _lookup(self, name, cls, type, timeout):
"""
Build a L{dns.Query} for the given parameters and dispatch it via UDP.
If this query is already outstanding, it will not be re-issued.
Instead, when the outstanding query receives a response, that response
will be re-used for this query as well.
@type name: C{str}
@type type: C{int}
@type cls: C{int}
@return: A L{Deferred} which fires with a three-tuple giving the
answer, authority, and additional sections of the response or with
a L{Failure} if the response code is anything other than C{dns.OK}.
"""
key = (name, type, cls)
waiting = self._waiting.get(key)
if waiting is None:
self._waiting[key] = []
d = self.queryUDP([dns.Query(name, type, cls)], timeout)
def cbResult(result):
for d in self._waiting.pop(key):
d.callback(result)
return result
d.addCallback(self.filterAnswers)
d.addBoth(cbResult)
else:
d = defer.Deferred()
waiting.append(d)
return d
# This one doesn't ever belong on UDP
def lookupZone(self, name, timeout=10):
address = self.pickServer()
if address is None:
return defer.fail(IOError("No domain name servers available"))
host, port = address
d = defer.Deferred()
controller = AXFRController(name, d)
factory = DNSClientFactory(controller, timeout)
factory.noisy = False # stfu
connector = self._reactor.connectTCP(host, port, factory)
controller.timeoutCall = self._reactor.callLater(
timeout or 10, self._timeoutZone, d, controller, connector, timeout or 10
)
def eliminateTimeout(failure):
controller.timeoutCall.cancel()
controller.timeoutCall = None
return failure
return d.addCallbacks(
self._cbLookupZone, eliminateTimeout, callbackArgs=(connector,)
)
def _timeoutZone(self, d, controller, connector, seconds):
connector.disconnect()
controller.timeoutCall = None
controller.deferred = None
d.errback(
error.TimeoutError("Zone lookup timed out after %d seconds" % (seconds,))
)
def _cbLookupZone(self, result, connector):
connector.disconnect()
return (result, [], [])
class AXFRController:
timeoutCall = None
def __init__(self, name, deferred):
self.name = name
self.deferred = deferred
self.soa = None
self.records = []
self.pending = [(deferred,)]
def connectionMade(self, protocol):
# dig saids recursion-desired to 0, so I will too
message = dns.Message(protocol.pickID(), recDes=0)
message.queries = [dns.Query(self.name, dns.AXFR, dns.IN)]
protocol.writeMessage(message)
def connectionLost(self, protocol):
# XXX Do something here - see #3428
pass
def messageReceived(self, message, protocol):
# Caveat: We have to handle two cases: All records are in 1
# message, or all records are in N messages.
# According to http://cr.yp.to/djbdns/axfr-notes.html,
# 'authority' and 'additional' are always empty, and only
# 'answers' is present.
self.records.extend(message.answers)
if not self.records:
return
if not self.soa:
if self.records[0].type == dns.SOA:
# print "first SOA!"
self.soa = self.records[0]
if len(self.records) > 1 and self.records[-1].type == dns.SOA:
# print "It's the second SOA! We're done."
if self.timeoutCall is not None:
self.timeoutCall.cancel()
self.timeoutCall = None
if self.deferred is not None:
self.deferred.callback(self.records)
self.deferred = None
from twisted.internet.base import ThreadedResolver as _ThreadedResolverImpl
class ThreadedResolver(_ThreadedResolverImpl):
def __init__(self, reactor=None):
if reactor is None:
from twisted.internet import reactor
_ThreadedResolverImpl.__init__(self, reactor)
warnings.warn(
"twisted.names.client.ThreadedResolver is deprecated since "
"Twisted 9.0, use twisted.internet.base.ThreadedResolver "
"instead.",
category=DeprecationWarning,
stacklevel=2,
)
class DNSClientFactory(protocol.ClientFactory):
def __init__(self, controller, timeout=10):
self.controller = controller
self.timeout = timeout
def clientConnectionLost(self, connector, reason):
pass
def clientConnectionFailed(self, connector, reason):
"""
Fail all pending TCP DNS queries if the TCP connection attempt
fails.
@see: L{twisted.internet.protocol.ClientFactory}
@param connector: Not used.
@type connector: L{twisted.internet.interfaces.IConnector}
@param reason: A C{Failure} containing information about the
cause of the connection failure. This will be passed as the
argument to C{errback} on every pending TCP query
C{deferred}.
@type reason: L{twisted.python.failure.Failure}
"""
# Copy the current pending deferreds then reset the master
# pending list. This prevents triggering new deferreds which
# may be added by callback or errback functions on the current
# deferreds.
pending = self.controller.pending[:]
del self.controller.pending[:]
for pendingState in pending:
d = pendingState[0]
d.errback(reason)
def buildProtocol(self, addr):
p = dns.DNSProtocol(self.controller)
p.factory = self
return p
def createResolver(servers=None, resolvconf=None, hosts=None):
r"""
Create and return a Resolver.
@type servers: C{list} of C{(str, int)} or L{None}
@param servers: If not L{None}, interpreted as a list of domain name servers
to attempt to use. Each server is a tuple of address in C{str} dotted-quad
form and C{int} port number.
@type resolvconf: C{str} or L{None}
@param resolvconf: If not L{None}, on posix systems will be interpreted as
an alternate resolv.conf to use. Will do nothing on windows systems. If
L{None}, /etc/resolv.conf will be used.
@type hosts: C{str} or L{None}
@param hosts: If not L{None}, an alternate hosts file to use. If L{None}
on posix systems, /etc/hosts will be used. On windows, C:\windows\hosts
will be used.
@rtype: C{IResolver}
"""
if platform.getType() == "posix":
if resolvconf is None:
resolvconf = b"/etc/resolv.conf"
if hosts is None:
hosts = b"/etc/hosts"
theResolver = Resolver(resolvconf, servers)
hostResolver = hostsModule.Resolver(hosts)
else:
if hosts is None:
hosts = r"c:\windows\hosts"
from twisted.internet import reactor
bootstrap = _ThreadedResolverImpl(reactor)
hostResolver = hostsModule.Resolver(hosts)
theResolver = root.bootstrap(bootstrap, resolverFactory=Resolver)
L = [hostResolver, cache.CacheResolver(), theResolver]
return resolve.ResolverChain(L)
theResolver = None
def getResolver():
"""
Get a Resolver instance.
Create twisted.names.client.theResolver if it is L{None}, and then return
that value.
@rtype: C{IResolver}
"""
global theResolver
if theResolver is None:
try:
theResolver = createResolver()
except ValueError:
theResolver = createResolver(servers=[("127.0.0.1", 53)])
return theResolver
def getHostByName(name, timeout=None, effort=10):
"""
Resolve a name to a valid ipv4 or ipv6 address.
Will errback with C{DNSQueryTimeoutError} on a timeout, C{DomainError} or
C{AuthoritativeDomainError} (or subclasses) on other errors.
@type name: C{str}
@param name: DNS name to resolve.
@type timeout: Sequence of C{int}
@param timeout: Number of seconds after which to reissue the query.
When the last timeout expires, the query is considered failed.
@type effort: C{int}
@param effort: How many times CNAME and NS records to follow while
resolving this name.
@rtype: C{Deferred}
"""
return getResolver().getHostByName(name, timeout, effort)
def query(query, timeout=None):
return getResolver().query(query, timeout)
def lookupAddress(name, timeout=None):
return getResolver().lookupAddress(name, timeout)
def lookupIPV6Address(name, timeout=None):
return getResolver().lookupIPV6Address(name, timeout)
def lookupAddress6(name, timeout=None):
return getResolver().lookupAddress6(name, timeout)
def lookupMailExchange(name, timeout=None):
return getResolver().lookupMailExchange(name, timeout)
def lookupNameservers(name, timeout=None):
return getResolver().lookupNameservers(name, timeout)
def lookupCanonicalName(name, timeout=None):
return getResolver().lookupCanonicalName(name, timeout)
def lookupMailBox(name, timeout=None):
return getResolver().lookupMailBox(name, timeout)
def lookupMailGroup(name, timeout=None):
return getResolver().lookupMailGroup(name, timeout)
def lookupMailRename(name, timeout=None):
return getResolver().lookupMailRename(name, timeout)
def lookupPointer(name, timeout=None):
return getResolver().lookupPointer(name, timeout)
def lookupAuthority(name, timeout=None):
return getResolver().lookupAuthority(name, timeout)
def lookupNull(name, timeout=None):
return getResolver().lookupNull(name, timeout)
def lookupWellKnownServices(name, timeout=None):
return getResolver().lookupWellKnownServices(name, timeout)
def lookupService(name, timeout=None):
return getResolver().lookupService(name, timeout)
def lookupHostInfo(name, timeout=None):
return getResolver().lookupHostInfo(name, timeout)
def lookupMailboxInfo(name, timeout=None):
return getResolver().lookupMailboxInfo(name, timeout)
def lookupText(name, timeout=None):
return getResolver().lookupText(name, timeout)
def lookupSenderPolicy(name, timeout=None):
return getResolver().lookupSenderPolicy(name, timeout)
def lookupResponsibility(name, timeout=None):
return getResolver().lookupResponsibility(name, timeout)
def lookupAFSDatabase(name, timeout=None):
return getResolver().lookupAFSDatabase(name, timeout)
def lookupZone(name, timeout=None):
return getResolver().lookupZone(name, timeout)
def lookupAllRecords(name, timeout=None):
return getResolver().lookupAllRecords(name, timeout)
def lookupNamingAuthorityPointer(name, timeout=None):
return getResolver().lookupNamingAuthorityPointer(name, timeout)
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