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# -*- test-case-name: twisted.names.test.test_rootresolve -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Resolver implementation for querying successive authoritative servers to
lookup a record, starting from the root nameservers.
@author: Jp Calderone
todo::
robustify it
documentation
"""
from twisted.internet import defer
from twisted.names import common, dns, error
from twisted.python.failure import Failure
class _DummyController:
"""
A do-nothing DNS controller. This is useful when all messages received
will be responses to previously issued queries. Anything else received
will be ignored.
"""
def messageReceived(self, *args):
pass
class Resolver(common.ResolverBase):
"""
L{Resolver} implements recursive lookup starting from a specified list of
root servers.
@ivar hints: See C{hints} parameter of L{__init__}
@ivar _maximumQueries: See C{maximumQueries} parameter of L{__init__}
@ivar _reactor: See C{reactor} parameter of L{__init__}
@ivar _resolverFactory: See C{resolverFactory} parameter of L{__init__}
"""
def __init__(self, hints, maximumQueries=10, reactor=None, resolverFactory=None):
"""
@param hints: A L{list} of L{str} giving the dotted quad
representation of IP addresses of root servers at which to
begin resolving names.
@type hints: L{list} of L{str}
@param maximumQueries: An optional L{int} giving the maximum
number of queries which will be attempted to resolve a
single name.
@type maximumQueries: L{int}
@param reactor: An optional L{IReactorTime} and L{IReactorUDP}
provider to use to bind UDP ports and manage timeouts.
@type reactor: L{IReactorTime} and L{IReactorUDP} provider
@param resolverFactory: An optional callable which accepts C{reactor}
and C{servers} arguments and returns an instance that provides a
C{queryUDP} method. Defaults to L{twisted.names.client.Resolver}.
@type resolverFactory: callable
"""
common.ResolverBase.__init__(self)
self.hints = hints
self._maximumQueries = maximumQueries
self._reactor = reactor
if resolverFactory is None:
from twisted.names.client import Resolver as resolverFactory
self._resolverFactory = resolverFactory
def _roots(self):
"""
Return a list of two-tuples representing the addresses of the root
servers, as defined by C{self.hints}.
"""
return [(ip, dns.PORT) for ip in self.hints]
def _query(self, query, servers, timeout, filter):
"""
Issue one query and return a L{Deferred} which fires with its response.
@param query: The query to issue.
@type query: L{dns.Query}
@param servers: The servers which might have an answer for this
query.
@type servers: L{list} of L{tuple} of L{str} and L{int}
@param timeout: A timeout on how long to wait for the response.
@type timeout: L{tuple} of L{int}
@param filter: A flag indicating whether to filter the results. If
C{True}, the returned L{Deferred} will fire with a three-tuple of
lists of L{twisted.names.dns.RRHeader} (like the return value of
the I{lookup*} methods of L{IResolver}. IF C{False}, the result
will be a L{Message} instance.
@type filter: L{bool}
@return: A L{Deferred} which fires with the response or a timeout
error.
@rtype: L{Deferred}
"""
r = self._resolverFactory(servers=servers, reactor=self._reactor)
d = r.queryUDP([query], timeout)
if filter:
d.addCallback(r.filterAnswers)
return d
def _lookup(self, name, cls, type, timeout):
"""
Implement name lookup by recursively discovering the authoritative
server for the name and then asking it, starting at one of the servers
in C{self.hints}.
"""
if timeout is None:
# A series of timeouts for semi-exponential backoff, summing to an
# arbitrary total of 60 seconds.
timeout = (1, 3, 11, 45)
return self._discoverAuthority(
dns.Query(name, type, cls), self._roots(), timeout, self._maximumQueries
)
def _discoverAuthority(self, query, servers, timeout, queriesLeft):
"""
Issue a query to a server and follow a delegation if necessary.
@param query: The query to issue.
@type query: L{dns.Query}
@param servers: The servers which might have an answer for this
query.
@type servers: L{list} of L{tuple} of L{str} and L{int}
@param timeout: A C{tuple} of C{int} giving the timeout to use for this
query.
@param queriesLeft: A C{int} giving the number of queries which may
yet be attempted to answer this query before the attempt will be
abandoned.
@return: A L{Deferred} which fires with a three-tuple of lists of
L{twisted.names.dns.RRHeader} giving the response, or with a
L{Failure} if there is a timeout or response error.
"""
# Stop now if we've hit the query limit.
if queriesLeft <= 0:
return Failure(error.ResolverError("Query limit reached without result"))
d = self._query(query, servers, timeout, False)
d.addCallback(self._discoveredAuthority, query, timeout, queriesLeft - 1)
return d
def _discoveredAuthority(self, response, query, timeout, queriesLeft):
"""
Interpret the response to a query, checking for error codes and
following delegations if necessary.
@param response: The L{Message} received in response to issuing C{query}.
@type response: L{Message}
@param query: The L{dns.Query} which was issued.
@type query: L{dns.Query}.
@param timeout: The timeout to use if another query is indicated by
this response.
@type timeout: L{tuple} of L{int}
@param queriesLeft: A C{int} giving the number of queries which may
yet be attempted to answer this query before the attempt will be
abandoned.
@return: A L{Failure} indicating a response error, a three-tuple of
lists of L{twisted.names.dns.RRHeader} giving the response to
C{query} or a L{Deferred} which will fire with one of those.
"""
if response.rCode != dns.OK:
return Failure(self.exceptionForCode(response.rCode)(response))
# Turn the answers into a structure that's a little easier to work with.
records = {}
for answer in response.answers:
records.setdefault(answer.name, []).append(answer)
def findAnswerOrCName(name, type, cls):
cname = None
for record in records.get(name, []):
if record.cls == cls:
if record.type == type:
return record
elif record.type == dns.CNAME:
cname = record
# If there were any CNAME records, return the last one. There's
# only supposed to be zero or one, though.
return cname
seen = set()
name = query.name
record = None
while True:
seen.add(name)
previous = record
record = findAnswerOrCName(name, query.type, query.cls)
if record is None:
if name == query.name:
# If there's no answer for the original name, then this may
# be a delegation. Code below handles it.
break
else:
# Try to resolve the CNAME with another query.
d = self._discoverAuthority(
dns.Query(str(name), query.type, query.cls),
self._roots(),
timeout,
queriesLeft,
)
# We also want to include the CNAME in the ultimate result,
# otherwise this will be pretty confusing.
def cbResolved(results):
answers, authority, additional = results
answers.insert(0, previous)
return (answers, authority, additional)
d.addCallback(cbResolved)
return d
elif record.type == query.type:
return (response.answers, response.authority, response.additional)
else:
# It's a CNAME record. Try to resolve it from the records
# in this response with another iteration around the loop.
if record.payload.name in seen:
raise error.ResolverError("Cycle in CNAME processing")
name = record.payload.name
# Build a map to use to convert NS names into IP addresses.
addresses = {}
for rr in response.additional:
if rr.type == dns.A:
addresses[rr.name.name] = rr.payload.dottedQuad()
hints = []
traps = []
for rr in response.authority:
if rr.type == dns.NS:
ns = rr.payload.name.name
if ns in addresses:
hints.append((addresses[ns], dns.PORT))
else:
traps.append(ns)
if hints:
return self._discoverAuthority(query, hints, timeout, queriesLeft)
elif traps:
d = self.lookupAddress(traps[0], timeout)
def getOneAddress(results):
answers, authority, additional = results
return answers[0].payload.dottedQuad()
d.addCallback(getOneAddress)
d.addCallback(
lambda hint: self._discoverAuthority(
query, [(hint, dns.PORT)], timeout, queriesLeft - 1
)
)
return d
else:
return Failure(
error.ResolverError("Stuck at response without answers or delegation")
)
def makePlaceholder(deferred, name):
def placeholder(*args, **kw):
deferred.addCallback(lambda r: getattr(r, name)(*args, **kw))
return deferred
return placeholder
class DeferredResolver:
def __init__(self, resolverDeferred):
self.waiting = []
resolverDeferred.addCallback(self.gotRealResolver)
def gotRealResolver(self, resolver):
w = self.waiting
self.__dict__ = resolver.__dict__
self.__class__ = resolver.__class__
for d in w:
d.callback(resolver)
def __getattr__(self, name):
if name.startswith("lookup") or name in ("getHostByName", "query"):
self.waiting.append(defer.Deferred())
return makePlaceholder(self.waiting[-1], name)
raise AttributeError(name)
def bootstrap(resolver, resolverFactory=None):
"""
Lookup the root nameserver addresses using the given resolver
Return a Resolver which will eventually become a C{root.Resolver}
instance that has references to all the root servers that we were able
to look up.
@param resolver: The resolver instance which will be used to
lookup the root nameserver addresses.
@type resolver: L{twisted.internet.interfaces.IResolverSimple}
@param resolverFactory: An optional callable which returns a
resolver instance. It will passed as the C{resolverFactory}
argument to L{Resolver.__init__}.
@type resolverFactory: callable
@return: A L{DeferredResolver} which will be dynamically replaced
with L{Resolver} when the root nameservers have been looked up.
"""
domains = [chr(ord("a") + i) for i in range(13)]
L = [resolver.getHostByName("%s.root-servers.net" % d) for d in domains]
d = defer.DeferredList(L, consumeErrors=True)
def buildResolver(res):
return Resolver(
hints=[e[1] for e in res if e[0]], resolverFactory=resolverFactory
)
d.addCallback(buildResolver)
return DeferredResolver(d)
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