/usr/lib/python2.7/dist-packages/twisted/names/root.py is in python-twisted-names 13.2.0-1ubuntu1.2.
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# 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
"""
import warnings
from twisted.python.failure import Failure
from twisted.internet import defer
from twisted.names import dns, common, error
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: A C{list} of C{str} giving the dotted quad representation
of IP addresses of root servers at which to begin resolving names.
@ivar _maximumQueries: A C{int} giving the maximum number of queries
which will be attempted to resolve a single name.
@ivar _reactor: A L{IReactorTime} and L{IReactorUDP} provider to use to
bind UDP ports and manage timeouts.
"""
def __init__(self, hints, maximumQueries=10, reactor=None):
common.ResolverBase.__init__(self)
self.hints = hints
self._maximumQueries = maximumQueries
self._reactor = reactor
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{RRHeaders} (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}
"""
from twisted.names import client
r = client.Resolver(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{RRHeaders} 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{RRHeaders} 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):
"""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.
"""
domains = [chr(ord('a') + i) for i in range(13)]
# f = lambda r: (log.msg('Root server address: ' + str(r)), r)[1]
f = lambda r: r
L = [resolver.getHostByName('%s.root-servers.net' % d).addCallback(f) for d in domains]
d = defer.DeferredList(L)
d.addCallback(lambda r: Resolver([e[1] for e in r if e[0]]))
return DeferredResolver(d)
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