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# -*- test-case-name: twisted.names.test.test_rootresolve -*-
# Copyright (c) 2001-2009 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
break discoverAuthority into several smaller functions
documentation
"""
from twisted.internet import defer
from twisted.names import dns
from twisted.names import common
def retry(t, p, *args):
assert t, "Timeout is required"
t = list(t)
def errback(failure):
failure.trap(defer.TimeoutError)
if not t:
return failure
return p.query(timeout=t.pop(0), *args
).addErrback(errback
)
return p.query(timeout=t.pop(0), *args
).addErrback(errback
)
class _DummyController:
def messageReceived(self, *args):
pass
class Resolver(common.ResolverBase):
def __init__(self, hints):
common.ResolverBase.__init__(self)
self.hints = hints
def _lookup(self, name, cls, type, timeout):
d = discoverAuthority(name, self.hints
).addCallback(self.discoveredAuthority, name, cls, type, timeout
)
return d
def discoveredAuthority(self, auth, name, cls, type, timeout):
from twisted.names import client
q = dns.Query(name, type, cls)
r = client.Resolver(servers=[(auth, dns.PORT)])
d = r.queryUDP([q], timeout)
d.addCallback(r.filterAnswers)
return d
def lookupNameservers(host, atServer, p=None):
# print 'Nameserver lookup for', host, 'at', atServer, 'with', p
if p is None:
p = dns.DNSDatagramProtocol(_DummyController())
p.noisy = False
return retry(
(1, 3, 11, 45), # Timeouts
p, # Protocol instance
(atServer, dns.PORT), # Server to query
[dns.Query(host, dns.NS, dns.IN)] # Question to ask
)
def lookupAddress(host, atServer, p=None):
# print 'Address lookup for', host, 'at', atServer, 'with', p
if p is None:
p = dns.DNSDatagramProtocol(_DummyController())
p.noisy = False
return retry(
(1, 3, 11, 45), # Timeouts
p, # Protocol instance
(atServer, dns.PORT), # Server to query
[dns.Query(host, dns.A, dns.IN)] # Question to ask
)
def extractAuthority(msg, cache):
records = msg.answers + msg.authority + msg.additional
nameservers = [r for r in records if r.type == dns.NS]
# print 'Records for', soFar, ':', records
# print 'NS for', soFar, ':', nameservers
if not nameservers:
return None, nameservers
if not records:
raise IOError("No records")
for r in records:
if r.type == dns.A:
cache[str(r.name)] = r.payload.dottedQuad()
for r in records:
if r.type == dns.NS:
if str(r.payload.name) in cache:
return cache[str(r.payload.name)], nameservers
for addr in records:
if addr.type == dns.A and addr.name == r.name:
return addr.payload.dottedQuad(), nameservers
return None, nameservers
def discoverAuthority(host, roots, cache=None, p=None):
if cache is None:
cache = {}
rootAuths = list(roots)
parts = host.rstrip('.').split('.')
parts.reverse()
authority = rootAuths.pop()
soFar = ''
for part in parts:
soFar = part + '.' + soFar
# print '///////', soFar, authority, p
msg = defer.waitForDeferred(lookupNameservers(soFar, authority, p))
yield msg
msg = msg.getResult()
newAuth, nameservers = extractAuthority(msg, cache)
if newAuth is not None:
# print "newAuth is not None"
authority = newAuth
else:
if nameservers:
r = str(nameservers[0].payload.name)
# print 'Recursively discovering authority for', r
authority = defer.waitForDeferred(discoverAuthority(r, roots, cache, p))
yield authority
authority = authority.getResult()
# print 'Discovered to be', authority, 'for', r
## else:
## # print 'Doing address lookup for', soFar, 'at', authority
## msg = defer.waitForDeferred(lookupAddress(soFar, authority, p))
## yield msg
## msg = msg.getResult()
## records = msg.answers + msg.authority + msg.additional
## addresses = [r for r in records if r.type == dns.A]
## if addresses:
## authority = addresses[0].payload.dottedQuad()
## else:
## raise IOError("Resolution error")
# print "Yielding authority", authority
yield authority
discoverAuthority = defer.deferredGenerator(discoverAuthority)
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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