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""" 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.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: 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)