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Filename : root.py
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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.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)