Mini Shell

# -*- test-case-name: twisted.names.test -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
An in-memory caching resolver.
"""


from twisted.internet import defer
from twisted.names import common, dns
from twisted.python import failure, log


class CacheResolver(common.ResolverBase):
    """
    A resolver that serves records from a local, memory cache.

    @ivar _reactor: A provider of L{interfaces.IReactorTime}.
    """

    cache = None

    def __init__(self, cache=None, verbose=0, reactor=None):
        common.ResolverBase.__init__(self)

        self.cache = {}
        self.verbose = verbose
        self.cancel = {}
        if reactor is None:
            from twisted.internet import reactor
        self._reactor = reactor

        if cache:
            for query, (seconds, payload) in cache.items():
                self.cacheResult(query, payload, seconds)

    def __setstate__(self, state):
        self.__dict__ = state

        now = self._reactor.seconds()
        for (k, (when, (ans, add, ns))) in self.cache.items():
            diff = now - when
            for rec in ans + add + ns:
                if rec.ttl < diff:
                    del self.cache[k]
                    break

    def __getstate__(self):
        for c in self.cancel.values():
            c.cancel()
        self.cancel.clear()
        return self.__dict__

    def _lookup(self, name, cls, type, timeout):
        now = self._reactor.seconds()
        q = dns.Query(name, type, cls)
        try:
            when, (ans, auth, add) = self.cache[q]
        except KeyError:
            if self.verbose > 1:
                log.msg("Cache miss for " + repr(name))
            return defer.fail(failure.Failure(dns.DomainError(name)))
        else:
            if self.verbose:
                log.msg("Cache hit for " + repr(name))
            diff = now - when

            try:
                result = (
                    [
                        dns.RRHeader(
                            r.name.name, r.type, r.cls, r.ttl - diff, r.payload
                        )
                        for r in ans
                    ],
                    [
                        dns.RRHeader(
                            r.name.name, r.type, r.cls, r.ttl - diff, r.payload
                        )
                        for r in auth
                    ],
                    [
                        dns.RRHeader(
                            r.name.name, r.type, r.cls, r.ttl - diff, r.payload
                        )
                        for r in add
                    ],
                )
            except ValueError:
                return defer.fail(failure.Failure(dns.DomainError(name)))
            else:
                return defer.succeed(result)

    def lookupAllRecords(self, name, timeout=None):
        return defer.fail(failure.Failure(dns.DomainError(name)))

    def cacheResult(self, query, payload, cacheTime=None):
        """
        Cache a DNS entry.

        @param query: a L{dns.Query} instance.

        @param payload: a 3-tuple of lists of L{dns.RRHeader} records, the
            matching result of the query (answers, authority and additional).

        @param cacheTime: The time (seconds since epoch) at which the entry is
            considered to have been added to the cache. If L{None} is given,
            the current time is used.
        """
        if self.verbose > 1:
            log.msg("Adding %r to cache" % query)

        self.cache[query] = (cacheTime or self._reactor.seconds(), payload)

        if query in self.cancel:
            self.cancel[query].cancel()

        s = list(payload[0]) + list(payload[1]) + list(payload[2])
        if s:
            m = s[0].ttl
            for r in s:
                m = min(m, r.ttl)
        else:
            m = 0

        self.cancel[query] = self._reactor.callLater(m, self.clearEntry, query)

    def clearEntry(self, query):
        del self.cache[query]
        del self.cancel[query]