twisted/names/cache.py

   1 # -*- test-case-name: twisted.names.test -*-
   2 # Copyright (c) Twisted Matrix Laboratories.
   3 # See LICENSE for details.
   4
   5 from zope.interface import implements
   6
   7 from twisted.names import dns, common
   8 from twisted.python import failure, log
   9 from twisted.internet import interfaces, defer
  10
  11
  12
  13 class CacheResolver(common.ResolverBase):
  14     """
  15     A resolver that serves records from a local, memory cache.
  16
  17     @ivar _reactor: A provider of L{interfaces.IReactorTime}.
  18     """
  19
  20     implements(interfaces.IResolver)
  21
  22     cache = None
  23
  24     def __init__(self, cache=None, verbose=0, reactor=None):
  25         common.ResolverBase.__init__(self)
  26
  27         self.cache = {}
  28         self.verbose = verbose
  29         self.cancel = {}
  30         if reactor is None:
  31             from twisted.internet import reactor
  32         self._reactor = reactor
  33
  34         if cache:
  35             for query, (seconds, payload) in cache.items():
  36                 self.cacheResult(query, payload, seconds)
  37
  38
  39     def __setstate__(self, state):
  40         self.__dict__ = state
  41
  42         now = self._reactor.seconds()
  43         for (k, (when, (ans, add, ns))) in self.cache.items():
  44             diff = now - when
  45             for rec in ans + add + ns:
  46                 if rec.ttl < diff:
  47                     del self.cache[k]
  48                     break
  49
  50
  51     def __getstate__(self):
  52         for c in self.cancel.values():
  53             c.cancel()
  54         self.cancel.clear()
  55         return self.__dict__
  56
  57
  58     def _lookup(self, name, cls, type, timeout):
  59         now = self._reactor.seconds()
  60         q = dns.Query(name, type, cls)
  61         try:
  62             when, (ans, auth, add) = self.cache[q]
  63         except KeyError:
  64             if self.verbose > 1:
  65                 log.msg('Cache miss for ' + repr(name))
  66             return defer.fail(failure.Failure(dns.DomainError(name)))
  67         else:
  68             if self.verbose:
  69                 log.msg('Cache hit for ' + repr(name))
  70             diff = now - when
  71             return defer.succeed((
  72                 [dns.RRHeader(str(r.name), r.type, r.cls, max(0, r.ttl - diff), r.payload) for r in ans],
  73                 [dns.RRHeader(str(r.name), r.type, r.cls, max(0, r.ttl - diff), r.payload) for r in auth],
  74                 [dns.RRHeader(str(r.name), r.type, r.cls, max(0, r.ttl - diff), r.payload) for r in add]
  75             ))
  76
  77
  78     def lookupAllRecords(self, name, timeout = None):
  79         return defer.fail(failure.Failure(dns.DomainError(name)))
  80
  81
  82     def cacheResult(self, query, payload, cacheTime=None):
  83         """
  84         Cache a DNS entry.
  85
  86         @param query: a L{dns.Query} instance.
  87
  88         @param payload: a 3-tuple of lists of L{dns.RRHeader} records, the
  89             matching result of the query (answers, authority and additional).
  90
  91         @param cacheTime: The time (seconds since epoch) at which the entry is
  92             considered to have been added to the cache. If C{None} is given,
  93             the current time is used.
  94         """
  95         if self.verbose > 1:
  96             log.msg('Adding %r to cache' % query)
  97
  98         self.cache[query] = (cacheTime or self._reactor.seconds(), payload)
  99
 100         if self.cancel.has_key(query):
 101             self.cancel[query].cancel()
 102
 103         s = list(payload[0]) + list(payload[1]) + list(payload[2])
 104         if s:
 105             m = s[0].ttl
 106             for r in s:
 107                 m = min(m, r.ttl)
 108         else:
 109             m = 0
 110
 111         self.cancel[query] = self._reactor.callLater(m, self.clearEntry, query)
 112
 113
 114     def clearEntry(self, query):
 115         del self.cache[query]
 116         del self.cancel[query]