text: # -*- test-case-name: twisted.names.test.test_names,twisted.names.test.test_server -*-
  # Copyright (c) Twisted Matrix Laboratories.
  # See LICENSE for details.
  
  """
  Async DNS server
  
  Future plans:
      - Better config file format maybe
      - Make sure to differentiate between different classes
      - notice truncation bit
  
  Important: No additional processing is done on some of the record types.
  This violates the most basic RFC and is just plain annoying
  for resolvers to deal with.  Fix it.
  
  @author: Jp Calderone
  """
  
  import time
  
  from twisted.internet import protocol
  from twisted.names import dns, resolve
  from twisted.python import log
  
  
  class DNSServerFactory(protocol.ServerFactory):
      """
      Server factory and tracker for L{DNSProtocol} connections.  This class also
      provides records for responses to DNS queries.
  
      @ivar cache: A L{Cache<twisted.names.cache.Cache>} instance whose
          C{cacheResult} method is called when a response is received from one of
          C{clients}. Defaults to L{None} if no caches are specified. See
          C{caches} of L{__init__} for more details.
      @type cache: L{Cache<twisted.names.cache.Cache} or L{None}
  
      @ivar canRecurse: A flag indicating whether this server is capable of
          performing recursive DNS resolution.
      @type canRecurse: L{bool}
  
      @ivar resolver: A L{resolve.ResolverChain} containing an ordered list of
          C{authorities}, C{caches} and C{clients} to which queries will be
          dispatched.
      @type resolver: L{resolve.ResolverChain}
  
      @ivar verbose: See L{__init__}
  
      @ivar connections: A list of all the connected L{DNSProtocol} instances
          using this object as their controller.
      @type connections: C{list} of L{DNSProtocol} instances
  
      @ivar protocol: A callable used for building a DNS stream protocol. Called
          by L{DNSServerFactory.buildProtocol} and passed the L{DNSServerFactory}
          instance as the one and only positional argument.  Defaults to
          L{dns.DNSProtocol}.
      @type protocol: L{IProtocolFactory} constructor
  
      @ivar _messageFactory: A response message constructor with an initializer
           signature matching L{dns.Message.__init__}.
      @type _messageFactory: C{callable}
      """
  
      protocol = dns.DNSProtocol
      cache = None
      _messageFactory = dns.Message
  
  
      def __init__(self, authorities=None, caches=None, clients=None, verbose=0):
          """
          @param authorities: Resolvers which provide authoritative answers.
          @type authorities: L{list} of L{IResolver} providers
  
          @param caches: Resolvers which provide cached non-authoritative
              answers. The first cache instance is assigned to
              C{DNSServerFactory.cache} and its C{cacheResult} method will be
              called when a response is received from one of C{clients}.
          @type caches: L{list} of L{Cache<twisted.names.cache.Cache} instances
  
          @param clients: Resolvers which are capable of performing recursive DNS
              lookups.
          @type clients: L{list} of L{IResolver} providers
  
          @param verbose: An integer controlling the verbosity of logging of
              queries and responses. Default is C{0} which means no logging. Set
              to C{2} to enable logging of full query and response messages.
          @param verbose: L{int}
          """
          resolvers = []
          if authorities is not None:
              resolvers.extend(authorities)
          if caches is not None:
              resolvers.extend(caches)
          if clients is not None:
              resolvers.extend(clients)
  
          self.canRecurse = not not clients
          self.resolver = resolve.ResolverChain(resolvers)
          self.verbose = verbose
          if caches:
              self.cache = caches[-1]
          self.connections = []
  
  
      def _verboseLog(self, *args, **kwargs):
          """
          Log a message only if verbose logging is enabled.
  
          @param args: Positional arguments which will be passed to C{log.msg}
          @param kwargs: Keyword arguments which will be passed to C{log.msg}
          """
          if self.verbose > 0:
              log.msg(*args, **kwargs)
  
  
      def buildProtocol(self, addr):
          p = self.protocol(self)
          p.factory = self
          return p
  
  
      def connectionMade(self, protocol):
          """
          Track a newly connected L{DNSProtocol}.
  
          @param protocol: The protocol instance to be tracked.
          @type protocol: L{dns.DNSProtocol}
          """
          self.connections.append(protocol)
  
  
      def connectionLost(self, protocol):
          """
          Stop tracking a no-longer connected L{DNSProtocol}.
  
          @param protocol: The tracked protocol instance to be which has been
              lost.
          @type protocol: L{dns.DNSProtocol}
          """
          self.connections.remove(protocol)
  
  
      def sendReply(self, protocol, message, address):
          """
          Send a response C{message} to a given C{address} via the supplied
          C{protocol}.
  
          Message payload will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          @param protocol: The DNS protocol instance to which to send the message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The DNS message to be sent.
          @type message: L{dns.Message}
  
          @param address: The address to which the message will be sent or L{None}
              if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          if self.verbose > 1:
              s = ' '.join([str(a.payload) for a in message.answers])
              auth = ' '.join([str(a.payload) for a in message.authority])
              add = ' '.join([str(a.payload) for a in message.additional])
              if not s:
                  log.msg("Replying with no answers")
              else:
                  log.msg("Answers are " + s)
                  log.msg("Authority is " + auth)
                  log.msg("Additional is " + add)
  
          if address is None:
              protocol.writeMessage(message)
          else:
              protocol.writeMessage(message, address)
  
          self._verboseLog(
              "Processed query in %0.3f seconds" % (
                  time.time() - message.timeReceived))
  
  
      def _responseFromMessage(self, message, rCode=dns.OK,
                               answers=None, authority=None, additional=None):
          """
          Generate a L{Message} instance suitable for use as the response to
          C{message}.
  
          C{queries} will be copied from the request to the response.
  
          C{rCode}, C{answers}, C{authority} and C{additional} will be assigned to
          the response, if supplied.
  
          The C{recAv} flag will be set on the response if the C{canRecurse} flag
          on this L{DNSServerFactory} is set to L{True}.
  
          The C{auth} flag will be set on the response if *any* of the supplied
          C{answers} have their C{auth} flag set to L{True}.
  
          The response will have the same C{maxSize} as the request.
  
          Additionally, the response will have a C{timeReceived} attribute whose
          value is that of the original request and the
  
          @see: L{dns._responseFromMessage}
  
          @param message: The request message
          @type message: L{Message}
  
          @param rCode: The response code which will be assigned to the response.
          @type message: L{int}
  
          @param answers: An optional list of answer records which will be
              assigned to the response.
          @type answers: L{list} of L{dns.RRHeader}
  
          @param authority: An optional list of authority records which will be
              assigned to the response.
          @type authority: L{list} of L{dns.RRHeader}
  
          @param additional: An optional list of additional records which will be
              assigned to the response.
          @type additional: L{list} of L{dns.RRHeader}
  
          @return: A response L{Message} instance.
          @rtype: L{Message}
          """
          if answers is None:
              answers = []
          if authority is None:
              authority = []
          if additional is None:
              additional = []
          authoritativeAnswer = False
          for x in answers:
              if x.isAuthoritative():
                  authoritativeAnswer = True
                  break
  
          response = dns._responseFromMessage(
              responseConstructor=self._messageFactory,
              message=message,
              recAv=self.canRecurse,
              rCode=rCode,
              auth=authoritativeAnswer
          )
  
          # XXX: Timereceived is a hack which probably shouldn't be tacked onto
          # the message. Use getattr here so that we don't have to set the
          # timereceived on every message in the tests. See #6957.
          response.timeReceived = getattr(message, 'timeReceived', None)
  
          # XXX: This is another hack. dns.Message.decode sets maxSize=0 which
          # means that responses are never truncated. I'll maintain that behaviour
          # here until #6949 is resolved.
          response.maxSize = message.maxSize
  
          response.answers = answers
          response.authority = authority
          response.additional = additional
  
          return response
  
  
      def gotResolverResponse(self, (ans, auth, add), protocol, message, address):
          """
          A callback used by L{DNSServerFactory.handleQuery} for handling the
          deferred response from C{self.resolver.query}.
  
          Constructs a response message by combining the original query message
          with the resolved answer, authority and additional records.
  
          Marks the response message as authoritative if any of the resolved
          answers are found to be authoritative.
  
          The resolved answers count will be logged if C{DNSServerFactory.verbose}
          is C{>1}.
  
          @param ans: A list of answer records
          @type ans: L{list} of L{dns.RRHeader} instances
  
          @param auth: A list of authority records
          @type auth: L{list} of L{dns.RRHeader} instances
  
          @param add: A list of additional records
          @type add: L{list} of L{dns.RRHeader} instances
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          response = self._responseFromMessage(
              message=message, rCode=dns.OK,
              answers=ans, authority=auth, additional=add)
          self.sendReply(protocol, response, address)
  
          l = len(ans) + len(auth) + len(add)
          self._verboseLog("Lookup found %d record%s" % (l, l != 1 and "s" or ""))
  
          if self.cache and l:
              self.cache.cacheResult(
                  message.queries[0], (ans, auth, add)
              )
  
  
      def gotResolverError(self, failure, protocol, message, address):
          """
          A callback used by L{DNSServerFactory.handleQuery} for handling deferred
          errors from C{self.resolver.query}.
  
          Constructs a response message from the original query message by
          assigning a suitable error code to C{rCode}.
  
          An error message will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          @param failure: The reason for the failed resolution (as reported by
              C{self.resolver.query}).
          @type failure: L{Failure<twisted.python.failure.Failure>}
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          if failure.check(dns.DomainError, dns.AuthoritativeDomainError):
              rCode = dns.ENAME
          else:
              rCode = dns.ESERVER
              log.err(failure)
  
          response = self._responseFromMessage(message=message, rCode=rCode)
  
          self.sendReply(protocol, response, address)
          self._verboseLog("Lookup failed")
  
  
      def handleQuery(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} when a query message is
          received.
  
          Takes the first query from the received message and dispatches it to
          C{self.resolver.query}.
  
          Adds callbacks L{DNSServerFactory.gotResolverResponse} and
          L{DNSServerFactory.gotResolverError} to the resulting deferred.
  
          Note: Multiple queries in a single message are not supported because
          there is no standard way to respond with multiple rCodes, auth,
          etc. This is consistent with other DNS server implementations. See
          U{http://tools.ietf.org/html/draft-ietf-dnsext-edns1-03} for a proposed
          solution.
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
  
          @return: A C{deferred} which fires with the resolved result or error of
              the first query in C{message}.
          @rtype: L{Deferred<twisted.internet.defer.Deferred>}
          """
          query = message.queries[0]
  
          return self.resolver.query(query).addCallback(
              self.gotResolverResponse, protocol, message, address
          ).addErrback(
              self.gotResolverError, protocol, message, address
          )
  
  
      def handleInverseQuery(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} when an inverse query
          message is received.
  
          Replies with a I{Not Implemented} error by default.
  
          An error message will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          Override in a subclass.
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          message.rCode = dns.ENOTIMP
          self.sendReply(protocol, message, address)
          self._verboseLog("Inverse query from %r" % (address,))
  
  
      def handleStatus(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} when a status message is
          received.
  
          Replies with a I{Not Implemented} error by default.
  
          An error message will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          Override in a subclass.
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          message.rCode = dns.ENOTIMP
          self.sendReply(protocol, message, address)
          self._verboseLog("Status request from %r" % (address,))
  
  
      def handleNotify(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} when a notify message is
          received.
  
          Replies with a I{Not Implemented} error by default.
  
          An error message will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          Override in a subclass.
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          message.rCode = dns.ENOTIMP
          self.sendReply(protocol, message, address)
          self._verboseLog("Notify message from %r" % (address,))
  
  
      def handleOther(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} when a message with
          unrecognised I{OPCODE} is received.
  
          Replies with a I{Not Implemented} error by default.
  
          An error message will be logged if C{DNSServerFactory.verbose} is C{>1}.
  
          Override in a subclass.
  
          @param protocol: The DNS protocol instance to which to send a response
              message.
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param message: The original DNS query message for which a response
              message will be constructed.
          @type message: L{dns.Message}
  
          @param address: The address to which the response message will be sent
              or L{None} if C{protocol} is a stream protocol.
          @type address: L{tuple} or L{None}
          """
          message.rCode = dns.ENOTIMP
          self.sendReply(protocol, message, address)
          self._verboseLog(
              "Unknown op code (%d) from %r" % (message.opCode, address))
  
  
      def messageReceived(self, message, proto, address=None):
          """
          L{DNSServerFactory.messageReceived} is called by protocols which are
          under the control of this L{DNSServerFactory} whenever they receive a
          DNS query message or an unexpected / duplicate / late DNS response
          message.
  
          L{DNSServerFactory.allowQuery} is called with the received message,
          protocol and origin address. If it returns L{False}, a C{dns.EREFUSED}
          response is sent back to the client.
  
          Otherwise the received message is dispatched to one of
          L{DNSServerFactory.handleQuery}, L{DNSServerFactory.handleInverseQuery},
          L{DNSServerFactory.handleStatus}, L{DNSServerFactory.handleNotify}, or
          L{DNSServerFactory.handleOther} depending on the I{OPCODE} of the
          received message.
  
          If C{DNSServerFactory.verbose} is C{>0} all received messages will be
          logged in more or less detail depending on the value of C{verbose}.
  
          @param message: The DNS message that was received.
          @type message: L{dns.Message}
  
          @param proto: The DNS protocol instance which received the message
          @type proto: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param address: The address from which the message was received. Only
              provided for messages received by datagram protocols. The origin of
              Messages received from stream protocols can be gleaned from the
              protocol C{transport} attribute.
          @type address: L{tuple} or L{None}
          """
          message.timeReceived = time.time()
  
          if self.verbose:
              if self.verbose > 1:
                  s = ' '.join([str(q) for q in message.queries])
              else:
                  s = ' '.join([dns.QUERY_TYPES.get(q.type, 'UNKNOWN')
                                for q in message.queries])
              if not len(s):
                  log.msg(
                      "Empty query from %r" % (
                          (address or proto.transport.getPeer()),))
              else:
                  log.msg(
                      "%s query from %r" % (
                          s, address or proto.transport.getPeer()))
  
          if not self.allowQuery(message, proto, address):
              message.rCode = dns.EREFUSED
              self.sendReply(proto, message, address)
          elif message.opCode == dns.OP_QUERY:
              self.handleQuery(message, proto, address)
          elif message.opCode == dns.OP_INVERSE:
              self.handleInverseQuery(message, proto, address)
          elif message.opCode == dns.OP_STATUS:
              self.handleStatus(message, proto, address)
          elif message.opCode == dns.OP_NOTIFY:
              self.handleNotify(message, proto, address)
          else:
              self.handleOther(message, proto, address)
  
  
      def allowQuery(self, message, protocol, address):
          """
          Called by L{DNSServerFactory.messageReceived} to decide whether to
          process a received message or to reply with C{dns.EREFUSED}.
  
          This default implementation permits anything but empty queries.
  
          Override in a subclass to implement alternative policies.
  
          @param message: The DNS message that was received.
          @type message: L{dns.Message}
  
          @param protocol: The DNS protocol instance which received the message
          @type protocol: L{dns.DNSDatagramProtocol} or L{dns.DNSProtocol}
  
          @param address: The address from which the message was received. Only
              provided for messages received by datagram protocols. The origin of
              Messages received from stream protocols can be gleaned from the
              protocol C{transport} attribute.
          @type address: L{tuple} or L{None}
  
          @return: L{True} if the received message contained one or more queries,
              else L{False}.
          @rtype: L{bool}
          """
          return len(message.queries)
  