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# -*- coding: binary -*-
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#---
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# $Id: Header.rb,v 1.5 2006/07/30 16:54:28 bluemonk Exp $
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#+++
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require 'net/dns/dns'
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module Net # :nodoc:
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  module DNS 
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    #
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    # =Name
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    #
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    # Net::DNS::Header - DNS packet header class
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    #
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    # =Synopsis
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    # 
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    #   require 'net/dns/header'
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    #
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    # =Description
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    # 
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    # The Net::DNS::Header class represents the header portion of a 
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    # DNS packet. An Header object is created whenever a new packet
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    # is parsed or as user request.
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    # 
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    #   header = Net::DNS::Header.new
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    #     # ;; id = 18123
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    #     # ;; qr = 0       opCode: 0       aa = 0  tc = 0  rd = 1
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    #     # ;; ra = 0       ad = 0  cd = 0  rcode = 0
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    #     # ;; qdCount = 1  anCount = 0     nsCount = 0     arCount = 0
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    #
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    #   header.format
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |             18123             |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |0|   0   |0|0|1|0|0| 0 |   0   |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |               1               |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |               0               |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |               0               |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #     #  |               0               |
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    #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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    #
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    #   # packet is an instance of Net::DNS::Packet
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    #   header = packet.header
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    #   puts "Answer is #{header.auth? ? '' : 'non'} authoritative"
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    #
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    # A lot of methods were written to keep a compatibility layer with
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    # the Perl version of the library, as long as methods name which are
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    # more or less the same. 
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    #
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    # =Error classes
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    #
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    # Some error classes has been defined for the Net::DNS::Header class,
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    # which are listed here to keep a light and browsable main documentation.
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    # We have:
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    #
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    # * HeaderArgumentError:  canonical argument error
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    # * HeaderWrongCount:     a wrong +count+ parameter has been passed
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    # * HeaderWrongRecursive: a wrong +recursive+ parameter has been passed
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    # * HeaderWrongOpcode:    a not valid +opCode+ has been specified
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    # * HeaderDuplicateID:    the requested ID is already in use
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    #
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    # =Copyright
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    # 
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    # Copyright (c) 2006 Marco Ceresa
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    #
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    # All rights reserved. This program is free software; you may redistribute 
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    # it and/or modify it under the same terms as Ruby itself.
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    #
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    class Header
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      #
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      # =Name
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      #
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      # Net::DNS::Header::RCode - DNS Header RCode handling class
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      #
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      # =Synopsis
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      #
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      # It should be used internally by Net::DNS::Header class. However, it's still
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      # possible to instantiate it directly.
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      #
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      #   require 'net/dns/header'
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      #   rcode = Net::DNS::Header::RCode.new 0
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      #
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      # =Description
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      #
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      # The RCode class represents the RCode field in the Header portion of a  
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      # DNS packet. This field (called Response Code) is used to get information  
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      # about the status of a DNS operation, such as a query or an update. These
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      # are the values in the original Mockapetris's standard (RFC1035):
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      #
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      # * 0               No error condition
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      # * 1               Format error - The name server was unable to interpret 
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      #                   the query.
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      # * 2               Server failure - The name server was
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      #                   unable to process this query due to a
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      #                   problem with the name server.
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      # * 3               Name Error - Meaningful only for
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      #                   responses from an authoritative name
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      #                   server, this code signifies that the
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      #                   domain name referenced in the query does
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      #                   not exist.
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      # * 4               Not Implemented - The name server does
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      #                   not support the requested kind of query.
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      # * 5               Refused - The name server refuses to
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      #                   perform the specified operation for
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      #                   policy reasons.  For example, a name
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      #                   server may not wish to provide the
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      #                   information to the particular requester,
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      #                   or a name server may not wish to perform
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      #                   a particular operation (e.g., zone
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      #                   transfer) for particular data.
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      # * 6-15            Reserved for future use.
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      #
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      # In the next DNS RFCs, codes 6-15 has been assigned to the following 
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      # errors:
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      #
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      # * 6               YXDomain
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      # * 7               YXRRSet
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      # * 8               NXRRSet
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      # * 9               NotAuth
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      # * 10              NotZone
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      #
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      # More RCodes has to come for TSIGs and other operations.
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      #
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      class RCode
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        # Constant for +rcode+ Response Code No Error
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        NOERROR = 0
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        # Constant for +rcode+ Response Code Format Error
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        FORMAT = 1
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        # Constant for +rcode+ Response Code Server Format Error
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        SERVER = 2
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        # Constant for +rcode+ Response Code Name Error
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        NAME = 3
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        # Constant for +rcode+ Response Code Not Implemented Error
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        NOTIMPLEMENTED = 4
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        # Constant for +rcode+ Response Code Refused Error
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        REFUSED = 5
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        RCodeType = %w[NoError FormErr ServFail NXDomain NotImp  
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                      Refused YXDomain YXRRSet NXRRSet NotAuth NotZone]   
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        RCodeErrorString = ["No errors",
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          "The name server was unable to interpret the query",
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          "The name server was unable to process this query due to problem with the name server",
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          "Domain name referenced in the query does not exist",
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          "The name server does not support the requested kind of query",
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          "The name server refuses to perform the specified operation for policy reasons",
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          "",
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          "",
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          "",
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          "",
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          ""]
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        attr_reader :code, :type, :explanation
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        def initialize(code)
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          if (0..10).include? code
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            @code         = code
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            @type         = RCodeType[code]
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            @explanation  = RCodeErrorString[code] 
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          else
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            raise HeaderArgumentError, "RCode #{code} out of range"
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          end
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        end
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        def to_s
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          @code.to_s
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        end
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      end
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      # Constant for +opCode+ query
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      QUERY   = 0
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      # Constant for +opCode+ iquery
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      IQUERY  = 1
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      # Constant for +opCode+ status
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      STATUS  = 2
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      # Array with given strings
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      OPARR = %w[QUERY IQUERY STATUS]
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      @@id_arr = []
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      # Reader for +id+ attribute  
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      attr_reader :id
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      # Reader for the operational code
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      attr_reader :opCode
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      # Reader for the rCode instance
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      attr_reader :rCode
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      # Reader for question section entries number
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      attr_reader :qdCount
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      # Reader for answer section entries number
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      attr_reader :anCount
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      # Reader for authority section entries number
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      attr_reader :nsCount
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      # Reader for addictional section entries number
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      attr_reader :arCount
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      # Creates a new Net::DNS::Header object with the desired values,
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      # which can be specified as an Hash argument. When called without
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      # arguments, defaults are used. If a data string is passed, values 
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      # are taken from parsing the string.
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      #
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      # Examples:
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      #
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      #   # Create a new Net::DNS::Header object
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      #   header = Net::DNS::Header.new
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      #
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      #   # Create a new Net::DNS::Header object passing values
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      #   header = Net::DNS::Header.new(:opCode => 1, :rd => 0)
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      #
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      #   # Create a new Net::DNS::Header object with binary data
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      #   header = Net::DNS::Header.new(data)
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      #
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      # Default values are:
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      #
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      #   :id => auto generated
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      #   :qr      => 0 # Query response flag
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      #   :aa      => 0 # Authoritative answer flag
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      #   :tc      => 0 # Truncated packet flag
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      #   :ra      => 0 # Recursiond available flag
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      #   :rCode   => 0 # Response code (status of the query)
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      #   :opCode  => 0 # Operational code (purpose of the query)
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      #   :cd      => 0 # Checking disable flag
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      #   :ad      => 0 # Only relevant in DNSSEC context
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      #   :rd      => 1 # Recursion desired flag
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      #   :qdCount => 1 # Number of questions in the dns packet
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      #   :anCount => 0 # Number of answer RRs in the dns packet
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      #   :nsCount => 0 # Number of authoritative RRs in the dns packet
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      #   :arCount => 0 # Number of additional RRs in the dns packet
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      #
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      # See also each option for a detailed explanation of usage.
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      #
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      def initialize(arg = {})
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        if arg.kind_of? Hash
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          new_from_hash(arg)
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        else
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          raise HeaderArgumentError, "Wrong argument class: #{arg.class}"
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        end
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      end
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      # Creates a new Net::DNS::Header object from binary data, which is 
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      # passed as a string object as argument.
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      # The configurations parameters are taken from parsing the string.
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      #
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      # Example:
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      #
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      #   # Create a new Net::DNS::Header object with binary data
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      #   header = Net::DNS::Header.new(data)
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      #
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      #   header.auth? 
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      #     #=> "true" if it comes from authoritative name server 
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      #
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      def self.parse(arg)
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        if arg.kind_of? String
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          o = allocate
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          o.send(:new_from_binary, arg)
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          o
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        else
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          raise HeaderArgumentError, "Wrong argument class: #{arg.class}"
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        end
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      end
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      # Inspect method, prints out all the options and relative values.
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      # 
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      #   p Net::DNS::Header.new
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      #     # ;; id = 18123
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      #     # ;; qr = 0       opCode: 0       aa = 0  tc = 0  rd = 1
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      #     # ;; ra = 0       ad = 0  cd = 0  rcode = 0
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      #     # ;; qdCount = 1  anCount = 0     nsCount = 0     arCount = 0
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      #
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      # This method will maybe be changed in the future to a more pretty
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      # way of display output.
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      #
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      def inspect 
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        ";; id = #@id\n" +
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          if false # @opCode == "UPDATE"
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            #do stuff
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          else
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            ";; qr = #@qr\t" +
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              "opCode: #{opCode_str}\t" +
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              "aa = #@aa\t" +
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              "tc = #@tc\t" +
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              "rd = #@rd\n" +
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              ";; ra = #@ra\t" +
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              "ad = #@ad\t" +
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              "cd = #@cd\t" +
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              "rcode = #{@rCode.type}\n" +
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              ";; qdCount = #@qdCount\t"+
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              "anCount = #@anCount\t"+
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              "nsCount = #@nsCount\t"+
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              "arCount = #@arCount\n"
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          end
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      end
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      # The Net::DNS::Header#format method prints out the header
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      # in a special ascii representation of data, in a way 
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      # similar to those often found on RFCs. 
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      #   
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      #   p Net::DNS::Header.new.format
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |             18123             |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |0|   0   |0|0|1|0|0| 0 |   0   |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |               1               |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |               0               |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |               0               |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #     #  |               0               |
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      #     #  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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      #
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      # This can be very useful for didactical purpouses :)
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      #
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      def format 
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        del = ("+-" * 16) + "+\n"
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        len = del.length
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        str = del + "|" + @id.to_s.center(len-3) + "|\n"
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        str << del + "|" + @qr.to_s
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        str << "|" + @opCode.to_s.center(7)
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        str << "|" + @aa.to_s
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        str << "|" + @tc.to_s
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        str << "|" + @rd.to_s
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        str << "|" + @ra.to_s
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        str << "|" + @ad.to_s
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        str << "|" + @cd.to_s.center(3)
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        str << "|" + @rCode.to_s.center(7) + "|\n"
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        str << del + "|" + @qdCount.to_s.center(len-3) + "|\n"
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        str << del + "|" + @anCount.to_s.center(len-3) + "|\n"
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        str << del + "|" + @nsCount.to_s.center(len-3) + "|\n"
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        str << del + "|" + @arCount.to_s.center(len-3) + "|\n" + del
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        str
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      end
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      # Returns the header data in binary format, appropriate 
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      # for use in a DNS query packet.
345
      #
346
      #   hdata = header.data
347
      #   puts "Header is #{hdata.size} bytes"
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      #
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      def data
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        arr = []
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        arr.push(@id)
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        arr.push((@qr<<7)|(@opCode<<3)|(@aa<<2)|(@tc<<1)|@rd)
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        arr.push((@ra<<7)|(@ad<<5)|(@cd<<4)|@rCode.code)
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        arr.push(@qdCount)
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        arr.push(@anCount)
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        arr.push(@nsCount)
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        arr.push(@arCount)
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        arr.pack("n C2 n4")
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      end
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361
      # Set the ID for the current header. Useful when
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      # performing security tests.
363
      #
364
      def id=(val)
365
        if @@id_arr.include? val
366
          raise HeaderDuplicateID, "ID #{val} already used"
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        end
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        if (1..65535).include? val
369
          @id = val
370
          @@id_arr.push val
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        else
372
          raise HeaderArgumentError, "ID #{val} out of range"
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        end
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      end
375
      
376
      # Checks whether the header is a query (+qr+ bit set to 0)
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      #
378
      def query?
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        @qr == 0
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      end
381

382
      # Set the +qr+ query response flag to be either +true+ or 
383
      # +false+. You can also use the values 0 and 1. This flag 
384
      # indicates if the DNS packet contains a query or an answer,
385
      # so it should be set to +true+ in DNS answer packets.
386
      # If +qr+ is +true+, the packet is a response.
387
      #
388
      def qr=(val)
389
        case val
390
        when true
391
          @qr = 1
392
        when false
393
          @qr = 0
394
        when 0,1
395
          @qr = val
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        else
397
          raise HeaderArgumentError, ":qr must be true(or 1) or false(or 0)"
398
        end
399
      end
400

401
      # Checks whether the header is a response 
402
      # (+qr+ bit set to 1)
403
      #
404
      def response?
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        @qr == 1
406
      end
407

408
      # Returns a string representation of the +opCode+
409
      #
410
      #   puts "Packet is a #{header.opCode_str}"
411
      #     #=> Packet is a QUERY
412
      #
413
      def opCode_str
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        OPARR[@opCode]
415
      end
416

417
      # Set the +opCode+ variable to a new value. This fields indicates
418
      # the type of the question present in the DNS packet; +val+ can be 
419
      # one of the values QUERY, IQUERY or STATUS. 
420
      #
421
      # * QUERY is the standard DNS query
422
      # * IQUERY is the inverse query
423
      # * STATUS is used to query the nameserver for its status
424
      #
425
      # Example:
426
      # 
427
      #   include Net::DNS
428
      #   header = Header.new
429
      #   header.opCode = Header::STATUS
430
      #
431
      def opCode=(val)
432
        if (0..2).include? val
433
          @opCode = val
434
        else
435
          raise HeaderWrongOpcode, "Wrong opCode value (#{val}), must be QUERY, IQUERY or STATUS"
436
        end
437
      end
438

439
      # Checks whether the response is authoritative
440
      #
441
      #   if header.auth?
442
      #     puts "Response is authoritative"
443
      #   else
444
      #     puts "Answer is NOT authoritative"
445
      #   end
446
      #
447
      def auth?
448
        @aa == 1
449
      end
450

451
      # Set the +aa+ flag (authoritative answer) to either +true+
452
      # or +false+. You can also use 0 or 1. 
453
      #
454
      # This flag indicates whether a DNS answer packet contains
455
      # authoritative data, meaning that is was generated by a 
456
      # nameserver authoritative for the domain of the question.
457
      #
458
      # Must only be set to +true+ in DNS answer packets.
459
      #
460
      def aa=(val)
461
        case val
462
        when true
463
          @aa = 1
464
        when false
465
          @aa = 0
466
        when 0,1
467
          @aa = val
468
        else
469
          raise HeaderArgumentError, ":aa must be true(or 1) or false(or 0)"
470
        end
471
      end
472
      
473
      # Checks whether the packet was truncated
474
      #
475
      #   # Sending packet using UDP
476
      #   if header.truncated?
477
      #     puts "Warning, packet has been truncated!"
478
      #     # Sending packet using TCP
479
      #   end
480
      #   # Do something with the answer
481
      #
482
      def truncated?
483
        @tc == 1
484
      end
485

486
      # Set the +tc+ flag (truncated packet) to either +true+ 
487
      # ot +false+. You can also use 0 or 1.
488
      #
489
      # The truncated flag is used in response packets to indicate
490
      # that the amount of data to be trasmitted exceedes the 
491
      # maximum allowed by the protocol in use, typically UDP, and 
492
      # that the data present in the packet has been truncated. 
493
      # A different protocol (such has TCP) need to be used to 
494
      # retrieve full data.
495
      #
496
      # Must only be set in DNS answer packets.
497
      #
498
      def tc=(val)
499
        case val
500
        when true
501
          @tc = 1
502
        when false
503
          @tc = 0
504
        when 0,1
505
          @tc = val
506
        else
507
          raise HeaderArgumentError, ":tc must be true(or 1) or false(or 0)"
508
        end
509
      end
510
      
511
      # Checks whether the packet has a recursion bit
512
      # set, meaning that recursion is desired
513
      #
514
      def recursive?
515
        @rd == 1
516
      end
517

518
      # Sets the recursion desidered bit.
519
      # Remember that recursion query support is
520
      # optional.
521
      #
522
      #   header.recursive = true
523
      #   hdata = header.data # suitable for sending
524
      #
525
      # Consult RFC1034 and RFC1035 for a detailed explanation
526
      # of how recursion works.
527
      #
528
      def recursive=(val)
529
        case val
530
        when true
531
          @rd = 1
532
        when false
533
          @rd = 0
534
        when 1
535
          @rd = 1
536
        when 0
537
          @rd = 0
538
        else
539
          raise HeaderWrongRecursive, "Wrong value (#{val}), please specify true (1) or false (0)"
540
        end
541
      end
542

543
      # Alias for Header#recursive= to keep compatibility
544
      # with the Perl version.
545
      #
546
      def rd=(val)
547
        self.recursive = val
548
      end
549
      
550
      # Checks whether recursion is available.
551
      # This flag is usually set by nameservers to indicate
552
      # that they support recursive-type queries.
553
      #
554
      def r_available?
555
        @ra == 1
556
      end
557

558
      # Set the +ra+ flag (recursion available) to either +true+ or
559
      # +false+. You can also use 0 and 1.
560
      #
561
      # This flag must only be set in DNS answer packets.
562
      #
563
      def ra=(val)
564
        case val
565
        when true
566
          @ra = 1
567
        when false
568
          @ra = 0
569
        when 0,1
570
          @ra = val
571
        else
572
          raise HeaderArgumentError, ":ra must be true(or 1) or false(or 0)"
573
        end
574
      end
575

576
      # Checks whether checking is enabled or disabled.
577
      #
578
      # Checking is enabled by default.
579
      #
580
      def checking?
581
        @cd == 0
582
      end
583

584
      # Set the +cd+ flag (checking disabled) to either +true+ 
585
      # ot +false+. You can also use 0 or 1.
586
      #
587
      def cd=(val)
588
        case val
589
        when true
590
          @cd = 1
591
        when false
592
          @cd = 0
593
        when 0,1
594
          @cd = val
595
        else
596
          raise HeaderArgumentError, ":cd must be true(or 1) or false(or 0)"
597
        end
598
      end
599

600
      # Checks whether +ad+ flag has been set.
601
      #
602
      # This flag is only relevant in DNSSEC context.
603
      #
604
      def verified?
605
        @ad == 1
606
      end
607

608
      # Set the +ad+ flag  to either +true+ 
609
      # ot +false+. You can also use 0 or 1.
610
      #
611
      # The AD bit is only set on answers where signatures have 
612
      # been cryptographically verified or the server is 
613
      # authoritative for the data and is allowed to set the bit by policy.
614
      #
615
      def ad=(val)
616
        case val
617
        when true
618
          @ad = 1
619
        when false
620
          @ad = 0
621
        when 0,1
622
          @ad = val
623
        else
624
          raise HeaderArgumentError, ":ad must be true(or 1) or false(or 0)"
625
        end
626
      end
627
      
628
      # Returns an error array for the header response code, or
629
      # +nil+ if no error is generated.
630
      #
631
      #   error, cause = header.rCode_str
632
      #   puts "Error #{error} cause by: #{cause}" if error
633
      #     #=> Error ForErr caused by: The name server
634
      #     #=> was unable to interpret the query
635
      #
636
      def rCode_str
637
        return rCode.type, rCode.explanation
638
      end
639

640
      # Checks for errors in the DNS packet
641
      #
642
      #   unless header.error?
643
      #     puts "No errors in DNS answer packet"
644
      #   end
645
      #
646
      def error?
647
        @rCode.code > 0
648
      end
649
      
650
      # Set the rCode value. This should only be done in DNS 
651
      # answer packets.
652
      #
653
      def rCode=(val)
654
        @rCode = RCode.new(val)
655
      end
656
      
657
      # Sets the number of entries in a question section
658
      #
659
      def qdCount=(val)
660
        if (0..65535).include? val
661
          @qdCount = val
662
        else
663
          raise HeaderWrongCount, "Wrong number of count (#{val}), must be 0-65535"
664
        end
665
      end
666

667
      # Sets the number of RRs in an answer section
668
      #
669
      def anCount=(val)
670
        if (0..65535).include? val
671
          @anCount = val
672
        else
673
          raise HeaderWrongCount, "Wrong number of count (#{val}), must be 0-65535"
674
        end
675
      end
676

677
      # Sets the number of RRs in an authority section
678
      #
679
      def nsCount=(val)
680
        if (0..65535).include? val
681
          @nsCount = val
682
        else
683
          raise HeaderWrongCount, "Wrong number of count (#{val}), must be 0-65535"
684
        end
685
      end
686

687
      # Sets the number of RRs in an addictional section
688
      #
689
      def arCount=(val)
690
        if (0..65535).include? val
691
          @arCount = val
692
        else
693
          raise HeaderWrongCount, "Wrong number of count (#{val}), must be 0-65535"
694
        end
695
      end
696

697
      private
698
      
699
      def new_from_scratch
700
        @id = genID # generate ad unique id
701
        @qr = @aa = @tc = @ra = @ad = @cd = 0
702
        @rCode = RCode.new(0) # no error 
703
        @anCount = @nsCount = @arCount = 0
704
        @rd = @qdCount = 1
705
        @opCode = QUERY # standard query, default message 
706
      end
707
      
708
      def new_from_binary(str)
709
        unless str.size == Net::DNS::HFIXEDSZ
710
          raise HeaderArgumentError, "Header binary data has wrong size: #{str.size} bytes"
711
        end
712
        arr = str.unpack("n C2 n4")
713
        @id          =  arr[0]
714
        @qr          = (arr[1] >> 7) & 0x01
715
        @opCode      = (arr[1] >> 3) & 0x0F
716
        @aa          = (arr[1] >> 2) & 0x01
717
        @tc          = (arr[1] >> 1) & 0x01
718
        @rd          =  arr[1] & 0x1
719
        @ra          = (arr[2] >> 7) & 0x01
720
        @ad          = (arr[2] >> 5) & 0x01
721
        @cd          = (arr[2] >> 4) & 0x01
722
        @rCode       = RCode.new(arr[2] & 0xf)
723
        @qdCount     =  arr[3]
724
        @anCount     =  arr[4]
725
        @nsCount     =  arr[5]
726
        @arCount     =  arr[6]
727
      end
728
        
729
      def new_from_hash(hash)
730
        new_from_scratch
731
        hash.each do |key,val|
732
          eval "self.#{key.to_s} = val"
733
        end
734
      end
735
        
736
      def genID
737
        while (@@id_arr.include?(q = rand(65535)))
738
        end
739
        @@id_arr.push(q)
740
        q
741
      end
742

743
    end # class Header
744

745
  end # class DNS
746
end # module Net
747

748

749
class HeaderArgumentError < ArgumentError # :nodoc: all
750
end
751

752
class HeaderWrongCount < ArgumentError # :nodoc: all
753
end
754

755
class HeaderWrongRecursive < ArgumentError # :nodoc: all
756
end
757

758
class HeaderWrongOpcode < ArgumentError # :nodoc: all
759
end
760

761
class HeaderDuplicateID < ArgumentError # :nodoc: all
762
end
763

764