DNS (Domain Name Service) packet: Ruby parsing library

(No support for Auth-Name + Add-Name for simplicity)

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of DNS (Domain Name Service) packet using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for Ruby generated by Kaitai Struct depends on the Ruby runtime library. You have to install it before you can parse data.

The Ruby runtime library can be installed from RubyGems:

gem install kaitai-struct

Code

Parse a local file and get structure in memory:

data = DnsPacket.from_file("path/to/local/file.DNS (Domain Name Service) packet")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = DnsPacket.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.transaction_id # => ID to keep track of request/responces

Ruby source code to parse DNS (Domain Name Service) packet

dns_packet.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.9')
  raise "Incompatible Kaitai Struct Ruby API: 0.9 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# (No support for Auth-Name + Add-Name for simplicity)
class DnsPacket < Kaitai::Struct::Struct

  CLASS_TYPE = {
    1 => :class_type_in_class,
    2 => :class_type_cs,
    3 => :class_type_ch,
    4 => :class_type_hs,
  }
  I__CLASS_TYPE = CLASS_TYPE.invert

  TYPE_TYPE = {
    1 => :type_type_a,
    2 => :type_type_ns,
    3 => :type_type_md,
    4 => :type_type_mf,
    5 => :type_type_cname,
    6 => :type_type_soa,
    7 => :type_type_mb,
    8 => :type_type_mg,
    9 => :type_type_mr,
    10 => :type_type_null,
    11 => :type_type_wks,
    12 => :type_type_ptr,
    13 => :type_type_hinfo,
    14 => :type_type_minfo,
    15 => :type_type_mx,
    16 => :type_type_txt,
    28 => :type_type_aaaa,
    33 => :type_type_srv,
  }
  I__TYPE_TYPE = TYPE_TYPE.invert
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @transaction_id = @_io.read_u2be
    @flags = PacketFlags.new(@_io, self, @_root)
    if flags.is_opcode_valid
      @qdcount = @_io.read_u2be
    end
    if flags.is_opcode_valid
      @ancount = @_io.read_u2be
    end
    if flags.is_opcode_valid
      @nscount = @_io.read_u2be
    end
    if flags.is_opcode_valid
      @arcount = @_io.read_u2be
    end
    if flags.is_opcode_valid
      @queries = Array.new(qdcount)
      (qdcount).times { |i|
        @queries[i] = Query.new(@_io, self, @_root)
      }
    end
    if flags.is_opcode_valid
      @answers = Array.new(ancount)
      (ancount).times { |i|
        @answers[i] = Answer.new(@_io, self, @_root)
      }
    end
    if flags.is_opcode_valid
      @authorities = Array.new(nscount)
      (nscount).times { |i|
        @authorities[i] = Answer.new(@_io, self, @_root)
      }
    end
    if flags.is_opcode_valid
      @additionals = Array.new(arcount)
      (arcount).times { |i|
        @additionals[i] = Answer.new(@_io, self, @_root)
      }
    end
    self
  end
  class MxInfo < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @preference = @_io.read_u2be
      @mx = DomainName.new(@_io, self, @_root)
      self
    end
    attr_reader :preference
    attr_reader :mx
  end
  class PointerStruct < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @value = @_io.read_u1
      self
    end
    def contents
      return @contents unless @contents.nil?
      io = _root._io
      _pos = io.pos
      io.seek((value + ((_parent.length - 192) << 8)))
      @contents = DomainName.new(io, self, @_root)
      io.seek(_pos)
      @contents
    end

    ##
    # Read one byte, then offset to that position, read one domain-name and return
    attr_reader :value
  end
  class Label < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @length = @_io.read_u1
      if is_pointer
        @pointer = PointerStruct.new(@_io, self, @_root)
      end
      if !(is_pointer)
        @name = (@_io.read_bytes(length)).force_encoding("utf-8")
      end
      self
    end
    def is_pointer
      return @is_pointer unless @is_pointer.nil?
      @is_pointer = length >= 192
      @is_pointer
    end

    ##
    # RFC1035 4.1.4: If the first two bits are raised it's a pointer-offset to a previously defined name
    attr_reader :length
    attr_reader :pointer

    ##
    # Otherwise its a string the length of the length value
    attr_reader :name
  end
  class Query < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @name = DomainName.new(@_io, self, @_root)
      @type = Kaitai::Struct::Stream::resolve_enum(DnsPacket::TYPE_TYPE, @_io.read_u2be)
      @query_class = Kaitai::Struct::Stream::resolve_enum(DnsPacket::CLASS_TYPE, @_io.read_u2be)
      self
    end
    attr_reader :name
    attr_reader :type
    attr_reader :query_class
  end
  class DomainName < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @name = []
      i = 0
      begin
        _ = Label.new(@_io, self, @_root)
        @name << _
        i += 1
      end until  ((_.length == 0) || (_.length >= 192)) 
      self
    end

    ##
    # Repeat until the length is 0 or it is a pointer (bit-hack to get around lack of OR operator)
    attr_reader :name
  end
  class AddressV6 < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @ip_v6 = @_io.read_bytes(16)
      self
    end
    attr_reader :ip_v6
  end
  class Service < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @priority = @_io.read_u2be
      @weight = @_io.read_u2be
      @port = @_io.read_u2be
      @target = DomainName.new(@_io, self, @_root)
      self
    end
    attr_reader :priority
    attr_reader :weight
    attr_reader :port
    attr_reader :target
  end
  class Txt < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @length = @_io.read_u1
      @text = (@_io.read_bytes(length)).force_encoding("utf-8")
      self
    end
    attr_reader :length
    attr_reader :text
  end
  class TxtBody < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @data = []
      i = 0
      while not @_io.eof?
        @data << Txt.new(@_io, self, @_root)
        i += 1
      end
      self
    end
    attr_reader :data
  end
  class Address < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @ip = @_io.read_bytes(4)
      self
    end
    attr_reader :ip
  end
  class Answer < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @name = DomainName.new(@_io, self, @_root)
      @type = Kaitai::Struct::Stream::resolve_enum(DnsPacket::TYPE_TYPE, @_io.read_u2be)
      @answer_class = Kaitai::Struct::Stream::resolve_enum(DnsPacket::CLASS_TYPE, @_io.read_u2be)
      @ttl = @_io.read_s4be
      @rdlength = @_io.read_u2be
      case type
      when :type_type_srv
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = Service.new(_io__raw_payload, self, @_root)
      when :type_type_a
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = Address.new(_io__raw_payload, self, @_root)
      when :type_type_cname
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = DomainName.new(_io__raw_payload, self, @_root)
      when :type_type_ns
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = DomainName.new(_io__raw_payload, self, @_root)
      when :type_type_soa
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = AuthorityInfo.new(_io__raw_payload, self, @_root)
      when :type_type_mx
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = MxInfo.new(_io__raw_payload, self, @_root)
      when :type_type_txt
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = TxtBody.new(_io__raw_payload, self, @_root)
      when :type_type_ptr
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = DomainName.new(_io__raw_payload, self, @_root)
      when :type_type_aaaa
        @_raw_payload = @_io.read_bytes(rdlength)
        _io__raw_payload = Kaitai::Struct::Stream.new(@_raw_payload)
        @payload = AddressV6.new(_io__raw_payload, self, @_root)
      else
        @payload = @_io.read_bytes(rdlength)
      end
      self
    end
    attr_reader :name
    attr_reader :type
    attr_reader :answer_class

    ##
    # Time to live (in seconds)
    attr_reader :ttl

    ##
    # Length in octets of the following payload
    attr_reader :rdlength
    attr_reader :payload
    attr_reader :_raw_payload
  end
  class PacketFlags < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @flag = @_io.read_u2be
      self
    end
    def qr
      return @qr unless @qr.nil?
      @qr = ((flag & 32768) >> 15)
      @qr
    end
    def ra
      return @ra unless @ra.nil?
      @ra = ((flag & 128) >> 7)
      @ra
    end
    def tc
      return @tc unless @tc.nil?
      @tc = ((flag & 512) >> 9)
      @tc
    end
    def is_opcode_valid
      return @is_opcode_valid unless @is_opcode_valid.nil?
      @is_opcode_valid =  ((opcode == 0) || (opcode == 1) || (opcode == 2)) 
      @is_opcode_valid
    end
    def rcode
      return @rcode unless @rcode.nil?
      @rcode = ((flag & 15) >> 0)
      @rcode
    end
    def opcode
      return @opcode unless @opcode.nil?
      @opcode = ((flag & 30720) >> 11)
      @opcode
    end
    def aa
      return @aa unless @aa.nil?
      @aa = ((flag & 1024) >> 10)
      @aa
    end
    def z
      return @z unless @z.nil?
      @z = ((flag & 64) >> 6)
      @z
    end
    def rd
      return @rd unless @rd.nil?
      @rd = ((flag & 256) >> 8)
      @rd
    end
    def cd
      return @cd unless @cd.nil?
      @cd = ((flag & 16) >> 4)
      @cd
    end
    def ad
      return @ad unless @ad.nil?
      @ad = ((flag & 32) >> 5)
      @ad
    end
    attr_reader :flag
  end
  class AuthorityInfo < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @primary_ns = DomainName.new(@_io, self, @_root)
      @resoponsible_mailbox = DomainName.new(@_io, self, @_root)
      @serial = @_io.read_u4be
      @refresh_interval = @_io.read_u4be
      @retry_interval = @_io.read_u4be
      @expire_limit = @_io.read_u4be
      @min_ttl = @_io.read_u4be
      self
    end
    attr_reader :primary_ns
    attr_reader :resoponsible_mailbox
    attr_reader :serial
    attr_reader :refresh_interval
    attr_reader :retry_interval
    attr_reader :expire_limit
    attr_reader :min_ttl
  end

  ##
  # ID to keep track of request/responces
  attr_reader :transaction_id
  attr_reader :flags

  ##
  # How many questions are there
  attr_reader :qdcount

  ##
  # Number of resource records answering the question
  attr_reader :ancount

  ##
  # Number of resource records pointing toward an authority
  attr_reader :nscount

  ##
  # Number of resource records holding additional information
  attr_reader :arcount
  attr_reader :queries
  attr_reader :answers
  attr_reader :authorities
  attr_reader :additionals
end