IPv4 network packet: Ruby parsing library

KS implementation details

License: CC0-1.0
Minimal Kaitai Struct required: 0.8

References

This page hosts a formal specification of IPv4 network 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 = Ipv4Packet.from_file("path/to/local/file.IPv4 network packet")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = Ipv4Packet.new(Kaitai::Struct::Stream.new(bytes))

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

data.b1 # => get b1

Ruby source code to parse IPv4 network packet

ipv4_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

class Ipv4Packet < Kaitai::Struct::Struct
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @b1 = @_io.read_u1
    @b2 = @_io.read_u1
    @total_length = @_io.read_u2be
    @identification = @_io.read_u2be
    @b67 = @_io.read_u2be
    @ttl = @_io.read_u1
    @protocol = @_io.read_u1
    @header_checksum = @_io.read_u2be
    @src_ip_addr = @_io.read_bytes(4)
    @dst_ip_addr = @_io.read_bytes(4)
    @_raw_options = @_io.read_bytes((ihl_bytes - 20))
    _io__raw_options = Kaitai::Struct::Stream.new(@_raw_options)
    @options = Ipv4Options.new(_io__raw_options, self, @_root)
    @_raw_body = @_io.read_bytes((total_length - ihl_bytes))
    _io__raw_body = Kaitai::Struct::Stream.new(@_raw_body)
    @body = ProtocolBody.new(_io__raw_body, protocol)
    self
  end
  class Ipv4Options < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @entries = []
      i = 0
      while not @_io.eof?
        @entries << Ipv4Option.new(@_io, self, @_root)
        i += 1
      end
      self
    end
    attr_reader :entries
  end
  class Ipv4Option < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @b1 = @_io.read_u1
      @len = @_io.read_u1
      @body = @_io.read_bytes((len > 2 ? (len - 2) : 0))
      self
    end
    def copy
      return @copy unless @copy.nil?
      @copy = ((b1 & 128) >> 7)
      @copy
    end
    def opt_class
      return @opt_class unless @opt_class.nil?
      @opt_class = ((b1 & 96) >> 5)
      @opt_class
    end
    def number
      return @number unless @number.nil?
      @number = (b1 & 31)
      @number
    end
    attr_reader :b1
    attr_reader :len
    attr_reader :body
  end
  def version
    return @version unless @version.nil?
    @version = ((b1 & 240) >> 4)
    @version
  end
  def ihl
    return @ihl unless @ihl.nil?
    @ihl = (b1 & 15)
    @ihl
  end
  def ihl_bytes
    return @ihl_bytes unless @ihl_bytes.nil?
    @ihl_bytes = (ihl * 4)
    @ihl_bytes
  end
  attr_reader :b1
  attr_reader :b2
  attr_reader :total_length
  attr_reader :identification
  attr_reader :b67
  attr_reader :ttl
  attr_reader :protocol
  attr_reader :header_checksum
  attr_reader :src_ip_addr
  attr_reader :dst_ip_addr
  attr_reader :options
  attr_reader :body
  attr_reader :_raw_options
  attr_reader :_raw_body
end