Read TCP, UDP, IP header by Ruby

ipv4header.rb

# coding: utf-8
require_relative 'protocol'

# TODO: チェックサムを確認する
class IPv4Header

  attr_reader :version,:header_length,:packet_length,:identification,:frag_dont,:frag_more,:frag_offset,:ttl,:protocol,:checksum,:sndr_addr,:dest_addr,
    :data_length

  def initialize(packet,offset=0)
    @packet = packet.force_encoding("ASCII-8BIT")
    @offset = offset
    header = packet.unpack("x#{offset}n10")
    @version = header[0] >> 12
    @header_length  = ((header[0] >> 8) & 0x0f)*4
    @packet_length = header[1]
    @identification = header[2]
    @frag_dont = (header[3] >> 14) & 0x01 != 0
    @frag_more  = (header[3] >> 13) & 0x01 != 0
    @frag_offset = header[3] & 0x1fff
    @ttl = header[4] >> 8
    @protocol = header[4] & 0x00ff
    @checksum = header[5]
    @sndr_addr = ip_to_s(packet[12..15])
    @dest_addr = ip_to_s(packet[16..19])
    @data_length = @packet_length - @header_length

    @virtual_header = packet[12..19] + [0,6,@data_length].pack("CCn")

  end

  def upper
    upper_header = Protocol.to_class(@protocol)
    offset = @offset+@header_length
    upper_header.new(@packet,offset,@data_length,self)
  end
  
  def data
    start = @offset+@header_length
    @packet[start..start+@data_length]
  end

  def get_virtual_header
    @virtual_header
  end

  def ip_to_s(ip)
    ip = ip.unpack("n2")
    sprintf("%d.%d.%d.%d",ip[0]>>8,ip[0]&0x00ff,ip[1]>>8,ip[1]&0x00ff)
  end

  def to_s
    "IPv4 Header\n" <<
    "  Version            : #{@version}\n" <<
    "  Header Length      : #{@header_length}\n" <<
    "  Packet Length      : #{@packet_length}\n" <<
    "  Identification     : #{@identification}\n" <<
    "  Don't fragment     : #{@frag_dont}\n" <<
    "  More fragments     : #{@frag_more}\n" <<
    "  Fragment Offset    : #{@frag_offset}\n" <<
    "  TTL                : #{@ttl}\n" <<
    "  Protocol           : #{Protocol.to_s(@protocol)}\n" <<
    "  Header Checksum    : #{@checksum}\n" <<
    "  Sender Address     : #{@sndr_addr}\n" <<
    "  Destination Address: #{@dest_addr}\n" <<
    "  (Data Length)      : #{@data_length}"
  end

end

protocol.rb

require_relative 'ipv4header'
require_relative 'udpheader'
require_relative 'tcpheader'

class Protocol
  ICMP = 0x01
  IGMP = 0x02
  TCP  = 0x06
  UDP  = 0x11
  IPv6 = 0x29

  def self.to_class protocol
    case protocol
    when Protocol::ICMP
      raise "ICMP is not supported"
    when Protocol::IGMP
      raise "IGMP is not supported"
    when Protocol::TCP
      TCPHeader
    when Protocol::UDP
      UDPHeader
    when Protocol::IPv6
      raise "IPv6 is not supported"
    else
      raise "Protocol:"+sprintf("0x%2X",protocol)+" is not supported"
    end
  end
 
  def self.to_s protocol
    case protocol
    when Protocol::ICMP
      "ICMP"
    when Protocol::IGMP
      "IGMP"
    when Protocol::TCP
      "TCP"
    when Protocol::UDP
      "UDP"
    when Protocol::IPv6
      "IPv6"
    else
      sprintf("0x%2X",protocol)
    end
  end

end

tcpheader.rb

class TCPHeader

  attr_reader :sndr_port,:dest_port,:seq_num,:ack_num,:header_length,
    :urg,:ack,:psh,:rst,:syn,:fin,:win_size,:checksum,:emgcy_ptr,
    :packet_length,:data_length,:lower

  def initialize(packet,offset=0,length=nil,lower=nil)
    @packet = packet.force_encoding("ASCII-8BIT")
    @offset = offset
    @length = length || packet.bytesize-offset
    header = packet.unpack("x#{offset}n2N2n4")
    @sndr_port = header[0]
    @dest_port = header[1]
    @seq_num = header[2]
    @ack_num = header[3]
    @header_length = (header[4]>>12)*4
    @urg = (header[4] & 0b100000) != 0
    @ack = (header[4] & 0b010000) != 0
    @psh = (header[4] & 0b001000) != 0
    @rst = (header[4] & 0b000100) != 0
    @syn = (header[4] & 0b000010) != 0
    @fin = (header[4] & 0b000001) != 0
    @win_size = header[5]
    @checksum = header[6]
    @emgcy_ptr = header[7]

    @packet_length = @length
    @data_length = @packet_length-@header_length

    @lower = lower

    # check checksum
    calc_cs = false
    if calc_cs
    tmp =  @packet[@offset..@offset+@length]
    if (tmp.length % 2) != 0
      tmp += "\0"
    end
    data = @lower.get_virtual_header + tmp
    sum = 0
    list = data.unpack("n*")
    list.each do |d|
      sum += d
    end
    sum  = (sum & 0xffff) + (sum >> 16)
    sum  = (sum & 0xffff) + (sum >> 16)
    raise if sum != 65535
    end




  end

  def data
    if(@data_length>0)
      @packet[@offset+@header_length..@offset+@length]
    else
      ""
    end
  end

  def to_s
    "TCP Header\n" <<
    "  Sender Port     : #{@sndr_port}\n" <<
    "  Destination Port: #{@dest_port}\n" <<
    "  Sequence Number : #{@seq_num}\n" <<
    "  ACK Number      : #{@ack_num}\n" <<
    "  Header Length   : #{@header_length}\n" <<
    "  URG             : #{@urg}\n" <<
    "  ACK             : #{@ack}\n" <<
    "  PSH             : #{@psh}\n" <<
    "  RST             : #{@rst}\n" <<
    "  SYN             : #{@syn}\n" <<
    "  FIN             : #{@fin}\n" <<
    "  Window Size     : #{@win_size}\n" <<
    "  Checksum        : #{@checksum}\n" <<
    "  Emergency Ptr   : #{@emgcy_ptr}\n" <<
    "  (Packet Length) : #{@packet_length}\n" <<
    "  (Data Length)   : #{@data_length}"
  end
end

udpheader.rb

class UDPHeader

  attr_reader :sndr_port,:dist_port,:packet_length,:checksum,
    :data_length,:lower

  def initialize(packet,offset=0,length=nil,lower=nil)
    @packet = packet
    @offset = offset
    header = packet.unpack("x#{offset}n4")
    @sndr_port = header[0]
    @dist_port = header[1]
    @packet_length = header[2]
    @checksum = header[3]
    @data_length = @packet_length - 8
    @lower = lower
  end

  def data
    if(@packet_length>8)
      @packet[@offset+8..@offset+@packet_length]
    else
      ""
    end
  end

  def to_s
    "" <<
    "UDP Header\n" <<
    "  Sender Port     : #{@sndr_port}\n" <<
    "  Distication Port: #{@dist_port}\n" <<
    "  Packet Length   : #{@packet_length}\n" <<
    "  Checksum        : #{@checksum}\n" <<
    "  (Data Length)   : #{@data_length}"
  end
 
end