Class: PacketGen::Header::TCP

Inherits:

Object
Types::Fields
Base
PacketGen::Header::TCP

Defined in:: lib/packetgen/header/tcp.rb,
lib/packetgen/header/tcp.rb,
lib/packetgen/header/tcp/option.rb,
lib/packetgen/header/tcp/options.rb

Overview

TCP header (RFC 793)

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Source Port          |       Destination Port        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sequence Number                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Acknowledgment Number                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Data |           |U|A|P|R|S|F|                               |
| Offset| Reserved  |R|C|S|S|Y|I|            Window             |
|       |           |G|K|H|T|N|N|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Checksum            |         Urgent Pointer        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Options                    |    Padding    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             data                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A TCP header consists of:

a source port (#sport, Types::Int16 type),
a destination port (#dport, Int16 type),
a sequence number (#seqnum, Types::Int32 type),
an acknownledge number (#acknum, Int32 type),
a 16-bit field (#u16, Int16 type) composed of:
- a 4-bit #data_offset self,
- a 3-bit #reserved field,
- a 9-bit #flags field,
a #window field (Int16 type),
a #checksum field (Int16 type),
a urgent pointer (#urg_pointer, Int16 type),
an optional #options field (Options type),
and a #body (Types::String type).

# standalone
tcph = PacketGen::Header::TCP.new
# in a IP packet
pkt = PacketGen.gen('IP').add('TCP')
# access to TCP header
pkt.tcp   # => PacketGen::Header::TCP

TCP attributes

tcph.sport = 4500
tcph.dport = 80
tcph.seqnum = 43
tcph.acknum = 0x45678925
tcph.wsize = 0x240
tcph.urg_pointer = 0x40
tcph.body.read 'this is a body'

Flags

TCP flags may be accesed as a 9-bit integer:

tcph.flags = 0x1002

Each flag may be accessed independently:

tcph.flag_syn?    # => Boolean
tcph.flag_rst = true

Options

#options TCP attribute is a Options. Option may added to it:

tcph.options << PacketGen::Header::TCP::MSS.new(1250)

or:

tcph.options << { opt: 'MSS', self[attr]: 1250 }

Author:

Sylvain Daubert

Defined Under Namespace

Classes: ECHO, ECHOREPLY, EOL, MSS, NOP, Option, Options, SACK, SACKOK, TS, WS

Constant Summary collapse

IP_PROTOCOL = IP protocol number for TCP

Instance Attribute Summary collapse

#acknum ⇒ Integer (also: #acknowledgement_number)

32-bit TCP acknowledgement number.
#body ⇒ Types::String, Header::Base
#checksum ⇒ Integer

16-bit TCP checksum.
#data_offset ⇒ Integer (also: #hlen)

4-bit data offset from #u16.
#dport ⇒ Integer (also: #destination_port)

16-bit TCP destination port.
#flag_ack ⇒ Boolean

1-bit ACK flag.
#flag_cwr ⇒ Boolean

1-bit CWR flag.
#flag_ece ⇒ Boolean

1-bit ECE flag.
#flag_fin ⇒ Boolean

1-bit FIN flag.
#flag_ns ⇒ Boolean

1-bit NS flag.
#flag_psh ⇒ Boolean

1-bit PSH flag.
#flag_rst ⇒ Boolean

1-bit RST flag.
#flag_syn ⇒ Boolean

1-bit SYN flag.
#flag_urg ⇒ Boolean

1-bit URG flag.
#flags ⇒ Integer

9-bit flags from #u16.
#options ⇒ Options

TCP options.
#reserved ⇒ Integer

3-bit reserved from #u16.
#seqnum ⇒ Integer (also: #sequence_number)

32-bit TCP sequence number.
#sport ⇒ Integer (also: #source_port)

16-bit TCP source port.
#u16 ⇒ Integer

16-bit word used by flags and bit fields.
#urg_pointer ⇒ Integer

16-bit TCP urgent data pointer.
#window ⇒ Integer (also: #wsize)

16-bit TCP window size.

Instance Method Summary collapse

#calc_checksum ⇒ Integer

Compute checksum and set checksum field.
#calc_length ⇒ Integer

Compute header length and set data_offset field.
#initialize(options = {}) ⇒ TCP constructor

Call {Base#initialize), then handle specific options to set u16 by part: * :data_offset * :hlen * :reserved * :flags.
#inspect ⇒ String
#reply! ⇒ self

Invert source and destination port numbers.

Constructor Details

#initialize(options = {}) ⇒ `TCP`

Call {Base#initialize), then handle specific options to set u16 by part:

:data_offset
:hlen
:reserved
:flags

Parameters:

options (Hash) (defaults to: {})

Options Hash (options):

:sport (Integer)
:dport (Integer)
:seqnum (Integer)
:acknum (Integer)
:data_offset (Integer)
:reserved (Integer)
:flags (Integer)
:window (Integer)
:checksum (Integer)
:urg_pointer (Integer)
:body (String)

# File 'lib/packetgen/header/tcp.rb', line 157

def initialize(options={})
  opts = { data_offset: 5 }.merge!(options)
  super(opts)
end

Instance Attribute Details

#acknum ⇒ `Integer` Also known as: acknowledgement_number

32-bit TCP acknowledgement number

Returns:

(Integer)

105	# File 'lib/packetgen/header/tcp.rb', line 105 define_field :acknum, Types::Int32

#body ⇒ `Types::String`, `Header::Base`

Returns:

(Types::String, Header::Base)

127	# File 'lib/packetgen/header/tcp.rb', line 127 define_field :body, Types::String

#checksum ⇒ `Integer`

16-bit TCP checksum

Returns:

(Integer)

116	# File 'lib/packetgen/header/tcp.rb', line 116 define_field :checksum, Types::Int16

#data_offset ⇒ `Integer` Also known as: hlen

Returns 4-bit data offset from #u16.

Returns:

(Integer) —

4-bit data offset from #u16

168	# File 'lib/packetgen/header/tcp.rb', line 168 define_bit_fields_on :u16, :data_offset, 4, :reserved, 3, :flags, 9

#dport ⇒ `Integer` Also known as: destination_port

16-bit TCP destination port

Returns:

(Integer)

97	# File 'lib/packetgen/header/tcp.rb', line 97 define_field :dport, Types::Int16

#flag_ack ⇒ `Boolean`

Returns 1-bit ACK flag.

Returns:

(Boolean) —

1-bit ACK flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_cwr ⇒ `Boolean`

Returns 1-bit CWR flag.

Returns:

(Boolean) —

1-bit CWR flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_ece ⇒ `Boolean`

Returns 1-bit ECE flag.

Returns:

(Boolean) —

1-bit ECE flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_fin ⇒ `Boolean`

Returns 1-bit FIN flag.

Returns:

(Boolean) —

1-bit FIN flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_ns ⇒ `Boolean`

Returns 1-bit NS flag.

Returns:

(Boolean) —

1-bit NS flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_psh ⇒ `Boolean`

Returns 1-bit PSH flag.

Returns:

(Boolean) —

1-bit PSH flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_rst ⇒ `Boolean`

Returns 1-bit RST flag.

Returns:

(Boolean) —

1-bit RST flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_syn ⇒ `Boolean`

Returns 1-bit SYN flag.

Returns:

(Boolean) —

1-bit SYN flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flag_urg ⇒ `Boolean`

Returns 1-bit URG flag.

Returns:

(Boolean) —

1-bit URG flag



190
191

# File 'lib/packetgen/header/tcp.rb', line 190

define_bit_fields_on :u16, :_, 7, :flag_ns, :flag_cwr, :flag_ece, :flag_urg,
:flag_ack, :flag_psh, :flag_rst, :flag_syn, :flag_fin

#flags ⇒ `Integer`

Returns 9-bit flags from #u16.

Returns:

(Integer) —

9-bit flags from #u16

168	# File 'lib/packetgen/header/tcp.rb', line 168 define_bit_fields_on :u16, :data_offset, 4, :reserved, 3, :flags, 9

#options ⇒ `Options`

TCP options

Returns:

(Options)

124	# File 'lib/packetgen/header/tcp.rb', line 124 define_field :options, TCP::Options, builder: ->(h, t) { t.new(length_from: -> { h.data_offset > 5 ? (h.data_offset - 5) * 4 : 0 }) }

#reserved ⇒ `Integer`

Returns 3-bit reserved from #u16.

Returns:

(Integer) —

3-bit reserved from #u16

168	# File 'lib/packetgen/header/tcp.rb', line 168 define_bit_fields_on :u16, :data_offset, 4, :reserved, 3, :flags, 9

#seqnum ⇒ `Integer` Also known as: sequence_number

32-bit TCP sequence number

Returns:

(Integer)

101	# File 'lib/packetgen/header/tcp.rb', line 101 define_field :seqnum, Types::Int32, default: ->(_) { rand(2**32) }

#sport ⇒ `Integer` Also known as: source_port

16-bit TCP source port

Returns:

(Integer)

93	# File 'lib/packetgen/header/tcp.rb', line 93 define_field :sport, Types::Int16

#u16 ⇒ `Integer`

Returns 16-bit word used by flags and bit fields.

Returns:

(Integer) —

16-bit word used by flags and bit fields

108	# File 'lib/packetgen/header/tcp.rb', line 108 define_field :u16, Types::Int16

#urg_pointer ⇒ `Integer`

16-bit TCP urgent data pointer

Returns:

(Integer)

120	# File 'lib/packetgen/header/tcp.rb', line 120 define_field :urg_pointer, Types::Int16

#window ⇒ `Integer` Also known as: wsize

16-bit TCP window size

Returns:

(Integer)

112	# File 'lib/packetgen/header/tcp.rb', line 112 define_field :window, Types::Int16

Instance Method Details

#calc_checksum ⇒ `Integer`

Compute checksum and set checksum field

Returns:

(Integer)

# File 'lib/packetgen/header/tcp.rb', line 195

def calc_checksum
  sum = ip_header(self).pseudo_header_checksum
  sum += IP_PROTOCOL
  sum += self.sz
  sum += IP.sum16(self)
  self.checksum = IP.reduce_checksum(sum)
end

#calc_length ⇒ `Integer`

Compute header length and set data_offset field

Returns:

(Integer)



205
206
207

# File 'lib/packetgen/header/tcp.rb', line 205

def calc_length
  self[:data_offset] = 5 + self[:options].sz / 4
end

#inspect ⇒ `String`

Returns:

(String)

# File 'lib/packetgen/header/tcp.rb', line 210

def inspect
  super do |attr|
    next unless attr == :u16

    shift = Inspect.shift_level
    str = Inspect.inspect_attribute(attr, self[attr])
    doff = Inspect.int_dec_hex(data_offset, 1)
    str << shift << Inspect::FMT_ATTR % ['', 'data_offset', doff]
    str << shift << Inspect::FMT_ATTR % ['', 'reserved', reserved]
    str << shift << Inspect::FMT_ATTR % ['', 'flags', flags2string]
  end
end

#reply! ⇒ `self`

Invert source and destination port numbers

Returns:

(self)

Since:

2.7.0

# File 'lib/packetgen/header/tcp.rb', line 226

def reply!
  self[:sport], self[:dport] = self[:dport], self[:sport]
  self
end

Class: PacketGen::Header::TCP

Overview

Create a TCP header

TCP attributes

Flags

Options

Defined Under Namespace

Constant Summary collapse

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods inherited from Base

Methods included from PacketGen::Headerable

Methods inherited from Types::Fields

Constructor Details

#initialize(options = {}) ⇒ TCP

Instance Attribute Details

#acknum ⇒ Integer Also known as: acknowledgement_number

#body ⇒ Types::String, Header::Base

#checksum ⇒ Integer

#data_offset ⇒ Integer Also known as: hlen

#dport ⇒ Integer Also known as: destination_port

#flag_ack ⇒ Boolean

#flag_cwr ⇒ Boolean

#flag_ece ⇒ Boolean

#flag_fin ⇒ Boolean

#flag_ns ⇒ Boolean

#flag_psh ⇒ Boolean

#flag_rst ⇒ Boolean

#flag_syn ⇒ Boolean

#flag_urg ⇒ Boolean

#flags ⇒ Integer

#options ⇒ Options

#reserved ⇒ Integer

#seqnum ⇒ Integer Also known as: sequence_number

#sport ⇒ Integer Also known as: source_port

#u16 ⇒ Integer

#urg_pointer ⇒ Integer

#window ⇒ Integer Also known as: wsize

Instance Method Details

#calc_checksum ⇒ Integer

#calc_length ⇒ Integer

#inspect ⇒ String

#reply! ⇒ self

#initialize(options = {}) ⇒ `TCP`

#acknum ⇒ `Integer` Also known as: acknowledgement_number

#body ⇒ `Types::String`, `Header::Base`

#checksum ⇒ `Integer`

#data_offset ⇒ `Integer` Also known as: hlen

#dport ⇒ `Integer` Also known as: destination_port

#flag_ack ⇒ `Boolean`

#flag_cwr ⇒ `Boolean`

#flag_ece ⇒ `Boolean`

#flag_fin ⇒ `Boolean`

#flag_ns ⇒ `Boolean`

#flag_psh ⇒ `Boolean`

#flag_rst ⇒ `Boolean`

#flag_syn ⇒ `Boolean`

#flag_urg ⇒ `Boolean`

#flags ⇒ `Integer`

#options ⇒ `Options`

#reserved ⇒ `Integer`

#seqnum ⇒ `Integer` Also known as: sequence_number

#sport ⇒ `Integer` Also known as: source_port

#u16 ⇒ `Integer`

#urg_pointer ⇒ `Integer`

#window ⇒ `Integer` Also known as: wsize

#calc_checksum ⇒ `Integer`

#calc_length ⇒ `Integer`

#inspect ⇒ `String`

#reply! ⇒ `self`