Class: Racket::L4::TCP

Inherits:
RacketPart show all
Defined in:
lib/racket/l4/tcp.rb

Overview

RFC793 (www.faqs.org/rfcs/rfc793.html)

Instance Attribute Summary

Attributes inherited from RacketPart

#autofix

Instance Method Summary collapse

Methods inherited from RacketPart

#autofix?, #pretty

Constructor Details

#initialize(*args) ⇒ TCP

Returns a new instance of TCP.



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# File 'lib/racket/l4/tcp.rb', line 122

def initialize(*args)
  @options = []
  super
  @autofix = false
end

Instance Method Details

#add_option(number, value) ⇒ Object

Add an TCP option to this TCP object. All rejiggering will happen when the call to fix! happens automagically. If the result is not on a 32-bit boundry, pad with NOPs.



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# File 'lib/racket/l4/tcp.rb', line 75

def add_option(number, value)
  t = Misc::TLV.new(1,1)
  t.type = number
  t.value = value
  t.length = value.length + 2
  opts = t.encode
  opts += ("\x01" * (4-(opts.size % 4))) if (opts.size % 4) != 0
  @options << opts
end

#add_raw_option(value) ⇒ Object

Add a raw TCP option to this packet. It is entirely your responsibility (or irresponsibility, as the case may be) to properly pad or otherwise define this



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# File 'lib/racket/l4/tcp.rb', line 88

def add_raw_option(value)
  @options << value
end

#checksum!(ip_src, ip_dst) ⇒ Object

Compute and set the checksum for this TCP packet



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# File 'lib/racket/l4/tcp.rb', line 98

def checksum!(ip_src, ip_dst)
  self.checksum = compute_checksum(ip_src, ip_dst)
end

#checksum?(ip_src, ip_dst) ⇒ Boolean

Check the checksum for this TCP packet

Returns:

  • (Boolean) 


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# File 'lib/racket/l4/tcp.rb', line 93

def checksum?(ip_src, ip_dst)
  self.checksum == compute_checksum(ip_src, ip_dst)
end

#fix!(ip_src, ip_dst, next_payload) ⇒ Object

Fix this packet up for proper sending. Sets the length and checksum properly.



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# File 'lib/racket/l4/tcp.rb', line 104

def fix!(ip_src, ip_dst, next_payload)
  newpayload = @options.join
  
  # pad to a multiple of 32 bits
  if ((self.class.bit_length/8 + newpayload.length) % 4 != 0) 
    # fill the beginning as needed with NOPs
    while ((self.class.bit_length/8 + newpayload.length) % 4 != 4)
      puts (self.class.bit_length/8 + newpayload.length) % 4
      newpayload = "\x01#{newpayload}"
    end
  end

  self.payload = newpayload + self.payload + next_payload
  self.offset = self.class.bit_length/32 + newpayload.length/4
  self.checksum!(ip_src, ip_dst)
  self.payload = newpayload
end