Class: Racket::L3::IPv4

Inherits:
RacketPart show all
Defined in:
lib/racket/l3/ipv4.rb

Overview

RFC791 (www.ietf.org/rfc/rfc791.txt)

Instance Attribute Summary

Attributes inherited from RacketPart

#autofix

Instance Method Summary collapse

Methods inherited from RacketPart

#autofix?, #pretty

Constructor Details

#initialize(*args) ⇒ IPv4

Returns a new instance of IPv4.



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# File 'lib/racket/l3/ipv4.rb', line 63

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

Instance Method Details

#add_option(number, value) ⇒ Object

Add an IPv4 option to this IPv4 object. All rejiggering will happen when the call to fix! happens automagically



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# File 'lib/racket/l3/ipv4.rb', line 71

def add_option(number, value)
  t = Racket::Misc::TLV.new(1,1)
  t.type = number
  t.value = value
  t.length = value.length + 2
  @options << t.encode
end

#checksum! ⇒ Object

Compute and set the checksum for this IP datagram



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# File 'lib/racket/l3/ipv4.rb', line 85

def checksum!
  self.checksum = compute_checksum
end

#checksum? ⇒ Boolean

Check the checksum for this IP datagram

Returns:

  • (Boolean) 


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# File 'lib/racket/l3/ipv4.rb', line 80

def checksum?
  self.checksum == compute_checksum
end

#fix! ⇒ Object

Perform all the niceties necessary prior to sending this IP datagram out. Append the options, update len and hlen, and fix the checksum.



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# File 'lib/racket/l3/ipv4.rb', line 92

def fix!
  newpayload = @options.join
  
  # pad to a multiple of 32 bits
  if (newpayload.length % 4 != 0) 
    # fill the beginning as needed with NOPs
    while (newpayload.length % 4 != 3)
      newpayload = "\x01#{newpayload}"
    end

    # make sure the last byte is an EOL
    if (newpayload.length % 4 == 3)
      newpayload += "\x00"
    end
  end

  self.payload = newpayload + self.payload
  self.hlen += newpayload.length/4
  self.len = self.payload.length + self.class.bit_length/8
  self.checksum!
end