# Copyright (c) 2005, Neville-Neil Consulting
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#
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# modification, are permitted provided that the following conditions are
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# File: $Id: udpv4.py,v 1.1 2005/10/14 00:53:16 gnn Exp $
#
# Author: George V. Neville-Neil
#
# Description: A class which implements UDP v4 packets

import sys
sys.path.append("../src")

import pcs

class udpv4(pcs.Packet):

    _layout = pcs.Layout()

    def __init__(self, bytes = None):
        """Initialize a UDP packet for IPv4"""
        sport = pcs.Field("sport", 16)
        dport = pcs.Field("dport", 16)
        length = pcs.Field("length", 16)
        checksum = pcs.Field("checksum", 16)
        pcs.Packet.__init__(self, [sport, dport, length, checksum], bytes)

@@ -1736,16 +1736,30 @@
 port pcs
+%0Aimport socket
 %0A%0Aclass 
@@ -2130,8 +2130,656 @@
  bytes)%0A
+%0A    def cksum(self, ip, data = %22%22):%0A        %22%22%22return tcpv4 checksum%22%22%22%0A        from pcs.packets.ipv4 import pseudoipv4%0A        import struct%0A        total = 0%0A        tmpip = pseudoipv4(None, None, socket.IPPROTO_UDP)%0A        tmpip.src = ip.src%0A        tmpip.dst = ip.dst%0A        tmpip.length = len(self.getbytes()) + len(data)%0A        pkt = tmpip.getbytes() + self.getbytes() + data%0A        if len(pkt) %25 2 == 1:%0A            pkt += %22%5C0%22%0A        for i in range(len(pkt)/2):%0A            total += (struct.unpack(%22!H%22, pkt%5B2*i:2*i+2%5D)%5B0%5D)%0A        total = (total %3E%3E 16) + (total & 0xffff)%0A        total += total %3E%3E 16%0A        return  ~total & 0xffff%0A

Add a method to compute checksums over UDP payloads.