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# File: $Id: udpv6.py,v 1.1 2006/07/06 09:31:57 gnn Exp $
#
# Author: George V. Neville-Neil
#
# Description: A class which implements UDP v6 packets

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

import pcs
from pseudoipv6 import *

class udpv6(pcs.Packet):

    layout = pcs.Layout()

    def __init__(self, bytes = None):
        """Initialize a UDP packet for IPv6"""
        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)
        
    def cksum(self, ip, data = "", nx = 0):
        """return udpv6 checksum"""
        total = 0
        p6 = pseudoipv6()
        p6.src = ip.src
        p6.dst = ip.dst
        p6.length = len(self.getbytes()) + len (data)
        if nx:
            p6.next_header = nx
        else:
            p6.next_header = ip.next_header
        pkt = p6.getbytes() + self.getbytes() + data
        if len(pkt) % 2 == 1:
            pkt += "\0"
        for i in range(len(pkt)/2):
            total += (struct.unpack("!H", pkt[2*i:2*i+2])[0])
        total = (total >> 16) + (total & 0xffff)
        total += total >> 16
        return  ~total