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# File: $Id: icmpv4.py,v 1.7 2006/09/05 07:30:56 gnn Exp $
#
# Author: George V. Neville-Neil
#
# Description: A class which describes an ICMPv4 packet

import pcs
from pcs.packets import payload

class icmpv4(pcs.Packet):
    """ICMPv4 Packet

    Internet Control Message Protocol (RFC 792) packet.  This is the
    most generic version and contains only a type, code, and checksum
    field.  It is not generally useful without other information.
    """

    layout = pcs.Layout()

    def __init__(self, bytes = None):
        """initialize a ICMPv4 packet"""
        type = pcs.Field("type", 8)
        code = pcs.Field("code", 8)
        cksum = pcs.Field("checksum", 16)
        pcs.Packet.__init__(self, [type, code, cksum], bytes)
        self.description = "ICMPv4"

        if (bytes != None):
            offset = type.width + code.width + cksum.width
            self.data = payload.payload(bytes[offset:len(bytes)])
        else:
            self.data = None


class icmpv4echo(pcs.Packet):
    """ICMPv4 Echo (aka ping) Packet

    This packet has sufficient fields to form an ICMPv4 echo packet
    also known as a 'ping' due to the name of the program that most
    often uses it.

    Echo packets contain all the fields of an ICMPv4 packet plus an id
    and sequence field.
    """

    layout = pcs.Layout()

    def __init__(self, bytes = None):
        """initialize an ICMPv4 echo packet, used by ping(8) and others"""
        id = pcs.Field("id", 16)
        seq = pcs.Field("sequence", 16)
        pcs.Packet.__init__(self, [id, seq], bytes)
        self.description = "ICMPv4 Echo"

        if (bytes != None):
            offset = id.width + seq.width
            self.data = payload.payload(bytes[offset:len(bytes)])
        else:
            self.data = None