NAME

       NetPacket::UDP - Assemble and disassemble UDP (User Datagram Protocol) packets.

VERSION

       version 1.4.4

SYNOPSIS

         use NetPacket::UDP;

         $udp_obj = NetPacket::UDP->decode($raw_pkt);
         $udp_pkt = $udp_obj->encode($l3_obj);
         $udp_data = NetPacket::UDP::strip($raw_pkt);

DESCRIPTION

       "NetPacket::UDP" provides a set of routines for assembling and disassembling packets using
       UDP (User Datagram Protocol).

   Methods
       "NetPacket::UDP->decode([RAW PACKET])"
           Decode the raw packet data given and return an object containing instance data.  This
           method will quite happily decode garbage input.  It is the responsibility of the
           programmer to ensure valid packet data is passed to this method.

       "$udp_packet-<gt"encode($l3_obj)>
           Return the encoded version of the UDP packet object. Needs part of the IP header
           contained (src_ip and dest_ip specifically) in $l3_obj, in order to calculate the UDP
           checksum. The length field will also be set automatically based on values provided.

   Functions
       "NetPacket::UDP::strip([RAW PACKET])"
           Return the encapsulated data (or payload) contained in the UDP packet.  This data is
           suitable to be used as input for other "NetPacket::*" modules.

           This function is equivalent to creating an object using the "decode()" constructor and
           returning the "data" field of that object.

   Instance data
       The instance data for the "NetPacket::UDP" object consists of the following fields.

       src_port
           The source UDP port for the datagram.

       dest_port
           The destination UDP port for the datagram.

       len The length (including length of header) in bytes for this packet.

       cksum
           The checksum value for this packet.

       data
           The encapsulated data (payload) for this packet.

   IP data
       The IP data for the $l3_obj object consists of the following fields.  Additional items may
       be supplied as well as passing the whole object returned by NetPacket::IP->decode but are
       unnecessary.

       src_ip
           The source IP for the datagram

       dest_ip
           The destination IP for the datagram

   Exports
       default
           none

       exportable
           udp_strip

       tags
           The following tags group together related exportable items.

           ":strip"
               Import the strip function "udp_strip".

           ":ALL"
               All the above exportable items.

EXAMPLE

       The following example prints the source IP address and port, the destination IP address
       and port, and the UDP packet length:

         #!/usr/bin/perl -w

         use strict;
         use Net::PcapUtils;
         use NetPacket::Ethernet qw(:strip);
         use NetPacket::IP;
         use NetPacket::UDP;

         sub process_pkt {
             my($arg, $hdr, $pkt) = @_;

             my $ip_obj = NetPacket::IP->decode(eth_strip($pkt));
             my $udp_obj = NetPacket::UDP->decode($ip_obj->{data});

             print("$ip_obj->{src_ip}:$udp_obj->{src_port} -> ",
                   "$ip_obj->{dest_ip}:$udp_obj->{dest_port} ",
                   "$udp_obj->{len}\n");
         }

         Net::PcapUtils::loop(\&process_pkt, FILTER => 'udp');

       The following is an example use in combination with Net::Divert to alter the payload of
       packets that pass through. All occurences of foo will be replaced with bar. This example
       is easy to test with netcat, but otherwise makes little sense. :) Adapt to your needs:

           use Net::Divert;
           use NetPacket::IP qw(IP_PROTO_UDP);
           use NetPacket::UDP;

           $divobj = Net::Divert->new('yourhost',9999);

           $divobj->getPackets(\&alterPacket);

           sub alterPacket
           {
               my ($data, $fwtag) = @_;

               $ip_obj = NetPacket::IP->decode($data);

               if($ip_obj->{proto} == IP_PROTO_UDP) {

                   # decode the UDP header
                   $udp_obj = NetPacket::UDP->decode($ip_obj->{data});

                   # replace foo in the payload with bar
                   $udp_obj->{data} =~ s/foo/bar/g;

                   # re-encode the packet
                   $ip_obj->{data} = $udp_obj->encode($udp_obj, $ip_obj);
                   $data = $ip_obj->encode;

               }

               $divobj->putPacket($data,$fwtag);
           }

COPYRIGHT

       Copyright (c) 2001 Tim Potter.

       Copyright (c) 1995,1996,1997,1998,1999 ANU and CSIRO on behalf of the participants in the
       CRC for Advanced Computational Systems ('ACSys').

       This module is free software.  You can redistribute it and/or modify it under the terms of
       the Artistic License 2.0.

       This program is distributed in the hope that it will be useful, but without any warranty;
       without even the implied warranty of merchantability or fitness for a particular purpose.

AUTHOR

       Tim Potter <tpot@samba.org>

       Stephanie Wehner <atrak@itsx.com>

       Yanick Champoux <yanick@cpan.org>