NetPacket::UDP(3pm) User Contributed Perl Documentation NetPacket::UDP(3pm)
NAME
NetPacket::UDP - Assemble and disassemble UDP (User Datagram Protocol) packets.
VERSION
version 1.3.0
SYNOPSIS
use NetPacket::UDP;
$udp_obj = NetPacket::UDP->decode($raw_pkt);
$udp_pkt = NetPacket::UDP->encode($ip_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.
"NetPacket::UDP->encode($ip_obj)"
Return a UDP packet encoded with the instance data specified. Needs parts of the IP header contained in $ip_obj, the IP object, in
order to calculate the UDP checksum. The length field will also be set automatically.
Functions
"NetPacket::UDP::strip([RAW PACKET])"
Return the encapsulated data (or payload) contained in the UDP packet. This data is suitable to be used as input for other
"NetPacket::*" modules.
This function is equivalent to creating an object using the "decode()" constructor and returning the "data" field of that object.
Instance data
The instance data for the "NetPacket::UDP" object consists of the following fields.
src_port
The source UDP port for the datagram.
dest_port
The destination UDP port for the datagram.
len The length (including length of header) in bytes for this packet.
cksum
The checksum value for this packet.
data
The encapsulated data (payload) for this packet.
Exports
default
none
exportable
udp_strip
tags
The following tags group together related exportable items.
":strip"
Import the strip function "udp_strip".
":ALL"
All the above exportable items.
EXAMPLE
The following example prints the source IP address and port, the destination IP address and port, and the UDP packet length:
#!/usr/bin/perl -w
use strict;
use Net::PcapUtils;
use NetPacket::Ethernet qw(:strip);
use NetPacket::IP;
use NetPacket::UDP;
sub process_pkt {
my($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}
");
}
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} = $udp_obj->encode($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>
perl v5.14.2 2011-11-20 NetPacket::UDP(3pm)