NAME¶
NetPacket::UDP - Assemble and disassemble UDP (User Datagram Protocol) packets.
VERSION¶
version 1.5.0
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>