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.\" ========================================================================
.\"
.IX Title "NetPacket::UDP 3pm"
.TH NetPacket::UDP 3pm "2022-11-19" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
NetPacket::UDP \- Assemble and disassemble UDP (User Datagram Protocol) packets.
.SH "VERSION"
.IX Header "VERSION"
version 1.7.2
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use NetPacket::UDP;
\&
\&  $udp_obj = NetPacket::UDP\->decode($raw_pkt);
\&  $udp_pkt = $udp_obj\->encode($l3_obj);
\&  $udp_data = NetPacket::UDP::strip($raw_pkt);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`NetPacket::UDP\*(C'\fR provides a set of routines for assembling and
disassembling packets using \s-1UDP\s0 (User Datagram Protocol).
.SS "Methods"
.IX Subsection "Methods"
.ie n .IP """NetPacket::UDP\->decode([RAW PACKET])""" 4
.el .IP "\f(CWNetPacket::UDP\->decode([RAW PACKET])\fR" 4
.IX Item "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.
.ie n .IP """$udp_packet\-<gt""encode($l3_obj)>" 4
.el .IP "\f(CW$udp_packet\-<gt\fRencode($l3_obj)>" 4
.IX Item "$udp_packet-<gtencode($l3_obj)>"
Return the encoded version of the \s-1UDP\s0 packet object. Needs
part of the \s-1IP\s0 header contained (src_ip and dest_ip specifically) in \f(CW$l3_obj\fR,
in order to calculate the \s-1UDP\s0 checksum. The length field will also be set
automatically based on values provided.
.SS "Functions"
.IX Subsection "Functions"
.ie n .IP """NetPacket::UDP::strip([RAW PACKET])""" 4
.el .IP "\f(CWNetPacket::UDP::strip([RAW PACKET])\fR" 4
.IX Item "NetPacket::UDP::strip([RAW PACKET])"
Return the encapsulated data (or payload) contained in the \s-1UDP\s0
packet.  This data is suitable to be used as input for other
\&\f(CW\*(C`NetPacket::*\*(C'\fR modules.
.Sp
This function is equivalent to creating an object using the
\&\f(CW\*(C`decode()\*(C'\fR constructor and returning the \f(CW\*(C`data\*(C'\fR field of that
object.
.SS "Instance data"
.IX Subsection "Instance data"
The instance data for the \f(CW\*(C`NetPacket::UDP\*(C'\fR object consists of
the following fields.
.IP "src_port" 4
.IX Item "src_port"
The source \s-1UDP\s0 port for the datagram.
.IP "dest_port" 4
.IX Item "dest_port"
The destination \s-1UDP\s0 port for the datagram.
.IP "len" 4
.IX Item "len"
The length (including length of header) in bytes for this packet.
.IP "cksum" 4
.IX Item "cksum"
The checksum value for this packet.
.IP "data" 4
.IX Item "data"
The encapsulated data (payload) for this packet.
.SS "\s-1IP\s0 data"
.IX Subsection "IP data"
The \s-1IP\s0 data for the \f(CW$l3_obj\fR 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.
.IP "src_ip" 4
.IX Item "src_ip"
The source \s-1IP\s0 for the datagram
.IP "dest_ip" 4
.IX Item "dest_ip"
The destination \s-1IP\s0 for the datagram
.SS "Exports"
.IX Subsection "Exports"
.IP "default" 4
.IX Item "default"
none
.IP "exportable" 4
.IX Item "exportable"
udp_strip
.IP "tags" 4
.IX Item "tags"
The following tags group together related exportable items.
.RS 4
.ie n .IP """:strip""" 4
.el .IP "\f(CW:strip\fR" 4
.IX Item ":strip"
Import the strip function \f(CW\*(C`udp_strip\*(C'\fR.
.ie n .IP """:ALL""" 4
.el .IP "\f(CW:ALL\fR" 4
.IX Item ":ALL"
All the above exportable items.
.RE
.RS 4
.RE
.SH "EXAMPLE"
.IX Header "EXAMPLE"
The following example prints the source \s-1IP\s0 address and port, the
destination \s-1IP\s0 address and port, and the \s-1UDP\s0 packet length:
.PP
.Vb 1
\&  #!/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}\en");
\&  }
\&
\&  Net::PcapUtils::loop(\e&process_pkt, FILTER => \*(Aqudp\*(Aq);
.Ve
.PP
The following is an example use in combination with Net::Divert
to alter the payload of packets that pass through. All occurrences
of foo will be replaced with bar. This example is easy to test with
netcat, but otherwise makes little sense. :) Adapt to your needs:
.PP
.Vb 3
\&    use Net::Divert;
\&    use NetPacket::IP qw(IP_PROTO_UDP);
\&    use NetPacket::UDP;
\&
\&    $divobj = Net::Divert\->new(\*(Aqyourhost\*(Aq,9999);
\&
\&    $divobj\->getPackets(\e&alterPacket);
\&
\&    sub alterPacket
\&    {
\&        my ($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);
\&    }
.Ve
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 2001 Tim Potter.
.PP
Copyright (c) 1995,1996,1997,1998,1999 \s-1ANU\s0 and \s-1CSIRO\s0 on behalf of
the participants in the \s-1CRC\s0 for Advanced Computational Systems
('ACSys').
.PP
This module is free software.  You can redistribute it and/or
modify it under the terms of the Artistic License 2.0.
.PP
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.
.SH "AUTHOR"
.IX Header "AUTHOR"
Tim Potter <tpot@samba.org>
.PP
Stephanie Wehner <atrak@itsx.com>
.PP
Yanick Champoux <yanick@cpan.org>