1NetPacket::UDP(3)     User Contributed Perl Documentation    NetPacket::UDP(3)
2
3
4

NAME

6       NetPacket::UDP - Assemble and disassemble UDP (User Datagram Protocol)
7       packets.
8

VERSION

10       version 1.7.2
11

SYNOPSIS

13         use NetPacket::UDP;
14
15         $udp_obj = NetPacket::UDP->decode($raw_pkt);
16         $udp_pkt = $udp_obj->encode($l3_obj);
17         $udp_data = NetPacket::UDP::strip($raw_pkt);
18

DESCRIPTION

20       "NetPacket::UDP" provides a set of routines for assembling and
21       disassembling packets using UDP (User Datagram Protocol).
22
23   Methods
24       "NetPacket::UDP->decode([RAW PACKET])"
25           Decode the raw packet data given and return an object containing
26           instance data.  This method will quite happily decode garbage
27           input.  It is the responsibility of the programmer to ensure valid
28           packet data is passed to this method.
29
30       "$udp_packet-<gt"encode($l3_obj)>
31           Return the encoded version of the UDP packet object. Needs part of
32           the IP header contained (src_ip and dest_ip specifically) in
33           $l3_obj, in order to calculate the UDP checksum. The length field
34           will also be set automatically based on values provided.
35
36   Functions
37       "NetPacket::UDP::strip([RAW PACKET])"
38           Return the encapsulated data (or payload) contained in the UDP
39           packet.  This data is suitable to be used as input for other
40           "NetPacket::*" modules.
41
42           This function is equivalent to creating an object using the
43           "decode()" constructor and returning the "data" field of that
44           object.
45
46   Instance data
47       The instance data for the "NetPacket::UDP" object consists of the
48       following fields.
49
50       src_port
51           The source UDP port for the datagram.
52
53       dest_port
54           The destination UDP port for the datagram.
55
56       len The length (including length of header) in bytes for this packet.
57
58       cksum
59           The checksum value for this packet.
60
61       data
62           The encapsulated data (payload) for this packet.
63
64   IP data
65       The IP data for the $l3_obj object consists of the following fields.
66       Additional items may be supplied as well as passing the whole object
67       returned by NetPacket::IP->decode but are unnecessary.
68
69       src_ip
70           The source IP for the datagram
71
72       dest_ip
73           The destination IP for the datagram
74
75   Exports
76       default
77           none
78
79       exportable
80           udp_strip
81
82       tags
83           The following tags group together related exportable items.
84
85           ":strip"
86               Import the strip function "udp_strip".
87
88           ":ALL"
89               All the above exportable items.
90

EXAMPLE

92       The following example prints the source IP address and port, the
93       destination IP address and port, and the UDP packet length:
94
95         #!/usr/bin/perl -w
96
97         use strict;
98         use Net::PcapUtils;
99         use NetPacket::Ethernet qw(:strip);
100         use NetPacket::IP;
101         use NetPacket::UDP;
102
103         sub process_pkt {
104             my($arg, $hdr, $pkt) = @_;
105
106             my $ip_obj = NetPacket::IP->decode(eth_strip($pkt));
107             my $udp_obj = NetPacket::UDP->decode($ip_obj->{data});
108
109             print("$ip_obj->{src_ip}:$udp_obj->{src_port} -> ",
110                   "$ip_obj->{dest_ip}:$udp_obj->{dest_port} ",
111                   "$udp_obj->{len}\n");
112         }
113
114         Net::PcapUtils::loop(\&process_pkt, FILTER => 'udp');
115
116       The following is an example use in combination with Net::Divert to
117       alter the payload of packets that pass through. All occurrences of foo
118       will be replaced with bar. This example is easy to test with netcat,
119       but otherwise makes little sense. :) Adapt to your needs:
120
121           use Net::Divert;
122           use NetPacket::IP qw(IP_PROTO_UDP);
123           use NetPacket::UDP;
124
125           $divobj = Net::Divert->new('yourhost',9999);
126
127           $divobj->getPackets(\&alterPacket);
128
129           sub alterPacket
130           {
131               my ($data, $fwtag) = @_;
132
133               $ip_obj = NetPacket::IP->decode($data);
134
135               if($ip_obj->{proto} == IP_PROTO_UDP) {
136
137                   # decode the UDP header
138                   $udp_obj = NetPacket::UDP->decode($ip_obj->{data});
139
140                   # replace foo in the payload with bar
141                   $udp_obj->{data} =~ s/foo/bar/g;
142
143                   # re-encode the packet
144                   $ip_obj->{data} = $udp_obj->encode($udp_obj, $ip_obj);
145                   $data = $ip_obj->encode;
146
147               }
148
149               $divobj->putPacket($data,$fwtag);
150           }
151

153       Copyright (c) 2001 Tim Potter.
154
155       Copyright (c) 1995,1996,1997,1998,1999 ANU and CSIRO on behalf of the
156       participants in the CRC for Advanced Computational Systems ('ACSys').
157
158       This module is free software.  You can redistribute it and/or modify it
159       under the terms of the Artistic License 2.0.
160
161       This program is distributed in the hope that it will be useful, but
162       without any warranty; without even the implied warranty of
163       merchantability or fitness for a particular purpose.
164

AUTHOR

166       Tim Potter <tpot@samba.org>
167
168       Stephanie Wehner <atrak@itsx.com>
169
170       Yanick Champoux <yanick@cpan.org>
171
172
173
174perl v5.30.1                      2020-01-30                 NetPacket::UDP(3)
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