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NetPacket::TCP

Section: User Contributed Perl Documentation (3)
Updated: perl 5.005, patch 03
Index

NAME

NetPacket::TCP - Assemble and disassemble TCP (Transmission ControlProtocol) packets.

SYNOPSIS

  use NetPacket::TCP;

  $tcp_obj = NetPacket::TCP->decode($raw_pkt);  $tcp_pkt = NetPacket::TCP->encode(params...);   # Not implemented  $tcp_data = NetPacket::TCP::strip($raw_pkt);

DESCRIPTION

NetPacket::TCP provides a set of routines for assembling anddisassembling packets using TCP (Transmission Control Protocol).

Methods

NetPacket::TCP->decode([RAW PACKET]): Decode the raw packet data given and return an object containinginstance data. This method will quite happily decode garbage input.It is the responsibility of the programmer to ensure valid packet datais passed to this method.
NetPacket::TCP->encode(param => value): Return a TCP packet encoded with the instance data specified. Notimplemented.

Functions

NetPacket::TCP::strip([RAW PACKET]): Return the encapsulated data (or payload) contained in the TCPpacket. This data is suitable to be used as input for otherNetPacket::* modules.
This function is equivalent to creating an object using thedecode() constructor and returning the data field of thatobject.

Instance data

The instance data for the NetPacket::TCP object consists ofthe following fields.

src_port: The source TCP port for the packet.
dest_port: The destination TCP port for the packet.
seqnum: The TCP sequence number for this packet.
acknum: The TCP acknowledgement number for this packet.
hlen: The header length for this packet.
reserved: The 6-bit ``reserved'' space in the TCP header.
flags: Contains the urg, ack, psh, rst, syn and fin flags for this packet.
winsize: The TCP window size for this packet.
cksum: The TCP checksum.
urg: The TCP urgent pointer.
options: Any TCP options for this packet in binary form.
data: The encapsulated data (payload) for this packet.

Exports

default: none
exportable: tcp_strip
tags: The following tags group together related exportable items.
:strip: Import the strip function tcp_strip.
:ALL: All the above exportable items.

EXAMPLE

The following script is a primitive pop3 sniffer.

  #!/usr/bin/perl

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

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

      my $tcp_obj = NetPacket::TCP->decode(ip_strip(eth_strip($pkt)));

      if (($tcp_obj->{src_port} == 110) or ($tcp_obj->{dest_port} == 110)) {          print($tcp_obj->{data});      }  }

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

TODO

Implement encode() function
Assembly of TCP fragments into a data stream
Option processing
Nicer processing of TCP flags

COPYRIGHT

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

  ACSys makes this software and all associated data and documentation  ('Software') available free of charge.  You may make copies of the   Software but you must include all of this notice on any copy.

  The Software was developed for research purposes and ACSys does not  warrant that it is error free or fit for any purpose.  ACSys  disclaims any liability for all claims, expenses, losses, damages  and costs any user may incur as a result of using, copying or  modifying the Software.

AUTHOR

Tim Potter <tpotAATTacsys.anu.edu.au>

Protocol) packets."

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