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NetPacket::UDP (3)
  • >> NetPacket::UDP (3) ( Разные man: Библиотечные вызовы )
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    NAME

    "NetPacket::UDP" - Assemble and disassemble UDP (User Datagram
    Protocol) packets.
     
    

    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(param => value)
    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
    igmp_strip IGMP_VERSION_RFC998 IGMP_VERSION_RFC1112 IGMP_MSG_HOST_MQUERY IGMP_MSG_HOST_MREPORT IGMP_IP_NO_HOSTS IGMP_IP_ALL_HOSTS IGMP_IP_ALL_ROUTERS
    tags
    The following tags group together related exportable items.
    :strip
    Import the strip function "igmp_strip".
    :versions
    IGMP_VERSION_RFC998 IGMP_VERSION_RFC1112
    :msgtypes
    IGMP_HOST_MQUERY IGMP_HOST_MREPORT
    :group_addrs
    IGMP_IP_NO_HOSTS IGMP_IP_ALL_HOSTS IGMP_IP_ALL_ROUTERS
    :ALL
    All the above exportable items.
     

    EXAMPLE

    The following script dumps IGMP the contents of IGMP frames to standard output.

      #!/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:

    #!/usr/bin/perl

    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;
    
    

            # reencode the packet
            $ip_obj->{data} = $udp_obj->encode($ip_obj);
            $data = $ip_obj->encode;
    
    

        }
    
    

        $divobj->putPacket($data,$fwtag);
    }
    
    
     

    COPYRIGHT

      Copyright (c) 2001 Tim Potter.
    
    

      This package is free software and is provided "as is" without express 
      or implied warranty.  It may be used, redistributed and/or modified 
      under the terms of the Perl Artistic License (see
      http://www.perl.com/perl/misc/Artistic.html)
    
    

      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 <tpot@samba.org>

    Stephanie Wehner <atrak@itsx.com>


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    Methods
    Functions
    Instance data
    Exports
    EXAMPLE
    COPYRIGHT
    AUTHOR


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