NetPacket::ICMP - Assemble and disassemble ICMP (Internet Control Message Protocol) packets.

  use NetPacket::ICMP;

  $icmp_obj = NetPacket::ICMP->decode($raw_pkt);
  $icmp_pkt = NetPacket::ICMP->encode();
  $icmp_data = NetPacket::ICMP::strip($raw_pkt);

  #!/usr/bin/perl -w

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

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

      my $ip_obj = NetPacket::IP->decode(eth_strip($pkt));
      my $icmp_obj = NetPacket::ICMP->decode(ip_strip($ip_obj));

      print("Type: $icmp_obj->{type}\n");
      print("Code: $icmp_obj->{code}\n");
      print("Checksum: $icmp_obj->{cksum}\n\n");
  }

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

package NetPacket::ICMP;
BEGIN {
  $NetPacket::ICMP::AUTHORITY = 'cpan:yanick';
}
BEGIN {
  $NetPacket::ICMP::VERSION = '1.1.2';
}
# ABSTRACT: Assemble and disassemble ICMP (Internet Control Message Protocol) packets. 

use strict;
use vars qw( @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS);


BEGIN {
    @ISA = qw(Exporter NetPacket);

# Items to export into callers namespace by default
# (move infrequently used names to @EXPORT_OK below)

    @EXPORT = qw(
    );

# Other items we are prepared to export if requested

    @EXPORT_OK = qw(icmp_strip
                    ICMP_ECHOREPLY ICMP_UNREACH ICMP_SOURCEQUENCH
                    ICMP_REDIRECT ICMP_ECHO ICMP_ROUTERADVERT
                    ICMP_ROUTERSOLICIT ICMP_TIMXCEED ICMP_PARAMPROB
                    ICMP_TSTAMP ICMP_TSTAMPREPLY ICMP_IREQ ICMP_IREQREPLY
                    ICMP_MASKREQ ICMP_MASKREPLY
    );

# Tags:

    %EXPORT_TAGS = (
    ALL         => [@EXPORT, @EXPORT_OK],
    types       => [qw(ICMP_ECHOREPLY ICMP_UNREACH ICMP_SOURCEQUENCH
                       ICMP_REDIRECT ICMP_ECHO ICMP_ROUTERADVERT 
                       ICMP_ROUTERSOLICIT ICMP_TIMXCEED ICMP_PARAMPROB
                       ICMP_TSTAMP ICMP_TSTAMPREPLY ICMP_IREQ ICMP_IREQREPLY
                       ICMP_MASKREQ ICMP_MASKREPLY)],
    strip       => [qw(icmp_strip)],
);

}

# ICMP Types

use constant ICMP_ECHOREPLY       => 0;
use constant ICMP_UNREACH         => 3;
use constant ICMP_SOURCEQUENCH    => 4;
use constant ICMP_REDIRECT        => 5;
use constant ICMP_ECHO            => 8;
use constant ICMP_ROUTERADVERT    => 9;
use constant ICMP_ROUTERSOLICIT   => 10;
use constant ICMP_TIMXCEED        => 11;
use constant ICMP_PARAMPROB       => 12;
use constant ICMP_TSTAMP          => 13;
use constant ICMP_TSTAMPREPLY     => 14;
use constant ICMP_IREQ            => 15;
use constant ICMP_IREQREPLY       => 16;
use constant ICMP_MASKREQ         => 17;
use constant ICMP_MASKREPLY       => 18;

#
# Decode the packet
#

sub decode {
    my $class = shift;
    my($pkt, $parent, @rest) = @_;
    my $self = {};

    # Class fields

    $self->{_parent} = $parent;
    $self->{_frame} = $pkt;

    # Decode ICMP packet

    if (defined($pkt)) {

	($self->{type}, $self->{code}, $self->{cksum}, $self->{data}) =
	    unpack("CCna*", $pkt);
    }

    # Return a blessed object

    bless($self, $class);
    return $self;
}

#
# Strip a packet of its header and return the data
#

undef &icmp_strip;
*icmpstrip = \&strip;

sub strip {
    my ($pkt, @rest) = @_;

    my $icmp_obj = decode($pkt);
    return $icmp_obj->{data};
}

#
# Encode a packet
#

sub encode {
    my $self = shift;
    my ($ip) = @_;
    my ($packet);
    
    # Checksum the packet
    $self->checksum();

    # Put the packet together
    $packet = pack("CCna*", $self->{type}, $self->{code}, 
                $self->{cksum}, $self->{data});

    return($packet); 
}

#
# Calculate ICMP checksum

sub checksum {
    my $self = shift;
    my ($ip) = @_;
    my ($packet,$zero);

    # Put the packet together for checksumming
    $zero = 0;
    $packet = pack("CCna*", $self->{type}, $self->{code},
                $zero, $self->{data});

    $self->{cksum} = NetPacket::htons(NetPacket::in_cksum($packet));
}


#
# Module initialisation
#

1;

# autoloaded methods go after the END token (&& pod) below

__END__


# any real autoloaded methods go after this line