NAME

Algorithm::FloodControl - Limit event processing to count/time ratio.

SYNOPSIS

Functional interface

use Algorithm::FloodControl;

my $wait = flood_check( 5, 60, 'FLOOD EVENT NAME' );

if( $wait ) {
    print "Please wait $wait sec. before requesting this resource again.";
} else {
    print "Ok, here you are.";
}  

Object-oriented interface

use Algorithm::FloodControl ();

my $flood_control = Algorithm::FloodControl->new(
    storage => $memd, 
    limits => {
        limit_name => [
            {
                period => 60,
                attempts => 5,
            }, {
                period => 3600,
                attempts => 30,
            }
        ]
    }
);

$flood_control->register_attempt( limit_name => 'vasja_pupkin' );

my $attempt_count = $flood_control->get_attempt_count( limit_name => 'vasja_pupkin' ); # 1

if ( $flood_control->is_user_overrated( limit_name => 'vasja_pupkin' ) ) {
    die "Ненене, Девид Блейн (:";
}

DESCRIPTION

"Flood control" method is used to restrict the number of events to happen or to be processed in specific perion of time. Few examples are: web server can limit requsets number to a page or you may want to receive no more than 10 SMS messages on your GSM Phone per hour. Applications of this method are unlimited.

FUNCTIONS

This module exports several functions:

flood_check( $count, $time, $event_name )

This function is the core of the module. It receives 3 arguments: maximum event count, maximum time period (in seconds) for this event count and finally the event name. There is internal storage so flood_check() can track several events by name.

Third argument could be omitted. In this case the event name will be constructed from the package name, file name and line number from the calling point. However this is not recommendet unless you need it for very simple program.

The return value is time in seconds that this event must wait to be processed or 0 if event can be processed immediately.

flood_storage( <$ref> )

If you want to save and restore the internal storage (for example for cgi use), you can get reference to it with flood_storage() function which returns this reference and it can be stored with other module like FreezeThaw or Storable. When restoring you must pass the storage reference as single argument to flood_storage().

METHODS

new( storage => $cache, limits => \%limits )

Creates new object. $cache can be Cache::Memcached or Cache::Memcached::Fast object.

register_attempt( $identifier )

Increments attempt counter for $identifier.

forget_attempts( $identifier )

Sets attempt counter to zero

get_attempt_count( $identifier )

Returns count of attempts

is_user_overrated( $identifier )

If user have reached his limits returns time to unlocking in seconds. Otherwise returns 0

EXAMPLE

CGI script is very usefull as example because it has all elements of Algorithm::FloodControl use:

#!/usr/bin/perl
use strict;
use Storable qw( store retrieve ); # used to save/restore the internal data
use LockFile::Simple qw( lock unlock ); # used to lock the data file
use Algorithm::FloodControl;

my $flood_file = "/tmp/flood-cgi.dat";

lock( $flood_file );                                   # lock the storage
my $FLOOD = retrieve( $flood_file ) if -r $flood_file; # read storage data
flood_storage( $FLOOD ) if $FLOOD;                     # load storage 
my $wait = flood_check( 5, 60, 'FLOOD TEST CGI' );     # check for flood
store( flood_storage(), $flood_file );                 # save storage data
unlock( $flood_file );                                 # unlock the file

print "Content-type: text/plain\n\n";
if( $wait ) {
    print "Please wait $wait seconds before requesting this page again.\n";
    exit;
}
print "Hello, this is main script here\n";

This example is just one of very large number of cases where flood control can be useful. I used it in IRC bots, email notifications, web site updates, etc.

AUTHOR

Vladi Belperchinov-Shabanski "Cade"

<cade@biscom.net> <cade@datamax.bg> <cade@cpan.org>

http://cade.datamax.bg

Andrey Kostenko "GuGu" <andrey@kostenko.name>

http://kostenko.name

VERSION

$Id: FloodControl.pm 7 2008-11-06 12:51:33Z gugu $