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PATL / Event-SlidingWindow-0.05 / SlidingWindow.pm 

            

              
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package Event::SlidingWindow ;
use strict ;
use Carp ;
$Event::SlidingWindow::VERSION = '0.05' ;
sub new {
        my $class = shift ;
        my $nb_buckets = int(shift) ;           # Number of buckets, i.e. window size
        my $bucket_size = int(shift) || 1 ; # Bucket size in seconds
         
        # Validate paramters...
        if ($nb_buckets <= 0){
                croak("nb_buckets must be an integer > 0") ;
        }
         
        my $this = {
                nb_buckets => $nb_buckets,
                bucket_size => $bucket_size,
                loop => [],
        } ;
        bless($this, $class) ;
        $this->_init() ;
         
        return $this ;
}
sub _init {
        my $this = shift ;
        my $now = shift || time() ;
         
        $this->{cur_ts} = $now ;
        for (my $i = 0 ; $i < $this->{nb_buckets} ; $i++){
                $this->{loop}->[$i] = 0 ;
        }
        $this->{cur_idx} = 0 ;
}
sub record_event {
        my $this = shift ;
        my $now = shift ;
        my $incr = shift || 1 ;
         
        $this->_update($now) ;
        $this->{loop}->[$this->{cur_idx}] += $incr ;
}
sub count_events {
        my $this = shift ;
        my $now = shift ;
         
        $this->_update($now) ;
        my $cnt = 0 ;
        foreach my $c (@{$this->{loop}}){
                $cnt += $c ;
        }
         
        return $cnt ;
}
# This method is responsible for keeping the loop in sync for
# from current time value.
sub _update {
        my $this = shift ;
        my $now = shift || time() ;
        my $interval = int(($now - $this->{cur_ts}) / $this->{bucket_size}) ;
        if (! $interval){
                return ;
        }
        if ($interval >= $this->{nb_buckets}){
                $this->_init($now) ;
                return ;
        }
         
        # Now we really have some work to do.
        for (my $i = 0 ; $i < $interval ; $i++){
                $this->{loop}->[($this->{cur_idx} + $i + 1) % $this->{nb_buckets}] = 0 ;
        }       
        $this->{cur_idx} = ($this->{cur_idx} + $interval) % $this->{nb_buckets} ;
        $this->{cur_ts} = $now ;
}
sub _dump {
        my $this = shift ;
         
        my @ret = () ;
        for (my $i = 0 ; $i < $this->{nb_buckets} ; $i++){
                push @ret, $this->{loop}->[($this->{cur_idx} + $i + 1) % $this->{nb_buckets}] ;
        }
         
        return \@ret ;
}
1 ;
__END__
=head1 NAME
Event::SlidingWindow - Count events that occur within a fixed sliding window of time
=head1 SYNOPSIS
  use Event::SlidingWindow ;
   
  my $esw = new Event::SlidingWindow(30) ;
  $esw->record_event() ;
  my $cnt = $esw->count_events() ;
=head1 DESCRIPTION
Event::SlidingWindow allows you to create a time window of a fixed length and 
keeps track of how many events have occured within that window as it advances 
in time. It was created for use in daemons in order to detect denial of service 
attacks.
=head1 AUTHOR
Patrick LeBoutillier, E<lt>patl@cpan.orgE<gt>
=head1 COPYRIGHT AND LICENSE
Copyright 2004-2005 by Patrick LeBoutillier
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself. 
=cut