package Mail::Audit::KillDups;
use Mail::Audit;
use vars qw(@VERSION $dupfile $cache_bytes);
$VERSION     = '2.224';
$dupfile     = ".msgid-cache";
$cache_bytes = 10000;
1;

package Mail::Audit;
use strict;
use Fcntl;

sub killdups {
  my $self        = shift;
  my $mid         = shift || $self->get("Message-Id");
  my $end_of_ring = 0;
  my $current_pos;

  unless (length $mid) {
    $self->_log(1, "message has no message-id; skipping duplicate check");
    return;
  }

  unless (sysopen MSGID, $Mail::Audit::KillDups::dupfile, O_RDWR | O_CREAT) {
    $self->_log(1, "Error opening $Mail::Audit::KillDups::dupfile: $!");
    return 1;
  }

  chomp $mid;
  while (<MSGID>) {
    chomp;
    if ($_ eq $mid) {
      $self->_log(1, "Duplicate, ignoring");
      $self->ignore;
      return -1;
    }

    $current_pos = tell MSGID;
    if ($current_pos > $Mail::Audit::KillDups::cache_bytes && $end_of_ring == 0)
    {
      # we've gotten too big, write this mid back at the top of the file
      last;
    } elsif ($_ eq "" && $end_of_ring == 0 && $current_pos > 0) {
      # Found the end of the ring buffer, so save position.
      $end_of_ring = $current_pos - 1;
    }
  }

  # Didn't find mid, so write it to the end of the ring buffer
  unless (seek MSGID, $end_of_ring, 0) {
    $self->_log(1, "seek to position $end_of_ring failed: $!");
    close MSGID;
    return 1;
  }

  print MSGID "$mid\n\n";
  close MSGID;

  return;
}

1;
__END__

=pod

=head1 NAME

Mail::Audit::KillDups - Mail::Audit plugin for duplicate suppression

=head1 SYNOPSIS

    use Mail::Audit qw(KillDups);
    $Mail::Audit::KillDups::dupfile = "/home/simon/.msgid-cache";
        my $mail = Mail::Audit->new;
    $mail->killdups;

=head1 DESCRIPTION

This is a Mail::Audit plugin which provides a method for checking
and supressing duplicate messages; that is, mails with message-ids which
have been previously seen.

=head2 METHODS

=over 4

=item C<killdups>

Checks the incoming message against a file of previously seen message
ids, ignores it if it's already seen, and adds it if it hasn't been.
C<$Mail::Audit::KillDups::dupfile> contains the name of the file used;
if you don't set this, it will be F<.msgid-cache> in the current
directory. (Probably your home directory.)

The data in C<$Mail::Audit::KillDups::dupfile> will be treated as a
ring buffer, where the end of the buffer will be delimited by two
newline characters.  When the file size exceeds
C<$Mail::Audit::KillDups::cache_bytes> bytes, the message id will be
written at the beginning of the file.  Old message ids in the file
will be overwritten.  The default cache size is 10000 bytes, which is
enough space for about 200 message-ids.

The semantics are tortured; the return values are as follows:

  false - not a duplicate
  +1    - an error occured during dupcheck
  -1    - message is a duplicate

=back

=head1 AUTHOR

Simon Cozens <simon@cpan.org>

=head1 SEE ALSO

L<Mail::Audit>