qpsmtpd/plugins/loop

#!perl -w

=head1 NAME

loop - Detect mail loops

=head1 DESCRIPTION

This plugin detects loops by counting "Received" and "Delivered-To"
header lines.  It's a kluge but it duplicates what qmail-smtpd does,
and it does at least prevent messages from looping forever.

=head1 CONFIGURATION

Takes one optional parameter, the maximum number of "hops" ("Received"
and lines plus "Delivered-To" lines) allowed.  The default is 100, the
same as in qmail-smtpd.

=head1 AUTHOR

Written by Keith C. Ivey

=head1 LICENSE

Released to the public domain, 17 June 2005.

=cut

use Qpsmtpd::DSN;

sub init {
    my ($self, $qp, @args) = @_;

    $self->{_max_hops} = $args[0] || 100;

    if ($self->{_max_hops} !~ /^\d+$/) {
        $self->log(LOGWARN, "Invalid max_hops value -- using default");
        $self->{_max_hops} = 100;
    }
    $self->log(LOGWARN, "Ignoring additional arguments") if @args > 1;
}

sub hook_data_post {
    my ($self, $transaction) = @_;

    my $hops = 0;
    $hops++
      for $transaction->header->get('Received'),
      $transaction->header->get('Delivered-To');

    if ($hops >= $self->{_max_hops}) {

        # default of too_many_hops is DENY, see comment in POD of Qpsmtpd::DSN
        return Qpsmtpd::DSN->too_many_hops();
    }

    return DECLINED;
}