qpsmtpd/plugins/count_unrecognized_commands

# -*- perl -*-
=head1 NAME

count_unrecognized_commands - Count unrecognized commands and disconnect when we have too many

=head1 DESCRIPTION

Disconnect the client if it sends too many unrecognized commands.
Good for rejecting spam sent through open HTTP proxies.

=head1 CONFIGURATION

Takes one parameter, the number of allowed unrecognized commands
before we disconnect the client.  Defaults to 4.

=cut

sub register {
  my ($self, $qp, @args) = @_;
  $self->register_hook("unrecognized_command", "check_unrec_cmd");

  if (@args > 0) {
    $self->{_unrec_cmd_max} = $args[0];
    $self->log(LOGWARN, "WARNING: Ignoring additional arguments.") if (@args > 1);
  } else {
    $self->{_unrec_cmd_max} = 4;
  }

  $qp->connection->notes('unrec_cmd_count', 0);

}

sub check_unrec_cmd {
  my ($self, $cmd) = @_[0,2];
  
  $self->log(LOGINFO, "Unrecognized command '$cmd'");

  my $badcmdcount = 
    $self->qp->connection->notes( 'unrec_cmd_count',
        ($self->qp->connection->notes('unrec_cmd_count') || 0) + 1
    );

  if ($badcmdcount >= $self->{_unrec_cmd_max}) {
    $self->log(LOGINFO, "Closing connection. Too many unrecognized commands.");
    return (DENY_DISCONNECT, "Closing connection. $badcmdcount unrecognized commands.  Perhaps you should read RFC 2821?");
  }

  return DECLINED;
}