Decoding packets further with NetPacket::TCP

    use NetPacket::TCP qw(:ALL);
    ...
    
    while (1) {
        my $msg = $ipq->get_message;
        my $ip = NetPacket::IP->decode($msg->payload);
        
        if ($ip->{proto} == IP_PROTO_TCP) {
            my $tcp = NetPacket::TCP->decode($ip->{data});
        
            if (grep {$tcp->{dest_port} == $_} (22, 25, 80)) {
                $ipq->set_verdict($msg->packet_id, NF_ACCEPT);
                next;
            }
        }
        
        $ipq->set_verdict($msg->packet_id, NF_DROP);
    }