Question

I am receiving messages of 14 bytes via a socket’s InputStream.
They look like this: a55a0b051000000000223664300c
and they have a specific pattern. The first two bytes are for synchronization and are always constant.

I am looking for the best way to verify this message.
First the length of 14 bytes would have to be verified, then the first 2 Bytes etc.

This is my approach until now:

public void handleMessage(String msg){

    if(msg.length() == 14){
        if(msg.substring(0, 1).equals("a5") && msg.substring(2, 3).equals("5a") ){

            //Determine tpye
            if(msg.substring(4, 5).equals("0b")){

                //Type = 05
                if(msg.substring(6, 7).equals("05")){

                    if(msg.substring(8, 15).equals("0b")){

                    }
                }

            }
            else if(msg.substring(4, 5).equals("6b")){
                //Type = 05
                if(msg.substring(6, 7).equals("05")){

                    if(msg.substring(8, 15).equals("0b")){

                    }
                }
            }
            else if(msg.substring(4, 5).equals("4b")){
                // ...
            }
            else if(msg.substring(4, 5).equals("ab")){
                // ...
            }
            else System.out.println("Error: telegram type");

        }else System.out.println("Error: Sync Bytes.");



    }else System.out.println("Error: Telegram length.");



}

But I want to avoid all those nested ifs and the redundant code that comes with them.
Any ideas on how to handle the string in a more efficient way?
Thanks!

Answer 1

first as I said in the comments don’t convert to string when you don’t need to

you can invert the guard causes and put an early return there to avoid those indents

also a switch on top level might be prudent as this is more readable then if-else cascade (less prone to typos)

public void handleMessage(byte[] msg, int off){
    if(msg.length()-off < 14){//just use the first 14 after offset          System.out.println("Error: Telegram length.");
        return;
    }
    if(msg[0+off]!=0xa5 || msg[0+off]!=0xa5 ){
        System.out.println("Error: Sync Bytes.");
        return;
    }
    //Determine tpye
    switch(msg[2+off]){
    case 0x0b:
        if(msg[3+off]==0x05){

            if(msg[4+off]==0x0b){
            }

        }
        break;
    case 0x6b:
        if(msg[3+off]==0x05){

            if(msg[4+off]==0x0b){

            }
        }
        break;
    case 0x4b:
        //...
        break;
    case 0xab:
        //...
        break;
    default:System.out.println("Error: telegram type");
        break;
    }
}