CODEWITHSUNDEEP
java
user1530147
user1530147

Reputation: 153

How to read 1 bit from udp packet

I want to read 1 bit from a udp packet.

The udp packet looks like this (c code):

struct typedef struct s_foo
{
   __u32 foo;
   __u8  bar:1,
         bob:1;
} __attribute__((packed)) s_foo;

How in java can i read this?

So far I have this but i can't read foo nor bar or bob...

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class BroadcastListener
{
    public static void main(String[] args) throws IOException
    {
        if (args.length != 1) {
            System.out.println("usage: <program> port");
            System.exit(1);
        }

        int port = Integer.parseInt(args[0]);
        DatagramSocket dgram = new DatagramSocket(port);

        byte[] buffer = new byte[2048];
        DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

        while (true) {
            dgram.receive(packet);

            String msg = new String(buffer, 0, packet.getLength());

            System.out.println(packet.getAddress().getHostName() + ": "
                    + msg);

            packet.setLength(buffer.length);
        }
    }
}

Upvotes: 1

Views: 387

Answers (1)

Alexandre Lavoie
Alexandre Lavoie

Reputation: 8771

To test a bit you must use bitwise operators example :

This will test that value has the bit 0b00001000 set

boolean result = value & 0x0A;

This will return you the content of the bit 0b00001000

int value = value & ~0x0A;

Here is a link that will help you : http://vipan.com/htdocs/bitwisehelp.html

EDIT :

To read two bit at a time :

int nMask = 0x1A; // 0b00011000

nValue = nValue & nMask;
nValue = nValue >> 3;

nValue will contain bits at 0b00000011

Upvotes: 2

Related Questions