Using Java's Bit Stuffing Error Detection Technique

Bit stuffing is a technique used in data communications systems to detect and correct errors that may occur during data transmission. It works by adding extra bits to the data being transmitted to flag errors when they occur.

A common way to implement bit stuffing in Java is to use a flag byte (such as 0x7E) to indicate the start and end of a frame, and a special escape byte (such as 0x7D) to indicate the next frame byte is a padding bit. For example, the sender will add a padding bit before each occurrence of the flag byte in the sent data so that the flag byte is not mistaken for the beginning or end of the frame at the receiver.

This is an example of how to implement bit stuffing in Java -

public static byte[] bitStuff(byte[] data) {
    final byte FLAG = 0x7E;
    final byte ESCAPE = 0x7D;

    // Create a new byte array to store the stuffed data
    byte[] stuffedData = new byte[data.length * 2];

    // Keep track of the current index in the stuffed data array
    int stuffedIndex = 0;

    // Iterate through the original data
    for (int i = 0; i < data.length; i++) {
        byte b = data[i];

        // If the current byte is the flag or escape byte, stuff it
        if (b == FLAG || b == ESCAPE) {
            stuffedData[stuffedIndex++] = ESCAPE;
            stuffedData[stuffedIndex++] = (byte) (b ^ 0x20);
        } else {
            stuffedData[stuffedIndex++] = b;
        }
    }

    return stuffedData;
}

On the receiving end, you can use similar concepts to retrieve the raw data.

public static byte[] bitUnStuff(byte[] data) {
    final byte FLAG = 0x7E;
    final byte ESCAPE = 0x7D;

    // Create a new byte array to store the unstuffed data
    byte[] unstuffedData = new byte[data.length];

    // Keep track of the current index in the unstuffed data array
    int unstuffedIndex = 0;

    // Iterate through the stuffed data
    for (int i = 0; i < data.length; i++) {
        byte b = data[i];

        // If the current byte is the escape byte, unstuff the next byte
        if (b == ESCAPE) {
            unstuffedData[unstuffedIndex++] = (byte) (data[++i] ^ 0x20);
        } else {
            unstuffedData[unstuffedIndex++] = b;
        }
    }

    return unstuffedData;
}

This is a basic example of the bit stuffing technique, which can be enhanced to handle more error conditions and verify the data using a CRC or checksum.

Example

certainly! Here is an example of how to use bitStuff() and bitUnStuff() methods in a simple program -

public static void main(String[] args) {
   byte[] data = {0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x7E};  // Hello~
   byte[] stuffedData = bitStuff(data);
   System.out.println("Original Data: "+Arrays.toString(data));
   System.out.println("Stuffed Data: "+ Arrays.toString(stuffedData));

   byte[] unstuffedData = bitUnStuff(stuffedData);
   System.out.println("Unstuffed Data: "+ Arrays.toString(unstuffedData));
}

When you run this program, it will first call the bitStuff() method to fill in the original data, and then print out the original data and the filled data.

Then it will call the bitUnStuff() method to retrieve the original data, then it will print the unstuffed data.

Example

For the given data example

0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x7E,

Output

You will get the output

Original Data: [72, 101, 108, 108, 111, 126]
Stuffed Data: [72, 101, 108, 108, 111, 93, 30, 126]
Unstuffed Data: [72, 101, 108, 108, 111, 126]

You can see that the padding data has one more byte 93, 30, which is the padding version of 7E.

You can also see that the unpopulated data is the same as the original data, which confirms that the data was successfully retrieved without any errors.

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