Ytukyg

Really need some suggestions here.

I am trying to manually add a tEXt chunk into an existing PNG file just for learning purposes.

While it appeared to be a success, after deliberating editing the image, for e.g. deleting a small portion off the image or rotate it and save, my tEXt chunk is gone. Maybe some part of my code went wrong, some reviews would be appreciated.

byte RAWFILEBYTES = new byte[(int) pngFile.length()];

            FileInputStream ins = new FileInputStream(pngFile);



        for (int i = 0; i < RAWFILEBYTES.length; i++) {

            RAWFILEBYTES[i] = (byte) ins.read();

        }



        byte size = {(byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x0e};

        byte crc32 = new byte[4];

        String chunkNameAndKey = "tEXtGreeting";

        String value = "hello";



        //Declaring size equal to the length of chunk name + key value pair

        byte tEXtAndValue = new byte[chunkNameAndKey.getBytes().length + 1 + value.getBytes().length];



        //Forming byte array of chunk name and key value pair

        System.arraycopy(chunkNameAndKey.getBytes(), 0, tEXtAndValue, 0, chunkNameAndKey.getBytes().length);

        tEXtAndValue[chunkNameAndKey.getBytes().length] = (byte) 0x00; //Follow specification key pair value separate by null

        System.arraycopy(value.getBytes(), 0, tEXtAndValue, chunkNameAndKey.getBytes().length + 1, value.getBytes().length);



        //Calculating checksum comprise of chunk name and value

        //E.g. tEXtGreeting[null]hello

        Checksum checksum = new CRC32();

        checksum.update(tEXtAndValue, 0, tEXtAndValue.length);



        //Convert checksum result to 4 bytes according to PNG.

        ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);

        buffer.putLong(checksum.getValue());   

        System.arraycopy(buffer.array(), buffer.array().length - 4, crc32, 0, 4);



        //Entire tEXt chunk comprise of size, chunk name, key-value pair and CRC in order.

        byte textChunkArr = new byte[4 + tEXtAndValue.length + 4];

        System.arraycopy(size, 0, textChunkArr, 0, size.length);

        System.arraycopy(tEXtAndValue, 0, textChunkArr, size.length, tEXtAndValue.length);

        System.arraycopy(crc32, 0, textChunkArr, size.length + tEXtAndValue.length, crc32.length);



        byte byte_array = new byte[RAWFILEBYTES.length + textChunkArr.length];



        //Place the text chunk directly before IEND chunk.

        System.arraycopy(RAWFILEBYTES, 0, byte_array, 0, RAWFILEBYTES.length - 12);

        System.arraycopy(textChunkArr, 0, byte_array, RAWFILEBYTES.length - 12, textChunkArr.length);

        System.arraycopy(RAWFILEBYTES, RAWFILEBYTES.length - 12, byte_array, RAWFILEBYTES.length - 12 + textChunkArr.length, 12);



        try (FileOutputStream fos = new FileOutputStream("final2_file.png")) {

            fos.write(byte_array);

        }

In summary, what I'm trying to do, I am creating and insert a tEXt chunk manually directly before IEND chunk.