I'm in the process of doing a binary protocol parsing where I'm trying to read a String from the Array of bytes. In this array of bytes, the first 4 bytes represent the length of the String. The length of String is represented as Int32. For example., here is the Byte array:
val arr = "45 0 0 0 65 59 78 76 89 89 78 67 56 67 78 89 98 56 67 78 89 90 98 56 67 78 89 90 56 67 78 89 90 56 67 78 89 90 56 67 78 89 90 56 67 78 89 56 67"
It can be seen from the array above that the first 4 bytes 45 0 0 0 represent the size of the following String which in this case is 45 bytes long.
I understand that Int32 needs 4 bytes to be represented on the JVM. But I don't understand how I can parse the first 4 bytes and infer that the size of the following String is going to be 45 in the example above!
So what I need basically is something that can convert the Array 45 0 0 0 to just 45! Am I talking sense? Any suggestions please?
res60: Array[Byte] = Array(45, 0, 0, 0)
scala> ByteBuffer.wrap(res60).getInt()
res61: Int = 754974720
res61 is not something that I'm expecting!
ByteBuffer has big endian byte order by default, but your int uses little endian byte order. You have to explicitly convert the ByteBuffer to be little endian e.g.:
byte[] input = { 45, 0, 0, 0 };
ByteBuffer bb = ByteBuffer.wrap(input).order(ByteOrder.LITTLE_ENDIAN); // <---
int length = bb.getInt();
System.out.println(length); // 45