BitTorrent, DHT, BEP42, Calculating my NodeId

Question

I'm trying to calculate NodeId's according that are compliant with BEP42

I'm not clever enough to understand the example code given in BEP42 However the algorithm for creating nodeId's is given as : crc32c((ip & 0x030f3fff) | (r << 29))

There is also a table of results, from which we can see that a good nodeID for the ip address 21.75.31.124 would start with 5a3ce9, if the random seed used was '86' (in decimal I'm supposing).

So I try the following :

InetSocketAddress a = new InetSocketAddress("21.75.31.124",6881);
byte[] ba = a.getAddress().getAddress();
int ia = ByteBuffer.wrap(ba).order(ByteOrder.BIG_ENDIAN).getInt();
int r = 86;
int calc = (ia & 0x030f3fff) | (r<<29);
Crc32C crc = new Crc32C();
crc.update(calc);
int foo = crc.getIntValue();
byte[] ret = ByteBuffer.allocate(4).putInt(foo).array();
String retStr = Hex.encodeHexString(ret);
System.out.println("should be : 5a3ce9 is " + retStr);

But I get 6ea6c88c, which is wrong in just about every way. the 8472 has some code used to decide if a client's nodeId is BEP42 compliant, but I don't understand that code either.

Could anyone tell me what is wrong with the code above?

Answer 1

All, please ignore, answer is :

    InetSocketAddress a = new InetSocketAddress("21.75.31.124",6881);
    byte[] ip = a.getAddress().getAddress();
    int r = 86;

    byte[] mask = { 0x03, 0x0f, 0x3f, (byte) 0xff };   
    for(int i=0;i<mask.length;i++) {
        ip[i] &= mask[i];
    }
    ip[0] |= r << 5;
    Crc32C c = new Crc32C();
    c.update(ip, 0, Math.min(ip.length, 8));
    int crcVal = (int)c.getValue();
    String s = Integer.toHexString(crcVal);             

    System.out.println("should be : 5a3ce9 is " + s);