[b]How to convert a Socket object in a C socket file descriptor[/b]

Question

Hi all,
I need to make a getsockopt() call using JNI, but I don't know how to convert a Java Socket object in the integer corresponding to the socket file descriptor.
Thank you in advance!
Fernando

Answer 1

I was wrong in my previous post. FileDescriptor is used for PlainSocketImpl. This means I can give you a solution.
The solution does involve rebuilding some built-in Java classes to make certain fields accessible.
You have to modify access to three classes:
1. You can either use my SocketGetImpl or just rebuild java.net.Socket and change from
SocketImpl getImpl() throws SocketException {
to
public SocketImpl getImpl() throws SocketException {
2. In java.net.SocketImpl change from
protected FileDescriptor getFileDescriptor() {
to
public FileDescriptor getFileDescriptor() {
3. In java.io.FileDescriptor I would add the method
public int getFd(){ return fd; }
Then my test program becomes:
package myhack;
import java.io.*;
import java.net.*;
public class DoSock {
        public static void main(String args[]) throws Exception{
                Socket s= new Socket("mywebserver",80);
                System.out.println("s="+s);
                SocketImpl si = SocketGetImpl.getImpl(s);
                System.out.println("si="+si);
                FileDescriptor fd = si.getFileDescriptor();
                System.out.println("fd="+fd);
                System.out.println("fd int="+fd.getFd());
}And you still have to invoke as:
java -Xbootclasspath/p:. myhack.DoSock
or boot path pointing at jar file, etc.