SocketHelper.java

package com.github.etacassiopeia.jna;

import com.sun.jna.LastErrorException;
import com.sun.jna.Native;
import com.sun.jna.Pointer;
import com.sun.jna.ptr.IntByReference;
import sun.nio.ch.DatagramSocketAdaptor;

import java.io.FileDescriptor;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.DatagramSocket;
import java.nio.channels.DatagramChannel;

/**
 * <h1>SocketHelper</h1>
 *
 * @author Mohsen Zainalpour
 * @version 1.0
 * @since 24/04/16
 */

/**
 * sample usage :
 *
 DatagramChannel channel = DatagramChannel.open();
 DatagramSocket socket = channel.socket();
 socket.setReuseAddress(true);
 SocketHelper.setSockOpt(socket, SocketHelper.SOL_SOCKET, SocketHelper.SO_REUSEPORT, 1);

 channel.socket().bind(new InetSocketAddress(5146));
 */
public class SocketHelper {

    public static int SO_REUSEPORT = 15;

    public static int SOL_SOCKET = 1;

    static {
        Native.register("c");
    }

    private SocketHelper() {
    }

    private static native int setsockopt(int fd, int level, int option_name, Pointer option_value, int option_len) throws LastErrorException;

    public static void setSockOpt(DatagramSocket socket, int level, int option, int option_value) throws IOException {

        if (socket instanceof DatagramSocketAdaptor) {
            DatagramSocketAdaptor datagramSocketAdaptor = (DatagramSocketAdaptor) socket;

            try {

                Method getChannelMethod = DatagramSocketAdaptor.class.getDeclaredMethod("getChannel");
                getChannelMethod.setAccessible(true);
                DatagramChannel datagramChannelImplInstance = (DatagramChannel) getChannelMethod.invoke(datagramSocketAdaptor);

                Field fileDescriptorField = datagramChannelImplInstance.getClass().getDeclaredField("fd");
                fileDescriptorField.setAccessible(true);
                FileDescriptor fileDescriptorInstance = (FileDescriptor) fileDescriptorField.get(datagramChannelImplInstance);

                Field numericFdValue = FileDescriptor.class.getDeclaredField("fd");
                numericFdValue.setAccessible(true);
                int fd = (int) numericFdValue.get(fileDescriptorInstance);

                IntByReference val = new IntByReference(option_value);

                setsockopt(fd, level, option, val.getPointer(), 4);

            } catch (Exception e) {
                throw new IOException(e.getMessage(), e);
            }
        }
    }
}