Java example source code file (NoLoopbackPackets.java)

This example Java source code file (NoLoopbackPackets.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, datagrampacket, exception, inetaddress, list, multicastsocket, net, network, networkinterface, noloopbackpackets, runtimeexception, sender, socketaddress, sockettimeoutexception, thread, util, windows

The NoLoopbackPackets.java Java example source code

/*
 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * @test
 * @bug 4742177
 * @summary Re-test IPv6 (and specifically MulticastSocket) with latest Linux & USAGI code
 */
import java.util.*;
import java.net.*;

public class NoLoopbackPackets {
    private static String osname;

    static boolean isWindows() {
        if (osname == null)
            osname = System.getProperty("os.name");
        return osname.contains("Windows");
    }

    private static boolean hasIPv6() throws Exception {
        List<NetworkInterface> nics = Collections.list(
                                        NetworkInterface.getNetworkInterfaces());
        for (NetworkInterface nic : nics) {
            if (!nic.isLoopback()) {
                List<InetAddress> addrs = Collections.list(nic.getInetAddresses());
                for (InetAddress addr : addrs) {
                    if (addr instanceof Inet6Address) {
                        return true;
                    }
                }
            }
        }

        return false;
    }

    public static void main(String[] args) throws Exception {
        if (isWindows()) {
            System.out.println("The test only run on non-Windows OS. Bye.");
            return;
        }

        if (!hasIPv6()) {
            System.out.println("No IPv6 available. Bye.");
            return;
        }

        MulticastSocket msock = null;
        List<SocketAddress> failedGroups = new ArrayList();
        try {
            msock = new MulticastSocket();
            int port = msock.getLocalPort();

            // we will send packets to three multicast groups :-
            // 224.1.1.1, ::ffff:224.1.1.2, and ff02::1:1
            //
            List<SocketAddress> groups = new ArrayList();
            groups.add(new InetSocketAddress(InetAddress.getByName("224.1.1.1"), port));
            groups.add(new InetSocketAddress(InetAddress.getByName("::ffff:224.1.1.2"), port));
            groups.add(new InetSocketAddress(InetAddress.getByName("ff02::1:1"), port));

            Thread sender = new Thread(new Sender(groups));
            sender.setDaemon(true); // we want sender to stop when main thread exits
            sender.start();

            // Now try to receive multicast packets. we should not see any of them
            // since we disable loopback mode.
            //
            msock.setSoTimeout(5000);       // 5 seconds

            byte[] buf = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buf, 0, buf.length);
            for (SocketAddress group : groups) {
                msock.joinGroup(group, null);

                try {
                    msock.receive(packet);

                    // it is an error if we receive something
                    failedGroups.add(group);
                } catch (SocketTimeoutException e) {
                    // we expect this
                }

                msock.leaveGroup(group, null);
            }
        } finally {
            if (msock != null) try { msock.close(); } catch (Exception e) {}
        }

        if (failedGroups.size() > 0) {
            System.out.println("We should not receive anything from following groups, but we did:");
            for (SocketAddress group : failedGroups)
                System.out.println(group);
            throw new RuntimeException("test failed.");
        }
    }

    static class Sender implements Runnable {
        private List<SocketAddress> sendToGroups;

        public Sender(List<SocketAddress> groups) {
            sendToGroups = groups;
        }

        public void run() {
            byte[] buf = "hello world".getBytes();
            List<DatagramPacket> packets = new ArrayList();

            try {
                for (SocketAddress group : sendToGroups) {
                    DatagramPacket packet = new DatagramPacket(buf, buf.length, group);
                    packets.add(packet);
                }

                MulticastSocket msock = new MulticastSocket();
                msock.setLoopbackMode(true);    // disable loopback mode
                for (;;) {
                    for (DatagramPacket packet : packets) {
                        msock.send(packet);
                    }

                    Thread.sleep(1000);     // 1 second
                }
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
}