Wifi Direct Multicast Datagrams throw SocketExceptions

[Micah Akin]

Does anyone know why Android would throw a SocketException when I try to send a DatagramPacket to a Multicast address from a Wifi Direct Group Owner?  

When connected to that host using the regular (wlan0) wifi, I send and receive Multicast without a problem.

(a) <--> (b) <--> (c)

(a) can send Multicast datagrams which (c) receives

(b) throws the below error when trying to send a multicast datagram

(b) is the Wifi Direct Group Owner (GO)

(a) and (c) are connected to (b) using legacy wifi

I am running Android 6.0.1 on a Samsung Galaxy Note 4

Here is a snippet of my code:

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);

WifiManager wifiManager = (WifiManager)this.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
wifiManager.setWifiEnabled(true);

MulticastLock mcastLock = wifiManager.createMulticastLock("lock");
mcastLock.acquire();

try {
    Enumeration<NetworkInterface> enumeration = NetworkInterface.getNetworkInterfaces();
    NetworkInterface p2p0 = null;
    NetworkInterface wlan0 = null;
    for (NetworkInterface iface : Collections.list(enumeration)) {

        try {
            if (iface.getName().equals("p2p0")) {
                p2p0 = iface;

                if(p2p0.supportsMulticast()){
                    debug.print("p2p0 supports multicast");
                } else
                {
                    debug.print("p2p0 does not supports multicast");
                }
            } else if (iface.getName().equals("wlan0")) {
                wlan0 = iface;
                if(wlan0.supportsMulticast()){
                    debug.print("wlan0 supports multicast");
                } else
                {
                    debug.print("wlan0 does not supports multicast");
                }
            }
        } catch (NullPointerException e){
            e.printStackTrace();
        }
    }
    if(mcastLock.isHeld()){
        debug.print("MCast Lock held");
    } else
    {
        debug.print("MCast Lock Not held");
    }


    String msg = "Hello from "+name;
    InetAddress group = InetAddress.getByName("224.0.0.1");
    MulticastSocket s = new MulticastSocket(5001);
    s.joinGroup(new InetSocketAddress(InetAddress.getByName("224.0.0.1"), 5001), p2p0);
    DatagramPacket hi = new DatagramPacket(msg.getBytes(), msg.length(), group, 5001);


    // get their responses!
    byte[] buf = new byte[1000];
    for(int i = 0; i< 30; i++) {
        s.send(hi);                          // line 261

        DatagramPacket recv = new DatagramPacket(buf, buf.length);
        s.receive(recv);
        if(recv.getLength()>0) {
            System.out.println("'"+new String(buf, 0 , recv.getLength())+"'");
        }

            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

    }

    // OK, I'm done talking - leave the group...
    s.leaveGroup(group);


} catch (IOException e){
    e.printStackTrace();
    //debug.print(e.);
}

Below is a snippet of the debug trace:  

04-23 19:20:19.492 7083-7083/edu.nps.minet I/System.out: p2p0 supports multicast

04-23 19:20:19.517 7083-7083/edu.nps.minet I/System.out: wlan0 supports multicast

04-23 19:20:19.552 7083-7083/edu.nps.minet I/System.out: MCast Lock held

04-23 19:20:19.572 7083-7083/edu.nps.minet I/System.out: Hello from BDD177B9C6

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err: java.net.SocketException: sendto failed: ENETUNREACH (Network is unreachable)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.IoBridge.maybeThrowAfterSendto(IoBridge.java:542)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.IoBridge.sendto(IoBridge.java:511)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at java.net.PlainDatagramSocketImpl.send(PlainDatagramSocketImpl.java:184)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at java.net.DatagramSocket.send(DatagramSocket.java:305)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at edu.nps.minet.MainActivity$3.onClick(MainActivity.java:261)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.view.View.performClick(View.java:5697)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.view.View$PerformClick.run(View.java:22526)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.os.Handler.handleCallback(Handler.java:739)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:95)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.os.Looper.loop(Looper.java:158)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:7225)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at java.lang.reflect.Method.invoke(Native Method)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err: Caused by: android.system.ErrnoException: sendto failed: ENETUNREACH (Network is unreachable)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.Posix.sendtoBytes(Native Method)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.Posix.sendto(Posix.java:211)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.BlockGuardOs.sendto(BlockGuardOs.java:278)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err:     at libcore.io.IoBridge.sendto(IoBridge.java:509)

04-23 19:20:19.597 7083-7083/edu.nps.minet W/System.err: ... 12 more