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POIs Multicast broken for Android 2.0.1 (currently on the DROID) or am I missing something?
 

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  1. POIs Multicast broken for Android 2.0.1 (currently on the DROID) or am I missing something?
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    <p>This code works perfectly in Ubuntu, Windows, and Mac OS X. It also works fine with a Nexus One running Android 2.1.1.</p> <p>I start sending and listening multicast datagrams, and all the computers and the Nexus One will see each other perfectly. Then I <strong>run the same code on a Droid</strong> (Firmware 2.0.1), and <strong>everybody will get the packets sent by the Droid, but the droid will listen only to its own packets</strong>.</p> <p>This is the <code>run()</code> method of a thread that's constantly listening on a Multicast group for incoming packets sent to that group.</p> <p>I'm running my tests on a local network where I have multicast support enabled in the router. My goal is to have devices meet each other as they come online by broadcasting packages to a multicast group.</p> <pre><code>public void run() { byte[] buffer = new byte[65535]; DatagramPacket dp = new DatagramPacket(buffer, buffer.length); try { MulticastSocket ms = new MulticastSocket(_port); ms.setNetworkInterface(_ni); //non loopback network interface passed ms.joinGroup(_ia); //the multicast address, currently 224.0.1.16 Log.v(TAG,"Joined Group " + _ia); while (true) { ms.receive(dp); String s = new String(dp.getData(),0,dp.getLength()); Log.v(TAG,"Received Package on "+ _ni.getName() +": " + s); Message m = new Message(); Bundle b = new Bundle(); b.putString("event", "Listener ("+_ni.getName()+"): \"" + s + "\""); m.setData(b); dispatchMessage(m); //send to ui thread } } catch (SocketException se) { System.err.println(se); } catch (IOException ie) { System.err.println(ie); } } </code></pre> <p>This is the code that sends the Multicast Datagram out of every valid network interface available (that's not the loopback interface).</p> <pre><code>public void sendPing() { MulticastSocket ms = null; try { ms = new MulticastSocket(_port); ms.setTimeToLive(TTL_GLOBAL); List&lt;NetworkInterface&gt; interfaces = getMulticastNonLoopbackNetworkInterfaces(); for (NetworkInterface iface : interfaces) { //skip loopback if (iface.getName().equals("lo")) continue; ms.setNetworkInterface(iface); _buffer = ("FW-"+ _name +" PING ("+iface.getName()+":"+iface.getInetAddresses().nextElement()+")").getBytes(); DatagramPacket dp = new DatagramPacket(_buffer, _buffer.length,_ia,_port); ms.send(dp); Log.v(TAG,"Announcer: Sent packet - " + new String(_buffer) + " from " + iface.getDisplayName()); } } catch (IOException e) { e.printStackTrace(); } catch (Exception e2) { e2.printStackTrace(); } } </code></pre> <p><strong>Update (April 2nd 2010)</strong> I found a way to have the Droid's network interface to communicate using Multicast: <a href="http://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html" rel="nofollow noreferrer">WifiManager.MulticastLock</a>.</p> <pre><code>MulticastLock _wifiMulticastLock = ((WifiManager) context.getSystemService(Context.WIFI_SERVICE)).createMulticastLock("multicastLockNameHere"); _wifiMulticastLock.acquire(); </code></pre> <p>Then when you're done...</p> <pre><code>if (_wifiMulticastLock != null &amp;&amp; _wifiMulticastLock.isHeld()) _wifiMulticastLock.release(); </code></pre> <p>After I did this, the Droid started sending and receiving UDP Datagrams on a Multicast group.</p> <p><strong>Update Jul-6-2010</strong></p> <p>Per request, here's my current code, the next method exists on an abstract class that can be used for both Broadcast and Multicast receivers.</p> <pre><code>public void run() { onInit(); try { byte[] data = new byte[65535]; while (isProcessing()) { try { DatagramPacket receivedDatagram = new DatagramPacket(data, data.length); _socket.receive(receivedDatagram); onDatagramReceived(receivedDatagram); data = new byte[65535]; // This pattern is for saving memory allocation. } catch (InterruptedIOException e) { if (!isProcessing()) break; } } // while } catch (Exception e) { Log.e(TAG, e.getMessage(), e); } finally { onStop(); _socket.close(); _socket.disconnect(); } } </code></pre> <p>Your extending classes should implement <code>onInit()</code> and <code>onDatagramReceived()</code></p> <p>For a <strong>Multicast</strong> receiver, <code>onInit()</code> <strong>looks something</strong> like this:</p> <pre><code>_socket = new MulticastSocket(PORT_MULTICAST); InetAddress groupAddress = InetAddress.getByAddress(MULTICAST_GROUP_ADDRESS); InetAddress groupInetAddress = FrostWireUtils.fastResolveAddress(groupAddress); //reflection hack to not resolve ips try { _socket.setSoTimeout(500); _socket.setTimeToLive(MULTICAST_TTL_GLOBAL); _socket.setReuseAddress(true); _socket.setNetworkInterface( WifiUtils.getWifiNetworkInterface()); _socket.joinGroup(groupInetAddress); WifiUtils.lockMulticast(); } catch (Exception e) { Log.e(TAG, e.getMessage(), e); } </code></pre>
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    1. COI am trying to receive Multicast packets on my Nexus-One (firmware 2.1.1). I used the above code, but had no luck so far. Can you please attach your complete source so I can compare it with mine? Thanks, Eyal
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    2. COEya, I've added an update, hope it helps.
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