Multicast Support on Android in Hotspot/Tethering mode

Question

I have a prototype Android app that is listening for multicast packets to 'discover' clients to communicate with. The socket set up is similar to this:

InetAddress group = InetAddress.getByName("228.1.2.3");
MulticastSocket s = new MulticastSocket(4000);
s.joinGroup(group);

This works very well when all the devices are connected via WiFi. I would like to support this with the phone acting as a portable hotspot. However, while all my devices appear to connect to the hotspot correctly I no longer receive multicast data. I'm wondering if there are restrictions that disallow this type of communication in hotspot mode, or if there are is any additional network configuration required to enable this? I've tried this on a couple different devices running Gingerbread and Froyo with no luck.

Answer 1

As this article show: https://plus.google.com/+Chainfire/posts/9NMemrKYnCd

MulticastSocket::setNetworkInterface()

would be the answer

you can find the wlan0 eth by :

public static NetworkInterface getWlanEth() {
    Enumeration<NetworkInterface> enumeration = null;
    try {
        enumeration = NetworkInterface.getNetworkInterfaces();
    } catch (SocketException e) {
        e.printStackTrace();
    }
    NetworkInterface wlan0 = null;
    StringBuilder sb = new StringBuilder();
    while (enumeration.hasMoreElements()) {
        wlan0 = enumeration.nextElement();
        sb.append(wlan0.getName() + " ");
        if (wlan0.getName().equals("wlan0")) {
            //there is probably a better way to find ethernet interface
            Log.i(TAG, "wlan0 found");
            return wlan0;
        }
    }

    return null;
}

Have a try and lemme know if it works or not in Hotspot mode...