Question

Has anyone gotten Multicast to work on Android 2.2, specifically JmDNS for Bonjour service detection. There are many questions & answers from the Android 1.5->2.0 timeframe, including on stackOverflow, that indicate varying levels of success, and a bug in the bug tracker that indicate it was fixed, and closed, for 2.2 (http://code.google.com/p/android/issues/detail?id=2323) . I’ve tried the “TuneControl” source code, but that worked on ~1.5 and has not been updated, and does not work for me on 2.2.

So, the questions…
1) Has anyone seen multicast work on 2.2, specifically JmDNS, and specifically for Bonjour service detection?

2) What is necessary in code to make this work?

I’m using the appropriate permissions:

<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

<uses-permission android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>

I acquire the multicast lock:

WifiManager wifi = (WifiManager)getSystemService( Context.WIFI_SERVICE );
if(wifi != null)
{
    MulticastLock mcLock = wifi.createMulticastLock("mylock");
    mcLock.acquire();
...

And then try to start jmDNS to look for servers:

    mdns = JmDNS.create(addr, HOSTNAME);
    jmdns.addServiceListener(TOUCH_ABLE_TYPE, listener);
    jmdns.addServiceListener(DACP_TYPE, listener);
    ...

The listener never sees any services. I’ve verified using Wireshark that the request packets are sent, and that the server responds, but the response packet are never seen by the socket listener code in the jmDNS library.

So… am I missing something? Is this still a bug? Has ANYONE gotten anything even remotely like this to work???

Answer 1

To (rudely) answer my own question, more information was provided at http://code.google.com/p/android/issues/detail?id=2917#c48 by another person. For posterity, as they say, here is brian.ro…@gmail.com‘s answer…

“I’ve spent quite a bit of time
debugging mDNS issues with JmDNS on my
Evo and HTC Hero (CDMA). What I found
is there appears to be a filter in
place in the broadcom wireless driver
on the Evo (and since I’m getting a
similiar reprt from an HTC Desire user
– with the same chipset, presumably that handset as well). The filter, by
default, blocks any non-unicast or
network broadcast traffic, including
multicast. Apparently the theory was
it’s a battery saver.

The problem appears to be the
wpa_supplicant on the Evo does not
support removing those filters when
you get a MulticastLock. (Check the
log output right after you get the
lock and you’ll see what I mean).
Unfortunately what has happened is the
hardware vendors have fragmented
multicast support…. :(“

So… it appears this is a device problem more than a coding problem. D’oh. 🙁 If I get an opportunity to test on another device…