mDNS discovery starts very slow. about rxdnssd

[kostadin24]

On Samsung Galaxy Tab S2 with android 7.0
works for 1 minute and stops. Begin to work only after device restart.

[andriydruk]

Hi, did you have this issue with both Bindable and Embedded versions?
I tested with Samsung Edge 7 with Android 8.0.0, don't have any issues
Did you make discovering in the foreground? Did you have issues in my app Service Browser?

[kostadin24]

Hi, I use discovery in foreground. Wasn't sure about my code. So I used Service browser -last version from github. Problem is not permanent, it appears from time to time. Let say 30% of time works. And when works discovery starts very slow - about 15 sec. Restarting router, phone and devices with mDNS services helps in 90% of cases. If not restart and leave all untouched - after half hour or more problem dissapears. No suspicious messages in logcat. And one new fact - not only Samsung devices with Android 7 and high have problem. Yesterday ASUS tablet with Android 6.0 discovered mdns very slow.

[kostadin24]

Forgot to say using bindable or embedded didnt make difference for tested Samsung devices. After using different network tools feel like some of them change device state and mDNS again starts to work.

[andriydruk]

What about another library? Did you try jmdns or Android NSD? Does it start quick?

[kostadin24]

Have a lot of work this days. Hope to find time to test it.

[kostadin24]

Yesterday made a lot of manual tests on Samsung Galaxy Tab A1 and S2. Starting and stopping app. Looks like engine initialization hang. Sometimes starts /embedded/ and returns services for 100-200ms. Sometimes for 30-40 seconds. And many times with nothing after waiting several minutes.
Same behaviour when test ServiceBrowser/both from google play and from github/.
Sadly this is not reproduced on other samsung devices - even from same model/os/build etc.

[kostadin24]

We probably have bad hardware here. Devices working fine with Xiaomi and not worlking at all with Samsung. Testers analyzed network traffic and result is - Xiaomi device can ping mDNS devices, but Samsung fails in almost all tests.

[kostadin24]

My coworker user Wireshark to watch network.
In case with Samsung devices - mDNS responses are longer than responses with non Samsung devices.

Attached file is with Samsung devices.

[kostadin24]

Is it easy to debug app?

[andriydruk]

Yes, just add a breakpoint in Java or C code in Android Studio
and choose `Debugger Type' == Dual

Did you have a chance to try jmdns or Android NSD?

[kostadin24]

Protocol IGMP is missing on problematic devices. Without ICMP works very rarely. With IGMP works better/again not 100% but 70-80%/.

[kostadin24]

Comparing network messages with iOS -> IGMP is not implemented on many android devices and may be is involved.

[andriydruk]

Samsung Galaxy S8 as well? I heard about devices that don't support multicasts, but I've never had access to one.

It would be nice if we have an ability to detect a device that doesn't support IGMP and show a message to a user

[kostadin24]

Unfortunately I found issue 2 weeks before release date :(
Maybe brute force scan will be used in case of no mDNS devices found.

[kostadin24]

Finally - some of android devices/mostly Samsung with android 8.0 and 8.1/ use IGMPv3 with broken logic.
Devices that implement IGMPv2 and IGMPv3 works fine at all. But some devices have version of android that use IGMPv3 with strangle broken behaviour. This causes router to not send them multicast packages.
So because this is in operating system - we can not fix this. In case of IGMPv3 with broken logic - will use other ways for discovery.