Flush pending deregistrations prior to stopping

[twasilczyk]

Original change on AOSP

[Abhayakara]

I'm not doubting that it is, but can you talk a bit about why this is necessary? It will help when I try to explain the proposed change to the group.

(That is, what was the symptom you were seeing that led to deciding to make this change)

[twasilczyk]

This was an old bug (fixed at our side almost 7 years ago) where the original author doesn't precisely remember it.

The initial problem was that our Nearby Connections API didn't get onEndpointLost call triggered. It seems that each advertisement has a TTL of 2min and the goodbye message is a way to let scanners know early, instead of waiting for that 2 minute expiration. This greatly improves the responsiveness of the scanning device.

[olivierlevon]

Note : Old mdnsresponder code (https://opensource.apple.com/source/mDNSResponder/mDNSResponder-107.6/mDNSCore/mDNS.c.auto.html) had this SendResponses line. Look at mDNS_Close function :

if (m->ResourceRecords) debugf("mDNS_Close: Sending final packets for deregistering records");
else debugf("mDNS_Close: No deregistering records remain");

// If any deregistering records remain, send their deregistration announcements before we exit
if (m->mDNSPlatformStatus != mStatus_NoError) DiscardDeregistrations(m);
else if (m->ResourceRecords) SendResponses(m);
if (m->ResourceRecords) LogMsg("mDNS_Close failed to send goodbye for: %s", ARDisplayString(m, m->ResourceRecords));)

[twasilczyk]

Do we need anything else to merge this?

[Abhayakara]

No, I just need to get done with my current development push. Sorry for the delay!

[twasilczyk]

Hey, it's been a while. While I'll be putting this work on Android side on hold for now (it's been effectively on hold anyway since 2021), just checking in if anything changed about the 6 open PRs.

[Abhayakara]

We’re still trying to get a better answer to the open source management question, but haven’t had time yet. Thread has been consuming all available bandwidth. :(