IPv6 connection attempts made in an IPv4 only network

[gerryfrancis]

• Operating System (Linux/Mac/Windows/iOS/Android):
  Android 14.

• Delta Chat Version:
  1.46.14 (nightly built 2024-09-27).

• Expected behavior:
  Connection attempts are made to IPv4 only addresses in an IPv4 only network.

• Actual behavior:
  Connection attempts are made to IPv4 and IPv6 addresses in a IPv4 only network, which may result in a connecting error in regard to IPv6.

• Steps to reproduce the problem:
  No idea, but the device must be connected to an IPv4 only network.

• Screenshots:
  N/A.

• Logs:
  deltachat-log-20241003-112408_2.txt

[gerryfrancis]

FYI, LinkProperties can be used to determine the currently connected IP address(es) on an Android device, also after onLinkPropertiesChanged has been fired.

[link2xt]

Is this somehow visible to the user except in the logs? According to the log timestamps, it takes 2 milliseconds between an attempt start and receiving "Network is unreachable" error, so it seems the error is returned locally by the operating system and no real attempt to send IPv6 packets happens. So if this does not cause any real user-visible problems, I would rather keep it as is and not add more code trying to determine if we have IPv6 connectivity instead of just trying to connect.

[gerryfrancis]

Is this somehow visible to the user except in the logs?

@link2xt It has not been visible to me, overall the whole connecting procedure may take longer than usual. I thought that too many failed attempts would trigger breaks/delays until the app is connected again. If you do not confirm/acknowledge, we may close here, of course.

[link2xt]

I thought that too many failed attempts would trigger breaks/delays until the app is connected again.

No, IPv6 connection attempts are done in parallel with IPv4 connection attempts since #5915, so IPv6 connection attempts do not slow down IPv4 even if they timeout instead of failing immediately.

Anyway, once #6024 is in, Delta Chat will stop reconnecting after each FCM notification (like in your log).

Closing this as I think it is not common to test for IPv6 connectivity before trying to connect. Looked a bit into hyper-util client implementation and some other places, don't think anyone does anything similar.