How to revive HttpClient after network connection has been restored? - exception

Question

How to revive HttpClient and make it see that the network is available again without fully restarting the application?
In case when a Xamarin.Forms app was launched with no network connection available and then later network connection is enabled, HttpClient.SendAsync(request) throws NameResolutionFailure and it does not recover, no matter how many times the request is repeated.
It seems, HttpClient does not know how to recover when network connection appears.
To reproduce the issue in Android emulator:
ensure your app is completely closed
turn network off (set Data status to Roaming in emulator settings or use the status bar to toggle the data or LTE switch).
launch your app, run a web request to verify that it does not work (obviously, you will need try/catch around the web request to avoid crashing)
while the app is still open, enable the network
run a web request - will get NameResolutionFailure
only full application restart will revive HttpClient
The issue does not happen if I use domain names specified in etc/hosts file.
I tried to fully recreate HttpClient and resend a new request when the issue occurs, but that does not help. Only full restart of the app helps.
Obviously, I cannot ask user to fully kill my app and start it again every time when user has turned on his network connection after launching my app.

Answer 1

This is a known issue. See:
Mono: https://bugzilla.xamarin.com/show_bug.cgi?id=45761
iOS: https://bugzilla.xamarin.com/show_bug.cgi?id=45763
Android: https://bugzilla.xamarin.com/show_bug.cgi?id=45383
The workaround is to manually set the DNS refresh:
System.Net.ServicePointManager.DnsRefreshTimeout = 0;