Blazor WASM app crashes (runtime terminated) when /bff/user polling times out

[nickmuller]

Package: Duende.BFF.Blazor.Client 4.3.0 (also present in 4.3.2), .NET 10, Blazor WebAssembly

Description

BffClientAuthenticationStateProvider polls /bff/user from TimerCallbackAsync, which is async void and has no catch. FetchUserService.FetchUserAsync only catches HttpRequestException and JsonException.

When the poll exceeds HttpClient.Timeout (100 s by default), HttpClient throws a TaskCanceledException. Nothing catches it, so it reaches the thread pool and terminates the WebAssembly runtime ([MONO] Process terminated). The page stays visible but no longer responds to input.

In practice this happens after the user has been idle for a while, for example when the browser throttles a background tab, the machine wakes from sleep, or the network is temporarily gone.

Steps to reproduce

1. Create a Blazor WASM app with AddBffBlazorClient().
2. Add server-side middleware that delays /bff/user for longer than 100 seconds, after login.
3. Wait for the next poll plus the timeout.
4. The runtime terminates:

[MONO] Process terminated.
Unhandled Exception:
System.Threading.Tasks.TaskCanceledException: net_http_request_timedout, 100
 ---> System.TimeoutException: OperationCanceled
   ...
   at Duende.Bff.Blazor.Client.Internals.FetchUserService.FetchUserAsync() in FetchUserService.cs:line 46
   at Duende.Bff.Blazor.Client.Internals.BffClientAuthenticationStateProvider.RefreshUserAsync() in BffClientAuthenticationStateProvider.cs:line 65
   at Duende.Bff.Blazor.Client.Internals.BffClientAuthenticationStateProvider.TimerCallbackAsync(Object _) in BffClientAuthenticationStateProvider.cs:line 47
   at System.Threading.ThreadPool.BackgroundJobHandler()

Expected: a failed or timed-out poll must never crash the application.

Suggested fix

• Catch exceptions in TimerCallbackAsync, or at least OperationCanceledException, and log them.
• Consider keeping the last known user on transient failures (timeouts, network errors) instead of treating them as a logout.

Current workaround

services.AddHttpClient("Duende.Bff.Blazor.Client:StateProvider")
    .ConfigureHttpClient(c => c.Timeout = Timeout.InfiniteTimeSpan);

This depends on the internal HttpClientName, so it is fragile.

[wcabus]

Hey @nickmuller,

Thanks for the detailed report and stack trace, this helped us to easily confirm the issue. A failed or timed-out poll should be logged and retried instead of crashing the WASM app, and a timeout on its own shouldn't be treated as the user being signed out.

Until there's a fix, the workaround you posted (setting the timeout on the named HttpClient) is the way to go. You're right that it relies on an internal name, so treat it as temporary and expect to remove it once a fixed version is available.

We'll post an update in this discussion when there's news.