Unobserved task exception in SignalR C# client

[dannyhaak]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

We get quite some Unobserved Task Exceptions in SignalR when using streaming from client to server.

TaskScheduler.UnobservedTaskException += (sender, eventArgs) =>
            {
                Log.Error(eventArgs.Exception ?? new Exception(), "Unobserved task exception in sender {Sender}", sender?.ToString());
            };

[15:22:16.320 ERR] Unobserved task exception in sender System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[System.Threading.Tasks.VoidTaskResult,Microsoft.AspNetCore.SignalR.Client.HubConnection+<CommonStreaming>d__67]
System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. (The 'CommonStreaming' method cannot be called if the connection is not active)
 ---> System.InvalidOperationException: The 'CommonStreaming' method cannot be called if the connection is not active
   at Microsoft.AspNetCore.SignalR.Client.HubConnection.ReconnectingConnectionState.WaitForActiveConnectionAsync(String methodName, CancellationToken token, String memberName, String filePath, Int32 lineNumber)
   at Microsoft.AspNetCore.SignalR.Client.HubConnection.SendWithLock(ConnectionState expectedConnectionState, HubMessage message, CancellationToken cancellationToken, String callerName)
   at Microsoft.AspNetCore.SignalR.Client.HubConnection.CommonStreaming(ConnectionState connectionState, String streamId, Func`1 createAndConsumeStream)
   --- End of inner exception stack trace ---

How we set-up streaming:

await connection.StartAsync(cancellationTokenSource.Token);
await connection.SendAsync("ObservationsStream", observationsChannel.Reader, cancellationTokenSource.Token);

Expected Behavior

No Unobserved Task Exceptions. This pollutes our log.

Steps To Reproduce

This typically happens with SignalR on unstable connections, where there are TCP/IP time-outs.

Exceptions (if any)

No response

.NET Version

6.0.400

Anything else?

SignalR.Client 6.0.8

[davidfowl]

@dannyhaak can you provide a full repro? Is the code above all of your code that is calling into SignalR client APIs?

[davidfowl]

@BrennanConroy told me we have a problem here 😄, no need for the full repro.

[dannyhaak]

OK, thanks.