Disconnecting from server causes exception

[brooksyott]

Hello,

So far, I'm liking this library a lot.
A major issue I have though at the moment is when a connection to the internet is lost, or the far end drops the connection, I get an exception when I use SendTextAsync(String). It appears I can't catch the exception (or so far I haven't been able to). Any ideas how to work around this issue? To reproduce this, I simply disable my internet connection while sending messages

The exception I get is:

System.IO.IOException: Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time,
or established connection failed because connected host has failed to respond.
---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time,
or established connection failed because connected host has failed to respond
at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
--- End of inner exception stack trace ---
at System.Net.Security.SslStream.EndRead(IAsyncResult asyncResult)
at System.Net.Security.SslStream.EndRead(IAsyncResult asyncResult)
at System.IO.Stream.<>c.b__43_1(Stream stream, IAsyncResult asyncResult)
at System.Threading.Tasks.TaskFactory1.FromAsyncTrimPromise1.Complete(TInstance thisRef, Func3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at WebsocketClientLite.PCL.Service.WebsocketListener.<ReadOneByteAtTheTimeAsync>d__26.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Reactive.PlatformServices.ExceptionServicesImpl.Rethrow(Exception exception) at System.Reactive.Stubs.<>c.<.cctor>b__2_1(Exception ex) at System.Reactive.AnonymousSafeObserver1.OnError(Exception error)
at System.Reactive.Linq.ObservableImpl.AsObservable1._.OnError(Exception error) at System.Reactive.Subjects.Subject1.OnError(Exception error)
at WebsocketClientLite.PCL.Service.WebsocketListener.b__27_1(Exception ex)
at System.Reactive.AnonymousSafeObserver1.OnError(Exception error) at System.Reactive.Linq.ObservableImpl.Where1..OnError(Exception error)
at System.Reactive.Linq.ObservableImpl.Select2._.OnError(Exception error) at System.Reactive.ScheduledObserver1.Dispatch(ICancelable cancel)
at System.Reactive.Concurrency.Scheduler.<>c.b__72_0(Action1 a, ICancelable c) at System.Reactive.Concurrency.DefaultScheduler.LongRunning.<>c__DisplayClass1_01.b__0(Object arg)
at System.Reactive.Concurrency.ConcurrencyAbstractionLayerImpl.<>c__DisplayClass7_0.b__0()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

[1iveowl]

Thank you for raising this. The documentation is not clear on this and I will update it.

What you need to do is to listen for the exception in your subscription. Like this:

        _subscribeToMessagesReceived = websocketClient.ObserveTextMessagesReceived.Subscribe(
            msg =>
            {
                System.Console.WriteLine($"Reply from test server: {msg}");
            },
            ex =>
            {
                System.Console.WriteLine(ex.Message);
            },
            () =>
            {
                System.Console.WriteLine($"Subscription Completed");
            });

In the above the subscription listens to three things:

1. The messages
2. Exceptions
3. Completion

This is the pattern used with Rx.

Please let me know if this helps?

[brooksyott]

It was very helpful, thank you.
The exception does come now, terrific.
If I leave the network disconnected what I see is:

• I'll get one exception from the Rx pattern above. Subsequent sends do not seem to generate it as per the pattern above, and result in my code needing to catch it via try/catch.
• when the network becomes available again, sends won't resume, they continue to fail
• what I've done is caught the exception as per your code above, then prevented the code from doing future sends until I've reconnected by creating a new MessageWebSocketRx

It seems to work, but it's not pretty :).

Again, thank you so much for the quick reply today. It definitely helped

[1iveowl]

Great to hear.

What you describe makes perfect sense.

When the connection fails you need to re-connect it before you try sending something new. Not sure you need to create a new instance of the MessageWebSocketRx object.

From the moment the connection fails to you receive an exception via Rx there is a time gap. In mine testing it was 20 seconds. This makes sense as the client don't know that the connection is gone. It has to timeout first.

[1iveowl]

Regarding looking pretty. I would it something like this:

    static void Main(string[] args)
    {

        var outerCancellationSource = new CancellationTokenSource();

        Task.Run(() => StartWebSocketAsyncWithRetry(outerCancellationSource), outerCancellationSource.Token);

        System.Console.WriteLine("Waiting...");
        System.Console.ReadKey();
        outerCancellationSource.Cancel();

        _subscribeToMessagesReceived.Dispose();
    }

    private static async Task StartWebSocketAsyncWithRetry(CancellationTokenSource outerCancellationTokenSource)
    {
        while (!outerCancellationTokenSource.IsCancellationRequested)
        {
            var innerCancellationSource = new CancellationTokenSource();
            await StartWebSocketAsync(innerCancellationSource);

            while (!innerCancellationSource.IsCancellationRequested)
            {
                await Task.Delay(TimeSpan.FromSeconds(10), innerCancellationSource.Token);
            }

            // Wait 5 seconds before trying again
            await Task.Delay(TimeSpan.FromSeconds(5), outerCancellationTokenSource.Token);
        }
    }

    private static async Task StartWebSocketAsync(CancellationTokenSource innerCancellationTokenSource)
    {
        using (var websocketClient = new MessageWebSocketRx())
        {
            _subscribeToMessagesReceived = websocketClient.ObserveTextMessagesReceived.Subscribe(
                msg =>
                {
                    // Msg receive code goes here
                },
                ex =>
                {
                    // Cancel the inner loop when exception
                    innerCancellationTokenSource.Cancel();
                },
                () =>
                {
                    // Cancel the inner loop when complete
                    innerCancellationTokenSource.Cancel();
                });
....

See example here