SignalR - SSE/LongPoll Close connection returns 404 about aspnetcore

[omorsky-pcor]

I did some debugging and (I might be completely wrong) here are my thoughts

There is long running GET (SSE) request.

• This requests creates a HttpConnectionContext object and registers it in HttpConnectionManager -

  aspnetcore/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs

  Line 135 in 8486d31

  var connection = await GetConnectionAsync(context);

  • This line creates some connection internal stuff including ApplicationTask which is completed once the connection closes
    

    aspnetcore/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs

    Line 156 in 8486d31

    if (connection.TryActivatePersistentConnection(connectionDelegate, sse, Task.CompletedTask, context, _logger))

  • And this line waits for the connection to close and then removes it from HttpConnectionManager

    aspnetcore/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs

    Line 158 in 8486d31

    await DoPersistentConnection(connection);

  • so after all this happens the connection is removed from the manager

Once the client calls stop there is a new POST request with MessageType=Close

• This call is processed by HttpConnectionDispatcher.ProcessSend but the connection does not exist anymore
  

  aspnetcore/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs

  Line 451 in 8486d31

  var connection = await GetConnectionAsync(context);

Now the question is who closes the long running SSE connection. From looking into ts client sources it seems that it is a client that closes SSE connection

• HubConnection.stop() -> HubConnection._stopInternal() => HttpConnection.stop() -> HttpConnection._stopInternal() => ServerSentEventsTransport.stop() -> ServerSentEventsTransport._close()

• aspnetcore/src/SignalR/clients/ts/signalr/src/ServerSentEventsTransport.ts

  Line 121 in 8486d31

  this._eventSource.close();

Now the issue seems to be a race-condition/not awaiting _sendCloseMessage() in HubConnection._stopInternal()

• aspnetcore/src/SignalR/clients/ts/signalr/src/HubConnection.ts

  Line 345 in 8486d31

  this._sendCloseMessage();

I will try to build custom client/reproduce it reliably using some network limiting in a browser.
I don't know what a proper solution should be. There is intentional comment/eslint to not await a close message. Also it does not feel right to have two "independent" methods to do conceptually the same thing.

[omorsky-pcor]

I was able to reliably reproduce the issue by adding a middleware like this

app.Use(async (context, next) =>
        {
            await Task.Delay(500);
            await next();
        });

here is a repository with a sample https://github.com/omorsky-pcor/signalr_close_404