SignalR ondisconnectedasync() not called when using Long Polling in aspnetcore

[DavidColemanUK]

Describe the bug

Following the tutorial here to create a simple SignalR Chat application in aspnetcore MVC.

We then enforce it to use HttpTransportType.LongPolling.

This settings seems to then stop OnDisconnectedAsync from being fired.

To Reproduce

1. Set up basic chat app from tutorial.
2. Enforce long polling as transport type.
3. Open a couple of clients.
4. Close a client.
5. Observe that OnDisconnectedAsync is not triggered.

Here's the code used (also here in this github repo)

public void ConfigureServices(IServiceCollection services)
        {
            services.AddRazorPages();

            services.AddSignalR(hubOptions =>
            {
                hubOptions.ClientTimeoutInterval = TimeSpan.FromSeconds(10);
                hubOptions.HandshakeTimeout = TimeSpan.FromSeconds(10);
                hubOptions.KeepAliveInterval = TimeSpan.FromSeconds(10);
                hubOptions.EnableDetailedErrors = true;
            });
        }

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
        ..........
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapRazorPages();
                endpoints.MapHub<ChatHub>("/chatHub", options =>
                {
                    options.Transports = HttpTransportType.LongPolling;
                });
            });
        }

public class ChatHub : Hub
    {
        public async Task SendMessage(string user, string message)
        {
            await Clients.All.SendAsync("ReceiveMessage", user, message);
        }

        public override async Task OnConnectedAsync()
        {
            await base.OnConnectedAsync();
        }

        public override async Task OnDisconnectedAsync(Exception exception)
        {
            await base.OnDisconnectedAsync(exception);
        }
    }

Further technical details

• ASP.NET Core version = 3.1
  Using Visual Studio 2019 16.4.4
• dotnet --info

.NET Core SDK (reflecting any global.json):
 Version:   3.1.101
 Commit:    b377529961

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17134
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.101\

Host (useful for support):
  Version: 3.1.1
  Commit:  a1388f194c

.NET Core SDKs installed:
`  2.1.602 [C:\Program Files\dotnet\sdk]
  2.1.604 [C:\Program Files\dotnet\sdk]
  2.1.700 [C:\Program Files\dotnet\sdk]
  2.1.701 [C:\Program Files\dotnet\sdk]
  2.1.801 [C:\Program Files\dotnet\sdk]
  2.1.802 [C:\Program Files\dotnet\sdk]
  2.1.803 [C:\Program Files\dotnet\sdk]
  2.2.100 [C:\Program Files\dotnet\sdk]
  2.2.110 [C:\Program Files\dotnet\sdk]
  2.2.202 [C:\Program Files\dotnet\sdk]
  2.2.204 [C:\Program Files\dotnet\sdk]
  2.2.207 [C:\Program Files\dotnet\sdk]
  2.2.300 [C:\Program Files\dotnet\sdk]
  2.2.301 [C:\Program Files\dotnet\sdk]
  2.2.401 [C:\Program Files\dotnet\sdk]
  2.2.402 [C:\Program Files\dotnet\sdk]
  3.1.101 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[BrennanConroy]

4\. Close a client.

How are you closing the client? If you have a debugger attached and close the client by closing the browser tab, then you'll never observe OnDisconnectedAsync being fired. This is because we check if a debugger is attached and don't trigger certain timeouts in order to making debugging easier. If you close by calling stop on the client then you should see OnDisconnectedAsync called.

[bashout]

Thanks for the quick reply Brennan, it turns out this was the issue and we were expecting the method to fire when we closed the browser instance. As some knowledge for myself how would we have discovered that this was the expected behavior without reading the source code?

Are there some docs specifying that this is the behavior?

[analogrelay]

it turns out this was the issue and we were expecting the method to fire when we closed the browser instance

If you want this to happen, you can do it yourself by hooking a browser unload event and closing the connection in it. Unfortunately, browsers are notoriously inconsistent about allowing HTTP requests in unload events which means we may not get the message.

Are there some docs specifying that this is the behavior?

Not specifically, but in general we can't guarantee that the OnDisconnectedAsync event will fire on any particular user event since it depends a lot of network conditions. Do you have a suggestion on where in the docs you would have looked for guidance here? API docs? A specific article?

[bashout]

If you want this to happen, you can do it yourself by hooking a browser unload event

Yeah I had already attempted to use a host listener on the browsers pre-unload event to clean up my tracking on the server side but well chrome and IE etc were not playing too nice.

Do you have a suggestion on where in the docs you would have looked for guidance here? API docs? A specific article?

I'd probably expect it to be alongside Handle events for a connection as it talks about both life cycle hooks (OnConnectedAsync & OnDisconnectedAsync). There already is an existing warning dialog - potentially adding it somewhere around there.

[analogrelay]

Seems reasonable. We'll put this on our backlog, but if you'd like to submit a PR to that doc (using the "Edit" button in the top-right), we'd be happy to review it!

[DavidColemanUK]

As @bashout has mentioned, thanks very much @BrennanConroy for your quick response and answer to this. It gave us what we needed to keep progressing.