[SignalR] (Hub)Exception in OnConnectedAsync sporadically not propagated to .NetClient

Describe the bug

I want to conditionally block some .NET-Client from connecting with my Hub in the OnConnectedAsync overide method by throwing an (hub)exception so that in the client-code the exceptional state gets raised too. Sporadically the (hub)exception does not get propagated to the client.

To Reproduce

Steps to reproduce the behavior:

1. Using this version of ASP.NET Core ‘2.2.0’, Microsoft.AspNetCore.SignalR.Client ‘1.1.0’
2. Using this code:

Server/Hub

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

        public override async Task OnConnectedAsync()
        {
            await base.OnConnectedAsync();
            throw new HubException("Denied");
        }
    }
}

Client

namespace Client
{
    class Program
    {
        static async Task Main(string[] args)
        {
            try
            {
                HubConnection connection = new HubConnectionBuilder()
                .WithUrl("http://localhost:5000/ChatHub")
                .Build();

                await connection.StartAsync();
                await connection.InvokeAsync("SendMessage", "Me", "Hello");
            }
            catch (HubException hubEx)
            {
                Console.WriteLine(hubEx.Message);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}

1. Run the server and then the client (in my case an console app) multiple times (one at a time).
2. See that the exception is not raised on the second try
3. After server-restart the (hub)exception is working again (one more time)

Expected behavior

(Hub)Exception gets propagated to client properly every time.

Screenshot

Additional context

.NET Core SDK Version: 2.2.106 Commit: aa79b139a8

Windows 7 - x64

Host (useful for support): Version: 2.2.4 Commit: f95848e524

[BrennanConroy]

1. Crash?

The server will wait for StartAsync to finish before starting to process invokes from the client.

If you really want to wait for some mapping to finish before doing an invoke on the client you could set up a client handler that StartAsync calls.

var tcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
connection.On("Finished", () =>
{
    tcs.TrySetResult(null);
});
connection.Closed += (ex) =>
{
    tcs.TrySetCanceled();
};
await connection.StartAsync();
await tcs.Task;
await connection.InvokeAsync(...);

public class ChatHub : Hub
{
    public override async Task OnConnectedAsync()
    {
        // mapping etc.
        await Clients.Client(Context.ConnectionId).SendAsync("Finished");
    }
}

[ddweber]

Thanks for the suggestion. I´ ll give it a try.