[SignalR] InvokeAsync<> hang in OnConnectedAsync on aspnet core (net7) Signalr

[maiemy]

Ciao to all,

I have a problem with InvokeAsync<> when I call it inside OnConnectedAsync in my hub implementation

    public override async Task OnConnectedAsync()
    {
        string connId = Context.ConnectionId;
        await Groups.AddToGroupAsync(connId, "SignalR Users");
        await _mia.Hub.Clients.All.SendAsync("NewComers", connId);
        string risultato = await _mia.Hub.Clients.Client(connId).InvokeAsync<string>("NewComerOnly", $"Da OnConnected Benvenuto {connId}", new CancellationToken());
        await base.OnConnectedAsync();
    }

Hub.Clients.All.SendAsync("NewComers", connId); works fine
Hub.Clients.Client(connId).InvokeAsync send correctly the message to the client, but hang for reply and not receive string result from client (no exceptions raised from server)

client code:

    connection.on("NewComerOnly", (mgs) => {
        console.log(mgs);
        return "Grazie!";
    });

If I do the same in separated method

    public async Task<string> MioMetodo(string valore)
    {
        string connId = Context.ConnectionId;
        string risultato = string.Empty ;
        try
        {
             risultato = await _mia.Hub.Clients.Client(connId).InvokeAsync<string>("NewComerOnly", $"Benvenuto {connId}", new CancellationToken());
        }catch(Exception ex)
        {
            var te = ex;
        }
        return risultato;
    }

all work fine.

Could you please help me to understand why?

ciao

[gfoidl]

Does AspNetCore.SignalR SendAsync not firing inside OnConnectedAsync apply here?

[maiemy]

InvokeAsync does not work inside OnConnectedAsync, we made the common scenario of using Context.Clients.Client(...).InvokeAsync throw, but you're doing an unusual call pattern to get around that check.

_mia.Hub.Clients.Client(connId) is the unusual call pattern. Even without involving InvokeAsync it looks suspicious. What is _mia.Hub? If it's a Hub instance then you're doing something wrong, Hub instances should not be stored or created by the user.

_mia is a simple test class that contains the instance of IHubContext
at startup time I do an AddSingleton on services initializing MiaClasseTest class passing the instance of HubContext taken from Services.
So _mia.Hub is the instance of HubContext coming from Services.

_mia.Hub isn't a instance of Hub but IHubContext.

at this time I do not have sourcecode available. I will post it to you as soon as possible.

[BrennanConroy]

Ah, well my previous statement still stands. You can't call InvokeAsync from OnConnectedAsync.

[maiemy]

Ah, well my previous statement still stands. You can't call InvokeAsync from OnConnectedAsync.

thank you.
can i ask you why it doesn't work? it's just my technical curiosity. :-)

[BrennanConroy]

We don't start the connections receive loop until OnConnectedAsync completes, so if you called InvokeAsync, it's waiting for a message from the client, but the receive loop isn't running yet, so it can't receive the message it's waiting for. If you used Context.Clients.Client(...).InvokeAsync we can detect that and throw an error. But using a random IHubContext the comes from outside of the Hub can't be detected sadly.

This is tracked in #41997 (comment), the only idea I have so far is an analyzer that will try to detect this at build time.

[maiemy]

We don't start the connections receive loop until OnConnectedAsync completes, so if you called InvokeAsync, it's waiting for a message from the client, but the receive loop isn't running yet, so it can't receive the message it's waiting for. If you used Context.Clients.Client(...).InvokeAsync we can detect that and throw an error. But using a random IHubContext the comes from outside of the Hub can't be detected sadly.

This is tracked in #41997 (comment), the only idea I have so far is an analyzer that will try to detect this at build time.

thank you very much for your explanation.
I used this solution to notify the client of activation by passing a specific parameter when connecting with the server.

at server startup I use this code for take a reference of HubContext in my MiaClasseTest

        builder.Services.AddSingleton<IMiaClasseTest>(
                iSerProvider => {
                     IHubContext<TestHub> hubContext = iSerProvider.GetRequiredService<IHubContext<TestHub>>();
                    return new MiaClasseTest("PIPPO!!", hubContext);
                });

I made this choice in order to always have hubcontext available to communicate to specific clients, because in production I will have a timer that will send data to clients.

thank you very much again for your explanations