How to get result in SignalR filter?

[SaleCar]

Hello,

I have SignalR filter and want to get result after method invocation, for example:

public async ValueTask<object> InvokeMethodAsync(HubInvocationContext context, Func<HubInvocationContext, ValueTask<object>> next) 
{
var result = await next(context);

But, result is always null (?!). I don't know why.

However, in minimal api filter, a can get result with:

public async ValueTask<object> InvokeAsync(EndpointFilterInvocationContext context, EndpointFilterDelegate next) 
{
var result = await next(context);

if (result is ProblemHttpResult) 
{
    //do something with it
}

return result;

It seems to me that the filters work differently which is quite strange.
Can someone help me how to get the result in the SignalR filter?

[BrennanConroy]

Are you returning anything from your hub method?

[davidfowl]

And it works, but it bypasses the Filter. Now you are saying that I should use "return" to return the data so that I can access it through the Filter? So how can I control who the data is returned to, all users, group or caller?

This is why Brennan pointed you at the other issue. There are no filters for outgoing messages from server to client.

[SaleCar]

Ok, but what is differance between "await Clients.All.SendAsync" and "return"? In both case user get its message.

[davidfowl]

When you call a hub method from the client, that method can have a return value (as pointed out here #52750 (reply in thread)). Calling await Clients.All.SendAsync isn't a return value, it's a server to client method invocation. Nothing is being "returned", instead, you are calling the "ReceiveMessage" method on the client side. That method itself has no return value, and it's not even possible in SignalR to get a return value from using All/Group etc.

[SaleCar]

Just to see if I got it right

When I use "return"
I can catch output in Filter
I cannot send to all or group
I cannot invoke client method

Client get this:
{"type":3,"invocationId":"0","result":"Hello message"}

When I use "await Clients..."
I can send message to caller, group and all
I can invoke method on client
But I cannot catch output in Filter?!

Client get this:
{"type":1,"target":"Test","arguments":["Hello message"]}

[davidfowl]

Right, we support filters for client to server invocations, but not server to client invocations.

[SaleCar]

Thanks to everyone for the replies, things are much clearer now. My suggestion is that the filters should be improved in the future and that the response of client method invocation can be intercepted. Also, the official SignalR documentation should be also improved because it doesn't clearly state that there are two types of responses (with return and client method invocation) and that some can be intercepted by filters while some can't.

[davidfowl]

We'll update the docs, it has nothing to do with responses, and everything to do with client method invocation.