SignalR .net core Filters

Question

Does SignalR have a similar options as the MVC Filters described here?

With MVC I can create an Action Filter (derived from IAsyncActionFilter) and use it as an attribute on a MVC method.

For example:

[ServiceFilter(typeof(MyCustomAsyncActionFilter))]
public async Task<IActionResult> GetAlbums() { }

With the above example, MyCustomAsyncActionFilter can then be implemented to handle custom code that needs to be executed prior to executing the method.

What's the equivalent of the above when working with SignalR methods?

Answer 1

AFAIK there is no feature like ASP.NET SignalR hub pipelines in SignalR Core yet (see this GitHub issue) and the MVC filters don't apply to SignalR.

A workaround might be to implement your own HubDispatcher and override the DispatchMessageAsync method:

public class CustomHubDispatcher<THub> : DefaultHubDispatcher<THub> where THub : Hub
{
    public CustomHubDispatcher(
        IServiceScopeFactory serviceScopeFactory,
        IHubContext<THub> hubContext,
        IOptions<HubOptions<THub>> hubOptions,
        IOptions<HubOptions> globalHubOptions,
        ILogger<CustomHubDispatcher<THub>> logger) : base(serviceScopeFactory, hubContext, hubOptions, globalHubOptions, logger)
    {
    }

    public override Task DispatchMessageAsync(HubConnectionContext connection, HubMessage hubMessage)
    {
        switch (hubMessage)
        {
            case InvocationMessage invocationMessage:
                {
                    // do something here
                    break;
                }
        }
        return base.DispatchMessageAsync(connection, hubMessage);
    }
}

and use it in ConfigureServices:

services.AddSignalR();
services.AddSingleton(typeof(HubDispatcher<>), typeof(CustomHubDispatcher<>));

Answer 2

.NET 5 supports Hub Filters

From the docs:

services.AddSignalR(options =>
{
    // Global filters will run first
    options.AddFilter<CustomFilter>();
}).AddHubOptions<ChatHub>(options =>
{
    // Local filters will run second
    options.AddFilter<CustomFilter2>();
});

Filters need to implement IHubFilter