How to Call SignalR Core Hub Methods from an ASP.NET Core Controller?

Calling SignalR Core Hub Methods from Asp.Net Core Controller

In this article, we'll explore how to invoke SignalR Core Hub methods from within an ASP.NET Core controller. This functionality allows for server-side communication to connected clients to broadcast events or update real-time data.

Problem Overview

In the provided scenario, an ASP.NET Core application receives a request from a Windows service upon task completion. The task is to notify all connected SignalR Core clients about this event. However, the Windows service cannot directly establish a connection to SignalR.

Solution 1: Injecting HubContext into Controller

One approach is to inject the appropriate HubContext into the controller class. This enables direct invocation of hub methods from the controller's action methods.

[Route("API/vardesigncomm")]
public class VarDesignCommController : Controller
{
    [HttpPut("ProcessVarDesignCommResponse/{id}")]
    public async Task<IActionResult> ProcessVarDesignCommResponse(int id)
    {
        await this.HubContext.Clients.All.InvokeAsync("Completed", id);
        return new JsonResult(true);
    }

    private IHubContext<VarDesignHub> HubContext
    {
        get; set;
    }
}

This approach allows direct communication with all connected clients, but may have performance implications depending on the number of clients.

Solution 2: Typed Hubs and Client Interfaces

Another approach involves defining a typed client interface and inheriting from the corresponding Hub with the typed client interface. This enables the injection of the typed HubContext into the controller for specific method invocations.

Typed Client Interface:

public interface ITypedHubClient
{
    Task BroadcastMessage(string name, string message);
}

Hub Inheriting from Typed Client Interface:

public class ChatHub : Hub<ITypedHubClient>
{
    public void Send(string name, string message)
    {
        Clients.All.BroadcastMessage(name, message);
    }
}

Controller Injection and Method Invocation:

[Route("api/demo")]
public class DemoController : Controller
{
    IHubContext<ChatHub, ITypedHubClient> _chatHubContext;

    public DemoController(IHubContext<ChatHub, ITypedHubClient> chatHubContext)
    {
        _chatHubContext = chatHubContext;
    }

    [HttpGet]
    public IEnumerable<string> Get()
    {
        _chatHubContext.Clients.All.BroadcastMessage("test", "test");
        return new string[] { "value1", "value2" };
    }
}

This approach allows for more targeted and efficient communication with clients.

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