从 SignalR 服务器（Asp.Net Core）调用特定客户端

Question

I'am using Asp.Net Core SignalR in C# with a Javascript client and I'am trying to call a client method from the Server. Now this is done via a Controller method, which is called from an external source. I invoke the Hub context in the Controller class, which allows me to use the hub context and using this I try to make a call to the specific client using a connection ID, which fails to work with no error thrown. I will show you what code I have so far.

This is my Hub class, which merely is used to return the connection ID to the client when requested.

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;

namespace SignalR1
{
    public class TestHub : Hub
    {
        public string GetConnectionId() => Context.ConnectionId;
    }
}

This is my JS client code to make the connection to the hub.

    var connection;
    var connId;
    
    async function signalRStart() {
        connection = new signalR.HubConnectionBuilder()
        .withUrl("https://localhost:44354/testHub")
        .configureLogging(signalR.LogLevel.Information)
        .build();
    
        connection.on("ClientFunction", (param) => {
            alert("ClientFunction got (" + param + ")");
        });

        connection.on("testHubToHothUpdate", () => {
            console.log("I've been called by the server!");
        });

        connection.onclose(async () => {
            await start();
        });

        // Start the connection.
        await start();
    }

    async function start() {
        try {
            await connection.start();
            console.log("SignalR Connected.");
            var connId = await connection.invoke("GetConnectionId");
            signalRPost(connId); // Business logic method
        } catch (err) {
            console.log(err);
            setTimeout(start, 5000);
        }
    };

You can see it makes a connection to the hub and then provides 2 methods at the client end "ClientFunction" and "testHubToHothUpdate". connId is used to store the value of the connection ID once it is retrieved from the server.

This is the controller class.

using Microsoft.AspNetCore.SignalR;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Web;

namespace SignalR1.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ValuesController : ControllerBase
    {
        private readonly IHubContext<HothHub> _hubContext;

        public ValuesController(IHubContext<HothHub> hubContext)
        {
            _hubContext = hubContext;
        }
        
        [HttpPost("{id}")]  // POST /api/values/xyz
        public async Task<IActionResult> PostAsync(string id)
        {
            Trace.TraceInformation("update Post()");

            // Make a call to the client based on the connection ID and call client method
            await _hubContext.Clients.Client(id).SendAsync("testHubToHothUpdate");

            return Ok();
        }
    }
}

I've used a controller class because persistent connections is not available for use in Asp.Net Core . Using Clients.All.SendAsync() works fine as the client method is hit but I need to be able to call a specific client based on the connection ID. The id passed into this Post method is correct and matches up with the live connection ID in the client (I have run several tests for this). Is using Client(id) not allowed any more or is there anything I need to make sure of to get this working? Any help is appreciated on this, thank you!

PS I should I'm not using user authentication on the client side so sending to a specific user id is not going to be possible. I'm trying to send to a specific connection id instead.

Answer 1

It looks like you have two different hubs. You connect to TestHub :

public class TestHub : Hub
{
    public string GetConnectionId() => Context.ConnectionId;
}

...
connection = new signalR.HubConnectionBuilder()
    .withUrl("https://localhost:44354/testHub")
...

but then you are trying to send to client using HothHub :

private readonly IHubContext<HothHub> _hubContext;