部署站点时SignalR消息不起作用

Question

I am building a web site using ASP.NET Core 2.2, and SignalR.

The prime use of SignalR is to send out notifications when donations are submitted. I have a scheduled job running Quartz.net that sends out a notification with the latest donations.

In the scheduled job, I inject an instance of IServiceScopeFactory and use it to create an IHubContext<CampaignHub> as follows (irrelevant code omitted for clarity)...

public class DonationsNotifierJob : IJob {
  private readonly IServiceScopeFactory _scopeFactory;

  public DonationsNotifierJob(IServiceScopeFactory scopeFactory) =>
    _scopeFactory = scopeFactory;

  public async Task Execute(IJobExecutionContext context) {
    using (IServiceScope scope = _scopeFactory.CreateScope()) {
      IHubContext<CampaignHub> hubContext = scope.ServiceProvider
        .GetRequiredService<IHubContext<CampaignHub>>();
      await hubContext.Clients.All
        .SendAsync("UpdatedCampaignData", new LiveCampaignData {
          // Data loaded here...
        });
    }
  }
}

The Razor for one of the pages that is supposed to pick up the notifications includes the following JavaScript...

  var connection = new signalR.HubConnectionBuilder()
    .withUrl("/campaignHub")
    .build();
  connection.start();

  connection.on("UpdatedCampaignData", function(d) {
    // Code omitted for clarity
  });

This works fine when I'm running in Visual Studio (2017 Enterprise), but when I deploy the site to a test server, the page that contains the JavaScript above never receives notifications.

I tried adding the usual "chat room" code you see in the samples, and that worked fine, so SignalR is working to some degree. Not only that, but one of the pages that sends out a SignalR notification directly (using the same hub method as shown above) works fine, so it seems to be a problem only in the scheduled job.

Injection is working fine, as I don't get any null reference exceptions.

I really have no idea how to start debugging this. It's the same code running in both cases, and I can see from the logging that the line in the scheduled job where the notification is sent is called, but I have no idea what happens to it then. I haven't found any way to tell if the notification isn't being sent, or if it is being sent but the target page doesn't pick it up.

Anyone able to give me any idea how I find out what's going wrong? Sorry if there isn't enough info here, but I don't know what else to tell you.

Thanks

Answer 1

I think you are missing the invoke method. Below is my example

(function () {
        var connection = new signalR.HubConnectionBuilder().withUrl("/connectionHub").build();

        connection.start().then(function () {
            console.log("connected");

            connection.invoke('getConnectionId')
                .then(function (connectionId) {
                    sessionStorage.setItem('conectionId', connectionId);
                    // Send the connectionId to controller
                }).catch(err => console.error(err.toString()));;


        });

        $("#sendmessage").click(function () {
            var connectionId = sessionStorage.getItem('conectionId');
            connection.invoke("Send", connectionId);
        });

        connection.on("ReceiveMessage", function (message) {
            console.log(message);
        });

    })();

And the hub code

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

namespace SignalR.Models
{
    public class ConnectionHub : Hub
    {
        public async Task Send(string userId)
        {
            var message = $"Send message to you with user id {userId}";
            await Clients.Client(userId).SendAsync("ReceiveMessage", message);
        }

        public string GetConnectionId()
        {
            return Context.ConnectionId;
        }
    }
}

You can read more here