How do I add SignalR to a .NET Core Windows Service?

Question

I can find tutorials to add it to MVC, and even from 2014, an article explaining how to add it to .NET 4.7 windows service.

However with a .NET Core 3.1 windows service, I just cannot figure out how to do it.

Most tutorials seem to revolve around a Startup.cs file which does not exist in a windows service. This is the latest tutorial I could find from Microsoft but it uses a Web App rather than a windows service.

The windows service runs using this code:

var builder = new HostBuilder() .ConfigureServices((hostContext, services) => { services.AddHostedService<MyWindowsService>(); });

I assume that SignalR needs to be set up around here.

I found some evidence you can do WebApp.Start("http://localhost:8080"); but this is OWIN. The example I found (an older version of the one above) then has a Startup class but there's no indication how this class is called. It takes an IAppBuilder and there's a method on it to add SignalR. However IAppBuilder does not appear to be .NET Core, nor could I find any SignalR methods of any kind.

I wonder if anyone could point me in the right direction?

Answer 1

SignalR Server-side requires a server that receives web requests, Kestrel or IIS normally. So you need a web app, you can still add hosted services to your webapp, there is even an example showing a web app with SignalR and a hosted service: https://docs.microsoft.com/aspnet/core/signalr/background-services?view=aspnetcore-5.0

Answer 2

For people wanting to develop a self-hosted ASPNETCore SignalR hub running in a Windows service, here's my barebones code. (Disclaimer: I'm new to ASPNET Core, and I don't know whether this approach would be approved by more knowledgeable folk.) The magic is in the ".UseStartup();" call.

1. Create a new service project using the VS 2019 "Worker Service" C# template.

2. Edit the service's .csproj file and insert the lines:

       <ItemGroup>
           <FrameworkReference Include="Microsoft.aspNetCore.App" />
       </ItemGroup>
   

3. Create a Startup class:

   using Microsoft.AspNetCore.Builder;
   using Microsoft.AspNetCore.Hosting;
   using Microsoft.Extensions.DependencyInjection;
   using System;
   using System.Collections.Generic;
   using System.Text;
   
   namespace My.SignalRCore.Service
   {
       public class Startup
       {
           public void ConfigureServices(IServiceCollection services)
           {
               services.AddSignalR();
               services.AddHostedService<Worker>();
           }
   
           public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
           {
               app.UseRouting();               // pre-requisite for app.UseEndpoints()
               app.UseEndpoints(endpoints =>
               {
                   string url = $"/ServerHub";
                   endpoints.MapHub<MyHub>(url);
               });
           }
       }
   }
   

4. Create a MyHub : Hub class:

   using Microsoft.AspNetCore.SignalR;
   using Microsoft.Extensions.Logging;
   using System;
   using System.Collections.Generic;
   using System.Text;
   using System.Threading.Tasks;
   
   namespace My.SignalRCore.Service
   {
       public class MyHub : Hub
       {
           public ILogger<Worker> _logger = null;
   
           public MyHub(ILogger<Worker> logger)
           {
               _logger = logger;
               //_logger.LogInformation($"{DateTimeOffset.Now} MyHub.Constructor()");
   
           }
           public async Task ProcessClientMessage(string user, string message)
           {
               // process an incoming message from a connected client
               _logger.LogInformation($"{DateTime.Now.ToString("hh:mm:ss.fff")}  MyHub.ProcessClientMessage({user}, {message})");
   
           }
       }
   }
   

5. Amend the Program class to use a "UseStartup" call:

   using Microsoft.AspNetCore.Hosting;
   using Microsoft.Extensions.Hosting;
   using System;
   
   namespace My.SignalRCore.Service
   {
       public class Program
       {
           public static void Main(string[] args)
           {
               CreateHostBuilder(args).Build().Run();
           }
   
           public static IHostBuilder CreateHostBuilder(string[] args) =>
               Host.CreateDefaultBuilder(args).ConfigureWebHostDefaults(webBuilder =>
               {
                   webBuilder.UseStartup<Startup>();
                   webBuilder.UseUrls("http://*:12457");
               });
       }
   }
   

6. Add a hub reference (if needed) in the Worker class:

   using Microsoft.AspNetCore.SignalR;
   using Microsoft.Extensions.Hosting;
   using Microsoft.Extensions.Logging;
   using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Threading;
   using System.Threading.Tasks;
   
   namespace My.SignalRCore.Service
   {
       public class Worker : BackgroundService
       {
           private readonly ILogger<Worker> _logger;
           private readonly IHubContext<MyHub> _signalRHub;
   
           public Worker(ILogger<Worker> logger, IHubContext<MyHub> signalRHub)
           {
               _logger = logger;
               _signalRHub = signalRHub;
           }
   
           protected override async Task ExecuteAsync(CancellationToken stoppingToken)
           {
               while (!stoppingToken.IsCancellationRequested)
               {
                   await Task.Delay(15000, stoppingToken);
                   _logger.LogInformation($"{DateTime.Now.ToString("hh:mm:ss.fff")} Sending ping to all clients");
                   await _signalRHub.Clients.All.SendAsync("ReceiveMessage", "Server", "ping");
               }
           }
       }
   }
   

That's it for the server code. I've not yet installed it as a service, but it works as a console app. On a non-dev machine, you might need to install the APSNET CORE 3.1 runtime, it's available here: https://dotnet.microsoft.com/download/dotnet/3.1

For the client:

1. Install nuget package: Microsoft.AspNetCore.SignalR.Client

2. Create a client class along the lines of (note: the reconnect code here isn't working):

   using Microsoft.AspNetCore.SignalR.Client;
   using System;
   using System.Threading.Tasks;
   
   namespace My.SignalRCoreClientLib
   {
       public class SignalRCoreClientLib
       {
           public EventHandler<string> MessageEvent;
   
           private HubConnection _connection;
   
           public async Task Connect(string serverIp, int port)
           {
               if (_connection == null)
               {
                   _connection = new HubConnectionBuilder()
                       .WithUrl($"http://{serverIp}:{port}/ServerHub")
                       .Build();
   
                   _connection.Closed += async (error) =>
                   {
                       await Task.Delay(new Random().Next(0, 5) * 1000);
                       await _connection.StartAsync();
                   };
   
                   _connection.On<string, string>("ReceiveMessage", (user, message) =>
                   {
                       string fullMessage = $"{user}: {message}";
                       MessageEvent?.Invoke(this, fullMessage);
                   });
               }
               try
               {
                   await _connection.StartAsync();
               }
               catch (Exception ex)
               {
                   MessageEvent?.Invoke(this, $"{ex.Message}; base Exception: {ex.GetBaseException().Message}");
                   await Task.Delay(new Random().Next(0, 5) * 1000);
                   await Connect(serverIp, port);
               }
           }
   
           public async Task SendMessage(string user, string message)
           {
               try
               {
                   await _connection.InvokeAsync("ProcessClientMessage", user, message);
               }
               catch (Exception ex)
               {
                   MessageEvent?.Invoke(this, ex.Message);
               }
           }
       }
   }
   

That's it. Hope this is helpful.