How to publish messages using the SignalR SqlMessageBus

Question

I have a Windows Service that I'd like to periodically publish some data. I know I can use the .NET HubConnection object to create a proxy to a SignalR hub and send a message through it but since the web app is hosted on an IIS web farm that can get a bit hacky. The web farm hubs are connected using the SQL Server-based SqlScaleoutConfiguration backplane. What I'd really like to do some thing like this:

var config = new SqlScaleoutConfiguration(sqlConnString);
GlobalHost.DependencyResolver.UseSqlServer(sqlConnString); //Redundent??

var messageBus = new SqlMessageBus(GlobalHost.DependencyResolver, config);
var message = new Message("DataHub", "RefreshData", payload);
messageBus.Publish(message);

Obviously this doesn't work. Any sample code/documentation on how to interact directly with the SignalR message bus would be greatly appreciated. Thanks!!

Answer 1

Something like this should work with the sql scale out bus although I haven't tested it.

From the SignalR.RabbitMQ project which is a scale out bus using RabbitMQ as the backplane.

Essentially configure the Message Bus in you console project. Grab a reference to the Hub you want to broadcast to. Then send your message...

        var factory = new ConnectionFactory
        {
            UserName = "guest",
            Password = "guest"
        };

        var exchangeName = "SignalR.RabbitMQ-Example";

        var configuration = new RabbitMqScaleoutConfiguration(factory, exchangeName);
        GlobalHost.DependencyResolver.UseRabbitMq(configuration); ;

        var hubContext = GlobalHost.ConnectionManager.GetHubContext<Chat>();

        Task.Factory.StartNew(
            () =>
                {
                    int i = 0;
                    while (true)
                    {
                        hubContext.Clients.All.onConsoleMessage(i++);
                        System.Console.WriteLine(i);
                        Thread.Sleep(100);
                    }
                }
            );

Mark's answer is correct but >>>>>>>>>>>>>>>>>>>>>

here is what I had to do to make this work for SQL Server scaleout:

Update service:

• Create an exact replica of the hub class (or just reference it) that will send the messages to the client. The hub class will need to contain a placeholder method to allow the messages to flow through it:

      public class DataHub : Hub {
          // other hub methods here ...
  
          public void RefreshData(SomeAppropriateType messageData)
          {
              // Placeholder method for tunneling data refreshes through the SQL Server scaleout backplane          
          }
      }
  

• Register the SQL Server database:

      var signalrDbConnectionString = ConfigurationManager.ConnectionStrings["signalr"].ConnectionString;
      GlobalHost.DependencyResolver.UseSqlServer(signalrDbConnectionString);
      routes.MapHubs();
  

• Broadcast the message to all client through the hub proxy class:

      var messageData = // instantiate the parameter value of the RefreshData method in the hub class
      var hubContext = GlobalHost.ConnectionManager.GetHubContext<DataHub>();
      Task.Factory.StartNew(() => hubContext.Clients.All.RefreshData(messageData)).Wait();
  

Web site:

• Same first step of the update service.

• Register the SQL Server database just as before but somewhere in the web app global setup.

• Write javascript for the appropriate pages along these lines to receive the messages:

      function listenForUpdates() {
          if (updater === undefined) {
              updater = $.connection.dataHub;
          }
  
          if (updater !== undefined) {
              // Declare a function on the hub so the server can invoke it
              updater.client.refreshData = function (value) {
                  // for debugging: console.log(value);
  
                  // update the appropriate page elements with the new data
              };
          }
      }