SignalR multiple hubs on different paths in same application?

Question

I have an application which contains multiple hubs all on unique paths, so when calling the default :

routes.MapHubs("path", new HubConfiguration(...));

It blows up saying that the signalr.hubs is already defined (as mentioned here MapHubs not needed in SignalR 1.01?).

Now I can understand that it should only be called once, but then you will only get 1 path, so is there any way to handle a path per hub scenario? like how with MVC you specify the controller and action? so something like:

routes.MapHub<SomeHub>("path", new HubConfiguration(...));

== Edit for more info ==

It is mentioned often that you should never need to call this map hubs more than once, and in most scenarios I can agree, however I would not say that this is going to be the case for all applications.

In this scenario it is a website which at runtime loads any plugins which are available, each plugin is exposed the dependency injection framework to include its dependencies and the route table to include its routes. The hubs may have nothing to do with each other (other than the fact that they are both hub objects). So the hubs are not all known up front and are only known after the plugins are loaded, and yes I could wait until after this and try binding the hubs there, however then how do I have custom routes for each one then?

This seems to be a case of SignalR trying to abstract a little too much, as I dont see it being a bad idea to have custom routes rather than the default "/signalr", and as the routes all have different responsibilities it seems bad to have one entry route for them all.

So anyway I think the question still stands, as I dont see this as being a bad use case or bad design it just seems to be that I want to be able to have a route with a hub applied to it, much like in mvc you apply a controller and action to a route.

khellang khellang · Accepted Answer · 2013-08-27T13:13:50

You shouldn't need more than the signalr.hubs route. If you point your browser to that route, you will see it automatically finds all public types assignable to IHub and creates a JavaScript proxy for them. You can interact with different hubs by name from JavaScript, i.e. if you have the following Hub:

public class GameHub : Hub

You can connect to that specific hub by doing:

var gameHubProxy = $.connection.gameHub;

You can also explicitly specify a name for your hub by adding the HubNameAttribute to the class:

[HubName("AwesomeHub")]
public class GameHub : Hub

You can then retrieve the specific proxy by doing

var awesomeHubProxy = $.connection.awesomeHub;

UPDATE:

I'm not sure whether SignalR will be able to run on multiple paths in the same application. It could potentially mess things up and the default assembly locator won't be able to pick up hubs loaded at runtime anyway.

However, there is a solution where you can implement your own IAssemblyLocator that will pick up hubs from your plugin assemblies:

public class PluginAssemblyLocator : DefaultAssemblyLocator
{
    private readonly IEnumerable<Assembly> _pluginAssemblies;

    public PluginAssemblyLocator(IEnumerable<Assembly> pluginAssemblies)
    {
        _pluginAssemblies = pluginAssemblies;
    }

    public override IList<Assembly> GetAssemblies()
    {
        return base.GetAssemblies().Union(_pluginAssemblies).ToList();
    }
}

After you've loaded your plugins, you should call MapHubs and register an override of SignalRs IAssemblyLocator service:

protected void Application_Start(object sender, EventArgs e)
{
    // Load plugins and let them specify their own routes (but not for hubs).
    var pluginAssemblies = LoadPlugins(RouteTable.Routes);

    RouteTable.Routes.MapHubs();

    GlobalHost.DependencyResolver.Register(typeof(IAssemblyLocator), () => new PluginAssemblyLocator(pluginAssemblies));
}

NOTE: Register the IAssemblyLocator AFTER you've called MapHubs because it will also override it.

Now, there are issues with this approach. If you're using the static JavaScript proxy, it won't be re-generated every time it's accessed. This means that if your /signalr/hubs proxy is accessed before all plugins/hubs has been loaded, they won't be picked up. You can get around this by either making sure that all hubs are loaded by the time you map the route or by not using the static proxy at all.

This solution still requires you to get a reference to your plugin assemblies, I hope that's feasible...

SignalR multiple hubs on different paths in same application?

1 Answers