OWIN + SignalR + Autofac

Question

Taken from: http://docs.autofac.org/en/latest/integration/signalr.html:

"A common error in OWIN integration is use of the GlobalHost. In OWIN you create the configuration from scratch. You should not reference GlobalHost anywhere when using the OWIN integration."

That sounds reasonable. However, how should one resolve IHubContext from an ApiController, like the usual (non-OWIN):

GlobalHost.ConnectionManager.GetHubContext<MyHub>()?

I can't find a reference on this one anywhere, and the only method I have by now is to register the HubConfiguration instance within the same container and do this:

public MyApiController : ApiController {
  public HubConfiguration HubConfig { get; set; } // Dependency injected by
                                                  // PropertiesAutowired()

  public IHubContext MyHubContext { 
    get { 
      return HubConfig
        .Resolver
        .Resolve<IConnectionManager>()
        .GetHubContext<MyHub>(); 
     } 
  }

  // ...

}

However, this seems quite verbose to me. What is the proper way to do it? To be more specific, is there a clean way to register IConnectionManager?

EDIT:

What I ended up doing is something like:

var container = builder.Build();
hubConfig.Resolver = new AutofacDependencyResolver(container); 

app.MapSignalR("/signalr", hubConfig);

var builder2 = new ContainerBuilder();
builder2
  .Register(ctx => hubConfig.Resolver.Resolve<IConnectionManager>())
  .As<IConnectionManager>();

builder2.Update(container);

but I have a feeling there must be an easier way to get that IConnectionManager injected in the controller.

Answer 1

This answer is a little belated but here goes.

• I recommend strongly typed hubs.
• You need to add specific registrations for the strongly typed hubs.
• I don't use the GlobalHost
  • Instead I use the Configuration created for OWIN registration.

Hub Declaration

public interface IMyHub
{
    // Any methods here for strongly-typed hubs
}

[HubName("myHub")]
public class MyHub : Hub<IMyHub>

Hub Registration

From your Autofac registration

// SignalR Configuration
var signalRConfig = new HubConfiguration();

var builder = // Create your normal AutoFac container here

builder.RegisterType<MyHub>().ExternallyOwned(); // SignalR hub registration

// Register the Hub for DI (THIS IS THE MAGIC LINE)
builder.Register(i => signalRConfig.Resolver.Resolve<IConnectionManager>().GetHubContext<MyHub, IMyHub>()).ExternallyOwned();

// Build the container
var container = builder.Build();

// SignalR Dependency Resolver
signalRConfig.Resolver = new Autofac.Integration.SignalR.AutofacDependencyResolver(container);

app.UseAutofacMiddleware(container);
app.MapSignalR("/signalr", signalRConfig);

Resolving the hub in background code

Using AutoFacs AutowiredProperties() extension method then it can resolve the correct context (can also be in the constructor if you like).

public IHubContext<IMyHub> InstanceHubContext { get; [UsedImplicitly] set; }

Answer 2

What you can do is to move some of this repeating code (I assume IHubContext is also used in some other classes and it is fetched in the same way) into container registration.

First thing is to register IHubContext instances, I assume you have multiple hubs in project. I that case, services have to be registered as named services.

builder
    .Register<IHubContext>(c => c.Resolve<IConnectionManager>().GetHubContext<MyHub>())
    .Named<IHubContext>("MyHub");

Classes, which want to use IHubContext can now receive it as constructor parameter or as property. But we have to tell container which instance it should inject. This can be done in container configuration, in multiple ways

Constructor can use ResolvedParameter to correctly select IHubContext implementation

// example class 
public class SampleClass {
    public SampleClass(IHubContext context) { }
}

// and registration for this class
builder.RegisterType<SampleClass>()
    .WithParameter(new ResolvedParameter((pi, ctx) =>
    {
        // only apply this to parameters of IHubContext type
        return pi.ParameterType == typeof(IHubContext);
    }, (pi, ctx) =>
    {
        // resolve context
        return ctx.ResolveNamed<IHubContext>("MyHub");
    }));

Property injection, is also a bit tricky. It is needed to resolve correct instance in OnActivated callback, for example like this:

// example class
public class SampleClass2
{
    public IHubContext Context { get; set; }
}

// registration for this case
builder.RegisterType<SampleClass2>()
    .PropertiesAutowired()
    .OnActivated(e => e.Instance.Context = e.Context.ResolveNamed<IHubContext>("MyHub"));

Answer 3

I did similar to yourself, which got it working in Owin for me

builder.RegisterInstance(config.Resolver).As<IDependencyResolver>();
builder.Update(container);

Then use this to get my hub

Resolve<IDependencyResolver>().Resolve<IConnectionManager>().GetHubContext<MyHub>();

Hope this helps others out there