EasyNetQ: Replace the Internal DI Container

EasyNetQ, is made up of a collection of independent components. Internally it uses a tiny internal DI (IoC) container called DefaultServiceProvider. If you look at the code for the static RabbitHutch class that you use to create instances of the core IBus interface, you will see that it simply creates a new DefaultServiceProvider, registers all of EasyNetQ’s components, and then calls container.Resolve<IBus>() creating a new instance of IBus with its tree of dependencies supplied by the container:

public static IBus CreateBus(IConnectionConfiguration connectionConfiguration, Action<IServiceRegister> registerServices)
{
    Preconditions.CheckNotNull(connectionConfiguration, "connectionConfiguration");
    Preconditions.CheckNotNull(registerServices, "registerServices");

    var container = createContainerInternal();
    if (container == null)
    {
        throw new EasyNetQException("Could not create container. " + 
            "Have you called SetContainerFactory(...) with a function that returns null?");
    }

    registerServices(container);
    container.Register(_ => connectionConfiguration);
    ComponentRegistration.RegisterServices(container);

    return container.Resolve<IBus>();
}

But what if you want EasyNetQ to use your container of choice? From version 0.25 the RabbitHutch class provides a static method, SetContainerFactory, that allows you to register an alternative container factory method that provides whatever implementation of EasyNetQ.IContainer that you care to supply.

In this example we are using the Castle Windsor IoC container:

// register our alternative container factory
RabbitHutch.SetContainerFactory(() =>
    {
        // create an instance of Windsor
        var windsorContainer = new WindsorContainer();
        // wrap it in our implementation of EasyNetQ.IContainer
        return new WindsorContainerWrapper(windsorContainer);
    });
// now we can create an IBus instance, but it's resolved from
// windsor, rather than EasyNetQ's default service provider.
var bus = RabbitHutch.CreateBus("host=localhost");

Here is how I implemented WindsorContainerWrapper:

public class WindsorContainerWrapper : IContainer, IDisposable
{
    private readonly IWindsorContainer windsorContainer;

    public WindsorContainerWrapper(IWindsorContainer windsorContainer)
    {
        this.windsorContainer = windsorContainer;
    }

    public TService Resolve<TService>() where TService : class
    {
        return windsorContainer.Resolve<TService>();
    }

    public IServiceRegister Register<TService>(System.Func<IServiceProvider, TService> serviceCreator) 
        where TService : class
    {
        windsorContainer.Register(
            Component.For<TService>().UsingFactoryMethod(() => serviceCreator(this)).LifeStyle.Singleton
            );
        return this;
    }

    public IServiceRegister Register<TService, TImplementation>() 
        where TService : class 
        where TImplementation : class, TService
    {
        windsorContainer.Register(
            Component.For<TService>().ImplementedBy<TImplementation>().LifeStyle.Singleton
            );
        return this;
    }

    public void Dispose()
    {
        windsorContainer.Dispose();
    }
}

Note that all EasyNetQ services should be registered as singletons.

It’s important that you dispose of Windsor correctly. EasyNetQ doesn’t provide a Dispose method on IContainer, but you can access the container via the advanced bus (yes, this is new too), and dispose of windsor that way:

((WindsorContainerWrapper)bus.Advanced.Container).Dispose();
bus.Dispose();

Happy containerisation!