Tuesday, September 25, 2012

Replacing EasyNetQ Components

EasyNetQ, my simple .NET API for RabbitMQ, is a library composed of small components. Until today, the code simply wired the components in a messy hard-coded routine. Now it has its own tiny internal IoC container.  When you write:
var bus = RabbitHutch.CreateBus("host=localhost");

... the static method CreateBus registers the components with the container and then resolves the IBus instance. The really cool thing about this is that it allows you, the user, to replace any of the internal components, including IBus, with your own implementations. An overload of the CreateBus method provides the hook which gives you access to the component registration. The signature looks like this:
public static IBus CreateBus(string connectionString, Action<IServiceRegister> registerServices)

The IServiceRegister interface provides a single method:
public interface IServiceRegister
    IServiceRegister Register<TService>(Func<IServiceProvider, TService> serviceCreator) where TService : class;

So to register your own logger, based on IEasyNetQLogger, you'd write this code:
var logger = new MyLogger(); // MyLogger implements IEasyNetQLogger
var bus = RabbitHutch.CreateBus(connectionString, 
    serviceRegister => serviceRegister.Register(serviceProvider => logger));

The Register method's argument, Func<IServiceProvider, TService>, is a function that's run when CreateBus pulls together the components to make an IBus instance. IServiceProvider looks like this:
public interface IServiceProvider
    TService Resolve<TService>() where TService : class;

This allows you to access other services that EasyNetQ provides. If for example you wanted to replace the default serializer with your own implementation of ISerializer, and you wanted to construct it with a reference to the internal logger, you could do this:
var bus = RabbitHutch.CreateBus(connectionString, serviceRegister => serviceRegister.Register(
    serviceProvider => new MySerializer(serviceProvider.Resolve<IEasyNetQLogger>())));

There’s nothing to stop you registering your own interfaces with the container that you can then use with your implementations of EasyNetQ’s service interfaces.
To see the complete list of components that make up the IBus instance, and how they are assembled, take a look at the ComponentRegistration class.


Ed Blackburn said...

Where do I put the XML :p

Mike Hadlow said...

I could tell you, but it might hurt :)