Intercepting the concrete implementation (as opposed to service) using Castle Windsor

Question

I'm experimenting with interception in Castle Windsor and notice that interceptors seem to be created as decorators of my service interface.

In other words, if I have an interface "ISomethingDoer" and a concrete "ConcreteSomethingDoer", the proxy implements ISomethingDoer but does not inherit from ConcreteSomethingDoer.

This is fine, and no doubt by design, but what I'm wondering is whether I can intercept protected virtual methods in my concrete classes that wouldn't be known by the public interface. I am doing this in order to add logging support, but I might want to log some of the specific internal details of a class.

In my slightly unimaginative test case I have this:

public interface ISomethingDoer
{
    void DoSomething(int Count);
}

[Loggable]
public class ConcreteSomethingDoer : ISomethingDoer
{
    public void DoSomething(int Count)
    {
        for (var A = 0; A < Count; A++)
        {
            DoThisThing(A);
        }
    }

    [Loggable]
    protected virtual void DoThisThing(int A)
    {
        ("Doing a thing with " + A.ToString()).Dump();
    }
}

So what I want to do is log calls to "DoThisThing" even though it's not part of the interface.

I've managed to get this working in Autofac. (I've created a Linqpad script here: http://share.linqpad.net/frn5a2.linq) but am struggling with Castle Windsor (see http://share.linqpad.net/wn7877.linq)

In both cases my interceptor is the same and looks like this:

public class Logger : IInterceptor
{
    public void Intercept(IInvocation Invocation)
    {
        String.Format("Calling method {0} on type {1} with parameters {2}",
            Invocation.Method.Name,
            Invocation.InvocationTarget.GetType().Name,
            String.Join(", ", Invocation.Arguments.Select(a => (a ?? "*null*").ToString()).ToArray())).Dump();
            Invocation.Proceed();
        "Done".Dump();
    }
}

What I really want to do is say "any classes with a [Loggable] attribute, should use the logging interceptor". In the Autofac example I've specifically attached a logger to the registration, whereas with Castle I'm using an IModelInterceptorsSelector which looks like this:

public class LoggerInterceptorSelector : IModelInterceptorsSelector
{
    public bool HasInterceptors(ComponentModel Model)
    {
        return Model.Implementation.IsDefined(typeof(LoggableAttribute), true);
    }

    public InterceptorReference[] SelectInterceptors(ComponentModel Model, InterceptorReference[] Interceptors)
    {   
        return new[]
        {       
            InterceptorReference.ForType<Logger>()
        };
    }
}

Finally, the code to execute all this is:

    var Container = new WindsorContainer();

    Container.Register(
        Component.For<Logger>().LifeStyle.Transient
    );

    Container.Kernel.ProxyFactory.AddInterceptorSelector(new LoggerInterceptorSelector());

    Container.Register(
        Component.For<ISomethingDoer>()
        .ImplementedBy<ConcreteSomethingDoer>()
        .LifeStyle.Transient
    );

    var Doer = Container.Resolve<ISomethingDoer>();
    Doer.DoSomething(5);

When run I would expect to see "Calling method DoThisThing with parameters x" for each time the method is called. Instead I only get the call to DoSomething logged.

I can see why Castle Windsor is doing this, but I'm wondering if there is a way to tweak the behaviour?

(As a side-note I don't want to use Windsor's own interceptor attributes as I don't want to introduce dependencies to Castle outside of my composition root.)

I have tried resolving the ConcreteSomethingDoer specifically and this works, but not if I'm resolving the ISomethingDoer.

Apologies for the long post, and also apologies because I am pretty new to Castle Windsor!

Marwijn Marwijn · Accepted Answer · 2013-04-05T14:34:39

I you could register like:

Container.Register(
    Component.For<ISomethingDoer, ConcreteSomethingDoer>()
    .ImplementedBy<ConcreteSomethingDoer>()
    .LifeStyle.Transient
);

This should create a class proxy by deriving from ConcreteSomethingDoer. However this won't work with dynamic interceptors. However you probably can work around that by creating a facility which registers the interceptor when needed.

Intercepting the concrete implementation (as opposed to service) using Castle Windsor

1 Answers