Ninject retrieve Custom Attributes on parameters inside interceptor

Question

I am attempting to enumerate the parameters of a decorated method to retrieve the custom attributes applied to those parameters to determine a specific value.

I have the following in my interceptor, which shows two different methods that I tried to use, both retreiving and enumerating GetParameters but one using IsDefined and the other using GetCustomAttributes:

public void Intercept(IInvocation invocation)
{
    try
    {

        var parameters = invocation.Request.Method.GetParameters();
        for (int index = 0; index < parameters.Length; index++)
        {
            foreach (var attrs in parameters[index]
                .GetCustomAttributes(typeof(EmulatedUserAttribute), true))
            {

            }

        }

        foreach (var param in invocation.Request.Method.GetParameters())
        {
            if (param.IsDefined(typeof (EmulatedUserAttribute), false))
            {
                invocation.Request.Arguments[param.Position] = 12345;
            }

        }


        invocation.Proceed();
    }
    catch(Exception ex)
    {
        throw;
    }
}

The attribute I am looking for is simple, no implementation:

public class EmulatedUserAttribute : Attribute { }

And the InterceptAttribute:

[AttributeUsage(AttributeTargets.Method)]
public class EmulateAttribute : InterceptAttribute
{
    public override IInterceptor CreateInterceptor(IProxyRequest request)
    {
        return request.Context.Kernel.Get<IEmulateUserInterceptor>();
    }
}

And the method I am intercepting:

[Emulate]
public virtual List<UserAssociation> GetAssociatedProviders([EmulatedUser] int userId)
{
    return _assocProvAccountRepo.GetAssociatedProviders(userId);
}

As you can see I decorated the userId with the EmulatedUser attribute, and the method with my interceptor attribute. Everything else works fine except that I cannot see the attribute on userId.

Any ideas why I cant see custom attributes on the method? Im guessing it has something to do with the Method not being the actual "invocation target" but I dont see any way to get around this. Please help!

score 1 · Accepted Answer · answered Mar 18 '14 at 15:40

Brandon,

Try this code out. I have made it work just fine. Here is how I defined the classes:

public class Interceptor : SimpleInterceptor
{
    protected override void BeforeInvoke(IInvocation invocation)
    {
        var invokedMethod = invocation.Request.Method;
        if (invokedMethod.IsDefined(typeof(EmulateAttribute), true))
        {
            var methodParameters = invokedMethod.GetParameters();
            for (int i = 0; i < methodParameters.Length; i++)
            {
                var param = methodParameters[i];
                if (param.IsDefined(typeof (EmulatedUserAttribute), true))
                {
                    invocation.Request.Arguments[i] = 5678;
                }
            }
        }
    }
}

public interface IIntercepted
{
    [Emulate]
    void InterceptedMethod([EmulatedUser] int userId);
}

public class Intercepted : IIntercepted
{
    [Emulate]
    public void InterceptedMethod([EmulatedUser] int userId)
    {
        Console.WriteLine("UserID: {0}", userId);
    }
}

I am requesting an instance of IIntercepted instead of Intercepted. If I request the concrete class, the interception will not work. Maybe this can get you in the right path.

var kernel = new StandardKernel();
kernel.Bind<IIntercepted>().To<Intercepted>().Intercept().With<Interceptor>();

var target = kernel.Get<IIntercepted>();

target.InterceptedMethod(1234); // Outputs 5678

Thank you that was exactly what I needed! Specifically adding the attributes to the interface. Any idea why that happens? — Brandon, Mar 18 '14 at 17:54
The "Service" (type) that is intercepted is the interface, not the implementation itself. If the interface doesn't have the attributes, you won't be able to see them inside your interceptor. You can debug to confirm using `invocation.Request.Service`, and it'll return `IIntercepted`, not `Intercepted` — cvbarros, Mar 19 '14 at 00:29

Ninject retrieve Custom Attributes on parameters inside interceptor

1 Answers1