AsyncInterceptor for Castle DynamicProxy

This small library provides an abstract base class AsyncInterceptor for Castle DynamicProxy which allows you to use .NET languages' async/await facilities during interception of awaitable methods.

This is currently in draft stage, but should be usable. Feedback and contributions are welcome!

Usage example

class Delay : AsyncInterceptor
{
    private readonly int milliseconds;

    public Delay(int milliseconds)
    {
        this.milliseconds = milliseconds;
    }

    // This gets called when a non-awaitable method is intercepted:
    protected override void Intercept(IInvocation invocation)
    {
        Thread.Sleep(this.milliseconds);
        invocation.Proceed();
    }

    // Or this gets called when an awaitable method is intercepted:
    protected override async ValueTask InterceptAsync(IAsyncInvocation invocation)
    {
        await Task.Delay(this.milliseconds);
        await invocation.ProceedAsync();
    }
}


class Return : AsyncInterceptor
{
    private readonly object value;

    public Return(object value)
    {
        this.value = value;
    }

    protected override void Intercept(IInvocation invocation)
    {
        invocation.ReturnValue = this.value;
    }

    protected override ValueTask InterceptAsync(IAsyncInvocation invocation)
    {
        // The property being set is called `Result` rather than `ReturnValue`.
        // This is a hint that its value doesn't have to be wrapped up as a task-like object:
        invocation.Result = this.value;
        return default;
    }
}


public interface ICalculator
{
    int GetResult();
    Task<int> GetResultAsync();
}


var generator = new ProxyGenerator();

var proxy = generator.CreateInterfaceProxyWithoutTarget<ICalculator>(
    new Delay(2500),
    new Return(42));

Assert.Equal(42, proxy.GetResult());
Assert.Equal(42, await proxy.GetResultAsync());