Simple pipeline example

gistfile1.cs

using NUnit.Framework;

namespace PipelineDemo
{
    public abstract class Handler<T>
    {
        protected Handler<T> next;

        public void SetInnerHandler(Handler<T> handler)
        {
            if (next == null)
            {
                next = handler;
            }
            else
            {
                next.SetInnerHandler(handler);
            }
        }

        public abstract void Invoke(T input);
    }
    
    public class Pipeline<T>
    {
        private Handler<T> outer;

        public Pipeline<T> Use(Handler<T> handler)
        {
            if (outer == null)
            {
                outer = handler;
            }
            else
            {
                outer.SetInnerHandler(handler);
            }

            return this;
        }

        public void Execute(T input)
        {
            outer.Invoke(input);
        }
    }

    public class Context
    {
        public string RequestUri { get; set; }
        public int Response { get; set; }
    }

    public class AuthHandler : Handler<Context>
    {
        public override void Invoke(Context context)
        {
            if (context.RequestUri == "/admin")
            {
                context.Response = 403;
            }
            else
            {
                next.Invoke(context);
            }
        }
    }

    public class DefaultHandler : Handler<Context>
    {
        public override void Invoke(Context input)
        {
            input.Response = 200;
        }
    }

    [TestFixture]
    public class PipelineTests
    {
        Pipeline<Context> pipeline;
        Context context;

        [SetUp]
        public void SetUp()
        {
            pipeline = new Pipeline<Context>()
                .Use(new AuthHandler())
                .Use(new DefaultHandler());

            context = new Context();
        }
        
        [Test]
        public void Requests_to_admin_returns_403()
        {
            context.RequestUri = "/admin";
            pipeline.Execute(context);
            Assert.AreEqual(403, context.Response);
        }

        [Test]
        public void Requests_to_root_returns_200()
        {
            context.RequestUri = "/";
            pipeline.Execute(context);
            Assert.AreEqual(200, context.Response);
        }
    }

}