Question

Just out of personal interest, I decided to try to write a basic web server using Reactive Extensions (aka Rx). Almost immediately, I came up against the following problem:

HttpListener’s async pattern doesn’t match the normal async pattern signature, the EndGetContext returns a HttpListenerContext instead of an IAsyncResult!

So my question is: is there a way around this?

Here’s some code – the compiler (rightly) complains about the second argument to Observable.FromAsyncPattern:

Update – As Jon rightly pointed out, it wasn’t the pattern, it’s complaining that I haven’t provided the return type – this works:

var observable = Observable.FromAsyncPattern<HttpListenerContext>(listener.BeginGetContext, listener.EndGetContext);

The original code:

using System;
using System.Net;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace RxWebTest
{
    class Program
    {
        static void Main(string[] args)
        {
            HttpListener listener = new HttpListener();
            try
            {
                listener.Start();

                var observable = Observable.FromAsyncPattern(listener.BeginGetContext, listener.EndGetContext);



                Console.ReadLine();
            }
            finally
            {
                listener.Abort();
            }
        }
    }
}

Answer 1

That is the normal pattern. It’s BeginGetContext which returns IAsyncResult; EndGetContext takes an IAsyncResult and returns the result of the asynchronous operation – the context. That’s exactly the same as (say) Stream.BeginRead/EndRead, where EndRead returns an int, the number of bytes read.

What happens when you try the code you’ve posted? I can’t immediately see why it wouldn’t work.