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Tweaking WCF to build highly scalable async REST API

, 31 Jul 2011 CPOL
You can build async REST API using WCF but due to some bug in WCF implementation it does not scale as you would want it to. Here's my journey with Microsoft's WCF team to explore the problem and find the right fix.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Net;

namespace WcfAsyncRestApi
{
    /// <summary>
    /// Summary description for AsyncHandler
    /// </summary>
    public class AsyncHandler : IHttpAsyncHandler
    {

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
        {
            HttpWebRequest request = WebRequest.Create(context.Request["url"]) as HttpWebRequest;
            return request.BeginGetResponse(cb, new MyState { Context = context, Request = request });
        }

        public void EndProcessRequest(IAsyncResult result)
        {
            var state = result.AsyncState as MyState;
            var webResponse = state.Request.EndGetResponse(result);
            var stream = webResponse.GetResponseStream();
            byte[] buffer = new byte[8000];
            int size = 0;

            state.Context.Response.AddHeader("Content-Type", "text/plain");
            do{
                size = stream.Read(buffer, 0, 8000);
                if (size > 0)
                    state.Context.Response.OutputStream.Write(buffer, 0, size);
            } while (size > 0);
            state.Context.Response.End();
        }


        public void ProcessRequest(HttpContext context)
        {
            throw new NotImplementedException();
        }
    }

    class MyState
    {
        public HttpContext Context;
        public HttpWebRequest Request;
    }
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Omar Al Zabir
Architect BT, UK (ex British Telecom)
United Kingdom United Kingdom

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