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Tweaking WCF to build highly scalable async REST API

, 31 Jul 2011
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.
namespace AsyncServiceLibrary
{
    using System;
    using System.Collections.Generic;
    using System.Text;
    using System.Web;
    using System.Reflection;
    using System.ServiceModel;
    using System.Security;

    class MyHttpModule : IHttpModule
    {
        static BeginEventHandler beginEventHandler;
        static EndEventHandler endEventHandler;
        static MethodInfo safeEnsureInitialized;
        static MethodInfo getExtensionSupported;
        static ConstructorInfo hostedHttpRequestAsyncResult;
        static MethodInfo hostedHttpRequestAsyncResultEnd;
        static Type hostedHttpRequestAsyncResultType;

        static bool disabled;

        public void Dispose()
        {
        }

        public void Init(HttpApplication context)
        {
            if (MyHttpModule.safeEnsureInitialized == null)
            {
                safeEnsureInitialized = typeof(ServiceHostingEnvironment).GetMethod("SafeEnsureInitialized", BindingFlags.NonPublic | BindingFlags.Static);
            }

            if (MyHttpModule.getExtensionSupported == null)
            {
                getExtensionSupported = typeof(ServiceHostingEnvironment).GetMethod("GetExtensionSupported", BindingFlags.NonPublic | BindingFlags.Static);
            }

            if (hostedHttpRequestAsyncResultType == null)
            {
                hostedHttpRequestAsyncResultType = typeof(ServiceHostingEnvironment).Assembly.GetType("System.ServiceModel.Activation.HostedHttpRequestAsyncResult");
            }

            if (MyHttpModule.hostedHttpRequestAsyncResult == null)
            {
                hostedHttpRequestAsyncResult = hostedHttpRequestAsyncResultType.GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public,
                    null, new Type[] { typeof(HttpApplication), typeof(bool), typeof(AsyncCallback), typeof(object) }, null);
            }

            if (MyHttpModule.hostedHttpRequestAsyncResultEnd == null)
            {
                hostedHttpRequestAsyncResultEnd = hostedHttpRequestAsyncResultType.GetMethod("End", BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public);
            }

            if (MyHttpModule.beginEventHandler == null)
            {
                MyHttpModule.beginEventHandler = new BeginEventHandler(BeginProcessRequest);
            }

            if (MyHttpModule.endEventHandler == null)
            {
                MyHttpModule.endEventHandler = new EndEventHandler(EndProcessRequest);
            }

            context.AddOnPostAuthenticateRequestAsync(
                MyHttpModule.beginEventHandler,
                MyHttpModule.endEventHandler);
        }

        static public IAsyncResult BeginProcessRequest(object sender, EventArgs e, AsyncCallback cb, object extraData)
        {
            if (MyHttpModule.disabled)
            {
                return new CompletedHttpAsyncResult(cb, extraData); ;
            }

            try
            {
                safeEnsureInitialized.Invoke(null, null);
            }
            catch (SecurityException)
            {
                MyHttpModule.disabled = true;
                return new CompletedHttpAsyncResult(cb, extraData);
            }

            if (ServiceHostingEnvironment.AspNetCompatibilityEnabled)
            {
                return new CompletedHttpAsyncResult(cb, extraData);
            }

            // Check to see whether the extension is supported by WCF.
            HttpApplication application = (HttpApplication)sender;
            string extension = System.IO.Path.GetExtension(application.Request.FilePath);
            if (extension == null || !(bool)getExtensionSupported.Invoke(null, new object[] {extension}))
            {
                return new CompletedHttpAsyncResult(cb, extraData);
            }

            return (IAsyncResult)hostedHttpRequestAsyncResult.Invoke(new object[] { application, false, cb, extraData });
        }

        static public void EndProcessRequest(IAsyncResult ar)
        {
            if (ar is CompletedHttpAsyncResult)
            {
                CompletedHttpAsyncResult.End(ar);
            }
            else
            {
                hostedHttpRequestAsyncResultEnd.Invoke(null, new object[] {ar});
            }
        }
    }
}


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Web01 | 2.8.140916.1 | Last Updated 31 Jul 2011
Article Copyright 2011 by Omar Al Zabir
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