HttpModule

HttpModules allow we to extend the existing ASP.NET pipeline.  The most common use of HTTPModules is pre and/ore postprecessing of requests.

From the article we can understand the principle, there is a detail flow when request is happen

HttpRequest --> inetinfor.exe --> AspNet_ISAPI.dll --> Http pipeline --> AspNet_WP.exe
--> HttpRuntime --> HttpApplication Factory --> HttpApplication --> HttpModule -->
HttpHandler Factory --> HttpHandler --> HttpHandler.ProcessRequest()

I wrote a test class inherit from interface IHttpModule

    public class MyHttpModule : IHttpModule 
    {
        public MyHttpModule()
        {
            //
            // TODO: Add constructor logic here
            //
        }

        public void Init(HttpApplication application)
        {
            application.BeginRequest += (new EventHandler(this.Application_BeginRequest));
            application.EndRequest += (new EventHandler(this.Application_EndRequest));
            application.PreRequestHandlerExecute +=(new EventHandler(this.Application_PreRequestHandlerExecute));
            application.PostRequestHandlerExecute +=(new EventHandler(this.Application_PostRequestHandlerExecute));
            application.ReleaseRequestState +=(new EventHandler(this.Application_ReleaseRequestState));
            application.AcquireRequestState +=(new EventHandler(this.Application_AcquireRequestState));
            application.AuthenticateRequest +=(new EventHandler(this.Application_AuthenticateRequest));
            application.AuthorizeRequest +=(new EventHandler(this.Application_AuthorizeRequest));
            application.ResolveRequestCache +=(new EventHandler(this.Application_ResolveRequestCache));
            application.PreSendRequestHeaders +=(new EventHandler(this.Application_PreSendRequestHeaders));
            application.PreSendRequestContent +=(new EventHandler(this.Application_PreSendRequestContent));
        }
        
        private void Application_PreRequestHandlerExecute(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_PreRequestHandlerExecute<br>");
        }

        private void Application_BeginRequest(Object source, EventArgs e) 
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_BeginRequest<br>");
        }

        private void Application_EndRequest(Object source, EventArgs e) 
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_EndRequest<br>");

        } 

        private void Application_PostRequestHandlerExecute(Object source,EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_PostRequestHandlerExecute<br>");

        }

        private void Application_ReleaseRequestState(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_ReleaseRequestState<br>");

        }

        private void Application_UpdateRequestCache(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_UpdateRequestCache<br>");

        }

        private void Application_AuthenticateRequest(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_AuthenticateRequest<br>");

        }

        private void Application_AuthorizeRequest(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_AuthorizeRequest<br>");

        }

        private void Application_ResolveRequestCache(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_ResolveRequestCache<br>");

        }

        private void Application_AcquireRequestState(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_AcquireRequestState<br>");

        }

        private void Application_PreSendRequestHeaders(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_PreSendRequestHeaders<br>");

        }

        private void Application_PreSendRequestContent(Object source, EventArgs e)
        {
            HttpApplication application = (HttpApplication)source;
            HttpContext context = application.Context;

            context.Response.Write("Application_PreSendRequestContent<br>");

        }

        public void Dispose(){}

    }

I am surprised to find that when the transcation in HttpHandler is finished the request will return to HttpModule,below is the lifcycle of request in HttpModule.

Http Request
        |
HttpModule
        |
HttpModule.BeginRequest()
        |
HttpModule.AuthenticateRequest()
        |
HttpModule.AuthorizeRequest()
        |
HttpModule.ResolveRequestCache()
        |
Create HttpHandler reference point
        |
（HttpHandler is begin）
        |
HttpModule.AcquireRequestState()
        |
HttpModule.PreRequestHandlerExecute()
        |
Enter into HttpHandler to treat with the HttpRequest
        |
HttpHandler.ProcessRequest()
        |
Return to HttpModule（HttpHandler is over）
        |
HttpModule.PostRequestHandlerExecute()
        |
HttpModule.ReleaseRequestState()
        |
HttpModule.UpdateRequestCache()
        |
HttpModule.EndRequest()
        |
HttpModule.PreSendRequestHeaders()
        |
HttpModule.PreSendRequestContent()
        |
return the data to client
        |
The whole transaction of  Http Request is over