Tuesday, March 2, 2010

ASP.net - implementing Asynchronous HTTP handler

Asynchronous programming has its own benefits. It helps in better usage of resources. In ASP.net when a user request for a resource which is to be processed by HTTP Handler a thread is created an allocated to the handler file. The thread will be idle till the file finish it’s processing. So as to minimize this “idle” period using asynchronous programming we can release the thread back to pool after passing the execution to handler file. When the asynchronous handler completes its work, the framework reassigns a thread to the original request and the handler can render content to the browser. For a better understanding of Asynchronous programming in .Net visit: Asynchronous Programming Overview

We can create an asynchronous HTTP handler by implementing the IHttpAsyncHandler interface, which is derived from the IHttpHandler interface. It adds two additional
methods:

  • IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData);—Called to start the asynchronous task.
  • void EndProcessRequest(IAsyncResult result)—Called when the asynchronous task completes

Create a new class like the following


    public class NewClass : IHttpAsyncHandler
    {
        private HttpContext _context;
        private WebRequest _request;

        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
        {
        }

        public void EndProcessRequest(IAsyncResult result)
        {
        }

        public bool IsReusable
        {
            get { return true; }
        }

        public void ProcessRequest(HttpContext context)
        {
            throw new Exception("The ProcessRequest method is not implemented.");
        }
    }

You can use this class to do a variety of tasks.

In the below Code I have used created a clss to read RSS data from web

public class RSSHandler : IHttpAsyncHandler
    {
        private HttpContext _context;
        private WebRequest _request;
        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
        {
            // Store context

            _context = context;
            // Initiate call to RSS feed
           
            _request = WebRequest.Create(context.Request.QueryString["rssURL"]);
            return _request.BeginGetResponse(cb, extraData);
        }
        public void EndProcessRequest(IAsyncResult result)
        {
            // Get the RSS feed
            string rss = String.Empty;
            WebResponse response = _request.EndGetResponse(result);
            using (response)
            {
                StreamReader reader = new StreamReader(response.GetResponseStream());
                rss = reader.ReadToEnd();
            }
            _context.Response.Write(rss);
        }
        public bool IsReusable
        {
            get { return true; }
        }
        public void ProcessRequest(HttpContext context)
        {
            throw new Exception("The ProcessRequest method is not implemented.");
        }


This class will read the RSS feed asynchronously.

The BeginProcessRequest() method uses the WebRequest class to request the page that
contains the RSS headlines. It received the URL as QueryString.The WebRequest.BeginGetResponse() method is used to retrieve the remote page asynchronously. When the BeginGetResponse() method completes, the handler’s EndProcessRequest() method is called. This method retrieves the page and renders the contents of the page to the browser.

Before we start using this handler we have to register this handler like the following in web.config

<httpHandlers>
      <add verb="*" path="*.rss" validate="false" type="AspNet.RSSHandler"/>
                  <add verb="*" path="*.xml" validate="false" type="AspNet.RSSHandler"/>
 httpHandlers>

After building and typing the following URL

I got an output similar to the one shown below
There was no file xyz.rss or sample.xml but since these extensions were mapped to the recently created HTTP handler output was generated by the framework




Related Articles :

  1. ASP.net - Http handlers - implementing IHttpHandler
  2. ASP.net - Http handlers - Generic Hander 

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