The tech guy in woods

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
http://localhost:2141/xyz.rss?rssURL=http://feeds.feedburner.com/blogspot/anKd
http://localhost:2141/sample.xml?rssURL=http://feeds.feedburner.com/blogspot/anKd

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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Posted By Abhi to The Tech Jungle at 3/02/2010 10:41:00 AM

The Tech Jungle Asp.Net – Creating a new custom HTTP Module

An HTTP Module is a .NET class that executes with each and every page request. You can use an HTTP Module to handle any of the HttpApplication events that you can handle in the Global.asax file.

You are already familiar with some of the HTTP Modules like

• FormsAuthenticationModule handles the Forms authentication
• WindowsAuthenticationModule handles the Windows authentication
• SessionStateModule manages the session state of ASP.net application
• OutputCacheModule deals with output caching
• ProfileModule used for interaction with user profiles

Each HTTP Module subscribes to one or more HttpApplication events. For example, when the HttpApplication object raises its AuthenticateRequest event, the FormsAuthenticationModule executes its code to authenticate the current user.

Below I have included a sample class which implements the IHttpModule interface

In the Init event I have created an EventHandler for the PostAuthorizeRequest event of Http Application

namespace AspNet

{
public class CustomContentModule : IHttpModule
{
public void Init(HttpApplication app)
{

app.PostAuthorizeRequest += new EventHandler(SendRequest);
}
public void SendRequest(Object sender, EventArgs e)
{
HttpApplication app = (HttpApplication)sender;
app.Response.Write("Hi content from HTTP Module
Pay my tax also !!!");
}

public void Dispose() { }

}
}

You can use any of the following events of HTTP Application; the events are raised in the following order:

1. BeginRequest
2. AuthenticateRequest
3. PostAuthenticateRequest
4. AuthorizeRequest
5. PostAuthorizeRequest
6. ResolveRequestCache
7. PostResolveRequestCache

After the PostResolveRequestCache event and before the PostMapRequestHandler event, an event handler (which is a page that corresponds to the request URL) is created. When a server is running IIS 7.0 in Integrated mode and at least the .NET Framework version 3.0, the MapRequestHandler event is raised. When a server is running IIS 7.0 in Classic mode or an earlier version of IIS, this event cannot be handled.

8. PostMapRequestHandler
9. AcquireRequestState
10. PostAcquireRequestState
11. PreRequestHandlerExecute

The event handler is executed.

12. PostRequestHandlerExecute
13. ReleaseRequestState
14. PostReleaseRequestState

After the PostReleaseRequestState event is raised, any existing response filters will filter the output.

15. UpdateRequestCache
16. PostUpdateRequestCache
17. LogRequest.

This event is supported in IIS 7.0 Integrated mode and at least the .NET Framework 3.0

18. PostLogRequest

This event is supported IIS 7.0 Integrated mode and at least the .NET Framework 3.0

19. EndRequest

After creating this class add the following entry in Web.config

<httpModules>
<add name="CustomContentModule" type="AspNet.CustomContentModule"/>
httpModules>

When you excute any page in this application HTTP Runtime will add the content from the HTTP module created by us. You can build on this to create more complex scenarious like custom authitication, generation.processing of data based on the paraametr availalle in the Http Application objects etc.

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Posted By Abhi to The Tech Jungle at 3/03/2010 07:17:00 AM

Anonymous types for dummies

Anonymous types are used to define strong types without defining the type. Anonymous types are strongly typed and checked at compile time. It provides a convenient way to encapsulate a set of read-only properties into a single object without having to first explicitly define a type. Anonymous types are reference types that derive directly from object. The compiler gives them a name although your application cannot access it. From the perspective of the common language runtime, an anonymous type is no different from any other reference type, except that it cannot be cast to any type except for object. This type is widely used by LINQ, because LINQ returns dynamically-shaped data, whose type is determined by the LINQ query

To understand better look at the following code

static void Main(string[] args)

{

string[] names = { "Abhi1", "abhi", "abhi11",

"george", "bush", "britney",

"gandhi", "David" };

IEnumerable<string> varAnnoyType = from str in names

orderby str

select str;

//following code also valid

//var varAnnoyType = from str in names

// orderby str

// select str;

foreach (string strname in varAnnoyType)

Console.WriteLine(strname);

Console.ReadLine();

}

As discussed in http://thetechjungle.blogspot.com/2009/12/linq-for-dummies-overview.html

anonymous type is an object which supports IEnumerable interface.

In the above example an array of names is created (took the array collection from msdn) , an IEnumerable<string> type is created, see the keyword like from used to iterate eact item in collection, orderby clause orders (without LINQ imagine the dictionaries , temp variables and other techniqies used to sort items now this is really cool). You can add a Where clause also before the select keyword. If any conditions are specified then select will retrieve only those items which satisfies the where clause.

var varAnnoyType = from str in names

where str.StartsWith("abhi")

orderby str

select str;

The for each iteration can be written like the following also.

foreach (var strname in varAnnoyType)

Console.WriteLine(strname);

If two or more anonymous types have the same number and type of properties in the same order, the compiler treats them as the same type and they share the same compiler-generated type information.

An anonymous type has method scope. To pass an anonymous type, or a collection that contains anonymous types, outside a method boundary, you must first cast the type to object. However, this defeats the strong typing of the anonymous type. If you must store your query results or pass them outside the method boundary, consider using an ordinary named struct or class instead of an anonymous type.

Anonymous types cannot contain unsafe types as properties.

Because the Equals and GetHashCode methods on anonymous types are defined in terms of the Equals and GetHashcode of the properties, two instances of the same anonymous type are equal only if all their properties are equal.

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Posted By Abhi to The Tech Jungle at 12/26/2009 08:06:00 AM