HTTP Modules Events

Every HTTP Module must implement following two methods of IHTTPModule interface:

Init: To register/initialize event handler to the events of HTTP Module for HTTP based application.

Dispose: To perform a clean up code means resource releasing, object removing from memory and such other resources releasing which used explicitly.

Following are list of events with their brief description:

BeginRequest: Event fired whenever any asp.net based request sent to web server. If you need to do perform at the beginning of a request for example, modify show banners, log HTTP Header information, Get/Set cultures, Response.Filter to generate response for browser according to your need.

AuthenticateRequest: If you want to check authentication of request that request comes from authenticated user or not means wants to implement custom authentication scheme. For example, look up a requested user credentials against a database to validate.

AuthorizeRequest: This method is used specifically to implement authorization mechanisms means authenticated user/request has what privileges/rights/access in that specific application for example, either user has access on all pages or not of that website or has write to create file or not or visit report pages and like this.

ResolveRequestCache: This event determines if a page served from the Output cache. If you want to write your own caching module (for example, build a file-based cache rather than a memory cache), synchronize this event to determine whether to serve the page from the cache.

AcquireRequestState: Session state is retrieved from the state store. If you want to build your own state management module, synchronize this event to grab the Session state from your state store.

PreRequestHandlerExecute: This event occurs before the HTTP handler is executed.

PostRequestHandlerExecute: This event occurs after the HTTP handler is executed.

ReleaseRequestState: Session state is stored back in the state store. If you are building a custom session state module, you must store your state back in your state store.

UpdateRequestCache: This event writes from output back to the Output cache. If you are building a custom cache module, you have to write the output back to your cache.

Error: this event always occurs when any exception (unhandled error occurs in application, this event specifically uses to handle or log error messages of that web application. (Heavily used in Error Logging Modules and Handlers (ELMAH) kind of applications). You can learn about ELMAH more from following link in detail:http://dotnetslackers.com/articles/aspnet/ErrorLoggingModulesAndHandlers.aspx

EndRequest: Request has been completed. You may want to build a debugging module that gathers information throughout the request and then writes the information on the page.

By above events list you must be getting wonder about difference between Global.asax as somehow events of Global.asax are pretty same, so let me tell you difference between Global.asax and HTTP Module (another common question asked in interviews)

But you need to register/initialize these Events explicitly in “Init” method; following is sample code of IHTTPModule implementation for couple of events.