HTTP Handlers and HTTP Modules Overview

An ASP.NET HTTP handler is the process (frequently referred to as the "endpoint") that runs in response to a request made to an ASP.NET Web application. The most common handler is an ASP.NET page handler that processes .aspx files. When users request an .aspx file, the request is processed by the page through the page handler. You can create your own HTTP handlers that render custom output to the browser.

Click here to see IHttpHandler Example Code

An HTTP module is an assembly that is called on every request that is made to your application. HTTP modules are called as part of the ASP.NET request pipeline and have access to life-cycle events throughout the request. HTTP modules let you examine incoming and outgoing requests and take action based on the request.

Click here to see IHttpModule Example Code

Scenarios:

Typical uses for custom HTTP handlers include the following:

• RSS feeds To create an RSS feed for a Web site, you can create a handler that emits RSS-formatted XML. You can then bind a file name extension such as .rss to the custom handler. When users send a request to your site that ends in .rss, ASP.NET calls your handler to process the request.

• Image server If you want a Web application to serve images in a variety of sizes, you can write a custom handler to resize images and then send them to the user as the handler's response.

Typical uses for HTTP modules include the following:

• Security Because you can examine incoming requests, an HTTP module can perform custom authentication or other security checks before the requested page, XML Web service, or handler is called. In Internet Information Services (IIS) 7.0 running in Integrated mode, you can extend forms authentication to all content types in an application.

• Statistics and logging Because HTTP modules are called on every request, you can gather request statistics and log information in a centralized module, instead of in individual pages.


• Custom headers or footers Because you can modify the outgoing response, you can insert content such as custom header information into every page or XML Web service response.

Features:

HTTP handler and module features include the following:

• The IHttpHandler and IHttpModule interfaces are the starting point for developing handlers and modules.

• The IHttpAsyncHandler interface is the starting point for developing asynchronous handlers.

• Custom handler and module source code can be put in the App_Code folder of an application, or it can be compiled and put in the Bin folder of an application.

• Handlers and modules developed for use in IIS 6.0 can be used in IIS 7.0 with little or no change. For more information, see Moving an ASP.NET Application from IIS 6.0 to IIS 7.0.

• Modules can subscribe to a variety of request-pipeline notifications. Modules can receive notification of events of the HttpApplication object.

• In IIS 7.0, the request pipeline is integrated with the Web server request pipeline. HTTP modules can be used for any request to the Web server, not just ASP.NET requests.