What is HTTP handler?

An ASP.NET HTTP handler is a process that runs in response to a request made to an ASP.NET Web application. The most common handler is the 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.

HTTP handlers were not present in the "Classic" ASP. They implement the System.Web.IHttpHandler interface. Unlike ASP.NET Web Forms, they have no HTML-markup file, no events and other supporting. All they have is a code-file that writes some data to the server HTTP response. HTTP handlers are similar to ISAPI extensions.

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.

Unlike ASP.NET Web Forms, that have ".aspx" file extension, ASP.NET handlers by default have ".ashx" file extension.