ASP.NET Internals IIS and the Process Model

Let's share some ASP.NET internals. This share a very general thing how IIS handles the request when it receive from the user. 




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ASP.NET Internals – IIS and the Process Model

Let’s discuss something interesting about the how IIS process a request, whenever a request sent by the client browser to the IIS requesting ASP.NET resources.The interaction between the client and server was very simple till the server side scripts come into the picture. Communications over the web occur via HTTP (Hyper Text Transfer Protocol), an application level protocol which relies on TCP and IP to transmit data between two nodes connected to the heterogeneous network known as World Wide Web. If the client request for static contents like html page, picture file, some client site script or css files server do not need to process anything, just retrieves the contents and sent back to the client in the response. But if the client is requesting for some dynamic content then server needs to process that request and generate the HTML and sent this to client example asp.

IIS and ISAPI Extensions

There ISAPI comes into the picture. ISAPI stands for the Internet Server Application Programming Interface. This is nothing but a .dll which process specific resources for IIS.
Mappings between ISAPI extensions and files are configured via the IIS snap-in and stored in the IIS metabase, where each file extension can be associated with a particular ISAPI extension, that is, when a request for such a file arrives, IIS handles it to the corresponding ISAPI extension, confident that it will be able to handle it.

Figure 1: Configuring ISAPI extensions mappings on IIS 5.0

As Figure 1 illustrates, the .asp extension is mapped to the asp.dll ISAPI extension; at the time of ASP this component was in charge of performing all the tasks required to generate a response, that is, collecting information about the request, made available into the ASP page via the Request, Response and other common ASP intrinsic objects, parsing and executing the ASP page and returning the resulting HTML. When installed, ASP.NET configures IIS to redirect requests for ASP.NET specific files to a new ISAPI extension called aspnet_isapi.dll.

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