Working with ISAPI Filters (IIS 6.0)
Like Internet Server API (ISAPI) extensions, ISAPI filters are programs that respond when the application server receives an HTTP request. However, unlike ISAPI extensions, ISAPI filters are always run in the server process. ISAPI filters are different from applications because they are driven by Web server events instead of a client request. You can associate an ISAPI filter with a particular Web server event; the filter is then notified every time its associated event occurs. For example, a filter could be notified when a Read or Write event occurs and then encrypt the raw data to be returned to the client.
If an HTTP request triggers an event for which the filter is registered, the filter will receive the data contained in the request regardless of whether the request is for a file, a CGI application, or an ISAPI extension.
This section contains the following information: