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ISAPI filters are DLLs that are loaded into the process of the Web server when it is started, and they stay in memory until the Web server shuts down. After they are loaded, ISAPI filters can be configured to receive a number of special filter-event notifications that occur with each HTTP request that the Web server receives, and with each response that the Web server generates in return.
When an ISAPI filter is loaded, the filter passes a structure to the Web server that contains, in addition to other information, a bit field that specifies the types of filter-event notifications for which the filter should be notified. Each time that the event occurs, an event notification is started, and every ISAPI filter that is set to monitor that event is notified.
Last updated on Friday, April 02, 2004