Microsoft Internet Security and Acceleration Server 2000

Web Filter Functions

Web (ISAPI) filters for the ISA Web proxy service implement the following standard entry functions:

These are described here briefly and in greater detail in the Web filter reference.


The GetFilterVersion function is the first entry-point function called by ISA Web proxy on your Web filter, and it must be present for the filter to work. The Web proxy service passes a pointer to a HTTP_FILTER_VERSION data structure, which can be used to supply key filter configuration information to the Web proxy. The most important information passed to the Web proxy is the bitmask that contains flags that specify which notification events your filter can process, and a flag that indicates the overall processing priority for your filter.


Whenever a notification event for which the filter has registered (in GetFilterVersion) occurs, the ISA Web proxy service calls the HttpFilterProc function. The Web proxy uses this function to pass information and control to the Web filter.


This function indicates to the filter that it is going to be removed from memory. When this function is called, you should make sure that the filter closes any attachments it has made to system resources.

Note  TerminateFilter is an optional function. However, you must provide this function if your filter needs to free any allocated or locked resources before being unloaded.