ISAPI Filters

ISAPI Filter plug-ins for Microsoft Internet Information Server and Personal WEB Server. Simple low-cost solutions for authentication, URL substitutions, pseudo-virtual WEB sites, redirection and traffic spreading.

What is ISAPI filter

There are two major types of plug-ins for the Microsoft WEB server products - ISAPI applications and ISAPI filters. The ISAPI applications are intended to do drive a WEB site or act as engine for which the actual server side code is written (e.g. ASP is an ISAPI application). The ISAPI filters on the other hand are plug-ins that interact with the work the WEB server does and perform additional actions, alter certain data or replace some of the server's functionality. The ISAPI filters are usually independent of the nature of the WEB content and the WEB applications running on the server. Still, very often they provide features these applications expect. For example an authenitaction filter makes possible to use custom user lists over which to authenticate the visitors instead of creating a system account for each of them. This can be "a must" for certain application, yet it is not part of it and there is no matter in what kind of language it is written.

There are many ISAPI filters on the WEB and many of them (including some of our filters) implement some tricks that are of indirect help for the webmasters or for the WEB developers. The benefits of using such a filter may not be obvious. Still, such filters are always a result of experience and problems solved. For example you can find on the Internet several different filters like our Variable Parser (shortly VarParser). They do something simple - convert the parameter part of the URL to plain URL syntax. This may look like nothing, but in fact it improves the WEB site appearance in the search sites drastically. In the past the search engines just ignored the parameters and thus ignored considerable and sometimes crucial parts of the WEB sites. Today the major search engines index everything, but still they prefer the plain URL and this speeds up the indexing drastically. No need to say that almost all the local and specialized search sites continue to ignore URL with parameters and knowing that they are usually limited on resources it is unlikely to expect that many of them will change in the future. Thus, such a simple, at first look, trick may be quite useful and bring times more visitors.