Internet server API
Internet Server API ( ISAPI ) is a programming interface (Application Programming Interface) from Microsoft that is used in Microsoft Internet Information Services ( web server ), Microsoft Exchange Server and Microsoft Internet Security and Acceleration Server ( firewall and web cache ). A distinction is made between ISAPI extensions and ISAPI filters.
ISAPI extensions
ISAPI extensions are to be regarded as the next generation of CGI applications, but can only be run on Microsoft servers without the corresponding additional programs from third-party providers. Unlike a PHP or ASP script, an ISAPI extension is a DLL file which, depending on the configuration, is loaded by the Microsoft Internet Information Server when it is started or only when required. Depending on the application security, ISAPI extensions can be executed jointly by a host application (this is required to execute DLLs) or separately from one another.
Advantages and disadvantages
The gain in speed should be mentioned as an advantage. In contrast to scripts like ASP or PHP , an ISAPI extension consists of compiled source text , as well as the system DLL files used in Microsoft operating systems. ISAPI extensions allow deeper intervention in the software of the executing system, whereby existing resources (e.g. RAM, but also other devices such as video cards, ISDN adapter cards, etc.) can be better used and addressed directly. In contrast to script files , ISAPI extensions cannot be read in the form of their source text, but are available as compiled binary files .
ISAPI filter
ISAPI filters are DLLs that can be added in the web service in order to intervene in advance on certain events. Unlike ISAPI extensions, ISAPI filters are already resident in memory after the web server is started.
ISAPI filters intervene directly in the data traffic of a web server or proxy . This allows you to read and change the transferred data. In Microsoft Exchange Server they are used for authentication , for example .
Application example
An example of ISAPI filters or ISAPI extensions is the asp.dll integrated in the Microsoft Internet Information Server, which is used to execute ASP files, and the separately installable php.dll, with which PHP files are executed on a Microsoft web server can be.
Web links
- ISAPI Extension Overview (MSDN) (English)