In computer science, Server Application Programming Interface (SAPI) is a generic term used to designate direct module interfaces to web server applications such as theApache HTTP Server, Microsoft IIS or iPlanet. Microsoft also uses the term in ISAPI and the defunct Netscape web server used the term NSAPI.[1] In other words, SAPI is actually an Application programming interface (API) provided by the web server to help other developers in extending the web server capabilities.
As an example, PHP has a direct module interface called SAPI for different web servers.[2] For PHP 5 and Apache 2.0 on Windows, it is in the form of a DLL file calledphp5apache2.dll
.[3] That DLL is a module which—among other functions—provides an interface between PHP and the web server, implemented in a form that the server understands. This form is what is known as a SAPI.
There are different kinds of SAPIs for different web server extensions. For example, another two SAPIs for the PHP language are PHP Common Gateway Interface (CGI) and PHPCommand-line interface (CLI).[2][4]