Sapis

SAPIs, in the context of PHP, stand for Server Application Programming Interfaces. The SAPI layer provides the interface between the PHP interpreter and the execution environment, such as a web server or a command-line shell. It defines how requests are received, how input is presented to PHP, and how output is delivered back to the client. By abstracting server-specific details, SAPIs allow PHP code to run in a variety of contexts with minimal changes.

Common SAPIs include the Apache module (mod_php), CGI, FastCGI, PHP-FPM (FastCGI Process Manager) used with web servers like Nginx, the PHP Command Line Interface (CLI), and the Embed SAPI for embedding PHP in other applications. Each SAPI implements the request lifecycle in a way appropriate to its environment, including initialization, handling of input data, output buffering, and error reporting.

PHP provides ways to identify the current SAPI at runtime, such as the php_sapi_name() function and the PHP_SAPI predefined constant. This information can be used to tailor behavior to the execution context, for example, to enable or disable CLI-only features or to adjust logging.

The choice of SAPI influences performance characteristics, security considerations, and feature availability. For instance, CLI lacks HTTP request handling, while FastCGI-based SAPIs are commonly used for scalable web deployments. The SAPI concept originated to accommodate PHP’s need to run in diverse servers and environments, and PHP’s source includes a sapi directory containing the implementation for each supported SAPI.