If buffering is disabled, the data is written straight to the output, which is the browser making the request in the case of PHP on a web server, or stdout for CLI based PHP.
php_stream_passthru() outputs all remaining data from stream to the active output buffer and returns the number of bytes output. If buffering is disabled, the data is written straight to the output, which is the browser making the request in the case of PHP on a web server, or stdout for CLI based PHP. This function will use memory mapped files if possible to help improve performance.