How to determine wether ob_start(); has been called already

Question

I use output buffering for gzip compression and access to what was put out before in a PHP script:

if(!ob_start(\"ob_gzhandler\")) ob_start();

Answer 1

ob_get_level returns the number of active output control handlers and ob_list_handlers returns a lift of those handlers. So you could do this:

if (!in_array('ob_gzhandler', ob_list_handlers())) {
    ob_start('ob_gzhandler');
} else {
    ob_start();
}

Although in general you can call ob_start any number of times you want, using ob_gzhandler as handler cannot as you would compress already compressed data.