Get the Retry-After HTTP header
int|null If an entity is temporarily unavailable, this instructs the client to try again after a specified period of time.
public function getRetryAfter() {
$time = $this
->getHeader('Retry-After', true);
if ($time === null) {
return null;
}
if (!is_numeric($time)) {
$time = strtotime($time) - time();
}
return (int) $time;
}