您可以使用parse_url

<?php
   $url = parse_url('https://example.org');

   if ($url['scheme'] == 'https') {
       // is https;
   }
?>

if (substr($string, 0, 7) == "http://") {
   $res = "http";
}

if (substr($string, 0, 8) == "https://") {
   $res = "https";
}

也许这个能帮上忙

$_SERVER['SERVER_PROTOCOL'];