Using protocol-relative URIs within “Location:” headers

Question

I note in the PHP manual which states the following:

HTTP/1.1 requires an absolute URI as argument to » Location: including the scheme, hostname and

Answer 1

As suggested by HTTP protocol, you should use absolute URI. You can still detect protocol, by using $_SERVER['HTTPS'] variable, with a condition like:

$protocol = "http" . (!empty($_SERVER['HTTPS']) ? "s" : "");

Answer 2

The HTTPbis update allows relative URIs. While not specifically mentioned, this includes protocol-relative URLs.

(It's foremost an update to the HTTP/1.1 spec that documents established browser behaviour.)