[php] How do I get the base URL with PHP?

I had the same question as the OP, but maybe a different requirement. I created this function...

/**
 * Get the base URL of the current page. For example, if the current page URL is
 * "https://example.com/dir/example.php?whatever" this function will return
 * "https://example.com/dir/" .
 *
 * @return string The base URL of the current page.
 */
function get_base_url() {

    $protocol = filter_input(INPUT_SERVER, 'HTTPS');
    if (empty($protocol)) {
        $protocol = "http";
    }

    $host = filter_input(INPUT_SERVER, 'HTTP_HOST');

    $request_uri_full = filter_input(INPUT_SERVER, 'REQUEST_URI');
    $last_slash_pos = strrpos($request_uri_full, "/");
    if ($last_slash_pos === FALSE) {
        $request_uri_sub = $request_uri_full;
    }
    else {
        $request_uri_sub = substr($request_uri_full, 0, $last_slash_pos + 1);
    }

    return $protocol . "://" . $host . $request_uri_sub;

}

...which, incidentally, I use to help create absolute URLs that should be used for redirecting.