php get http header value by key

php get http header value by key

function head_value($key) {
    $headers = [];
    if (!function_exists('getallheaders')) {
        foreach ($_SERVER as $name => $value) {
            /* RFC2616 (HTTP/1.1) defines header fields as case-insensitive entities. */
            if (strtolower(substr($name, 0, 5)) == 'http_') {
                $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value;
            }
        }
    } else {
        $headers = getallheaders();
    }
    return $headers[$key];
}