php短域名转换为实际域名

$url = "";
echo unshorten($url);
function unshorten($url) {
  $url = trim($url);
  $headers = get_headers($url);
  $location = $url;
  $short = false;
  foreach($headers as $head) {
    if($head=="HTTP/1.1 302 Found") $short = true;
    if($short && startwith($head,"Location: ")) {
      $location = substr($head,10);
    }
  }
  return $location;
}
function startwith($Haystack, $Needle){
    return strpos($Haystack, $Needle) === 0;
}