PHP takes binary file header to determine file type

/**
* PHP takes the binary file header to quickly determine the file type
*
* @param file $file
* @return string
* @author lrenwang
* @blog blog.lrenwang.com
*/
function get_extname($file)
{
  $fp = fopen($file, "rb");
  $bin = fread($fp, 2); //只读2字节
  fclose($fp);
  $bin_info  = @unpack("C2chars", $bin);
  $code = intval($bin_info['chars1'].$bin_info['chars2']);
  switch ($code) {
    case 7790:
      $type = 'exe';
      break;
    case 7784:
      $type = 'midi';
      break;
    case 8075:
      $type = 'zip';
      break;
    case 8297:
      $type = 'rar';
      break;
    case 255216:
      $type = 'jpg';
      break;
    case 7173:
      $type = 'gif';
      break;
    case 6677:
      $type = 'bmp';
      break;
    case 13780:
      $type = 'png';
      break;
    default:
      $type = $code;
      break;
  }
  return $type;
}
?>