PHP判断上传文件类型的解决办法

/** 
* 读取文件前几个字节 判断文件类型 
* @return String 
*/
function checkTitle($filename){ 
  $file=fopen($filename, "rb"); 
  $bin=fread($file, 2); //只读2字节 
  fclose($file); 
  $strInfo =@unpack("c2chars", $bin); 
  $typeCode=intval($strInfo['chars1'].$strInfo['chars2']); 
  $fileType=''; 
  switch($typeCode){ 
    case 7790: 
      $fileType='exe'; 
    break; 
    case 7784: 
      $fileType='midi'; 
    break; 
    case 8297: 
      $fileType='rar'; 
    break; 
    case 255216: 
      $fileType='jpg'; 
    break; 
    case 7173: 
      $fileType='gif'; 
    break; 
    case 6677: 
      $fileType='bmp'; 
    break; 
    case 13780: 
      $fileType='png'; 
    break; 
    default: 
      $fileType='unknown'.$typeCode; 
    break; 
  } 
  //Fix 
  if($strInfo['chars1']=='-1' && $strInfo['chars2']=='-40'){ 
    return 'jpg'; 
  } 
  if($strInfo['chars1']=='-119' && $strInfo['chars2']=='80'){ 
    return 'png'; 
  } 
  return $fileType; 
}