PHP 過濾頁面中的BOM(實現代碼)

function checkBOM ($filename) {
$contents = file_get_contents($filename);
$charset[1] = substr($contents, 0, 1);
$charset[2] = substr($contents, 1, 1);
$charset[3] = substr($contents, 2, 1);
if (ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191) {
$rest = substr($contents, 3);
rewrite $rest;
}else{
return false;
}
}