PHP通过二进制流判断文件类型

<?php
// 根据二进制流获取文件类型  
function getFileType($file, &$fileType)
{
	// 文件头标识 (2 bytes)
	$bin = substr($file,0,2);
	$strInfo = @unpack(\"C2chars\", $bin);; 
	$typeCode = intval($strInfo[\'chars1\'].$strInfo[\'chars2\']);
    $fileType = \"\";
    switch($typeCode)
    {
        case 255216 : 
            $fileType = \"image/jpeg\";
            $ret = 0;
            break; 
        case 7173 :
            $fileType = \"image/gif\";
            $ret = 0;
            break;
        case 13780 :
            $fileType = \"image/png\";
            $ret = 0;
            break;
        case 6677:
            $fileType = \'image/bmp\';
            $ret = 0;
            break;
		case 7790:
            $fileType = \'exe\';
			$ret = 0;
            break;
        case 7784:
            $fileType = \'midi\';
			$ret = 0;
            break;
        case 8297:
            $fileType = \'rar\';
			$ret = 0;
            break;
        default :
            $fileType = \"unknow\";
            $ret = -1;
            break;
    }

    return $ret;
}