不通过扩展名，去判断文件类型

第一种方法

通过php的finfo_file()

$handle=finfo_open(FILEINFO_MIME_TYPE);//This function opens a magic database and returns its resource. 
$fileInfo=finfo_file($handle,'./test.txt');// Return information about a file
finfo_close($handle);
print_r($fileInfo);
echo '==========="
"';

另外
finfo_buffer: Return information about a string buffer
finfo_close: Close fileinfo resource
mime_content_type:Detect MIME Content-type for a file (deprecated)

第二种方法

通过二进制流获取文件内容

$fp=fopen('test.txt','r')///实际是image/png
$bin = fread($fp, 2); //只读2字节
fclose($fp);
$str_info  = @unpack(“C2chars”, $bin);//Unpack data from binary string
$type_code = intval($str_info['chars1'].$str_info['chars2']);// Get the integer value of a variable
$file_type = ”;
switch ($type_code) {
case 7790:
$file_type = ‘exe’;
break;
case 7784:
$file_type = ‘midi’;
break;
case 8075:
$file_type = ‘zip’;
break;
case 8297:
$file_type = ‘rar’;
break;
case 255216:
$file_type = ‘jpg’;
break;
case 7173:
$file_type = ‘gif’;
break;
case 6677:
$file_type = ‘bmp’;
break;
case 13780:
$file_type = ‘png’;
break;
default:
$file_type = ‘unknown’;
break;
}