php文件上传类型限制

Question

I have a problem with file extensions in php.

if ($_FILES['file']['type'] != 'image/png' || 'image/jpg') {
                   echo "wrong type";
                   exit;
     }

this doesn't allow any type of file to upload

if ($_FILES['file']['type'] != ('image/png' || 'image/jpg')) {
                   echo "wrong type";
                   exit;
     }

this allows any type of file to upload.

Whats the matter?

Answer 1

Your conditional statement is incorrect. It should look like this:

if (($_FILES['file']['type'] != 'image/png') || 
       ($_FILES['file']['type'] != 'image/jpg')) {
                   echo "wrong type";
                   exit;
     }

Your first snipped always resolves to true because of || 'image/jpg' is always true.

The second snippet resolves ('image/png' || 'image/jpg') to true everytime, which DOES NOT equal $_FILES['file']['type']