PHP图像验证

Question

Thus anyone has any idea why this code is not working for me

$type1 = $_FILES['textfield2']['type'];
$type2 = $_FILES['textfield3']['type']; 

if($type1 == 'image/gif' || $type1 == 'image/png' && $type2 == 'image/gif' || $type2  == 'image/png')
{
    echo 'Valid';
    echo $type1.'<br />'.$type2;
}
else
{
    echo 'Invalid';
}

If i select 1st file as a zip or any other format and then next as png it is going to valid that what i should not

Answer 1

PHP's operator precedence makes && bind tighter than ||, so your test is coming out as:

if($type1 == 'image/gif' || ($type1 == 'image/png' && $type2 == 'image/gif') || $type2  == 'image/png')
                            ^----------------------------------------------^

Beyond that, do not use the user-provided ['type'] data for this. It's utterly trivial to forge, and someone can set to 'image/gif' while uploading nastyvirus.exe.

Answer 2

Try:

if(($type1 == 'image/gif' || $type1 == 'image/png') && 
   ($type2 == 'image/gif' || $type2  == 'image/png'))
        {
            echo 'Valid';

            echo $type1.'<br />'.$type2;
        }
        else
        {
            echo 'Invalid';
        }

This is due to operator precedence, which is documented here: http://php.net/manual/en/language.operators.precedence.php

Answer 3

This is due to operator precedence . && has higher precedence than || so your expression results in:

    $type1 == 'image/gif'
|| ($type1 == 'image/png' && $type2 == 'image/gif')
||  $type2 == 'image/png'

Use parentheses to make your intention clear:

   ($type1 == 'image/gif' || $type1 == 'image/png')
&& ($type2 == 'image/gif' || $type2 == 'image/png')

Additionally please note that the mime type is a client supplied data and thus is very easy to manipulate. Instead you should check for a valid GIF/PNG file header (using the GD library for example.)