Php | 验证base64_decode为图像| 不工作

Question

I created a function that will return the filetype of the supplied base64_decode argument. If it's not an image, the function will return false. However, when passing in encoded images (via jquery ajax (FormData object)) the function returns false everytime. I have tried many things, but am unable to get it working.

EDIT: I am now getting a Javascript error, here it is :
"Uncaught SyntaxError: Unexpected token in JSON at position 0"

function base64_extension($base64){
    $base64 = str_replace("data:image/png;base64,", "", $base64);
    $base64 = base64_decode($base64);

    $base64 = imagecreatefromstring($base64);

    if(!$base64){
        return 0; /* Not image */
    }


    if(imagepng($base64)){
        imagedestroy($base64);
        return 1;
    }else if(imagejpeg($base64)){
        imagedestroy($base64);
        return 2;
    }
    else if(imagegif($base64)){
        imagedestroy($base64);
        return 3;
    }
    else{
        return 4; /* Not image */
    }
}

CLIENT

var cropCanvas = $('#user-img').cropper('getCroppedCanvas');
var cropImg = cropCanvas.toDataURL("image/jpeg");
var formData = new FormData();
formData.append('pic', cropImg);

Then I pass the formData into ajax here.

Answer 1

As Jonathan Kuhn said

Once you have an image created with any of the imagecreate* functions, you can output any type of image like png, jpg, gif regardless of what the input format was. Creating the image means it is in GD's format that the extension can manipulate and then output in any image format it understands.

So your way is wrong you can get the MIME Type of Decoded base64 with finfo_* functions.

For Example :

$base64 = base64_decode($base64);
$finfo_handler = finfo_open();
$allowed_types = ["image/jpeg","image/png","image/gif"];
$mime_type = finfo_buffer($finfo_handler, $base64, FILEINFO_MIME_TYPE);
finfo_close($finfo_handler);
if(!in_array($mime_type, $allowed_types)){
    // Mime Type is not JPEG or PNG or GIF
    return false;
}else{
    // Mime Type is in Array and returns first index of exploded string by "/" char.
    // That means for image/jpeg exploded_array = [ 0 => "image", 1 => "jpeg"]
    // and it returns first index "jpeg" for "image/png" it returns "png"
    return explode("/", $mime_type)[1];
}