如何检查给定的字符串是否是 PHP 中的有效 base64 png/图像？

Question

The following code is intended to save a.png file in the disk from a base64 encoded image read from the POST sent by the user.

$base64_string = $_POST["photo"];
$output_file = trim(getcwd()."/uploads/".uuid4().'.png');    
file_put_contents($output_file, file_get_contents($base64_string));

But it saves anything in the server disk, forcing a.png extension though.

It seems very unsafe, how the POST string can be checked for a valid image to prevent the script from saving it?

Answer 1

You can check first the filetype and proper way to upload base64 image by using the code blow;

    $fileImg_parts  = explode(";base64,", $_POST['photo']);
    $image_type_aux = explode("image/", $fileImg_parts[0]);
    $image_type     = $image_type_aux[1];
    $image_base64   = base64_decode($fileImg_parts[1]);
    $file_name      = uniqid() . '.'.$image_type;

    //You can add condition here to check image type using $image_type variable
    
    $results        = FILE_UPLOAD_DIR . $file_name;
    file_put_contents($results, $image_base64);

It will check type first and then put it into the direcoty.