PHP file_exists With Contents Instead of Name?

Question

Is there a function built into PHP that acts like file_exists, but given file contents instead of the file name?

I need this because I have a site where people can upload an image. The image is stored in a file with a name determined by my program (image_0.png image_1.png image_2.png image_3.png image_4.png ...). I do not want my site to have multiple images with the same contents. This could happen if multiple people found a picture on the internet and all of them uploaded it to my site. I would like to check if there is already a file with the contents of the uploaded file to save on storage.

Answer 1

This is how you can compare exactly two files with PHP:

function compareFiles($file_a, $file_b)
{
    if (filesize($file_a) == filesize($file_b))
    {
        $fp_a = fopen($file_a, 'rb');
        $fp_b = fopen($file_b, 'rb');

        while (($b = fread($fp_a, 4096)) !== false)
        {
            $b_b = fread($fp_b, 4096);
            if ($b !== $b_b)
            {
                fclose($fp_a);
                fclose($fp_b);
                return false;
            }
        }

        fclose($fp_a);
        fclose($fp_b);

        return true;
    }

    return false;
}

If you keep the sha1 sum of each file you accept you can simply:

if ($known_sha1 == sha1_file($new_file))