Your Base64 Padding calculation is wrong

Hey! Found your project tonight and it was exactly what I needed! Thanks!! However, your Base64 padding calculation is incorrect.

Specifically, in JpegParser.cs in the ProcessExtendedXMPXML function, you're running a mod 4 on the length of the data, which returns the count of the chars that don't perfectly align on a four-byte boundary. In the case of Base64, that will always return 0, 2 or 3. The problem is you're using that value as the index into the substring "==" which is incorrect, and in the case of 3, crashes the app.

What you should be doing is padding the string to align on a multiple of four characters, meaning when you get 2 you pad with 2 but when you get a 3, you only pad with 1, and of course when you get back 0, you don't pad at all.

Here's the code you can use to get the correct padding which fixes your crash...

var padding = "";
switch (attribute.Value.Length % 4) {

    case 2:
        padding = "==";
        break;

    case 3:
        padding = "=";
        break;
};

Note: Normally I'd make a PR for you, but I've heavily modified your files so much it would be more work than just sharing this with you.

Hope this helps!

Vargol / VR180PhotoTools

Your Base64 Padding calculation is wrong #1