Last byte missing?

[lucashenning]

Hi @hir0min,

first off, thank you for putting this together. Must have been a lot of work!

I ran into a small problem when I was trying to decode the following base64url encoded value:

bytes n = hex'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';

Your library gives me the following result"

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

It's almost correct, but the last 2 characters in the hex representation seem to be missing. I tried decoding the same value on https://cryptii.com/pipes/base64-to-hex and the result is almost the same. However, there are 2 extra characters 29 at the end.

So, I looked at your code and changed this line

// When decoding base64 string, 4 characters are converted back to 3 bytes, skip padding "="
uint256 decodedLength = (data.length / 4) * 3;

to this:

uint256 decodedLength = (data.length / 4) * 3 + 1;

This solved the issue for me. I'm not sure why this last byte was missing but I thought I'd let you know and leave this here just in case anyone else is having issues with this.

Again, thank you for providing this library! Really appreciate your work!