I don't see how that would work.

    d[0..4].try_into()

The type of the result is something like:

    Result<[u8; 4], TryFromSliceError>

How do I convert that into

    Result<[u8; 4], Infallible>

As far as I can tell, Infallible is there because you're implementing a trait which returns an error, but you don't have an error to return at all.