We mostly use classical C strings, but the memory management around them
can get confusing and error prone. Let's use std::string for the cases
where we need to return a newly allocated string.

Avoid having our own custom stuff and instead use the modern, standard
types, for familiarity.

This allows us to separate accidental fall through from explicit ones,
which allows us to turn on such checks in the compiler.

If there isn't enough data, then the client reading the hash will fall
down and try to read the subtype instead, which isn't correct.

Invert the logic so we get a more consistent way through where we only
break out when there is insufficient data.

Do the same for the server code, for consistency.