That's kind of my point though: it didn't need to be written to expect a v6 upgrade, because the socket API is family-agnostic. 20 years ago, getaddrinfo() was

That's kind of my point though: it didn't need to be written to expect a v6 upgrade, because the socket API is family-agnostic. 20 years ago, getaddrinfo() was 7 years old. You should have been using it already by then.