That's not necessary; listening on the wildcard IPv6 address without the "IPv6 only" flag enabled on the socket is enough. A IPv4 connection arriving at it is m

That's not necessary; listening on the wildcard IPv6 address without the "IPv6 only" flag enabled on the socket is enough. A IPv4 connection arriving at it is mapped to a special IPv6 address, so the code doesn't have to care about IPv4. Unless you were using Windows, where IIRC the IPv4 and IPv6 stacks were separate, and a single socket couldn't be used to listen to both at the same time. (This might already have been fixed in more recent Windows releases.)