Is there some property on req object to get ip's family (IPv4 or IPv6)? Or how can I figure it out? I want to change behavior based on this info. I'm not sure if checking if the string contains a colon is the right way.
You can use the built-in net package for this:
You also have net.isIP(input) which will return 6, 4 or 0 if the parameter is respectively an IPv6, an IPv4, or not an IP.