Net.IpaddrSourceIP addresses.
The raw bytes of the IP address. It is either 4 bytes long (for an IPv4 address) or 16 bytes long (for IPv6).
pp formats IP addresses. For IPv6 addresses, it follows http://tools.ietf.org/html/rfc5952.
fold ~v4 ~v6 t is v4 t if t is an IPv4 address, or v6 t if it's an IPv6 address.