ExtractIP extract IP from net.Addr.

ExtractPort extract Port from net.Addr.

GlobalUnicastIP get a global unicast IP address.

GlobalUnicastIPString get a global unicast IP address string.

InterfaceIPs get public IP addresses by interface name.

InterfaceIPv4 get a public IPv4 address.

IPs get all IP addresses.

PickFreePort automatically chose a free port and return it.