Golang : Check if IP address is version 4 or 6

Problem :

Your Golang program needs to determine if a given IP address is version 4 or 6.

Solution :

Not really a fool proof solution, but it should be sufficient to detect if a given string has a decimal or colon in it. If the string has decimal as separator, then it is IP version 4 and if colon, then it is IP version 6.

Here you go :

 package main

 import (
 "fmt"
 "net"
 )

 func ip4or6(s string) string {
 for i := 0; i < len(s); i++ {
 switch s[i] {
 case '.':
 return "version 4"
 case ':':
 return "version 6"
 }
 }
 return "unknown"

 }

 func main() {

 var ipAddress string = "192.168.0.1"
 //sanity check
 testInput := net.ParseIP(ipAddress)

 if testInput.To4() == nil {
 fmt.Printf("%v is not a valid IPv4 address\n", testInput)
 }

 fmt.Printf("%s is IP address of : %s \n", ipAddress, ip4or6(ipAddress))

 var ip6Address string = "FE80::0202:B3FF:FE1E:8329"
 //sanity check
 testInputIP6 := net.ParseIP(ip6Address)

 if testInputIP6.To16() == nil {
 fmt.Printf("%v is not a valid IP address\n", testInputIP6)
 }

 fmt.Printf("%s is IP address of : %s \n", ip6Address, ip4or6(ip6Address))

 var ip6AddressURLPort string = "http://[2001:db8:0:1]:80"
 //sanity check
 testInputIP6URLPort := net.ParseIP(ip6AddressURLPort)

 if testInputIP6URLPort.To16() == nil {
 fmt.Printf("%v is not a valid IP address\n", ip6AddressURLPort)
 }

 fmt.Printf("%s is IP address of : %s \n", ip6AddressURLPort, ip4or6(ip6AddressURLPort))

 }

Output :

192.168.0.1 is IP address of : version 4

FE80::0202:B3FF:FE1E:8329 is IP address of : version 6

http://[2001:db8:0:1]:80 is not a valid IP address

http://[2001:db8:0:1]:80 is IP address of : version 6

References :

http://golang.org/pkg/net/#IP.To16

http://golang.org/src/net/ip.go?s=14522:14547#L641