Golang : Validate IP address

Problem :

You need to validate if a given IP address string is a valid IP address.

Solution :

Use regexp.Compile function to validate the string.

For example :

 package main

 import (
 "fmt"
 "regexp"
 "strings"
 )

 func validIP4(ipAddress string) bool {
 ipAddress = strings.Trim(ipAddress, " ")

 re, _ := regexp.Compile(`^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$`)
 if re.MatchString(ipAddress) {
 return true
 }
 return false
 }

 // NOTE : ip6 regular expression validation caused runtime error
 // runtime error: invalid memory address or nil pointer dereference

 //func validIP6(ip6Address string) bool {
 // ip6Address = strings.Trim(ip6Address, " ")

 // re, _ := regexp.Compile(`([0-9a-fA-F]{1,4}:){7,7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|fe80:(:[0-9a-fA-F]{0,4}){0,4}%[0-9a-zA-Z]{1,}|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]))`)
 // if re.MatchString(ip6Address) {
 // return true
 // }
 // return false
 //}

 func main() {
 ip1 := "192.168.0.0"

 vIP1 := validIP4(ip1)

 fmt.Printf("%s is a valid IP4 address : %v \n", ip1, vIP1)

 //-----------------------------

 ip2 := "192.168.a.0"

 vIP2 := validIP4(ip2)

 fmt.Printf("%s is a valid IP4 address : %v \n", ip2, vIP2)

 //-----------------------------

 fullIP6 := "FE80:0000:0000:0000:0202:B3FF:FE1E:8329"

 vfullIP6 := validIP4(fullIP6)

 fmt.Printf("%s is a valid IP4 address : %v \n", fullIP6, vfullIP6)

 //-----------------------------

 collapsedIP6 := "FE80::0202:B3FF:FE1E:8329"

 vcollapsedIP6 := validIP4(collapsedIP6)

 fmt.Printf("%s is a valid IP4 address : %v \n", collapsedIP6, vcollapsedIP6)

 //-----------------------------

 urlIP6 := "http://[2001:db8:0:1]:80"

 vurlIP6 := validIP4(urlIP6)

 fmt.Printf("%s is a valid IP4 address : %v \n", urlIP6, vurlIP6)

 }

Output :

192.168.0.0 is a valid IP4 address : true

192.168.a.0 is a valid IP4 address : false

FE80:0000:0000:0000:0202:B3FF:FE1E:8329 is a valid IP4 address : false

FE80::0202:B3FF:FE1E:8329 is a valid IP4 address : false

http://[2001:db8:0:1]:80 is a valid IP4 address : false

NOTE : I'm not able to get the right regular expression to validate ip6 address yet. If you have a solution, please leave a comment below. :-)

UPDATE : You can also use net.ParseIP() instead of regular expression to validate a given IP address. Except IP version 6 address with URL or port number.

 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)
 }

or

 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)
 }

Reference :

Regular expression to match hostname or ip address