Golang : How to check if IP address is in range

For security purpose, sometimes a server can only accept connection from clients that are trusted and of certain IP addresses. This tutorial will demonstrate how to use bytes.Compare() function to check to see if an incoming IP address is within the trusted range.

checkip.go

 package main

 import (
 "net"
 "bytes"
 "fmt"
 )

 var (
 // specify the range of trusted IP addresses
 start = net.ParseIP("198.162.1.100")
 end = net.ParseIP("198.162.1.199")
 )

 func checkIP(ip string) bool {

 //sanity check
 input := net.ParseIP(ip)
 if input.To4() == nil {
 fmt.Printf("%v is not a valid IPv4 address\n", input)
 return false
 }

 if bytes.Compare(input, start) >= 0 && bytes.Compare(input, end) <= 0 {
 fmt.Printf("%v is between %v and %v\n", input, start, end)
 return true
 }
 fmt.Printf("%v is NOT between %v and %v\n", input, start, end)
 return false
 }

 func main() {

 fmt.Println(checkIP("216.14.49.185"))
 fmt.Println(checkIP("1.2.3.4"))
 fmt.Println(checkIP("198.162.1.102"))
 fmt.Println(checkIP("1::16"))
 }

Output :

216.14.49.185 is NOT between 198.162.1.100 and 198.162.1.199

false

1.2.3.4 is NOT between 198.162.1.100 and 198.162.1.199

false

198.162.1.102 is between 198.162.1.100 and 198.162.1.199

true

1::16 is not an IPv4 address

false

Reference :

http://golang.org/pkg/bytes/#Compare