IsPrivateIP.go

package main

import "net"
import "fmt"

func main() {
	fmt.Println(IsPrivateIP("111.11.191.17"))
	fmt.Println(IsPrivateIP("192.168.0.100"))
	fmt.Println(IsPrivateIP("10.0.8.100"))
}

var PrivateBlocks []*net.IPNet

func IsPrivateIP(ip_str string) bool {
	if PrivateBlocks == nil {
		// Add each private block
		PrivateBlocks = make([]*net.IPNet, 3)
		_, block, err := net.ParseCIDR("10.0.0.0/8")
		if err != nil {
			panic(fmt.Sprintf("Bad cidr. Got %v", err))
		}
		PrivateBlocks[0] = block

		_, block, err = net.ParseCIDR("172.16.0.0/12")
		if err != nil {
			panic(fmt.Sprintf("Bad cidr. Got %v", err))
		}
		PrivateBlocks[1] = block

		_, block, err = net.ParseCIDR("192.168.0.0/16")
		if err != nil {
			panic(fmt.Sprintf("Bad cidr. Got %v", err))
		}
		PrivateBlocks[2] = block

		_, block, err = net.ParseCIDR("127.0.0.0/8")
		if err != nil {
			panic(fmt.Sprintf("Bad cidr. Got %v", err))
		}
	}
	ip := net.ParseIP(ip_str)
	for _, priv := range PrivateBlocks {
		if priv.Contains(ip) {
			return true
		}
	}
	return false
}