nextIP(): find next IP address in Go

nextip.go

package main

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

func main() {
	testNext("foo", "bar")
	testNext("10.0.0.0", "10.0.0.1")
	testNext("10.0.0.255", "10.0.1.0")
}

func testNext(ip, wanted string) {
	i := net.ParseIP(ip)
	w := net.ParseIP(wanted)
	if i == nil || w == nil {
		fmt.Printf("%s => %s BAD INPUT\n", ip, wanted)
		return
	}
	next := nextIP(i, 1)
	if bytes.Equal(next, w) {
		fmt.Printf("%s => %s OK\n", ip, wanted)
	} else {
		fmt.Printf("%s => %s FAIL got=%s\n", ip, wanted, next)
	}

}

func nextIP(ip net.IP, inc uint) net.IP {
	i := ip.To4()
	v := uint(i[0])<<24 + uint(i[1])<<16 + uint(i[2])<<8 + uint(i[3])
	v += inc
	v3 := byte(v & 0xFF)
	v2 := byte((v >> 8) & 0xFF)
	v1 := byte((v >> 16) & 0xFF)
	v0 := byte((v >> 24) & 0xFF)
	return net.IPv4(v0, v1, v2, v3)
}

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