before.go

known := map[string]struct{}{}
for {
	ips := []string{}
	if data, err := ioutil.ReadFile("ips.json"); err != nil {
		time.Sleep(3 * time.Second)
		continue
	} else if err := json.Unmarshal(data, &ips); err != nil {
		time.Sleep(3 * time.Second)
		continue
	}
	for _, ip := range ips {
		if _, ok := known[ip]; !ok {
			known[ip] = struct{}{}
			doSomething(ip)
		}
	}
	time.Sleep(3 * time.Second)
}