dialer.go

var ResovedAddress = make(map[string][]string)
var mu sync.RWMutex

func Dialer(network, addr string) (net.Conn, error) {
	host, port, _ := net.SplitHostPort(addr)
	mu.RLock()
	addrs, found := ResovedAddress[host]
	mu.RUnlock()
	if found {
		// log.Println("cache hit for", host)
	} else {
		// log.Println("cache miss for", host)
		var err error
		addrs, err = net.LookupHost(host)
		if err != nil || len(addrs) == 0 {
			return nil, err
		}
	}
	mu.Lock()
	ResovedAddress[host] = addrs
	mu.Unlock()

	// for DNS round robin
	n := rand.Intn(len(addrs))
	addr = addrs[n]
	var format string
	if strings.Contains(addr, ":") {
		// v6
		format = "[%s]:%s"
	} else {
		// v4
		format = "%s:%s"
	}
	resolved := fmt.Sprintf(format, addr, port)
	// log.Println("resolved", resolved)
	return net.Dial(network, resolved)
}