phhbjs 随机字符串 const letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789" b := make([]byte, 5) for i := range b { b[i] = letters[rand.Intn(len(letters))] } s := string(b)