func md5V(str string) string  {
    h := md5.New()
    h.Write([]byte(str))
    return hex.EncodeToString(h.Sum(nil))
} 

func md5V2(str string) string {
    data := []byte(str)
    has := md5.Sum(data)
    md5str := fmt.Sprintf("%x", has)
    return md5str
} 

func md5V3(str string) string {
    w := md5.New()
    io.WriteString(w, str)
    md5str := fmt.Sprintf("%x", w.Sum(nil))
    return md5str
}