var (
    codes   = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/~!@#$%^&*()_="
    codeLen = len(codes)
)

func RandNewStr(len int) string {
    data := make([]byte, len)
    rand.Seed(time.Now().UnixNano())

    for i := 0; i < len; i++ {
        idx := rand.Intn(codeLen)
        data[i] = byte(codes[idx])
    }

    return string(data)
}