golang 生成随机字符串

func RandStr(n int) string {
    const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
    const (
        letterIdxBits = 6                    // 6 bits to represent a letter index
        letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
        letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
    )
    var src = rand.NewSource(time.Now().UnixNano())
    b := make([]byte, n)
    // A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
    for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
        if remain == 0 {
            cache, remain = src.Int63(), letterIdxMax
        }
        if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
            b[i] = letterBytes[idx]
            i--
        }
        cache >>= letterIdxBits
        remain--
    }
    return string(b)
}