moleculer-go/moleculer

package util

import (
    "math/rand"
    "sync"
    "time"
)

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
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 randomSource = rand.NewSource(time.Now().UnixNano())
var randomSourceMu = sync.Mutex{}

func RandomString(size int) string {
    randomSourceMu.Lock()
    defer randomSourceMu.Unlock()

    buffer := make([]byte, size)
    // A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
    for index, cache, remain := size-1, randomSource.Int63(), letterIdxMax; index >= 0; {
        if remain == 0 {
            cache, remain = randomSource.Int63(), letterIdxMax
        }
        if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
            buffer[index] = letterBytes[idx]
            index--
        }
        cache >>= letterIdxBits
        remain--
    }
    return string(buffer)
}