fiveBytesID.go

package main

import (
	"encoding/base32"
	"encoding/binary"
	"fmt"
	"math/rand"
	"time"
)

const fourDays = time.Hour * 24 * 4

func main() {
	rand.Seed(time.Now().UnixNano())

	for i := 0; i < 5; i++ {
		data := gen(uint16(randInt(0, 6454)))
		crockford := base32.NewEncoding("0123456789ABCDEFGHJKMNPQRSTVWXYZ")
		str := crockford.EncodeToString(data[:])

		fmt.Println(data)
		fmt.Println(str)
	}
}

func gen(counter uint16) [5]byte {
	// 1 byte  => random number
	// 2 bytes => epoch / 4 days (so it will change every 4 days) (2 bytes is enough for until year 2500)
	// 2 bytes => counter (auto increase number)
	var buf [5]byte

	r := byte(randInt(0, 256))
	buf[0] = r

	ts := uint16(time.Now().UTC().UnixNano() / int64(fourDays))
	binary.LittleEndian.PutUint16(buf[1:3], ts)
	binary.LittleEndian.PutUint16(buf[3:], counter)
	return buf
}

func randInt(min int, max int) int {
	return min + rand.Intn(max-min)
}