Generate random, hex encoded tokens

generate_token.go

package main

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"time"
)

const (
	bytesTime int = 8 // uint64 = 8 bytes long
	bytesRand int = 56
	// 8 + 56 = 64 bytes in total
)

func newToken(ts time.Time) string {
	buf := make([]byte, bytesTime+bytesRand)
	t := uint64(ts.UnixNano())
	binary.BigEndian.PutUint64(buf[:bytesTime], t)

	_, err := rand.Read(buf[bytesTime:])
	if err != nil {
		panic(err)
	}

	h := sha256.New()
	h.Write(buf)
	return hex.EncodeToString(h.Sum(nil))
}

func main() {
	t := time.Now()
	for i := 0; i < 10; i++ {
		t = t.Add(time.Duration(i) * time.Second)
		fmt.Println(newToken(t))
	}
}