Generate pseudo random numbers

randomID.go

package main

import (
	"crypto/rand"
	"math/big"
)

var maxID = new(big.Int).SetUint64(^uint64(0))

func genRandomID() uint64 {
	id, err := rand.Int(rand.Reader, maxID)
	if err != nil { // this should never happen
		panic(err)
	}
	return id.Uint64()
}

// TEST

package main

import "testing"

func TestGenRandomID(t *testing.T) {
	const max = 1e6 // 1M

	seen := make(map[uint64]struct{})
	for i := 0; i < max; i++ {
		id := genRandomID()
		if _, found := seen[id]; found {
			t.Fatalf("id %d not unique", id)
		}
		seen[id] = struct{}{}
	}
}