tailscale/tstime/jitter.go

44 lines
941 B
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package tstime
import (
crand "crypto/rand"
"encoding/binary"
"math/rand"
"sync"
"time"
)
// crandSource is a rand.Source64 that gets its numbers from
// crypto/rand.Reader.
type crandSource struct{ sync.Mutex }
var _ rand.Source64 = (*crandSource)(nil)
func (s *crandSource) Int63() int64 { return int64(s.Uint64() >> 1) }
func (s *crandSource) Uint64() uint64 {
s.Lock()
defer s.Unlock()
var buf [8]byte
crand.Read(buf[:])
return binary.BigEndian.Uint64(buf[:])
}
func (*crandSource) Seed(seed int64) {} // nope
var durRand = rand.New(new(crandSource))
// RandomDurationBetween returns a random duration in range [min,max).
// If panics if max < min.
func RandomDurationBetween(min, max time.Duration) time.Duration {
diff := max - min
if diff == 0 {
return min
}
ns := durRand.Int63n(int64(diff))
return min + time.Duration(ns)
}