rate limiter example

[kamilsk]

The concept:

sem := limiter.ForUser(request.Context())
release, err := sem.Acquire(semaphore.WithTimeout(config.SLA))
if err != nil {
	http.Error(rw, "operation timeout", http.StatusGatewayTimeout)
	return
}
deadline := semaphore.WithDeadline(time.Now().Add(config.LimitRange))
go func() {
	release()
	release, err = sem.Acquire(deadline)
	if err != nil { return }
	<-deadline
	release()
}()
// handle user request