return fmt.Errorf("[%s] %w", c.lastErrTime.Format(time.RFC3339), c.lastErr)
}

// computes the exponential backoff duration according to
// https://www.awsarchitectureblog.com/2015/03/backoff.html
func exponentialBackoffWait(r *rand.Rand, unit, cap time.Duration) func(uint) time.Duration {
	if unit > time.Hour {
		// Protect against integer overflow
		panic("unit cannot exceed one hour")
	}
	return func(attempt uint) time.Duration {