remove time from the interval predictor

It makes it harder to test.

certexchange/polling/predictor.go

@@ -24,7 +24,6 @@ func newPredictor(minInterval, defaultInterval, maxInterval time.Duration) *pred
 type predictor struct {
 	minInterval, maxInterval time.Duration
 
-	next            time.Time
 	interval        time.Duration
 	wasIncreasing   bool
 	exploreDistance time.Duration
@@ -88,21 +87,11 @@ func (p *predictor) update(progress uint64) time.Duration {
 	}
 
 	// Apply either the backoff or predicted the interval.
+	nextInterval := p.interval
 	if p.backoff > 0 {
+		nextInterval = p.backoff
 		p.backoff = min(2*p.backoff, maxBackoffMultiplier*p.maxInterval)
-		p.next = p.next.Add(p.backoff)
-	} else {
-		p.next = p.next.Add(p.interval)
 	}
+	return nextInterval
 
-	// Polling takes time. If we run behind, predict that we should poll again immediately. We
-	// enforce a minimum interval above so this shouldn't be too often.
-	now := time.Now()
-	prediction := p.next.Sub(now)
-	if prediction < 0 {
-		p.next = now
-		return 0
-	}
-
-	return prediction
 }

certexchange/polling/subscriber.go

@@ -149,7 +149,7 @@ func (s *Subscriber) run(ctx context.Context, discoveredPeers <-chan peer.ID, po
 		select {
 		case p := <-discoveredPeers:
 			s.peerTracker.peerSeen(p)
-		case <-timer.C:
+		case pollTime := <-timer.C:
 			// First, see if we made progress locally. If we have, update
 			// interval prediction based on that local progress. If our interval
 			// was accurate, we'll keep predicting the same interval and we'll
@@ -159,16 +159,17 @@ func (s *Subscriber) run(ctx context.Context, discoveredPeers <-chan peer.ID, po
 			if err != nil {
 				return err
 			}
-			if progress > 0 {
-				timer.Reset(predictor.update(progress))
-				break
+			// Otherwise, poll the network.
+			if progress == 0 {
+				progress, err = s.poll(ctx, poller)
+				if err != nil {
+					return err
+				}
 			}
 
-			progress, err = s.poll(ctx, poller)
-			if err != nil {
-				return err
-			}
-			timer.Reset(predictor.update(progress))
+			nextInterval := predictor.update(progress)
+			nextPollTime := pollTime.Add(nextInterval)
+			timer.Reset(max(time.Until(nextPollTime), 0))
 		case <-ctx.Done():
 			return ctx.Err()
 		}