feat: long poller error backoff

v1/core/pollers/pollers.go

@@ -45,6 +45,19 @@ type TestPoller struct {
 	mu sync.Mutex
 }
 
+type backoff struct {
+	base time.Duration
+	max  time.Duration
+
+	window []bool
+	pos    int
+	count  int
+	errors int
+
+	sinceAdjust int
+	interval    time.Duration
+}
+
 type webhookOptions struct {
 	addr              string
 	tlsConfig         *tls.Config
@@ -275,24 +288,95 @@ func WithConnContext(fn func(ctx context.Context, c net.Conn) context.Context) W
 	})
 }
 
-func (lp *LongPoller) poll(ctx context.Context, ch chan model.Update) {
+func newBackoff(
-	var updates []model.Update
+	base, max time.Duration,
-	var marker int64
+	windowSize int,
-	var err error
+) *backoff {
+	if base <= 0 || max < base || windowSize <= 0 {
+		panic("backoff: invalid configuration")
+	}
 
-	// todo: backoff on errors
+	return &backoff{
+		base:     base,
+		max:      max,
+		window:   make([]bool, windowSize),
+		interval: base,
+	}
+}
+
+func (b *backoff) observe(err error) time.Duration {
+	failed := err != nil
+
+	if b.count == len(b.window) && b.window[b.pos] {
+		b.errors--
+	} else {
+		b.count++
+	}
+
+	b.window[b.pos] = failed
+	if failed {
+		b.errors++
+	}
+
+	b.pos = (b.pos + 1) % len(b.window)
+	b.sinceAdjust++
+
+	if b.count < len(b.window) ||
+		b.sinceAdjust < len(b.window) {
+		return b.interval
+	}
+
+	b.sinceAdjust = 0
+	errorRate := float64(b.errors) / float64(b.count)
+
+	switch {
+	case errorRate >= 0.3:
+		b.interval = min(b.interval*2, b.max)
+	case errorRate <= 0.1:
+		b.interval = max(b.interval/2, b.base)
+	}
+
+	return b.interval
+}
+
+func (lp *LongPoller) poll(ctx context.Context, ch chan model.Update) {
+	b := newBackoff(
+		lp.pollInterval,
+		30*time.Second,
+		20,
+	)
+
+	var marker int64
 
 	for {
-		select {
+		if err := wait(ctx, b.interval); err != nil {
-		case <-ctx.Done():
 			return
-		case <-time.Tick(lp.pollInterval):
-			start := time.Now()
-			updates, marker, err = lp.api.Subscriptions.GetUpdates(ctx, marker)
-			latency := time.Since(start)
-			if err != nil && !errors.Is(err, context.Canceled) {
-				lp.logger.Error().Err(err).Send()
 		}
+
+		start := time.Now()
+		updates, nextMarker, err := lp.api.Subscriptions.GetUpdates(ctx, marker)
+		latency := time.Since(start)
+
+		if err != nil {
+			if errors.Is(err, context.Canceled) ||
+				ctx.Err() != nil {
+				return
+			}
+
+			delay := b.observe(err)
+
+			lp.logger.Error().
+				Err(err).
+				Dur("latency", latency).
+				Dur("next_interval", delay).
+				Msg("failed to receive updates")
+
+			continue
+		}
+
+		b.observe(nil)
+		marker = nextMarker
+
 		lp.logger.Debug().
 			Int("received", len(updates)).
 			Dur("latency", latency).
@@ -304,7 +388,6 @@ func (lp *LongPoller) poll(ctx context.Context, ch chan model.Update) {
 			}
 		}
 	}
-	}
 }
 
 func newLongPollerOptions() *longPollerOptions {
@@ -335,3 +418,15 @@ func (low longPollerOptionWrapper) apply(opts *longPollerOptions) {
 func (wow webhookOptionWrapper) apply(opts *webhookOptions) {
 	wow.fn(opts)
 }
+
+func wait(ctx context.Context, delay time.Duration) error {
+	timer := time.NewTimer(delay)
+	defer timer.Stop()
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-timer.C:
+		return nil
+	}
+}