Add helper to wait with exponential backoff.

backoff.go

@@ -0,0 +1,76 @@
+/**
+ * Standalone signaling server for the Nextcloud Spreed app.
+ * Copyright (C) 2022 struktur AG
+ *
+ * @author Joachim Bauch <bauch@struktur.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package signaling
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+type Backoff interface {
+	Reset()
+	NextWait() time.Duration
+	Wait(context.Context)
+}
+
+type exponentialBackoff struct {
+	initial  time.Duration
+	maxWait  time.Duration
+	nextWait time.Duration
+}
+
+func NewExponentialBackoff(initial time.Duration, maxWait time.Duration) (Backoff, error) {
+	if initial <= 0 {
+		return nil, fmt.Errorf("initial must be larger than 0")
+	}
+	if maxWait < initial {
+		return nil, fmt.Errorf("maxWait must be larger or equal to initial")
+	}
+
+	return &exponentialBackoff{
+		initial: initial,
+		maxWait: maxWait,
+
+		nextWait: initial,
+	}, nil
+}
+
+func (b *exponentialBackoff) Reset() {
+	b.nextWait = b.initial
+}
+
+func (b *exponentialBackoff) NextWait() time.Duration {
+	return b.nextWait
+}
+
+func (b *exponentialBackoff) Wait(ctx context.Context) {
+	waiter, cancel := context.WithTimeout(ctx, b.nextWait)
+	defer cancel()
+
+	b.nextWait = b.nextWait * 2
+	if b.nextWait > b.maxWait {
+		b.nextWait = b.maxWait
+	}
+
+	<-waiter.Done()
+}

backoff_test.go

@@ -0,0 +1,64 @@
+/**
+ * Standalone signaling server for the Nextcloud Spreed app.
+ * Copyright (C) 2022 struktur AG
+ *
+ * @author Joachim Bauch <bauch@struktur.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package signaling
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestBackoff_Exponential(t *testing.T) {
+	backoff, err := NewExponentialBackoff(100*time.Millisecond, 500*time.Millisecond)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	waitTimes := []time.Duration{
+		100 * time.Millisecond,
+		200 * time.Millisecond,
+		400 * time.Millisecond,
+		500 * time.Millisecond,
+		500 * time.Millisecond,
+	}
+
+	for _, wait := range waitTimes {
+		if backoff.NextWait() != wait {
+			t.Errorf("Wait time should be %s, got %s", wait, backoff.NextWait())
+		}
+
+		a := time.Now()
+		backoff.Wait(context.Background())
+		b := time.Now()
+		if b.Sub(a) < wait {
+			t.Errorf("Should have waited %s, got %s", wait, b.Sub(a))
+		}
+	}
+
+	backoff.Reset()
+	a := time.Now()
+	backoff.Wait(context.Background())
+	b := time.Now()
+	if b.Sub(a) < 100*time.Millisecond {
+		t.Errorf("Should have waited %s, got %s", 100*time.Millisecond, b.Sub(a))
+	}
+}