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server/vendor/github.com/pion/sctp/ack_timer.go

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+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package sctp
+
+import (
+	"math"
+	"sync"
+	"time"
+)
+
+const (
+	ackInterval time.Duration = 200 * time.Millisecond
+)
+
+// ackTimerObserver is the inteface to an ack timer observer.
+type ackTimerObserver interface {
+	onAckTimeout()
+}
+
+type ackTimerState uint8
+
+const (
+	ackTimerStopped ackTimerState = iota
+	ackTimerStarted
+	ackTimerClosed
+)
+
+// ackTimer provides the retnransmission timer conforms with RFC 4960 Sec 6.3.1
+type ackTimer struct {
+	timer    *time.Timer
+	observer ackTimerObserver
+	mutex    sync.Mutex
+	state    ackTimerState
+	pending  uint8
+}
+
+// newAckTimer creates a new acknowledgement timer used to enable delayed ack.
+func newAckTimer(observer ackTimerObserver) *ackTimer {
+	t := &ackTimer{observer: observer}
+	t.timer = time.AfterFunc(math.MaxInt64, t.timeout)
+	t.timer.Stop()
+	return t
+}
+
+func (t *ackTimer) timeout() {
+	t.mutex.Lock()
+	if t.pending--; t.pending == 0 && t.state == ackTimerStarted {
+		t.state = ackTimerStopped
+		defer t.observer.onAckTimeout()
+	}
+	t.mutex.Unlock()
+}
+
+// start starts the timer.
+func (t *ackTimer) start() bool {
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
+
+	// this timer is already closed or already running
+	if t.state != ackTimerStopped {
+		return false
+	}
+
+	t.state = ackTimerStarted
+	t.pending++
+	t.timer.Reset(ackInterval)
+	return true
+}
+
+// stops the timer. this is similar to stop() but subsequent start() call
+// will fail (the timer is no longer usable)
+func (t *ackTimer) stop() {
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
+
+	if t.state == ackTimerStarted {
+		if t.timer.Stop() {
+			t.pending--
+		}
+		t.state = ackTimerStopped
+	}
+}
+
+// closes the timer. this is similar to stop() but subsequent start() call
+// will fail (the timer is no longer usable)
+func (t *ackTimer) close() {
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
+
+	if t.state == ackTimerStarted && t.timer.Stop() {
+		t.pending--
+	}
+	t.state = ackTimerClosed
+}
+
+// isRunning tests if the timer is running.
+// Debug purpose only
+func (t *ackTimer) isRunning() bool {
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
+
+	return t.state == ackTimerStarted
+}