Add delivery rate estimator

gcc/delivery_rate_estimator.go

@@ -0,0 +1,93 @@
+// SPDX-FileCopyrightText: 2025 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package gcc
+
+import (
+	"container/heap"
+	"time"
+)
+
+type deliveryRateHeapItem struct {
+	arrival time.Time
+	size    int
+}
+
+type deliveryRateHeap []deliveryRateHeapItem
+
+// Len implements heap.Interface.
+func (d deliveryRateHeap) Len() int {
+	return len(d)
+}
+
+// Less implements heap.Interface.
+func (d deliveryRateHeap) Less(i int, j int) bool {
+	return d[i].arrival.Before(d[j].arrival)
+}
+
+// Pop implements heap.Interface.
+func (d *deliveryRateHeap) Pop() any {
+	old := *d
+	n := len(old)
+	x := old[n-1]
+	*d = old[0 : n-1]
+
+	return x
+}
+
+// Push implements heap.Interface.
+func (d *deliveryRateHeap) Push(x any) {
+	// nolint
+	*d = append(*d, x.(deliveryRateHeapItem))
+}
+
+// Swap implements heap.Interface.
+func (d deliveryRateHeap) Swap(i int, j int) {
+	d[i], d[j] = d[j], d[i]
+}
+
+type deliveryRateEstimator struct {
+	window        time.Duration
+	latestArrival time.Time
+	history       *deliveryRateHeap
+}
+
+func newDeliveryRateEstimator(window time.Duration) *deliveryRateEstimator {
+	return &deliveryRateEstimator{
+		window:        window,
+		latestArrival: time.Time{},
+		history:       &deliveryRateHeap{},
+	}
+}
+
+func (e *deliveryRateEstimator) onPacketAcked(arrival time.Time, size int) {
+	if arrival.After(e.latestArrival) {
+		e.latestArrival = arrival
+	}
+	heap.Push(e.history, deliveryRateHeapItem{
+		arrival: arrival,
+		size:    size,
+	})
+}
+
+func (e *deliveryRateEstimator) getRate() int {
+	deadline := e.latestArrival.Add(-e.window)
+	for len(*e.history) > 0 && (*e.history)[0].arrival.Before(deadline) {
+		heap.Pop(e.history)
+	}
+	earliest := e.latestArrival
+	sum := 0
+	for _, i := range *e.history {
+		if i.arrival.Before(earliest) {
+			earliest = i.arrival
+		}
+		sum += i.size
+	}
+	d := e.latestArrival.Sub(earliest)
+	if d == 0 {
+		return 0
+	}
+	rate := 8 * float64(sum) / d.Seconds()
+
+	return int(rate)
+}

gcc/delivery_rate_estimator_test.go

@@ -0,0 +1,77 @@
+// SPDX-FileCopyrightText: 2025 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package gcc
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDeliveryRateEstimator(t *testing.T) {
+	type ack struct {
+		arrival time.Time
+		size    int
+	}
+	cases := []struct {
+		window       time.Duration
+		acks         []ack
+		expectedRate int
+	}{
+		{
+			window:       0,
+			acks:         []ack{},
+			expectedRate: 0,
+		},
+		{
+			window:       time.Second,
+			acks:         []ack{},
+			expectedRate: 0,
+		},
+		{
+			window: time.Second,
+			acks: []ack{
+				{time.Time{}, 1200},
+			},
+			expectedRate: 0,
+		},
+		{
+			window: time.Second,
+			acks: []ack{
+				{time.Time{}.Add(time.Millisecond), 1200},
+			},
+			expectedRate: 0,
+		},
+		{
+			window: time.Second,
+			acks: []ack{
+				{time.Time{}.Add(time.Second), 1200},
+				{time.Time{}.Add(1500 * time.Millisecond), 1200},
+				{time.Time{}.Add(2 * time.Second), 1200},
+			},
+			expectedRate: 28800,
+		},
+		{
+			window: time.Second,
+			acks: []ack{
+				{time.Time{}.Add(500 * time.Millisecond), 1200},
+				{time.Time{}.Add(time.Second), 1200},
+				{time.Time{}.Add(1500 * time.Millisecond), 1200},
+				{time.Time{}.Add(2 * time.Second), 1200},
+			},
+			expectedRate: 28800,
+		},
+	}
+	for i, tc := range cases {
+		t.Run(fmt.Sprintf("%v", i), func(t *testing.T) {
+			e := newDeliveryRateEstimator(tc.window)
+			for _, ack := range tc.acks {
+				e.onPacketAcked(ack.arrival, ack.size)
+			}
+			assert.Equal(t, tc.expectedRate, e.getRate())
+		})
+	}
+}