Implement sending NACKs on the upstream connection.

client.go

@@ -17,6 +17,7 @@ import (
 	"time"
 
 	"sfu/packetlist"
+	"sfu/packetwindow"
 
 	"github.com/gorilla/websocket"
 	"github.com/pion/rtcp"
@@ -259,6 +260,20 @@ func addUpConn(c *client, id string) (*upConnection, error) {
 		return nil, err
 	}
 
+	conn := &upConnection{id: id, pc: pc}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.up == nil {
+		c.up = make(map[string]*upConnection)
+	}
+	if c.up[id] != nil {
+		conn.pc.Close()
+		return nil, errors.New("Adding duplicate connection")
+	}
+	c.up[id] = conn
+
 	pc.OnICECandidate(func(candidate *webrtc.ICECandidate) {
 		sendICE(c, id, candidate)
 	})
@@ -294,6 +309,7 @@ func addUpConn(c *client, id string) (*upConnection, error) {
 			var packet rtp.Packet
 			var local []*downTrack
 			var localTime time.Time
+			window := packetwindow.New()
 			for {
 				now := time.Now()
 				if now.Sub(localTime) > time.Second/2 {
@@ -315,6 +331,17 @@ func addUpConn(c *client, id string) (*upConnection, error) {
 					continue
 				}
 
+				window.Set(packet.SequenceNumber)
+				if packet.SequenceNumber-window.First() > 24 {
+					first, bitmap := window.Get17()
+					if bitmap != ^uint16(0) {
+						err := conn.sendNACK(track, first, ^bitmap)
+						if err != nil {
+							log.Printf("%v", err)
+						}
+					}
+				}
+
 				list.Store(packet.SequenceNumber, buf[:i])
 
 				for _, l := range local {
@@ -330,19 +357,6 @@ func addUpConn(c *client, id string) (*upConnection, error) {
 		}()
 	})
 
-	conn := &upConnection{id: id, pc: pc}
-
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
-	if c.up == nil {
-		c.up = make(map[string]*upConnection)
-	}
-	if c.up[id] != nil {
-		conn.pc.Close()
-		return nil, errors.New("Adding duplicate connection")
-	}
-	c.up[id] = conn
 	return conn, nil
 }
 
@@ -567,7 +581,7 @@ func updateUpBitrate(up *upConnection) {
 		for _, l := range local {
 			ms := atomic.LoadUint64(&l.maxBitrate.timestamp)
 			bitrate := atomic.LoadUint64(&l.maxBitrate.bitrate)
-			if now < ms || now > ms + 5000 || bitrate == 0 {
+			if now < ms || now > ms+5000 || bitrate == 0 {
 				l.setMuted(false)
 				continue
 			}
@@ -588,7 +602,7 @@ func updateUpBitrate(up *upConnection) {
 func (up *upConnection) sendPLI(track *upTrack) error {
 	last := atomic.LoadUint64(&track.lastPLI)
 	now := msSinceEpoch()
-	if now >= last && now - last < 200 {
+	if now >= last && now-last < 200 {
 		return nil
 	}
 	atomic.StoreUint64(&track.lastPLI, now)
@@ -610,6 +624,25 @@ func sendREMB(pc *webrtc.PeerConnection, ssrc uint32, bitrate uint64) error {
 	})
 }
 
+func (up *upConnection) sendNACK(track *upTrack, first uint16, bitmap uint16) error {
+	return sendNACK(up.pc, track.track.SSRC(), first, bitmap)
+}
+
+func sendNACK(pc *webrtc.PeerConnection, ssrc uint32, first uint16, bitmap uint16) error {
+	packet := rtcp.Packet(
+		&rtcp.TransportLayerNack{
+			MediaSSRC: ssrc,
+			Nacks: []rtcp.NackPair{
+				rtcp.NackPair{
+					first,
+					rtcp.PacketBitmap(bitmap),
+				},
+			},
+		},
+	)
+	return pc.WriteRTCP([]rtcp.Packet{packet})
+}
+
 func sendRecovery(p *rtcp.TransportLayerNack, track *downTrack) {
 	var packet rtp.Packet
 	for _, nack := range p.Nacks {

packetwindow/packetwindow.go

@@ -0,0 +1,76 @@
+package packetwindow
+
+import (
+	"fmt"
+)
+
+type Window struct {
+	first  uint16
+	bitmap uint32
+}
+
+func New() *Window {
+	return &Window{}
+}
+
+func (w *Window) String() string {
+	buf := make([]byte, 32)
+	for i := 0; i < 32; i++ {
+		if (w.bitmap & (1 << i)) != 0 {
+			buf[i] = '1'
+		} else {
+			buf[i] = '0'
+		}
+	}
+
+	return fmt.Sprintf("[%04x %s]", w.first, buf)
+}
+
+func (w *Window) First() uint16 {
+	return w.first
+}
+
+func (w *Window) Reset() {
+	w.bitmap = 0
+}
+
+func (w *Window) Set(seqno uint16) {
+	if w.bitmap == 0 {
+		w.first = seqno
+		w.bitmap = 1
+		return
+	}
+
+	if ((seqno - w.first) & 0x8000) != 0 {
+		return
+	}
+
+	if seqno == w.first {
+		w.bitmap >>= 1
+		w.first += 1
+		for (w.bitmap & 1) == 1 {
+			w.bitmap >>= 1
+			w.first += 1
+		}
+		return
+	}
+
+	if seqno - w.first < 32 {
+		w.bitmap |= (1 << uint16(seqno - w.first))
+		return
+	}
+
+	shift := seqno - w.first - 31
+	w.bitmap >>= shift
+	w.first += shift
+	w.bitmap |= (1 << uint16(seqno - w.first))
+	return
+}
+
+func (w *Window) Get17() (uint16, uint16) {
+	first := w.first
+	bitmap := uint16((w.bitmap >> 1) & 0xFFFF)
+	w.bitmap >>= 17
+	w.first += 17
+	return first, bitmap
+}

packetwindow/packetwindow_test.go

@@ -0,0 +1,102 @@
+package packetwindow
+
+import (
+	"testing"
+
+	"github.com/pion/rtcp"
+)
+
+func TestWindow(t *testing.T) {
+	value := uint64(0xcdd58f1e035379c0)
+
+	w := New()
+
+	for i := 0; i < 64; i++ {
+		if (value & (1 << i)) != 0 {
+			w.Set(uint16(42 + i))
+		}
+	}
+
+	value >>= uint16(w.first - 42)
+	if uint32(value) != w.bitmap {
+		t.Errorf("Got %b, expected %b", w.bitmap, value)
+	}
+}
+
+func TestWindowWrap(t *testing.T) {
+	value := uint64(0xcdd58f1e035379c0)
+
+	w := New()
+
+	w.Set(0x7000)
+	w.Set(0xA000)
+	for i := 0; i < 64; i++ {
+		if (value & (1 << i)) != 0 {
+			w.Set(uint16(42 + i))
+		}
+	}
+
+	value >>= uint16(w.first - 42)
+	if uint32(value) != w.bitmap {
+		t.Errorf("Got %b, expected %b", w.bitmap, value)
+	}
+}
+
+func TestWindowGet(t *testing.T) {
+	value := uint64(0xcdd58f1e035379c0)
+
+	w := New()
+
+	for i := 0; i < 64; i++ {
+		if (value & (1 << i)) != 0 {
+			w.Set(uint16(42 + i))
+		}
+	}
+
+	pos := uint16(42)
+	for w.bitmap != 0 {
+		first, bitmap := w.Get17()
+		if first < pos || first >= pos+64 {
+			t.Errorf("First is %v, pos is %v", first, pos)
+		}
+		value >>= (first - pos)
+		pos = first
+		if (value & 1) != 0 {
+			t.Errorf("Value is odd")
+		}
+		value >>= 1
+		pos += 1
+		if bitmap != uint16(value&0xFFFF) {
+			t.Errorf("Got %b, expected %b", bitmap, (value & 0xFFFF))
+		}
+		value >>= 16
+		pos += 16
+	}
+	if value != 0 {
+		t.Errorf("Value is %v", value)
+	}
+}
+
+func TestWindowPacket(t *testing.T) {
+	value := uint64(0xcdd58f1e035379c0)
+	w := New()
+
+	for i := 0; i < 64; i++ {
+		if (value & (1 << i)) != 0 {
+			w.Set(uint16(42 + i))
+		}
+	}
+
+	first, bitmap := w.Get17()
+
+	p := rtcp.NackPair{first, rtcp.PacketBitmap(^bitmap)}
+	list := p.PacketList()
+
+	for _, s := range list {
+		if s < 42 || s >= 42 + 64 {
+			if (value & (1 << (s - 42))) != 0 {
+				t.Errorf("Bit %v unexpectedly set", s - 42)
+			}
+		}
+	}
+}