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feedback_adapter.go
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feedback_adapter.go
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package cc
import (
"container/list"
"errors"
"sync"
"time"
"github.com/asticode/interceptor/internal/ntp"
"github.com/pion/interceptor"
"github.com/pion/rtcp"
"github.com/pion/rtp"
)
// TwccExtensionAttributesKey identifies the TWCC value in the attribute collection
// so we don't need to reparse
const TwccExtensionAttributesKey = iota
var (
errMissingTWCCExtension = errors.New("missing transport layer cc header extension")
errInvalidFeedback = errors.New("invalid feedback")
)
// FeedbackAdapter converts incoming RTCP Packets (TWCC and RFC8888) into Acknowledgments.
// Acknowledgments are the common format that Congestion Controllers in Pion understand.
type FeedbackAdapter struct {
lock sync.Mutex
history *feedbackHistory
}
// NewFeedbackAdapter returns a new FeedbackAdapter
func NewFeedbackAdapter() *FeedbackAdapter {
return &FeedbackAdapter{history: newFeedbackHistory(250)}
}
func (f *FeedbackAdapter) onSentRFC8888(ts time.Time, header *rtp.Header, size int) error {
f.lock.Lock()
defer f.lock.Unlock()
f.history.add(Acknowledgment{
SequenceNumber: header.SequenceNumber,
SSRC: header.SSRC,
Size: size,
Departure: ts,
Arrival: time.Time{},
ECN: 0,
})
return nil
}
func (f *FeedbackAdapter) onSentTWCC(ts time.Time, extID uint8, header *rtp.Header, size int) error {
sequenceNumber := header.GetExtension(extID)
var tccExt rtp.TransportCCExtension
err := tccExt.Unmarshal(sequenceNumber)
if err != nil {
return errMissingTWCCExtension
}
f.lock.Lock()
defer f.lock.Unlock()
f.history.add(Acknowledgment{
SequenceNumber: tccExt.TransportSequence,
SSRC: 0,
Size: header.MarshalSize() + size,
Departure: ts,
Arrival: time.Time{},
ECN: 0,
})
return nil
}
// OnSent records that and when an outgoing packet was sent for later mapping to
// acknowledgments
func (f *FeedbackAdapter) OnSent(ts time.Time, header *rtp.Header, size int, attributes interceptor.Attributes) error {
hdrExtensionID := attributes.Get(TwccExtensionAttributesKey)
id, ok := hdrExtensionID.(uint8)
if ok && hdrExtensionID != 0 {
return f.onSentTWCC(ts, id, header, size)
}
return f.onSentRFC8888(ts, header, size)
}
func (f *FeedbackAdapter) unpackRunLengthChunk(start uint16, refTime time.Time, chunk *rtcp.RunLengthChunk, deltas []*rtcp.RecvDelta) (consumedDeltas int, nextRef time.Time, acks []Acknowledgment, err error) {
result := make([]Acknowledgment, chunk.RunLength)
deltaIndex := 0
end := start + chunk.RunLength
resultIndex := 0
for i := start; i != end; i++ {
key := feedbackHistoryKey{
ssrc: 0,
sequenceNumber: i,
}
if ack, ok := f.history.get(key); ok {
if chunk.PacketStatusSymbol != rtcp.TypeTCCPacketNotReceived {
if len(deltas)-1 < deltaIndex {
return deltaIndex, refTime, result, errInvalidFeedback
}
refTime = refTime.Add(time.Duration(deltas[deltaIndex].Delta) * time.Microsecond)
ack.Arrival = refTime
deltaIndex++
}
result[resultIndex] = ack
}
resultIndex++
}
return deltaIndex, refTime, result, nil
}
func (f *FeedbackAdapter) unpackStatusVectorChunk(start uint16, refTime time.Time, chunk *rtcp.StatusVectorChunk, deltas []*rtcp.RecvDelta) (consumedDeltas int, nextRef time.Time, acks []Acknowledgment, err error) {
result := make([]Acknowledgment, len(chunk.SymbolList))
deltaIndex := 0
resultIndex := 0
for i, symbol := range chunk.SymbolList {
key := feedbackHistoryKey{
ssrc: 0,
sequenceNumber: start + uint16(i),
}
if ack, ok := f.history.get(key); ok {
if symbol != rtcp.TypeTCCPacketNotReceived {
if len(deltas)-1 < deltaIndex {
return deltaIndex, refTime, result, errInvalidFeedback
}
refTime = refTime.Add(time.Duration(deltas[deltaIndex].Delta) * time.Microsecond)
ack.Arrival = refTime
deltaIndex++
}
result[resultIndex] = ack
}
resultIndex++
}
return deltaIndex, refTime, result, nil
}
// OnTransportCCFeedback converts incoming TWCC RTCP packet feedback to
// Acknowledgments.
func (f *FeedbackAdapter) OnTransportCCFeedback(ts time.Time, feedback *rtcp.TransportLayerCC) ([]Acknowledgment, error) {
f.lock.Lock()
defer f.lock.Unlock()
result := []Acknowledgment{}
index := feedback.BaseSequenceNumber
refTime := time.Time{}.Add(time.Duration(feedback.ReferenceTime) * 64 * time.Millisecond)
recvDeltas := feedback.RecvDeltas
for _, chunk := range feedback.PacketChunks {
switch chunk := chunk.(type) {
case *rtcp.RunLengthChunk:
n, nextRefTime, acks, err := f.unpackRunLengthChunk(index, refTime, chunk, recvDeltas)
if err != nil {
return nil, err
}
refTime = nextRefTime
result = append(result, acks...)
recvDeltas = recvDeltas[n:]
index = uint16(int(index) + len(acks))
case *rtcp.StatusVectorChunk:
n, nextRefTime, acks, err := f.unpackStatusVectorChunk(index, refTime, chunk, recvDeltas)
if err != nil {
return nil, err
}
refTime = nextRefTime
result = append(result, acks...)
recvDeltas = recvDeltas[n:]
index = uint16(int(index) + len(acks))
default:
return nil, errInvalidFeedback
}
}
return result, nil
}
// OnRFC8888Feedback converts incoming Congestion Control Feedback RTCP packet
// to Acknowledgments.
func (f *FeedbackAdapter) OnRFC8888Feedback(ts time.Time, feedback *rtcp.CCFeedbackReport) []Acknowledgment {
f.lock.Lock()
defer f.lock.Unlock()
result := []Acknowledgment{}
referenceTime := ntp.ToTime(uint64(feedback.ReportTimestamp) << 16)
for _, rb := range feedback.ReportBlocks {
for i, mb := range rb.MetricBlocks {
sequenceNumber := rb.BeginSequence + uint16(i)
key := feedbackHistoryKey{
ssrc: rb.MediaSSRC,
sequenceNumber: sequenceNumber,
}
if ack, ok := f.history.get(key); ok {
if mb.Received {
delta := time.Duration((float64(mb.ArrivalTimeOffset) / 1024.0) * float64(time.Second))
ack.Arrival = referenceTime.Add(-delta)
ack.ECN = mb.ECN
}
result = append(result, ack)
}
}
}
return result
}
type feedbackHistoryKey struct {
ssrc uint32
sequenceNumber uint16
}
type feedbackHistory struct {
size int
evictList *list.List
items map[feedbackHistoryKey]*list.Element
}
func newFeedbackHistory(size int) *feedbackHistory {
return &feedbackHistory{
size: size,
evictList: list.New(),
items: make(map[feedbackHistoryKey]*list.Element),
}
}
func (f *feedbackHistory) get(key feedbackHistoryKey) (Acknowledgment, bool) {
ent, ok := f.items[key]
if ok {
if ack, ok := ent.Value.(Acknowledgment); ok {
return ack, true
}
}
return Acknowledgment{}, false
}
func (f *feedbackHistory) add(ack Acknowledgment) {
key := feedbackHistoryKey{
ssrc: ack.SSRC,
sequenceNumber: ack.SequenceNumber,
}
// Check for existing
if ent, ok := f.items[key]; ok {
f.evictList.MoveToFront(ent)
ent.Value = ack
return
}
// Add new
ent := f.evictList.PushFront(ack)
f.items[key] = ent
// Evict if necessary
if f.evictList.Len() > f.size {
f.removeOldest()
}
}
func (f *feedbackHistory) removeOldest() {
if ent := f.evictList.Back(); ent != nil {
f.evictList.Remove(ent)
if ack, ok := ent.Value.(Acknowledgment); ok {
key := feedbackHistoryKey{
ssrc: ack.SSRC,
sequenceNumber: ack.SequenceNumber,
}
delete(f.items, key)
}
}
}