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Harden upstream FlexFEC handling

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This commit is contained in:
David Chen
2026-08-29 22:02:23 -07:00
parent 390d40e70a
commit a8b35cc818
9 changed files with 421 additions and 135 deletions
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pkg/sfu/buffer/buffer.go
+20 -9
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@@ -430,8 +430,8 @@ func (b *Buffer) SetPrimaryBufferForFEC(primaryBuffer *Buffer) {
ssrc := b.BufferBase.SSRC()
b.Unlock()
// let the primary know the repair stream SSRC so its decoder starts
// filling with media before the first FEC packet shows up
// Let the primary know the repair stream SSRC so its decoder is ready
// before the first FEC packet arrives.
primaryBuffer.setFECSSRC(ssrc)
for _, pp := range pkts {
@@ -486,17 +486,27 @@ func (b *Buffer) maybeCreateFECDecoderLocked() {
}
func (b *Buffer) getFECMediaPacketLocked(sequenceNumber uint16, dst []byte) (int, error) {
if b.bucket == nil {
if b.bucket == nil || b.rtpStats == nil {
return 0, errFECMediaPacketNotFound
}
headSequenceNumber := b.bucket.HeadSequenceNumber()
extendedSequenceNumber := int64(headSequenceNumber) + int64(int16(sequenceNumber-uint16(headSequenceNumber)))
// FlexFEC masks use the publisher's sequence-number space. BufferBase
// removes padding-only packets from the downstream space, so resolve the
// original extended sequence number and apply the same adjustment used
// when the packet was inserted into the bucket.
highestSequenceNumber := b.rtpStats.ExtendedHighestSequenceNumber()
extendedSequenceNumber := int64(highestSequenceNumber) + int64(int16(sequenceNumber-uint16(highestSequenceNumber)))
if extendedSequenceNumber < 0 {
return 0, errFECMediaPacketNotFound
}
return b.bucket.GetPacket(dst, uint64(extendedSequenceNumber))
extendedSN := uint64(extendedSequenceNumber)
sequenceNumberAdjustment, err := b.snRangeMap.GetValue(extendedSN)
if err != nil || sequenceNumberAdjustment > extendedSN {
return 0, errFECMediaPacketNotFound
}
return b.bucket.GetPacket(dst, extendedSN-sequenceNumberAdjustment)
}
// OnFECRecovery is called with counter deltas whenever FEC packets are
@@ -567,9 +577,9 @@ func (b *Buffer) feedFECLocked(
arrivalTime int64,
) (fecRecoveryDelta, func(received int, recovered int, discarded int, bytesReceived int)) {
statsBefore := b.fecDecoder.Stats()
recovered := b.fecDecoder.DecodeFec(pkt)
recovered := b.fecDecoder.DecodeFEC(pkt)
if b.fecPktBuf == nil {
if len(recovered) > 0 && b.fecPktBuf == nil {
b.fecPktBuf = make([]byte, bucket.RTPMaxPktSize)
}
for _, rp := range recovered {
@@ -581,7 +591,8 @@ func (b *Buffer) feedFECLocked(
// recovered packets flow through the regular pipeline: they are
// forwarded downstream and stop NACKs for the lost sequence numbers.
// they do not re-enter the decoder, it already has them in its window.
// They do not re-enter the decoder because chained recovery already
// completed within DecodeFEC.
b.calc(b.fecPktBuf[:n], rp, arrivalTime, false, true)
}