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server/vendor/github.com/pion/rtcp/slice_loss_indication.go

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+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package rtcp
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+)
+
+// SLIEntry represents a single entry to the SLI packet's
+// list of lost slices.
+type SLIEntry struct {
+	// ID of first lost slice
+	First uint16
+
+	// Number of lost slices
+	Number uint16
+
+	// ID of related picture
+	Picture uint8
+}
+
+// The SliceLossIndication packet informs the encoder about the loss of a picture slice
+type SliceLossIndication struct {
+	// SSRC of sender
+	SenderSSRC uint32
+
+	// SSRC of the media source
+	MediaSSRC uint32
+
+	SLI []SLIEntry
+}
+
+const (
+	sliLength = 2
+	sliOffset = 8
+)
+
+// Marshal encodes the SliceLossIndication in binary
+func (p SliceLossIndication) Marshal() ([]byte, error) {
+	if len(p.SLI)+sliLength > math.MaxUint8 {
+		return nil, errTooManyReports
+	}
+
+	rawPacket := make([]byte, sliOffset+(len(p.SLI)*4))
+	binary.BigEndian.PutUint32(rawPacket, p.SenderSSRC)
+	binary.BigEndian.PutUint32(rawPacket[4:], p.MediaSSRC)
+	for i, s := range p.SLI {
+		sli := ((uint32(s.First) & 0x1FFF) << 19) |
+			((uint32(s.Number) & 0x1FFF) << 6) |
+			(uint32(s.Picture) & 0x3F)
+		binary.BigEndian.PutUint32(rawPacket[sliOffset+(4*i):], sli)
+	}
+	hData, err := p.Header().Marshal()
+	if err != nil {
+		return nil, err
+	}
+
+	return append(hData, rawPacket...), nil
+}
+
+// Unmarshal decodes the SliceLossIndication from binary
+func (p *SliceLossIndication) Unmarshal(rawPacket []byte) error {
+	if len(rawPacket) < (headerLength + ssrcLength) {
+		return errPacketTooShort
+	}
+
+	var h Header
+	if err := h.Unmarshal(rawPacket); err != nil {
+		return err
+	}
+
+	if len(rawPacket) < (headerLength + int(4*h.Length)) {
+		return errPacketTooShort
+	}
+
+	if h.Type != TypeTransportSpecificFeedback || h.Count != FormatSLI {
+		return errWrongType
+	}
+
+	p.SenderSSRC = binary.BigEndian.Uint32(rawPacket[headerLength:])
+	p.MediaSSRC = binary.BigEndian.Uint32(rawPacket[headerLength+ssrcLength:])
+	for i := headerLength + sliOffset; i < (headerLength + int(h.Length*4)); i += 4 {
+		sli := binary.BigEndian.Uint32(rawPacket[i:])
+		p.SLI = append(p.SLI, SLIEntry{
+			First:   uint16((sli >> 19) & 0x1FFF),
+			Number:  uint16((sli >> 6) & 0x1FFF),
+			Picture: uint8(sli & 0x3F),
+		})
+	}
+	return nil
+}
+
+// MarshalSize returns the size of the packet once marshaled
+func (p *SliceLossIndication) MarshalSize() int {
+	return headerLength + sliOffset + (len(p.SLI) * 4)
+}
+
+// Header returns the Header associated with this packet.
+func (p *SliceLossIndication) Header() Header {
+	return Header{
+		Count:  FormatSLI,
+		Type:   TypeTransportSpecificFeedback,
+		Length: uint16((p.MarshalSize() / 4) - 1),
+	}
+}
+
+func (p *SliceLossIndication) String() string {
+	return fmt.Sprintf("SliceLossIndication %x %x %+v", p.SenderSSRC, p.MediaSSRC, p.SLI)
+}
+
+// DestinationSSRC returns an array of SSRC values that this packet refers to.
+func (p *SliceLossIndication) DestinationSSRC() []uint32 {
+	return []uint32{p.MediaSSRC}
+}