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|
package rtcp
import (
"encoding/binary"
"fmt"
"math"
)
// PacketBitmap shouldn't be used like a normal integral,
// so it's type is masked here. Access it with PacketList().
type PacketBitmap uint16
// NackPair is a wire-representation of a collection of
// Lost RTP packets
type NackPair struct {
// ID of lost packets
PacketID uint16
// Bitmask of following lost packets
LostPackets PacketBitmap
}
// The TransportLayerNack packet informs the encoder about the loss of a transport packet
// IETF RFC 4585, Section 6.2.1
// https://tools.ietf.org/html/rfc4585#section-6.2.1
type TransportLayerNack struct {
// SSRC of sender
SenderSSRC uint32
// SSRC of the media source
MediaSSRC uint32
Nacks []NackPair
}
var _ Packet = (*TransportLayerNack)(nil) // assert is a Packet
// NackPairsFromSequenceNumbers generates a slice of NackPair from a list of SequenceNumbers
// This handles generating the proper values for PacketID/LostPackets
func NackPairsFromSequenceNumbers(sequenceNumbers []uint16) (pairs []NackPair) {
if len(sequenceNumbers) == 0 {
return []NackPair{}
}
nackPair := &NackPair{PacketID: sequenceNumbers[0]}
for i := 1; i < len(sequenceNumbers); i++ {
m := sequenceNumbers[i]
if m-nackPair.PacketID > 16 {
pairs = append(pairs, *nackPair)
nackPair = &NackPair{PacketID: m}
continue
}
nackPair.LostPackets |= 1 << (m - nackPair.PacketID - 1)
}
pairs = append(pairs, *nackPair)
return
}
// Range calls f sequentially for each sequence number covered by n.
// If f returns false, Range stops the iteration.
func (n *NackPair) Range(f func(seqno uint16) bool) {
more := f(n.PacketID)
if !more {
return
}
b := n.LostPackets
for i := uint16(0); b != 0; i++ {
if (b & (1 << i)) != 0 {
b &^= (1 << i)
more = f(n.PacketID + i + 1)
if !more {
return
}
}
}
}
// PacketList returns a list of Nack'd packets that's referenced by a NackPair
func (n *NackPair) PacketList() []uint16 {
out := make([]uint16, 0, 17)
n.Range(func(seqno uint16) bool {
out = append(out, seqno)
return true
})
return out
}
const (
tlnLength = 2
nackOffset = 8
)
// Marshal encodes the TransportLayerNack in binary
func (p TransportLayerNack) Marshal() ([]byte, error) {
if len(p.Nacks)+tlnLength > math.MaxUint8 {
return nil, errTooManyReports
}
rawPacket := make([]byte, nackOffset+(len(p.Nacks)*4))
binary.BigEndian.PutUint32(rawPacket, p.SenderSSRC)
binary.BigEndian.PutUint32(rawPacket[4:], p.MediaSSRC)
for i := 0; i < len(p.Nacks); i++ {
binary.BigEndian.PutUint16(rawPacket[nackOffset+(4*i):], p.Nacks[i].PacketID)
binary.BigEndian.PutUint16(rawPacket[nackOffset+(4*i)+2:], uint16(p.Nacks[i].LostPackets))
}
h := p.Header()
hData, err := h.Marshal()
if err != nil {
return nil, err
}
return append(hData, rawPacket...), nil
}
// Unmarshal decodes the TransportLayerNack from binary
func (p *TransportLayerNack) 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 != FormatTLN {
return errWrongType
}
p.SenderSSRC = binary.BigEndian.Uint32(rawPacket[headerLength:])
p.MediaSSRC = binary.BigEndian.Uint32(rawPacket[headerLength+ssrcLength:])
for i := headerLength + nackOffset; i < (headerLength + int(h.Length*4)); i += 4 {
p.Nacks = append(p.Nacks, NackPair{
binary.BigEndian.Uint16(rawPacket[i:]),
PacketBitmap(binary.BigEndian.Uint16(rawPacket[i+2:])),
})
}
return nil
}
func (p *TransportLayerNack) len() int {
return headerLength + nackOffset + (len(p.Nacks) * 4)
}
// Header returns the Header associated with this packet.
func (p *TransportLayerNack) Header() Header {
return Header{
Count: FormatTLN,
Type: TypeTransportSpecificFeedback,
Length: uint16((p.len() / 4) - 1),
}
}
func (p TransportLayerNack) String() string {
out := fmt.Sprintf("TransportLayerNack from %x\n", p.SenderSSRC)
out += fmt.Sprintf("\tMedia Ssrc %x\n", p.MediaSSRC)
out += "\tID\tLostPackets\n"
for _, i := range p.Nacks {
out += fmt.Sprintf("\t%d\t%b\n", i.PacketID, i.LostPackets)
}
return out
}
// DestinationSSRC returns an array of SSRC values that this packet refers to.
func (p *TransportLayerNack) DestinationSSRC() []uint32 {
return []uint32{p.MediaSSRC}
}
|
