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140 lines
3.8 KiB
Go
140 lines
3.8 KiB
Go
package rtcp
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import (
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"encoding/binary"
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)
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// PacketType specifies the type of an RTCP packet
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type PacketType uint8
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// RTCP packet types registered with IANA. See: https://www.iana.org/assignments/rtp-parameters/rtp-parameters.xhtml#rtp-parameters-4
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const (
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TypeSenderReport PacketType = 200 // RFC 3550, 6.4.1
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TypeReceiverReport PacketType = 201 // RFC 3550, 6.4.2
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TypeSourceDescription PacketType = 202 // RFC 3550, 6.5
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TypeGoodbye PacketType = 203 // RFC 3550, 6.6
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TypeApplicationDefined PacketType = 204 // RFC 3550, 6.7 (unimplemented)
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TypeTransportSpecificFeedback PacketType = 205 // RFC 4585, 6051
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TypePayloadSpecificFeedback PacketType = 206 // RFC 4585, 6.3
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)
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// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
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const (
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FormatSLI uint8 = 2
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FormatPLI uint8 = 1
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FormatFIR uint8 = 4
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FormatTLN uint8 = 1
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FormatRRR uint8 = 5
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FormatREMB uint8 = 15
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//https://tools.ietf.org/html/draft-holmer-rmcat-transport-wide-cc-extensions-01#page-5
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FormatTCC uint8 = 15
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)
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func (p PacketType) String() string {
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switch p {
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case TypeSenderReport:
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return "SR"
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case TypeReceiverReport:
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return "RR"
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case TypeSourceDescription:
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return "SDES"
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case TypeGoodbye:
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return "BYE"
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case TypeApplicationDefined:
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return "APP"
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case TypeTransportSpecificFeedback:
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return "TSFB"
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case TypePayloadSpecificFeedback:
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return "PSFB"
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default:
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return string(p)
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}
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}
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const rtpVersion = 2
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// A Header is the common header shared by all RTCP packets
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type Header struct {
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// If the padding bit is set, this individual RTCP packet contains
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// some additional padding octets at the end which are not part of
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// the control information but are included in the length field.
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Padding bool
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// The number of reception reports, sources contained or FMT in this packet (depending on the Type)
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Count uint8
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// The RTCP packet type for this packet
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Type PacketType
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// The length of this RTCP packet in 32-bit words minus one,
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// including the header and any padding.
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Length uint16
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}
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const (
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headerLength = 4
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versionShift = 6
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versionMask = 0x3
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paddingShift = 5
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paddingMask = 0x1
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countShift = 0
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countMask = 0x1f
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countMax = (1 << 5) - 1
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)
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// Marshal encodes the Header in binary
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func (h Header) Marshal() ([]byte, error) {
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/*
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* 0 1 2 3
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* |V=2|P| RC | PT=SR=200 | length |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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rawPacket := make([]byte, headerLength)
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rawPacket[0] |= rtpVersion << versionShift
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if h.Padding {
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rawPacket[0] |= 1 << paddingShift
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}
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if h.Count > 31 {
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return nil, errInvalidHeader
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}
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rawPacket[0] |= h.Count << countShift
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rawPacket[1] = uint8(h.Type)
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binary.BigEndian.PutUint16(rawPacket[2:], h.Length)
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return rawPacket, nil
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}
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// Unmarshal decodes the Header from binary
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func (h *Header) Unmarshal(rawPacket []byte) error {
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if len(rawPacket) < headerLength {
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return errPacketTooShort
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}
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/*
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* 0 1 2 3
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* |V=2|P| RC | PT | length |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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version := rawPacket[0] >> versionShift & versionMask
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if version != rtpVersion {
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return errBadVersion
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}
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h.Padding = (rawPacket[0] >> paddingShift & paddingMask) > 0
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h.Count = rawPacket[0] >> countShift & countMask
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h.Type = PacketType(rawPacket[1])
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h.Length = binary.BigEndian.Uint16(rawPacket[2:])
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return nil
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}
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