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