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108 lines
3.1 KiB
Go
108 lines
3.1 KiB
Go
package rtcp
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import (
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"encoding/binary"
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"github.com/pkg/errors"
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)
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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 = 200 // RFC 3550, 6.4.1
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TypeReceiverReport = 201 // RFC 3550, 6.4.2
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TypeSourceDescription = 202 // RFC 3550, 6.5
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TypeGoodbye = 203 // RFC 3550, 6.6
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TypeApplicationDefined = 204 // RFC 3550, 6.7
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)
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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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// Identifies the version of RTP, which is the same in RTCP packets
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// as in RTP data packets.
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Version uint8
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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 report blocks contained in this packet.
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ReportCount uint8
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// The RTCP packet type for this packet
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Type uint8
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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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reportCountShift = 0
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reportCountMask = 0x1f
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)
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var (
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errInvalidVersion = errors.New("invalid version")
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errInvalidReportCount = errors.New("invalid report count")
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errHeaderTooShort = errors.New("rtcp header too short")
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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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if h.Version > 3 {
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return nil, errInvalidVersion
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}
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rawPacket[0] |= h.Version << 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.ReportCount > 31 {
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return nil, errInvalidReportCount
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}
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rawPacket[0] |= h.ReportCount << reportCountShift
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rawPacket[1] = 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 errHeaderTooShort
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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=SR=200 | length |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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h.Version = rawPacket[0] >> versionShift & versionMask
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h.Padding = (rawPacket[0] >> paddingShift & paddingMask) > 0
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h.ReportCount = rawPacket[0] >> reportCountShift & reportCountMask
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h.Type = 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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