67 lines
1.7 KiB
Go
67 lines
1.7 KiB
Go
// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
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// SPDX-License-Identifier: MIT
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package rtp
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import (
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"sync"
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)
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// Sequencer generates sequential sequence numbers for building RTP packets
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type Sequencer interface {
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NextSequenceNumber() uint16
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RollOverCount() uint64
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}
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// maxInitialRandomSequenceNumber is the maximum value used for the initial sequence
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// number when using NewRandomSequencer().
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// This uses only half the potential sequence number space to avoid issues decrypting
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// SRTP when the sequence number starts near the rollover and there is packet loss.
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// See https://webrtc-review.googlesource.com/c/src/+/358360
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const maxInitialRandomSequenceNumber = 1<<15 - 1
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// NewRandomSequencer returns a new sequencer starting from a random sequence
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// number
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func NewRandomSequencer() Sequencer {
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return &sequencer{
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sequenceNumber: uint16(globalMathRandomGenerator.Intn(maxInitialRandomSequenceNumber)),
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}
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}
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// NewFixedSequencer returns a new sequencer starting from a specific
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// sequence number
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func NewFixedSequencer(s uint16) Sequencer {
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return &sequencer{
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sequenceNumber: s - 1, // -1 because the first sequence number prepends 1
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}
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}
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type sequencer struct {
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sequenceNumber uint16
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rollOverCount uint64
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mutex sync.Mutex
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}
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// NextSequenceNumber increment and returns a new sequence number for
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// building RTP packets
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func (s *sequencer) NextSequenceNumber() uint16 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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s.sequenceNumber++
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if s.sequenceNumber == 0 {
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s.rollOverCount++
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}
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return s.sequenceNumber
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}
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// RollOverCount returns the amount of times the 16bit sequence number
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// has wrapped
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func (s *sequencer) RollOverCount() uint64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return s.rollOverCount
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}
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