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server/vendor/github.com/pion/rtp/sequencer.go

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+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package rtp
+
+import (
+	"math"
+	"sync"
+)
+
+// Sequencer generates sequential sequence numbers for building RTP packets
+type Sequencer interface {
+	NextSequenceNumber() uint16
+	RollOverCount() uint64
+}
+
+// NewRandomSequencer returns a new sequencer starting from a random sequence
+// number
+func NewRandomSequencer() Sequencer {
+	return &sequencer{
+		sequenceNumber: uint16(globalMathRandomGenerator.Intn(math.MaxUint16)),
+	}
+}
+
+// NewFixedSequencer returns a new sequencer starting from a specific
+// sequence number
+func NewFixedSequencer(s uint16) Sequencer {
+	return &sequencer{
+		sequenceNumber: s - 1, // -1 because the first sequence number prepends 1
+	}
+}
+
+type sequencer struct {
+	sequenceNumber uint16
+	rollOverCount  uint64
+	mutex          sync.Mutex
+}
+
+// NextSequenceNumber increment and returns a new sequence number for
+// building RTP packets
+func (s *sequencer) NextSequenceNumber() uint16 {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	s.sequenceNumber++
+	if s.sequenceNumber == 0 {
+		s.rollOverCount++
+	}
+
+	return s.sequenceNumber
+}
+
+// RollOverCount returns the amount of times the 16bit sequence number
+// has wrapped
+func (s *sequencer) RollOverCount() uint64 {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	return s.rollOverCount
+}