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Initial draft -Properly terminating when lifetime specified and has been reached #31

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Initial draft -Properly terminating when lifetime specified and has been reached #31

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a5b80f2
Initial draft
alexlivekit Nov 6, 2025
e21a83d
Respecting lifetime limits
alexlivekit Nov 6, 2025
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55 changes: 49 additions & 6 deletions srtp/srtp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,10 @@ package srtp

import (
"crypto/rand"
"errors"
"fmt"
"net"
"sync"

prtp "github.com/pion/rtp"
"github.com/pion/srtp/v3"
Expand Down Expand Up @@ -99,6 +101,7 @@ type Profile struct {

type Config = srtp.Config
type ContextOption = srtp.ContextOption
type SessionOption = func(session *session) error
type SessionKeys = srtp.SessionKeys

// Expects a byte slice containing MKI value encoded in big-endian.
Expand All @@ -107,25 +110,50 @@ func MasterKeyIndicator(mki []byte) ContextOption {
return srtp.MasterKeyIndicator(mki)
}

func NewSession(log logger.Logger, conn net.Conn, conf *Config) (rtp.Session, error) {
type SessionExpiredError error

// Lifetime, in packets encrypted, before session keys are invalidated
// Once limit is reached, WriteRTP will return SessionExpiredError
// Zero is the same as no limit
func WithLifetime(lifetime uint64) SessionOption {
return func(session *session) error {
session.lifetime = lifetime
return nil
}
}

func NewSession(log logger.Logger, conn net.Conn, conf *Config, opts ...SessionOption) (rtp.Session, error) {
s, err := srtp.NewSessionSRTP(conn, conf)
if err != nil {
return nil, err
}
return &session{log: log, s: s}, nil
ses := &session{log: log, s: s}
for i, opt := range opts {
if err := opt(ses); err != nil {
return nil, fmt.Errorf("option %d: %w", i, err)
}
}
return ses, nil
}

type session struct {
log logger.Logger
s *srtp.SessionSRTP
log logger.Logger
s *srtp.SessionSRTP
lifetime uint64
}

func (s *session) OpenWriteStream() (rtp.WriteStream, error) {
w, err := s.s.OpenWriteStream()
if err != nil {
return nil, err
}
return writeStream{w: w}, nil
newLifetime := uint64(s.lifetime)
return writeStream{
w: w,
lifetimeSet: s.lifetime > 0,
lifetimeRemaining: &newLifetime,
mu: &sync.RWMutex{},
}, nil
}

func (s *session) AcceptStream() (rtp.ReadStream, uint32, error) {
Expand All @@ -141,14 +169,29 @@ func (s *session) Close() error {
}

type writeStream struct {
w *srtp.WriteStreamSRTP
w *srtp.WriteStreamSRTP
lifetimeSet bool

mu *sync.RWMutex
lifetimeRemaining *uint64
}

func (w writeStream) String() string {

@alexlivekit alexlivekit Nov 6, 2025 •
edited
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No clue why we're passing w writeStream by value and not by ref (w *writeStream). This is basically churning memory.

But this is why I had to do the ugly thing with the lock and *uint64.

return "SRTPWriteStream"
}

func (w writeStream) WriteRTP(h *prtp.Header, payload []byte) (int, error) {
if w.lifetimeSet {
w.mu.Lock()
remaining := *w.lifetimeRemaining
if remaining > 0 {
*w.lifetimeRemaining = remaining - 1
}
w.mu.Unlock()
if remaining == 0 {
return 0, SessionExpiredError(errors.New("SRTP profile key lifetime expired"))
}
}
return w.w.WriteRTP(h, payload)
}

Expand Down
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