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dialog_client: preserve routing and isolate retransmitted ACKs #369

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Merged
emiago merged 3 commits into from
Oct 20, 2026
Merged

dialog_client: preserve routing and isolate retransmitted ACKs #369

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3c4790f
dialog_client: clone ACK per 2xx retransmission (fix PrependHeader pa…
ddas-rt Sep 17, 2026
9d5f4da
Preserve dialog routing when replaying ACKs
ddas-rt Sep 30, 2026
aa3557f
Remove added ACK regression tests as requested
ddas-rt Oct 1, 2026
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12 changes: 9 additions & 3 deletions dialog_client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -402,19 +402,25 @@ func (s *DialogClientSession) WriteAck(ctx context.Context, ack *sip.Request) er
// request is passed to the transport layer directly for transmission,
// rather than a client transaction. This is because the UAC core
// handles retransmissions of the ACK, not the transaction layer.
retransmissionAck := ack.Clone() // We need to clone for RACE safety
s.buildReq(ack)
if err := s.requestValidate(s.UA.Client, ack); err != nil {
return err
}
// Snapshot the fully routed ACK once; Clone pins the current destination.
// Replay fresh copies without rebuilding dialog headers to avoid races and header accumulation.
ackTemplate := ack.Clone()
s.inviteTx.OnRetransmission(func(r *sip.Response) {
// Detect retransmission
if r.StatusCode != 200 {
return
}

if err := s.WriteRequest(retransmissionAck); err != nil {
if err := s.UA.Client.WriteRequest(ackTemplate.Clone(), s.requestValidate); err != nil {

@emiago emiago Oct 8, 2026

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what is point of second Clone? After this request is serilaized

@ddas-rt ddas-rt Oct 8, 2026

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The second clone gives each retransmission its own request. Before serialization, ClientRequestConnection writes req.raddr and can update the Via host/port.

Retransmission callbacks can overlap because passUpRetransmission releases fsmMu before calling the hook. Reusing ackTemplate would let those writes race with another callback’s transport setup or serialization. The first clone isolates the template from the initial send; the second keeps the template immutable across retransmissions.

This is a defensive strategy to handle the case where UA receives retransmitted ACKs in quick succession, that is addressed to a different endpoint and it needs to forward it to the next destination.

@emiago emiago Oct 20, 2026

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then problem is overlapping, if I see, but I could only right now think more complex solution.

s.endWithCause(fmt.Errorf("ACK retransmission failed: %w", err))
}
})

if err := s.WriteRequest(ack); err != nil {
if err := s.UA.Client.WriteRequest(ack, s.requestValidate); err != nil {
// Make sure we close our error
// s.Close()
return err
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