fix(qmux): report a finished send stream as closed cleanly - #402
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| Frame::Stream(stream) if stream.fin => { | ||
| self.streams.lock().unwrap().send.remove(&stream.id); | ||
| if let Some(send) = self.streams.lock().unwrap().send.remove(&stream.id) { | ||
| send.inbound_signal.send(SendSignal::Finished).ok(); |
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When the transport write is backpressured or fails, this sends Finished before the frame is encoded or self.writer.send(bytes) completes. Consequently, SendStream::closed() can return success while the FIN is still in flight; if its caller then closes or drops the session, transmit_or_teardown may cancel that write and the peer never receives the FIN or all preceding bytes. Preserve the sender while retiring the stream, but emit Finished only after the transport send succeeds; the added test currently masks this race by reading the complete stream on the peer before awaiting closed().
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Agreed, fixed in 897865b. The writer holds the stream's signal sender across writer.send and sends Finished only after the write succeeds. A failed or abandoned write drops the sender, which closed() reports as Closed. New unit tests fin_signals_finished_after_write and failed_fin_write_does_not_signal_finished cover both outcomes; the second fails with the old ordering.
(Written by Opus 5.5)
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WalkthroughThe send-stream notification channel now carries either a peer Priority: ⬇️ Low Merge Risk: 🟡 Moderate · up to A send stream can appear successfully closed before its FIN is written, and later closure checks can contradict an earlier success. Correct both behaviors before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to A finished stream can be reported as successfully closed before its FIN write completes. That may affect callers that rely on closure before shutting down or advancing a protocol. No new trust boundary or confirmed security exploit was established. Retained concerns
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✨ Finishing Touches✨ Simplify code
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Inline comments:
In @rs/qmux/src/session.rs:
- Around line 522-523: In transmit, retain the send state while encoding and
writing the FIN; emit SendSignal::Finished and remove the stream from
self.streams only after writer.send succeeds. If encoding or writing fails, do
not signal completion or discard the send state.
- Around line 2407-2409: Update the method containing this
`inbound_signal.recv()` match to cache when it receives `SendSignal::Finished`,
returning `Ok(())` immediately on later calls before reading the channel.
Preserve the existing handling for stop signals and channel closure.
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rs/qmux/src/session.rsrs/qmux/tests/qmux02.rs
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SendStream::closed() returned Err(Closed) once the writer put the FIN on the wire, because retiring the stream dropped the channel it waited on. The writer now signals Finished before retiring it, so closed() returns Ok(()) as the trait documents for transports without FIN acknowledgement. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A backpressured or failed write left closed() reporting success for a FIN the peer never received. Hold the stream's signal sender across the write and drop it on failure, which closed() reports as Closed. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
28fa730 to
897865b
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…() calls closed() consumed the Finished signal, so a second call saw the dropped channel and reported Closed. Cache it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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| .send | ||
| .remove(&stream.id) | ||
| .map(|send| send.inbound_signal); |
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When the FIN write is backpressured, removing the send state here creates a window before writer.send(...).await completes in which the reader can receive STOP_SENDING, but the handler at session.rs:1412-1413 cannot find the stream and silently discards it. If the write later succeeds, Finished is delivered and closed() returns Ok(()), even though the peer stopped the stream; this contradicts the SendStream::closed contract in web-transport-trait/src/lib.rs:247-254. Keep the entry addressable during the awaited write, then retire it and resolve the queued Stopped/Finished outcome after transmission.
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Addressed review feedback:
Rebased on main. (Written by Opus 5.5) |
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Problem
qmux::SendStream::closed()returnsErr(Closed)("connection closed") for every stream that finished cleanly. The writer retires a stream when it puts the FIN on the wire, which drops the channelclosed()waits on, andclosed()read the dropped channel as a dead session.web-transport-traitsays a transport without FIN acknowledgement resolves once the FIN is sent.In moq this logs
WARN failed to send goaway: transport: connection closedon every GOAWAY over WebSocket, although the peer receives it, andfailed to send setupat debug on every lite SETUP stream (moq-dev/moq#4189 follow-up).Approach
The writer sends
SendSignal::Finishedon the stream's channel before retiring it, andclosed()returnsOk(())for it. STOP_SENDING rides the same channel asSendSignal::Stopped. A dropped channel still means the session is gone.Impact
SendStream::closed()returnsOk(())after a clean FIN instead ofErr(Closed).Tests
finished_send_stream_closes_cleanly(tests/qmux02.rs) fails before the change withClosedand passes after.cargo test -p qmux --all-featuresand clippy pass.Release
Ships in the next release from
main, withweb-transport-trait0.5 and qmux 0.6.0, alongside #399 and #401. Based on currentmain, no rebase needed. moq picks it up by bumping qmux to 0.6 in moq-dev/moq#4296. Checked against moq'swebsocket_upgrades_to_quicwith the fix applied to 0.5.1: the GOAWAY and SETUP warnings are gone.(Written by Opus 5.5)
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