fix(quic): resolve SendStream::stopped after a local reset by zshenker · Pull Request #6196 · moq-dev/moq

zshenker · 2026-10-21T17:59:52Z

Problem

quic::driver::SendStream::stopped() never resolves after a local reset(), reset_at(), or the drop reset from #5909. The driver wakes stopped waiters only on StreamEvent::Finished / StreamEvent::Stopped; a local reset produces neither, and moq-quic frees a reset stream without reporting it as finished. A pending stopped() waits until the connection closes, and its entry in the connection's stopped map lives that long. Since #5909, any stopped() future that outlives its dropped, unfinished stream hangs this way. quinn 0.11 has the same gap.

Approach

reset(), reset_at(), and the drop reset mark the stream's stopped waiters as reset, wake them, and drop their map entry.
stopped() joins the waiters when called instead of on first poll, so a reset in between still reaches it, and answers at once when the stream is already resolved or was reset through this handle, without registering a waiter.
Every event that resolves the waiters records its outcome in them, since the stream may be freed before a woken waiter polls.
It resolves Ok(None), which a fresh call already returned once the reset stream was freed; the peer's STOP_SENDING code still wins if it arrived first.
Recorded in moq-quic's "Carried changes".
stream_reset_resolves_stopped, stream_reset_at_resolves_stopped, stream_stopped_pending_across_reset, stream_reset_releases_stopped, and dropped_stream_resolves_stopped fail on main. stream_stop_before_reset_wins, stream_stop_after_reset_is_ignored, and stream_stop_survives_freed_reset pin which of a peer stop and a local reset wins. They cross real sockets, so they run on the wall clock.

Impact

quic::driver::SendStream::stopped() resolves Ok(None) after a local or drop reset instead of hanging. No signature or wire change.
quic::web::SendStream::stopped() / closed() inherit it: Ok(None) / Ok(()).

Alternatives

A new StoppedError::Reset variant. StoppedError is #[non_exhaustive], so it would not break, and it tells a local reset from a delivered finish. But quic::web would need a mapping for it, and main already answers Ok(None) for a freed reset stream, so the variant would have to cover that path too. The caller reset the stream itself, so Ok(None) ("the peer closing the stream is no longer meaningful") is honest and adds no API. Recommended: Ok(None).
Resolve when the reset is acknowledged: needs a new moq-quic event, and nothing waits on that moment; acked() already covers delivery of a reset_at prefix.
Release the waiter entry when the last stopped() future drops: a guard and refcounting, while the entry already lasts no longer than the stream.

Follow-ups

None.

(Written by Claude Opus 5.5)

The driver woke stopped() waiters only on StreamEvent::Finished or StreamEvent::Stopped. A local reset produces neither, and moq-quic frees a reset stream without an event, so a stopped() future pending across reset() or reset_at() never resolved, and its entry in the connection's stopped map stayed until the connection closed. A stopped() call after the reset also waited until the reset was acknowledged. reset() and reset_at() now flag and wake the stream's waiters and drop the entry. stopped() joins the waiters when called, not on its first poll, so a reset in between reaches it, and answers at once when the stream is already resolved or reset. The future resolves with Ok(None), as a fresh call already did once the reset stream was freed. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

A send stream dropped before finish() is now reset, which, like reset(), produces no stream event. Wake the stream's stopped() waiters there too, so a stopped() future that outlives its dropped stream resolves. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

chatgpt-codex-connector · 2026-10-21T18:00:37Z

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📝 Code Review	✅ Completed 2026-10-22T00:06:41.993824Z	`2dc536f`	New commits

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coderabbitai · 2026-10-21T18:08:12Z

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between d2d1f16 and aba1bd6.

📒 Files selected for processing: 3

rs/moq-tokio/src/quic/driver/connection.rs
rs/moq-tokio/src/quic/driver/send_stream.rs
rs/moq-tokio/src/quic/driver/tests.rs

🚧 Files skipped from review as they are similar to previous changes: 3

rs/moq-tokio/src/quic/driver/tests.rs
rs/moq-tokio/src/quic/driver/connection.rs
rs/moq-tokio/src/quic/driver/send_stream.rs

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Walkthrough

Local reset(), reset_at(), and successful drop-triggered resets now record reset state and notify stopped-stream waiters. stopped() returns the reset result, including when reset occurs before the future is polled. A prior peer STOP_SENDING code takes precedence over a later local reset. Tests cover reset timing, dropped streams, precedence, and waiter cleanup. The README documents this behavior.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to aba1b

The local-reset behavior is consistent with its documented contract, and no actionable merge-blocking issue remains.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 76.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 25 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: resolving SendStream::stopped after a local reset.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description check		The description directly explains the local-reset behavior addressed by the changes and describes the implementation, tests, impact, and alternatives.

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Inline comments:
Review comments at @rs/moq-tokio/src/quic/driver/send_stream.rs:
- Around line 303-336: Update Send::try_stop so it records a STOP_SENDING error
only when stop_reason is unset and the stream has not been locally reset, using
the existing is_reset() state check. Preserve the current stop reason when
STOP_SENDING arrives before ResetSent, and reject later stop reasons.

Review comments at @rs/moq-tokio/src/quic/driver/tests.rs:
- Line 1795: Remove start_paused = true from the five Tokio test attributes
covering the connect_self socket tests, so they execute using wall-clock time
while preserving the existing test bodies and behavior.

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rs/moq-quic/README.md
rs/moq-tokio/src/quic/driver/connection.rs
rs/moq-tokio/src/quic/driver/send_stream.rs
rs/moq-tokio/src/quic/driver/tests.rs

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moq-quic records a peer's stop code even after the stream was reset locally, so stopped() could answer Some(code) after a successful reset. A reset now records whether the peer had already stopped the stream, and stopped() answers from that record first: an earlier stop still yields its code, a later one is ignored. The socket tests run on the wall clock. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

kixelated · 2026-10-21T23:44:39Z

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chatgpt-codex-connector · 2026-10-21T23:51:30Z

+        if let Some(waiters) = self.stopped.remove(&id) {
+            let _ = waiters.reset.set(stopped);
+            waiters.notify.notify_waiters();


Preserve STOP outcomes when detaching waiters

When a stopped() future already exists and StreamEvent::Stopped is forwarded before a local reset or drop, wake_stream_notify has already removed its StopWaiters from this map. A subsequent call here therefore cannot set the detached future's reset cell; if the reset is acknowledged and moq-quic frees the send state before that future next polls, send_stream_stopped sees ClosedStream and returns Ok(None) instead of the earlier peer code. This makes the new “stop before reset wins” contract scheduler-dependent; record the STOP result in the detached waiter, or otherwise retain terminal state, when processing the event.

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Agreed, fixed in 2dc536f: every event that resolves the waiters (Stopped, Finished, local reset) now records its outcome in StopWaiters, so a waiter detached by Stopped keeps the peer code even if the reset stream is freed before it polls. stream_stop_survives_freed_reset reproduces it (fails with Ok(None) without the fix). This also drops wake_stream_notify.

(Written by Claude Opus 5.5)

…frees the stream A Stopped event detached the waiters before a later reset could record into them, so a waiter that polled after the reset was acknowledged and the stream freed saw Ok(None) instead of the peer's code. The waiters now record the outcome of every event that resolves them. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

kixelated · 2026-10-22T00:08:15Z

Merge summary:

SendStream::stopped() now resolves Ok(None) after reset(), reset_at(), or the drop reset instead of waiting for connection close, and the waiter entry is released with it. No signature or wire change.
Codex (head aba1bd66) found that a waiter detached by Stopped lost the peer code if the reset stream was freed before it polled. Fixed in 2dc536f on this branch: every event that resolves the waiters records its outcome, with regression test stream_stop_survives_freed_reset (fails on aba1bd66).
Both CodeRabbit findings were addressed in aba1bd66. Codex reviewed 2dc536f4 with no findings.
Decision kept: Ok(None) for a local reset rather than a new StoppedError::Reset variant, as argued in the description.
Local: cargo test -p moq-tokio --lib quic::driver::tests (44 passed), clippy -D warnings, and fmt are clean. Check runs in the merge queue.

(Written by Claude Opus 5.5)

zshenker and others added 2 commits October 21, 2026 11:47

zshenker marked this pull request as ready for review October 21, 2026 18:00

coderabbitai Bot reviewed Oct 21, 2026

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Comment thread rs/moq-tokio/src/quic/driver/send_stream.rs

Comment thread rs/moq-tokio/src/quic/driver/tests.rs Outdated

chatgpt-codex-connector Bot reviewed Oct 21, 2026

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kixelated enabled auto-merge October 22, 2026 00:08

kixelated added this pull request to the merge queue Oct 22, 2026

Merged via the queue into moq-dev:main with commit d2a0db3 Oct 22, 2026
3 checks passed

zshenker mentioned this pull request Oct 22, 2026

quest(m2): make the ack hook concrete in the QUIC drivers #6330

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fix(quic): resolve SendStream::stopped after a local reset - #6196

fix(quic): resolve SendStream::stopped after a local reset#6196
kixelated merged 4 commits into
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zshenker:fix/driver-stopped-after-reset

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