fix(net): settle an unanswered lite fetch when the subscriber closes - #4357
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Lite has no FETCH_OK, so fetchGroup waits for the publisher's first byte or FIN. A publisher that never answers held the caller forever, and Subscriber.close() left the pending fetch groups and their streams open. Close every in-flight fetch group from Subscriber.close(), with the session's error or SessionClosed on a deliberate close, and race the TRACK_INFO and acceptance waits against the group closing so the waiting callers reject and the FETCH stream is reset. Follow-up to #4221. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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MERGE Positive improvement, worth the complexity, and the chosen approach is the right one for this bug. WhyLite ComplexityNet +~18 lines in Notes (non-blocking)
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| await drainUntil(() => streams.length === 2); | ||
| await new Promise((resolve) => setTimeout(resolve, 0)); |
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The zero-delay timer makes this regression test scheduler-dependent and does not prove that #runFetch has reached its unanswered response wait before close() runs. Under a different stream scheduler, the test can close during request setup and pass without exercising the bug it claims to cover. Have the fake writable signal when the FETCH request has been written, then close the subscriber; this also follows the repository requirement that unit tests not depend on wall-clock sleeps.
AGENTS.md reference: AGENTS.md:L18-L19
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Fixed in 521999e. The fake session's readables use highWaterMark 0, so pull() fires only when the subscriber blocks on a read; the test awaits that (reader.done() on the FETCH stream) before closing. No timers.
(Written by Opus 5.5)
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| const info = await this.#trackInfo(broadcast, track); | ||
| const info = await untilClosed(group, this.#trackInfo(broadcast, track)); |
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If TRACK_INFO completes while the peer has exhausted its bidirectional-stream credit, execution leaves this guarded wait and blocks in the following Stream.open; closing the subscriber only closes group, so entry.accepted remains pending until the stream-open timeout, and the same gap exists during request writes. Race the remaining setup stages against group.closed as well, aborting any stream that opens after cancellation, so Subscriber.close() actually settles the fetch promptly in every setup phase.
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Fixed in 521999e. The whole setup (TRACK_INFO, Stream.open, FETCH writes, acceptance) is now one promise raced against the group closing, so a parked open no longer holds callers. Both streams run through a new #exchange helper that resets them on Subscriber.close(), including one that opens after the close. Regression test covers the parked-open stage.
(Written by Opus 5.5)
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. Walkthrough
Priority: ➖ Normal Merge Risk: 🟡 Moderate · up to Closing a subscriber can still leave streams or fetch callers waiting. Address these closure paths before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The fix releases callers waiting for an unanswered fetch. A fetch requested after the subscriber closes can still start new work, although normal connection shutdown also closes the transport. The resulting risk appears limited, but the close lifecycle is not fully contained. Retained concerns
Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
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Actionable comments posted: 3
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @js/net/src/lite/subscriber.ts:
- Around line 1149-1150: Update Subscriber.fetchGroup to check #closed before
creating a group or starting TRACK_INFO lookup, and reject with the existing
session close error when the subscriber has been closed. Keep fetch behavior
unchanged while the subscriber is open.
- Line 769: Update the FETCH setup in `#runFetch` so `Stream.open` and the FETCH
writes are raced against group closure, not just the later `untilClosed` wait;
if a stream opens after closure wins, abort it. Ensure closure settles
`#runFetch` and callers awaiting `entry.accepted` even when opening or writing
is blocked.
- Line 757: Update the flow around untilClosed and #trackInfo so closing the
group cancels the associated TRACK stream, even if the stream opens after
closure. Ensure the cancellation also unblocks a pending TrackInfo.decode when
TRACK_INFO is never received.
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Setup exchanges (TRACK and FETCH streams) now run through #exchange, which resets the stream when Subscriber.close() fires, including a stream that opens after the close, and refuses to open once closed. The whole fetch setup, including a parked stream open, is raced against the group closing. Tests wait on an observable read instead of a timer. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Merge summary
(Written by Opus 5.5) |
1 participant
Follow-up to #4221, addressing the unanswered CodeRabbit finding (#4221 (comment)).
Problem
Lite has no FETCH_OK, so
fetchGroupwaits for the publisher's first byte or FIN before resolving. That wait had no cancel path: a publisher that never answers held every caller forever, andSubscriber.close()left#fetchesand their TRACK/FETCH streams open. A fetch started afterclose()also opened new streams and could hang.Approach
Subscriber.close(err)aborts its#closedsignal witherr, or aSessionClosedstream error on a deliberate close, and closes every in-flight fetch group with it. A fetch cut off by the session is incomplete, so it never ends cleanly.#exchangehelper: it refuses to open once closed, resets its stream whenclose()fires mid-exchange, and resets a stream that opens after the close.#runFetchraces the whole setup (TRACK_INFO, stream open, FETCH writes, acceptance) against the group closing, so callers reject with the group's error at any stage, even while an open is parked on stream credit.This matches Rust
moq-net:FetchServeRunlives in the track's task set, so a closing session drops the pendinggroup::Request, which rejects every joinedfetch_groupwithError::Dropped.query()and subscribe setup share#trackInfo, so their TRACK streams are now also reset on close instead of waiting for the transport.Test
Driven over a fake session that never fails its streams, so only
close()can end a wait. Readables usehighWaterMark: 0, so the test waits on the subscriber actually blocking on a read rather than a timer.closing the subscriber rejects a fetch waiting on ...the TRACK_INFO, the FETCH (deliberate close and session error), and a parked stream open. Each asserts the error and that the stuck stream is reset.a fetch started after the subscriber closes rejects without opening a stream.The TRACK_INFO, parked-open, and post-close cases hang without the fix.
Impact
fetchGroupstill returnsPromise<GroupConsumer>; it now rejects when the subscriber closes instead of hanging.Alternatives
Stream.openand the writes, and leaked the TRACK stream.Follow-ups
A caller still cannot abandon a single pending fetch while the session stays up:
fetchGroupreturns a bare promise with no cancel handle. Rust gets this by dropping the future. Adding it would be a public API change (for example anAbortSignalinFetchGroupOptions), so it is left for a separate decision.(Written by Opus 5.5)
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