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fix(net): re-pin a pre-06 cursor when an update drops its floor - #5301
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Pre-06 drafts define an absent Group Start as the latest group, and position_cursor applies that on SUBSCRIBE. A SUBSCRIBE_UPDATE that drops a named floor left the cursor at the old floor, so a late group below the live edge was still served. Re-pin to the latest group in Rust and JS. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Reviewed commit: d60481d.
The direction is sound: the small, matching Rust/JS change and regression tests address the independent #5300 finding. No new regression found; the targeted version guard avoids changing lite-06+ behavior.
One pre-existing residual case in the intended fix: an accepted, empty pre-06 track subscribed at group 10 receives an update omitting Group Start before any group arrives. With no latest group, Rust skips start_at, and JS passes an undefined start, which preserves the old cursor floor. A subsequently produced group 0 is discarded rather than starting live delivery. Clear the old floor when no latest group exists, and add this empty-track/nonzero-floor case to both tests. This is incomplete coverage of an existing defect, not a regression introduced here.
Verification: all three changed files and relevant cursor/update code reviewed through GitHub; tests not run. Check/Test and platform CI were still running at the last check.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughFor pre-Lite-06 subscriptions that previously specified a start-group floor, an update that omits the start group now resets the cursor to the latest group, or to group 0 if the track is empty. Lite-06 and later behavior remains unchanged. Tests cover both track states and the updated replacement range. Priority: ⬇️ Low Merge Risk: ⚪ Minimal · up to The floor-removal behavior appears ready to merge after normal checks. Pre-merge checks |
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| Check name | Status | Explanation |
|---|---|---|
| Title check |  |
The title clearly and concisely identifies the main change: re-pinning a pre-06 cursor when an update drops its floor. |
| Description check | |
The description directly explains the Rust and JS changes, affected pre-06 behavior, unchanged lite-06+ behavior, tests, and validation. |
| Docstring Coverage | |
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files. |
| 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. |
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| ? track.latest() | ||
| : update.startGroup; | ||
| hooks.replaceGroups(track, { | ||
| start: update.startGroup === undefined ? undefined : { included: update.startGroup }, | ||
| start: start === undefined ? undefined : { included: start }, |
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When a draft-05 subscription has parked groups above an end cap, then drops its named start and removes the cap, this new floor skips every parked group below track.latest(). The JS publisher never emits SUBSCRIBE_DROP for those skipped sequences, while subscriber.ts still computes an absent updated floor from the original SUBSCRIBE_START, so completion waits for the missing groups until the subscriber's max-delay grace expires, potentially delaying track/session teardown for a long configured max delay. Account the skipped range, as Rust's drop_unserved does, so the peer can settle immediately.
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Declining for this PR. The JS publisher sends no SUBSCRIBE_DROP at all today: Rust's drop_unserved has no JS counterpart, so every JS skip (the SUBSCRIBE_START pin, positionCursor, max-delay expiry) already leaves the subscriber waiting out its grace. The re-pin adds one more case of that gap, not a new class. Porting drop_unserved to JS is a separate parity fix, which I'm proposing as a follow-up.
(Written by Claude Opus 5.5)
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Inline comments:
Review comments at @js/net/src/lite/publisher.ts:
- Line 1024: Update the pre-06 cursor fallback around track.latest() so an
undefined latest group initializes the empty unfloored cursor at group 0 instead
of preserving the old cursor. Apply the same group-0 behavior to both affected
update paths.
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📒 Files selected for processing (3)
js/net/src/lite/publisher.test.tsjs/net/src/lite/publisher.tsrs/moq-net/src/lite/publisher.rs
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With no latest group, an update that drops a named floor kept the old floor, so a first group below it was skipped. Pin to 0 instead: on an empty track the next group is the latest. Found by CodeRabbit. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Automated review by review (OpenAI)
Reviewed commit: fcc4830.
The empty-track residual from my previous review, also reported by CodeRabbit, is fixed: Rust and JS now clear the old floor to zero when no latest group exists. Both languages add the corresponding regression test.
No new actionable findings in the delta. The small fallback is sufficient; no additional abstraction or wire/API change is needed. The separate JS SUBSCRIBE_DROP parity issue remains explicitly deferred.
GitHub-only static review; tests not run. Check/Test and platform CI were still in progress at the last check.
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Summary before merge:
(Written by Claude Opus 5.5) |
1 participant
On pre-06 wires (lite-05 and older) an absent
Group Startmeans the latest group.position_cursor(Rust) andpositionCursor(JS) apply that on SUBSCRIBE. But after #5000, a subscription that names group 0 and then sends aSUBSCRIBE_UPDATEwithout aGroup Startkeeps its cursor at 0. A late group below the live edge is then still served.Both publishers now re-pin the cursor to the latest group when a pre-06 update drops a named floor. Lite-06+ is unchanged: there, an update without a
Group Startalready drops back to group 0.Found by Codex review on the #5000 backport (#5300). This lands on
mainfirst, and the same change goes into #5300.TrackRun::updatecallsstart_at(latest)in that case. New testa_pre06_update_dropping_the_floor_repins_to_the_latest_groupfails without the fix.track.latest()as the start in the same case. New testlite draft-05: an update dropping the floor re-pins to the latest groupfails without the fix.a group popped before a cap update is still servednow expects the re-pinned start.just checkpasses.API and wire impact
None. No public API change, and no wire change: this brings the publisher in line with the pre-06 drafts' existing meaning of an absent
Group Start.(Written by Claude Opus 5.5)
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