fix(websocket): an errno is not a verdict about the session - #41
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A socket reports `SO_RCVTIMEO` expiry and a spurious `EAGAIN` as the same error, and platforms disagree about when each happens. The deadline stream trusted the errno: outside a cancellable session, one `WouldBlock` ended the session as a timeout without asking whether the deadline had passed. The observation then said the peer ran out of time when it had seconds left. The retry that already existed for cancellable sessions now applies to every session, guarded by the clock rather than by the errno, with a millisecond pause so a socket reporting readiness it does not have waits for the deadline instead of spinning at it. A non-blocking socket reports exactly what a spurious wakeup reports, so the regression test reproduces the condition deterministically instead of waiting for a platform to produce it. Without the fix it fails in 0.00s — the same instant-timeout signature as the macOS CI failure that prompted this. The seeded oracle test now asserts the terminal cause before the exit code, so a future failure names the deadline that fired instead of only reporting that one did.
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📝 WalkthroughWalkthrough
ChangesDeadline timeout handling
Estimated code review effort: 3 (Moderate) | ~20 minutes Mergeability Score: 🔵 Low · up to The production timeout behavior is addressed, but the regression test can fail spuriously on a legal short read, making validation unreliable. The PR is otherwise mergeable with owner awareness or a small follow-up to read the full payload. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@crates/kahea-exec/src/websocket.rs`:
- Around line 3185-3187: Update the test’s payload read around deadline_stream
to use read_exact for the full four-byte “late” message, then compare the
complete buffer without relying on a single read returning all bytes.
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crates/kahea-exec/src/websocket.rs
`EINTR` says a signal arrived while a thread was blocked. It says nothing about the session: no deadline passed, no peer acted, nothing was decided. The executor mapped it straight to `cancelled`, so a stray signal ended a healthy session with exit 3 and a terminal cause claiming the caller had asked for it. This is the third reading of the same failure and the first that fits all of it. Exit 3 is `SessionTerminal::error`, which covers every error cause, not the timeouts alone — reading it as a deadline is what sent the previous two fixes after budgets and clocks. A signal explains what those could not: failures that land in milliseconds with the budget untouched, on whichever test happens to be reading, only on the noisiest runner. The deadline stream now retries a bare interruption, and the terminal cause is `cancelled` only when cancellation was actually requested. The two meanings were already conflated because `remaining` reports its own cancellation as `Interrupted`, so the flag decides, not the errno.
copyleftdev
changed the title
A single read may legally return fewer bytes than the peer sent, so the deadline test could fail on a short read for a reason it is not about. Review finding from #41.
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Fixed in 7472fa1 — the test uses I re-checked that the test still discriminates after the change: with the fix reverted it fails in 0.00s, which is the point of it. |
The diagnostic added earlier named the failure the moment it recurred: IoFailure after a session whose counters show the whole script ran. A peer that sends an acceptable close and then drops the socket resets the connection, and that reset lands on our acknowledging write. #35 made a rejected close outrank that reset and left an accepted one reporting IoFailure, calling it unchanged behaviour. It was the same mistake with the sign flipped: a session that met every expectation and received a close its plan accepts was reported as broken, on exactly the runs where the reset won the race. Whether our reply landed belongs in the transcript, not in the verdict. `close_precedence` now takes the acknowledgement and ignores it, so the signature still says out loud that it was considered.
1 participant
Two places where an errno was treated as a verdict about the session. Neither is test-only: both
change what a user is told about a session that did not fail the way the report claims.
Correction to this PR's earlier description
The first version claimed to fix the macOS failure on
main. It did not — macOS failed again on thisvery branch, on a different test. The
WouldBlockfix below is still right, but the failure had asecond cause, and the claim was wrong. That cause is now here too.
1.
EINTRreported as a cancelled sessionA signal arriving while a thread is blocked says nothing about the session: no deadline passed, no
peer acted, nothing was decided. The executor reported it as the caller having cancelled.
This is what was failing CI, and finding it required correcting an assumption I had been reasoning
from for two rounds:
exit 3isSessionTerminal::error, which covers every error cause, not thetimeouts alone. Reading exit 3 as "a deadline fired" is what sent the previous fixes after budgets
(#37) and clocks (below). A signal explains what those could not:
The two meanings were already conflated:
remaining()reports its own cancellation asInterruptedtoo. So the cancellation flag decides, not the errno. The deadline stream retries a bare
interruption;
socket_errorreportscancelledonly when cancellation was actually requested, andan interruption without it is an
io-failure.2.
WouldBlockreported as an expired deadlineSO_RCVTIMEOexpiry and a spuriousEAGAINarrive as the same error. Outside a cancellable sessionone
WouldBlockended the session as a timeout without asking whether the deadline had passed, so anobservation could report a peer out of time with seconds left. The retry that already existed for
cancellable sessions now applies to all of them, guarded by the clock, with a millisecond pause so a
socket reporting readiness it lacks waits for the deadline instead of spinning at it.
Verification
an_interrupted_syscall_is_only_cancellation_when_cancellation_was_requested— truth table overthe classification, the same shape as
close_precedencein fix(websocket): a close verdict outranks a failure to acknowledge it #35.a_would_block_before_the_deadline_is_not_a_timeout— a non-blocking socket reports exactly what aspurious wakeup reports, so the condition is deterministic. Fails in 0.00 s with the fix
reverted, which I checked rather than assumed.
scripts/gates.shgreen end to end.the cause instead of only reporting that one occurred. That gap cost two rounds here.
What this still does not prove
No local run reproduces the CI failure;
EINTRis not something I can make macOS deliver on demand.The case is that the mechanism fits every observation the other two theories contradicted, and that
the path from a signal to a verdict is gone. macOS CI is the test — and given the failure appears on
push builds whose PR runs pass, the push build on
mainafter merge is the one that counts.