fix(netwatch): guard divide-by-zero in poll_recv_noq trace when stride == 0#149
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flub merged 1 commit intoMay 19, 2026
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`UdpSocket::poll_recv_noq` evaluated `meta.len / meta.stride` directly inside `trace!()` macro arguments. `noq_udp::RecvMeta.stride` is allowed to be `0` in practice on the GRO path (empty datagrams, kernel falling back to a non-segmented receive), which crashes the host process with `attempt to divide by zero` — observed on Windows 11 24H2 and macOS 15.4/26.x against netwatch 0.16.0/0.17.0. Replace the bare division with `checked_div(...).unwrap_or(0)` so the trace field reports `0` when `stride == 0` and stays identical otherwise. Closes n0-computer#148.
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May 19, 2026
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ugh, no checks were required so github merged this immediately and then all CI fails because the commit is no longer there as it was squash-merged 😭 anyway, should be fine. thanks for the PR! |
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Description
netwatch::udp::UdpSocket::poll_recv_noqevaluatesmeta.len / meta.stridedirectly insidetrace!()macro arguments.noq_udp::RecvMeta.strideis allowed to be0in practice on the GRO path (empty datagrams, kernel falling back to a non-segmented receive), which makes the trace argument panic withattempt to divide by zeroand terminate the host process — the panic originates inside a tokio task with no upstream catch.This PR replaces the bare division with
checked_div(...).unwrap_or(0), behavior-preserving for all non-zero strides (the only case currently observable) and emittingcount = 0when stride is0.Observed in production on:
across 6 distinct fatal events since 2026-05-12. Same code path is present on
mainand in published0.16.0/0.17.0.Closes #148.
Breaking Changes
None. The new expression is identical to the original for any
stride > 0. Whenstride == 0the field now reports0instead of panicking.Notes & open questions
noq_udp::RecvMeta::stridedoes not forbidstride == 0, so guarding here looks correct regardless of whether the upstreamnoq-udp/ kernel behaviour is intentional.trace!()field, and reproducingstride == 0requires either kernel/GRO state or a mockednoq_udp::State::recv. Happy to add one if a maintainer prefers; otherwise the simpler patch seemed appropriate.Change checklist