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punktfunk/crates
enricobuehlerandClaude Opus 4.8 dd558be55b fix(core/client): fix the four ways a speed-test probe corrupts ABR and the report tick
There is one `ProbeState` per session and no correlation id, and two independent
requesters share it: the pump's startup link-capacity probe and the embedder's
`NativeClient::request_probe` (the shipped "Test connection" in the Windows GUI
and the Linux GTK app). The startup path had a busy check, a watchdog and a
window rebase; the embedder path had none of them, and the two collide by
default — both shipped speed tests call `request_probe` on the statement right
after `connect()`, and the pump's probe fires 2 s later, inside that burst.

Four defects, one cluster:

- The pump overwrote the shared slot unconditionally. Mid-burst it drops
  `base_packets`/`base_bytes`, the pump re-snapshots them against the host's
  full-burst denominator, and the user's speed test reports roughly an order of
  magnitude low; if the result lands first instead, the reset wipes `done` and
  the embedder's poll loop never sees its own measurement. Now it defers and
  retries rather than stealing the slot.

- An unanswered embedder probe never timed out. `probe_active` gates the entire
  report tick — LossReport, the ABR window feed, the standing-latency ladder and
  a pending ClockResync all live inside it. A host that ignores ProbeRequest is
  an anticipated configuration (the startup path was given a 6 s timeout for
  exactly that) so the embedder path could latch `active` forever and silently
  switch off every adaptation mechanism for the rest of the session. Now a
  watchdog covers a probe of either origin.

- `request_probe` latched `active` before `try_send`, so a full or closed ctrl
  channel returned `Closed` to the caller while leaving the session wedged in
  the state above. It now rolls back, mirroring the startup path.

- Only the startup path rebased the ABR window past the burst. Probe filler is
  counted into `bytes_received` for every accepted datagram but never reaches
  the decoder, and the tick is suppressed for the whole burst, so the first
  post-burst window read the burst rate as `actual_kbps`. That poisons
  `proven_kbps`, a monotone high-water mark that is never decayed, which
  disables the x1.5 evidence-gated climb guard for the session and authorizes a
  climb into a rate the decoder has never carried. The rebase now happens on the
  falling edge of any probe, and covers the loss/packet anchors too so the first
  post-burst LossReport isn't divided by a filler-inflated packet count.

Also: `wants_decode_latency` advertised on two of the three terms the pump
actually requires to arm ABR, omitting `resolved_bitrate_kbps > 0`, so against
an old host that reports no rate an embedder fed decode latency to a controller
that never runs.

No wire or ABI change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-20 07:42:37 +02:00
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