---
id: review-002-ws13-idle-progress
name: Idle deadline off demux progress + slow-legitimate-stream decision (WS-13)
status: completed
depends_on: []
scope: moderate
risk: high
impact: component
level: implementation
tags: [websocket, review-002]
---

## Description

Review 002 WS-13 [major]. The WS-01 remediation's idle timer
(`byte_adapter.rs:229-244`) wraps only the next-message await, so it
fails in both directions:

1. **The attack it exists for defeats it.** WS-01's dribble (declare a
   16 MiB chunk, deliver one byte per WS message per minute) keeps
   arriving messages → the deadline resets on every dribble → the demux
   still parks forever with the partial chunk. The doc (:117) claims
   "a peer that drips bytes cannot park the single demux loop longer
   than this without traffic" — under the actual attack the peer
   supplies traffic forever.
2. **Legitimate slowness is killed.** A >60 s-silent-but-alive session
   (long handler compute, quiet subscription) is disconnected with
   1001 mid-flight — no ping/pong keepalive exists, and chunk progress
   does not reset the timer.

The existing test (`idle_read_timeout_resets_on_traffic`) enshrines
reset-on-message as correct — it codifies the gap.

## Acceptance Criteria

- [ ] Decide + implement the progress semantics: the deadline resets
      on **demux progress** (bytes actually forwarded into `read_tx`),
      not message arrival — a peer that dribbles a chunk forever hits
      the deadline; a peer delivering complete chunks (even slowly
      per-message but productively) keeps the connection
- [ ] Decide + document the legitimate-silence stance (choose one and
      record it in the module doc + http-server/websocket.md):
      (a) add WS ping/pong keepalive so app-silence ≠ transport-silence,
      or (b) document that 60 s of *no progress* is an intentional
      eviction line even for silent subscriptions
- [ ] Acceptance test 1: chunk header `[ch][len=N]` dribbled in small
      messages with per-message gaps < timeout → connection closed
      (progress deadline fires)
- [ ] Acceptance test 2: scaled-down silent-but-alive session with a
      pending response is NOT disconnected when the knob's spirit says
      it should survive (e.g. messages flowing that make progress)
- [ ] The WS-01 knob surface (`with_ws_idle_timeout`) is unchanged;
      the semantics change is doc'd against it
- [ ] `cargo test`, `cargo clippy --all-targets -- -D warnings`,
      `cargo fmt --check` pass (tungstenite-path unit tests + one axum
      integration mirror)

## References

- docs/reviews/002-post-remediation-review.md (Part B', WS-13; Part G', COV-11b — the knob is currently untested on the axum path too)
- src/websocket/byte_adapter.rs:117 (doc claim), :229-253 (the timer), :782-1206 (tests)
- tasks/websocket/review-001-ws-session-limits.md (the WS-01 knob work)
- docs/architecture/websocket.md

## Notes

Highest-risk task in the batch (touching the shared pump's read loop —
the same loop the cap logic lives in). Slice suggestion: (1) progress
tracking + tests on the tungstenite path, (2) doc/keepalive decision,
(3) axum integration mirror. Coordinate with
review-002-con18b-ws-polish (same file) — sequence, don't parallelize.
If (a)-keepalive is chosen, note it interacts with FWD-15's
server-side keep-alives on the *HTTP* SSE path — different layers, but
document both in the same doc pass.

## Summary

Idle deadline resets on completed inbound chunks (InboundChunkProgress observer), not message arrival; decision (b) documented - no WS keepalive, 60s no-progress eviction is intentional (pong is attacker-equivalent traffic). Tungstenite unit + axum integration tests; knob surface unchanged.