84 lines
3.3 KiB
Markdown
84 lines
3.3 KiB
Markdown
# T2.4 — Relay conformance: Tier A (bitrate ceiling)
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**Status:** Pending Review
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**Agent:** Kimi Code CLI
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**Started:** 2026-05-11T17:20Z
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**Completed:** 2026-05-11T17:35Z
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**Commit:** 846c98e
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**PRD:** ../PRD-relay-conformance.md
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## What I changed
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- `crates/wzp-relay/src/conformance.rs` (new) — Conformance meter + violation enum:
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- `Violation` enum: `BitrateExceeded`, `PacketRateExceeded`, `TimestampDrift`.
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- `ConformanceMeter` with 1-second sliding window tracking `bytes_in_window`.
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- `ceiling_bps(codec)` — `nominal * 3 * 115 / 100` with floor of 2 kbps.
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- `observe()` returns `Err(Violation::BitrateExceeded)` when window bytes exceed `ceiling_bps / 8`.
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- `crates/wzp-relay/src/lib.rs` — Added `pub mod conformance;`.
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- `crates/wzp-relay/src/metrics.rs` — Added `conformance_violations: IntCounterVec` (label: `violation_type`).
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- `crates/wzp-relay/src/room.rs` — Wired `ConformanceMeter` into both forwarding loops:
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- `run_participant_plain` and `run_participant_trunked` each create a per-participant meter.
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- On violation: logs `tracing::warn!` + bumps Prometheus counter.
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- **Observe-only** — packets are never dropped.
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- `crates/wzp-client/src/featherchat.rs` — Added missing `TransportFeedback` match arm (back-fill from T2.1).
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## Why these choices
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Using a plain struct with `&mut self` (no atomics/mutex) is correct because each participant runs in exactly one async recv task. The meter is never shared across threads.
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The `* 3` factor accounts for FEC 2.0 (200% overhead = 3× total bitrate). The `* 115 / 100` adds a 15% safety margin. The 2 kbps floor prevents `ComfortNoise` (0 bps nominal) from having a zero ceiling.
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## Deviations from the task spec
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- Task example shows `parking_lot::Mutex<Instant>`. We don't have `parking_lot` in the relay crate, and it's unnecessary for a single-threaded async loop. Used plain `Instant` field instead.
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## Verification output
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```bash
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$ cargo test -p wzp-relay conformance
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running 4 tests
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test conformance::tests::bitrate_exceeded_for_opus24k ... ok
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test conformance::tests::ceiling_bps_floor ... ok
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test conformance::tests::small_packets_stay_within_ceiling ... ok
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test conformance::tests::window_resets_after_one_second ... ok
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test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 76 filtered out; finished in 0.00s
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```
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```bash
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$ cargo test -p wzp-relay
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running 86 tests
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...(all 86 pass)...
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test result: ok. 86 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s
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```
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## Test summary
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- Tests added: 4
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- `bitrate_exceeded_for_opus24k` — 1 MB/s payload declared as Opus24k correctly returns `BitrateExceeded`
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- `small_packets_stay_within_ceiling` — 100 small packets stay under limit
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- `window_resets_after_one_second` — window rollover works
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- `ceiling_bps_floor` — ComfortNoise gets 2 kbps floor
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- Tests modified: 0
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- `wzp-relay` test count: 86 (was 82 before T2.4)
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- `cargo clippy -p wzp-relay --lib`: pass (no new warnings)
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- `cargo fmt --all -- --check`: pass
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## Risks / follow-ups
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- Tier B (packet-rate) and Tier C (timestamp drift) are reserved for T2.5.
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- Currently observe-only. Future tasks may add drop/throttle behavior.
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## Reviewer checklist (filled in by reviewer)
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- [ ] Code matches PRD intent
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- [ ] Verification output is real
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- [ ] No backward-incompat surprises
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- [ ] Tests cover the new behavior
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- [ ] Approved
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