[$50 BOUNTY] [Rust] Add protocol frame codec recovery tests

[Peter7896]

Bounty: $50 (LT)

Area: backend/src/protocol/, backend/src/protocol/frame*, backend/src/protocol/validate*

Current state: Protocol validation has focused coverage, but the frame codec and decoder recovery boundaries need deterministic regression tests for malformed input and recovery after failed frames.

What's needed: Add Rust tests or helpers that validate protocol frame decode errors, state preservation, and recovery without requiring live services.

Acceptance criteria:

• Reject truncated headers, truncated payloads, and invalid frame lengths without panicking.
• Reject invalid reserved bytes or checksum-style integrity mismatches with clear errors.
• Assert a failed decode does not corrupt decoder state or accepted frame counters.
• Confirm a valid frame after invalid input can still be decoded successfully.
• Keep the tests deterministic and runnable on Windows and Unix-like hosts.

Required validation:

• Run cargo test --lib where the Rust toolchain is available
• Run python3 build.py
• Include the generated diagnostic .logd artifact from diagnostic/build-XXX.logd; also include diagnostic/build-XXX.json if present
• Use .github/pull_request_template.md for your submission

Tracker note: This issue is opened for the upstream LT bounty tracker; bounty eligibility and payout are determined by upstream review, merge, and tracker rules.

[fengyangxxx]

/attempt #2

[BERT70293]

Hey, I've put together the frame codec recovery tests for this one — the PR is up at #4.

Added 17 deterministic tests in codec.rs covering the full acceptance criteria:

• Truncated headers/payloads return Ok(None) cleanly (no panics), and truncated payloads correctly wait for more data
• Invalid magic → Err(InvalidMessage), unsupported versions → Err(UnsupportedVersion), oversized payload claims → Err(MessageTooLarge)
• Reserved bytes are now validated (must be all zeros) — previously they were silently skipped; non-zero reserved bytes now return Err(InvalidMessage); zero reserved bytes regression-tested to still work
• Failed decodes don't corrupt decoder state: after an invalid-magic error the buffer is cleared and a fresh valid frame decodes fine; after a checksum mismatch only the bad frame is drained and the next frame decodes correctly
• Valid frame after garbage interleaving / multiple invalid inputs — decoder recovers and produces the expected frame
• Partial-then-complete stream recovery (buffered reads)
• Buffer state tracking (buffered_bytes, reset), empty payloads, flags/checksum round-trips

Happy to iterate if anything needs tweaking. The tests are all plain #[cfg(test)] unit tests — cargo test --lib should cover them.

[Peter7896]

Thanks for the submissions. For this issue, the reviewable unit should stay focused on protocol frame codec recovery tests only.

A PR that bundles this with the diagnostic-redaction issue is not ready to forward as-is, because the upstream tracker needs one clearly scoped change per bounty. A bounty-ready PR also needs the exact script-generated diagnostic artifacts from python3 build.py: a matching diagnostic/build-*.json and diagnostic/build-*.logd pair in the changed files, generated by the build script.

I will review the single-purpose codec PR first. Please keep any follow-up PR scoped to this issue and reference this tracker issue clearly.

[bilalabsh]

Submitted PR #8 for this issue.

Adds regression tests around the protocol frame codec — malformed wire input (truncated headers/payloads, oversize lengths, bad reserved bytes, checksum mismatches), decoder state preservation via accepted_frames, and recovery when a valid frame follows a failed decode. Also fixes the 24-byte header mismatch in codec.rs (reserved field was 4 bytes, not 8) and rejects non-zero reserved bytes without panicking. All deterministic, no live services.

12 protocol tests passing locally:

cd backend
cargo test --lib protocol::frame_tests protocol::codec::tests
Full lib suite also green (cargo test --lib, 24/24).

Ready for upstream review when you have a chance.

[thanhle74]

I'd like to claim this bounty. Will submit a PR with the frame codec recovery tests.

[Ojas2095]

/claim

I'd like to take this on! Reviewing the repository right now and will submit a PR shortly.