---
id: review-001-sse-parser
name: Incremental byte-level SSE parser (FWD-06)
status: pending
depends_on: []
scope: narrow
risk: high
impact: component
level: implementation
tags: [adapters, review-001]
---

## Description

Review 001 finding FWD-06 — silent subscription data loss, empirically
verified: `parse_sse_frames` (`src/adapters/forward.rs:409-417`) keeps
only the *last* line of each TCP chunk and discards any pending
multi-line `data_buffer`, so a chunk ending exactly at `data: …\n`
(blank line not yet arrived) silently loses the event. Verified: chunks
`"data: {\"n\":1}\n"` + `"\ndata: {\"n\":2}\n\n"` yield only event 2.
Single-chunk delivery (as in the tests) works, which is why the suite
passes.

Additional defects in the same parser: per-chunk `String::from_utf8_lossy`
(`:357`) corrupts multi-byte characters split at a chunk boundary (JSON
parse failure → event degraded to raw string); the trailing partial line
has no length cap (unbounded buffering); an event pending at EOF is
dropped (SSE says dispatch at EOF). For a subscription forwarder this is
silent data loss with no error signal.

Fix: an incremental **byte-level** parser carrying buffer state across
chunks (decode UTF-8 once over the reassembled buffer, not per chunk).

## Acceptance Criteria

- [ ] Multi-chunk test: event split across two TCP chunks is delivered (the review's empirically-verified case — the acceptance gate)
- [ ] Split multi-byte UTF-8 across chunks parses (test)
- [ ] Pending event dispatched at EOF; trailing partial line length-capped (tests)
- [ ] Existing single-chunk SSE tests unchanged and green
- [ ] `cargo test` and `cargo clippy --all-targets -- -D warnings` pass

## References

- docs/reviews/001-initial-implementation-review.md (Part D, FWD-06; Part I, COV-01)

## Notes

> Agent fills during implementation. Parser rewrite is isolated
> from the response-decode fixes (content-type, size caps, error bodies)
> in review-001-response-decoding so the delicate stateful rewrite lands
> alone. Same file — sequence or coordinate.

## Summary

> Filled on completion.