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docs: correct rsync-parity claims and stale facts (#297)
Reclassify every rsync-compatibility row as parity / caveat / divergent
(replacing the misleading 143-OK / 0-divergence summary), and document the
protocol 2.23.0 behavior:

- Split the conflated `-M, --preserve` row: `-M` is `--remote-option`,
  `--preserve` is the FastSync `-p`+`-t` alias.
- Fix `MAX_CONNECTION_MEMORY` (256 MiB, not 1 GB), `--rsync-path`
  (client-only, never crosses the wire), and the `-p` mode behavior
  (strict rsync parity; no masking).
- `--specials` now recreates sockets, so `-D` is real parity; fake-super
  records the resolved owner and replays mode/time (never real-chowns).
- Document short options/clustering, checksum/compression choices, seed
  randomization, timeout/max-alloc defaults, temp-dir confinement + EXDEV,
  identity/map parity, verbatim symlinks, delete scoping, `--max-delete`
  partial + exit 25, `--chmod`, output caveats, and server `--port`.
- Bump version refs to 2.23.0 and add the 2.23.0 CHANGELOG entry.

Docs-only; no source changes.
2026-09-16 01:48:13 +02:00

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Markdown

# FastSync — Session Handoff (2026-09-14)
## Current status
- **Release `v2.21.0`** tagged (`919a729`, "Release v2.21.0"); full CI green
(run 552: lint, build-and-test, ASan, UBSan, fuzz-build, coverage, valgrind).
`dev` has the release commit plus later doc-only merges (a README refresh and
this handoff).
- **Release PR #284 (`dev` -> `main`)** open, CI green (run 553).
`main` is protected: it needs review/approval to merge.
https://gitea.tap-tap.win/TapTap/FastSync/pulls/284
- **`PROTOCOL_VERSION` = `"2.23.0"`** (`src/shared/config.h`); CMake
`project(FastFileTransfer VERSION 2.23.0)`.
- Working tree clean; no wave worktrees remain.
## What landed this session
1. **Wave 8 (refactors):** Config X-macro wire table; single-owner `authorized_root`;
daemon per-module/per-host caps + cross-process auth lockout (`daemon_limits.[ch]`);
`Data` charge returns to its owning `ProtocolSession`.
2. **Wave 9 (protocol 2.21.0):** optional `STATUS_ERROR_DETAIL` rejection reasons;
server-contacting `--dry-run` (`STATUS_DRY_RUN_TRANSFER`, receiver mutates nothing).
3. **Security wave:** ran 5 parallel audits (wire parsing; daemon/transport/TLS/auth;
receiver confinement; client/CLI/SSH; crypto/memory/limits). Fixed all HIGH and the
confirmed MEDIUMs:
- SSH `-o ProxyCommand=…` argument injection (RCE) — reject leading `-`, insert `--`.
- Truncated zstd frame infinite CPU loop (remote DoS).
- FIFO receiver opens lacked `O_NONBLOCK` (indefinite hang).
- `--inplace` could write a FIFO/device (bypass of `--write-devices` gate).
- `--force` not gated by server `--allow-delete`.
- Privileged standalone server defaulted super activities on; added `--allow-super`
(never honored with `--stdio`).
- `--dry-run` content/hash oracle on `read only`/basis files removed.
- Empty `hosts allow`/`deny`/`auth users` now rejected.
- TLS: AEAD-only 1.2 + server preference, TOCTOU-safe key load, IP-SAN verify,
CN-truncation guard. Glob backtracking bounded; line reads bounded; ACL xattrs
gated on `--acls`; decompression/chunk memory charged; pre-auth `basis_count`
NULL-deref fixed.
4. **Tooling:** benchmark accuracy (data mix, verification, percentiles, `tc`,
`build-bench/`, `--warm` mode); `shell.nix` full toolchain and no build-on-entry;
docs state push-only / remote-source unsupported.
5. **Preserve-attribute split (protocol 2.22.0)** landed on `feat/preserve-attr-split`: per-attribute `-p/-t/-o/-g` + `--no-*` negations, `-a` = `-rlptgoD`, and the 2.21.0 → 2.22.0 wire bump.
6. **Rsync-parity wave (protocol 2.23.0)** on `feat/rsync-parity`: rsync short options/clustering/attached values (`-r`/`-b`/`-L`/`-B`, `-av`, `-aAX`, `-B1000`, `-essh`, `-MOPT`), `-c` checksum quick-check, `--checksum-choice`/`--compress-choice` validation and seed randomization, rsync timeout/max-alloc defaults, temp-dir confinement + `EXDEV` fallback, ownership/mapping parity (numeric-ids modifier, map ranges/`*`/empty-FROM, `--chown`+map conflicts, fake-super resolved-owner record), verbatim symlink storage with rsync `--safe-links`/`--munge-links`, socket recreation under `--specials`, `--chmod` 3.4.1 semantics, and delete scoping + `--max-delete` partial/exit-25. Wire: appended delete-manifest synchronized-directory section and `STATUS_DELETE_LIMIT`.
## Next steps
1. **Merge PR #284** (`dev` -> `main`) once reviewed (protected branch).
2. **Deferred security items** (documented, not implemented):
- Pre-auth config/daemon-auth handshake has no aggregate wall-clock deadline
(per-message timeout only) — slowloris holds connection slots.
- Per-source registry fails open when the shared table is full (per-module/global
caps and host ACLs still apply); consider fail-closed or larger/evicting table.
- SCRAM-like daemon auth has no TLS channel binding (and is not RFC 5802).
- `cleanup()` signal handler calls non-async-signal-safe teardown; daemon `umask(0)`.
- Wire protocol assumes homogeneous word size/endianness (lengths are native
`size_t`) — document or move to fixed-width framing.
3. **Out of scope / intentional:** pull (remote source) mode is **not** planned —
FastSync is push-only; see `RSYNC_COMPAT.md#direction`.
## Key facts / commands
- CI image: `gitea.tap-tap.win/taptap/fastsync-ci:v11` (alias `fastsync-ci:local`).
- Build/test: `cmake -B build -S . -DSTRICT_WARNINGS=ON && cmake --build build -j$(nproc) && ./build/tests`
then `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"`.
- Dev shell: `nix-shell` (provides clang-format, cppcheck, pytest-xdist, openssh,
rsync, iproute2, valgrind, lcov; does not build on entry).
- Gitea API token: supplied out-of-band via the `TOKEN` environment variable; it is
intentionally **not** recorded in this file.
- CI polling: `GET /api/v1/repos/TapTap/FastSync/actions/runs?limit=N`, match `head_sha`,
then `/actions/runs/<id>/jobs`.