# TODO: mfer 1.0

## Design Questions

*sneak: please answer inline below each question. These are preserved for posterity.*

### Format Design

**1. Should `MFFileChecksum` be simplified?**
Currently it's a separate message wrapping a single `bytes multiHash` field. Since multihash already self-describes the algorithm, `repeated bytes hashes` directly on `MFFilePath` would be simpler and reduce per-file protobuf overhead. Is the extra message layer intentional (e.g. planning to add per-hash metadata like `verified_at`)?

> *answer:*

**2. Should file permissions/mode be stored?**
The format stores mtime/ctime but not Unix file permissions. For archival use (ExFAT, filesystem-independent checksums) this may not matter, but for software distribution or filesystem restoration it's a gap. Should we reserve a field now (e.g. `optional uint32 mode = 305`) even if we don't populate it yet?

> *answer:*

**3. Should `atime` be removed from the schema?**
Access time is volatile, non-deterministic, and often disabled (`noatime`). Including it means two manifests of the same directory at different times will differ, which conflicts with the determinism goal. Remove it, or document it as "never set by default"?

> *answer:*

**4. What are the path normalization rules?**
The proto has `string path` with no specification about: always forward-slash? Must be relative? No `..` components allowed? UTF-8 NFC vs NFD normalization (macOS vs Linux)? Max path length? This is a security issue (path traversal) and a cross-platform compatibility issue. What rules should the spec mandate?

> *answer:*

**5. Should we add a version byte after the magic?**
Currently `ZNAVSRFG` is followed immediately by protobuf. Adding a version byte (`ZNAVSRFG\x01`) would allow future framing changes without requiring protobuf parsing to detect the version. `MFFileOuter.Version` serves this purpose but requires successful deserialization to read. Worth the extra byte?

> *answer:*

**6. Should we add a length-prefix after the magic?**
Protobuf is not self-delimiting. If we ever want to concatenate manifests or append data after the protobuf, the current framing is insufficient. Add a varint or fixed-width length-prefix?

> *answer:*

### Signature Design

**7. What does the outer SHA-256 hash cover — compressed or uncompressed data?**
The review notes it currently hashes compressed data (good for verifying before decompression), but this should be explicitly documented. Which is the intended behavior?

> *answer:*

**8. Should `signatureString()` sign raw bytes instead of a hex-encoded string?**
Currently the canonical string is `MAGIC-UUID-MULTIHASH` with hex encoding, which adds a transformation layer. Signing the raw `sha256` bytes (or compressed `innerMessage` directly) would be simpler. Keep the string format or switch to raw bytes?

> *answer:*

**9. Should we support detached signature files (`.mf.sig`)?**
Embedded signatures are better for single-file distribution. Detached `.mf.sig` files follow the familiar `SHASUMS`/`SHASUMS.asc` pattern and are simpler for HTTP serving. Support both modes?

> *answer:*

**10. GPG vs pure-Go crypto for signatures?**
Shelling out to `gpg` is fragile (may not be installed, version-dependent output). `github.com/ProtonMail/go-crypto` provides pure-Go OpenPGP, or we could go Ed25519/signify (simpler, no key management). Which direction?

> *answer:*

### Implementation Design

**11. Should manifests be deterministic by default?**
This means: sort file entries by path, omit `createdAt` timestamp (or make it opt-in), no `atime`. Should determinism be the default, with a `--include-timestamps` flag to opt in?

> *answer:*

**12. Should we consolidate or keep both scanner/checker implementations?**
There are two parallel implementations: `mfer/scanner.go` + `mfer/checker.go` (typed with `FileSize`, `RelFilePath`) and `internal/scanner/` + `internal/checker/` (raw `int64`, `string`). The `mfer/` versions are superior. Delete the `internal/` versions?

> *answer:*

**13. Should the `manifest` type be exported?**
Currently unexported with exported constructors (`New`, `NewFromPaths`, etc.). Consumers can't declare `var m *mfer.manifest`. Export the type, or define an interface?

> *answer:*

**14. What should the Go module path be for 1.0?**
Currently mixed between `sneak.berlin/go/mfer` and `git.eeqj.de/sneak/mfer`. Which is canonical?

> *answer:*

---

## Implementation Plan

### Phase 1: Foundation (format correctness)

- [ ] Delete `internal/scanner/` and `internal/checker/` — consolidate on `mfer/` package versions; update CLI code
- [ ] Add deterministic file ordering — sort entries by path (lexicographic, byte-order) in `Builder.Build()`; add test asserting byte-identical output from two runs
- [ ] Add decompression size limit — `io.LimitReader` in `deserializeInner()` with `m.pbOuter.Size` as bound
- [ ] Fix `errors.Is` dead code in checker — replace with `os.IsNotExist(err)` or `errors.Is(err, fs.ErrNotExist)`
- [ ] Fix `AddFile` to verify size — check `totalRead == size` after reading, return error on mismatch
- [ ] Specify path invariants — add proto comments (UTF-8, forward-slash, relative, no `..`, no leading `/`); validate in `Builder.AddFile` and `Builder.AddFileWithHash`

### Phase 2: CLI polish

- [ ] Fix flag naming — all CLI flags use kebab-case as primary (`--include-dotfiles`, `--follow-symlinks`)
- [ ] Fix URL construction in fetch — use `BaseURL.JoinPath()` or `url.JoinPath()` instead of string concatenation
- [ ] Add progress rate-limiting to Checker — throttle to once per second, matching Scanner
- [ ] Add `--deterministic` flag (or make it default) — omit `createdAt`, sort files

### Phase 3: Robustness

- [ ] Replace GPG subprocess with pure-Go crypto — `github.com/ProtonMail/go-crypto` or Ed25519/signify
- [ ] Add timeout to any remaining subprocess calls
- [ ] Add fuzzing tests for `NewManifestFromReader`
- [ ] Add retry logic to fetch — exponential backoff for transient HTTP errors

### Phase 4: Format finalization

- [ ] Remove or deprecate `atime` from proto (pending design question answer)
- [ ] Reserve `optional uint32 mode = 305` in `MFFilePath` for future file permissions
- [ ] Add version byte after magic — `ZNAVSRFG\x01` for format version 1
- [ ] Write format specification document — separate from README: magic, outer structure, compression, inner structure, path invariants, signature scheme, canonical serialization

### Phase 5: Release prep

- [ ] Finalize Go module path
- [ ] Audit all error messages for consistency and helpfulness
- [ ] Add `--version` output matching SemVer
- [ ] Tag v1.0.0