# zit
[Fossil](https://fossil-scm.org)'s formats and sync protocol, reimplemented in
[Zig](https://ziglang.org) from their specifications.
zit is a library first — a Zig analog of libfossil: the delta encoding, the
artifact formats, derived repository state, and the HTTP sync protocol as a
clean, embeddable API. The `zit` binary is a thin CLI over that library.
The implementation is a direct port of four companion Internet-Drafts (frozen
reference copies in [`docs/rfcs/`](docs/rfcs/)):
| Module | RFC | What it specifies |
|--------|-----|-------------------|
| `delta` | `draft-fossil-delta-format-00` | byte-level delta encoding |
| `artifact` | `draft-fossil-artifact-format-00` | manifest / control-artifact card format, naming, checksums |
| `repostate` | `draft-fossil-repo-state-00` | derived branch / tag / leaf / current-trunk views |
| `sync` | `draft-fossil-sync-protocol-00` | HTTP sync / clone protocol |
Implementation follows the RFC dependency layering:
```
delta -> artifact -> repostate -> sync
```
## Design
The drafts are the authority, not Fossil's source. Test expectations come from
the spec text and its worked examples — every normative clause a module
implements gets a test citing its section. Fossil itself appears only in an
on-demand interop smoke check, which may confirm a spec-derived expectation but
never author one; a disagreement there means either zit misread the spec or the
spec is wrong, and the spec gets an erratum rather than the code a workaround.
No module touches ambient time, randomness, filesystem, or network; effects
arrive through injected interfaces. The sync client in particular is a pure
state machine — bytes in, bytes out — with transport supplied by the caller.
This keeps the library embeddable and makes the whole stack testable under
seeded deterministic simulation, where any failure replays exactly from its
seed.
## Scope
zit targets the **version-control substrate**: the check-in (manifest),
cluster, and tag/control artifact types. The collaboration types (wiki,
ticket, forum, attachment, technote) are carried opaquely — stored and
transported by hash, but not interpreted.
## Build
Requires Zig 0.16+.
```sh
zig build # build the `zit` binary into zig-out/bin/
zig build run -- version
zig build test # run unit tests
```
Further named steps: `zig build dst` (deterministic simulation, `--seed N` to
replay), `zig build fuzz -- <target> --seed N` (seeded fuzz targets),
`zig build bench` (benchmarks), and `zig build smoke` (interop check against a
`fossil` binary on PATH; run manually at milestones, never part of `test`).
## Source control
This project is itself under Fossil. The repository lives in `.zit.fossil`
(ignored); open a checkout with `fossil open --keep .zit.fossil`.