# Kvitt server

The Rust backend of Kvitt (SPEC §6.3): one Cargo workspace with three crates.

| Crate | Kind | Contents |
|---|---|---|
| `crates/kvitt-domain` | library, no I/O | Split, balance, allocation and settlement rules (SPEC §9.1, §9.3, §9.4, §14.5) and `next_occurrence_date` with the day clamping of §9.5. Passes every vector in `contracts/test-vectors/`. |
| `crates/kvitt-server` | binary `kvitt-server` plus `lib.rs` | Config, SQLite pool and migrations, HTTP API, auth, CLI. |
| `crates/kvitt-import` | binary `kvitt-import` | Splitwise importer (SPEC §10.8, milestone M9). In M2a it prints its usage and exits 2. |

The Rust toolchain is pinned in `rust-toolchain.toml` (rustup installs it on first use); `Dockerfile` uses the same
version.

## Run locally

```sh
cd server
KVITT_DATA_DIR=./data KVITT_PUBLIC_URL=http://localhost:8080 cargo run -p kvitt-server -- serve
# or, from server/crates/kvitt-server, where the package is implied:
KVITT_DATA_DIR=../../data cargo run -- serve
curl -s http://localhost:8080/health
```

`cargo run -- serve` without `-p` works from `crates/kvitt-server/`; at the workspace root Cargo needs
`-p kvitt-server` because the workspace has two binaries.

Configuration is environment variables only (SPEC §10.4, exhaustive):

| Variable | Default | Meaning |
|---|---|---|
| `KVITT_DATA_DIR` | `/data` | Holds `kvitt.sqlite` (+ `-wal`, `-shm`), `pictures/`, `apk/`. Created if missing. |
| `KVITT_BIND` | `0.0.0.0:8080` | Listen address. |
| `KVITT_PUBLIC_URL` | `https://icehack.asuscomm.com:8443` | Base URL in invite links and the landing page. |
| `KVITT_FCM_CREDENTIALS` | `/secrets/fcm-service-account.json` | FCM key; missing file = push disabled (warning at start). |
| `KVITT_FCM_PROJECT_ID` | `kvitt-1337` | FCM project. |
| `KVITT_TRUSTED_PROXY` | `caddy` | Host allowed to set `X-Forwarded-For`; a name that does not resolve means no proxy. |
| `RUST_LOG` | `info` | tracing filter; logs are JSON lines on stdout. |

The default data directory `/data` is the container volume. When running outside Docker, set `KVITT_DATA_DIR`
(for example `./data`, which `server/.gitignore` keeps out of git); the
database is then `$KVITT_DATA_DIR/kvitt.sqlite`. Every connection uses WAL, `foreign_keys = ON`,
`synchronous = NORMAL`, `busy_timeout = 5000` (SPEC §8.9). `serve` and `migrate` run the embedded migrations
(`crates/kvitt-server/migrations/`, `0001_init.sql` byte-identical to `contracts/schema/server-v1.sql`).

## Subcommands

`kvitt-server <command>` (SPEC §10.4, exhaustive):

| Command | State in M2a | Exit codes |
|---|---|---|
| `serve` | Works: migrations, `tasks::start`, HTTP server; SIGTERM drains in-flight requests for up to 10 s. | 0 on clean shutdown |
| `migrate` | Works: migrations only. | 0 |
| `healthcheck` | Works: `GET http://127.0.0.1:<port of KVITT_BIND>/health`, used by the compose healthcheck (no curl in the image). | 0 if 200, else 1 |
| `bootstrap` | Prints `not implemented in M2a` (M3). | 2 |
| `pair-device --user <user_id>` | Prints `not implemented in M2a` (M3). | 2 |
| `rotate-epoch` | Prints `not implemented in M2a` (M4). | 2 |

## HTTP API

Every route of SPEC §7 is registered in `src/router.rs`. `GET /health` (E-1) and `GET /setup/status` (E-2) are
implemented; every other handler returns 501 `not_implemented` until M3 (E-3 to E-30, E-33) and M4 (E-31, E-32)
fill in the body in their own `src/api/*.rs` file. The rules of SPEC §14.3.1 are layers in `router.rs`:
`X-Kvitt-Protocol: 1` on authenticated routes (426 otherwise, checked before the token), `X-Kvitt-Server-Version`
on every response, body limits 1 MiB / 5 MiB for `PUT /me/picture`, JSON 404 for unknown paths.

Building blocks for handler authors (`src/api/mod.rs`, `src/auth.rs`, `src/error.rs`):

* `AuthDevice` / `AdminDevice` extractors (SPEC §8.2, §8.4); put them first in the handler's arguments.
* `IdPath` for a UUID path segment (not a UUID: 404 `not_found`), `ApiJson<T>` for JSON bodies (400
  `invalid_request`, 413 `payload_too_large`), `JsonBody<T>` for JSON responses with `charset=utf-8`.
* `AppError` with every code of SPEC §14.3.2 and its status; `?` on `sqlx::Error` gives `unavailable` for a busy
  database and `internal` (logged with a request id) otherwise.
* `db::begin_immediate` for every write transaction and `db::next_server_version` inside it (SPEC §14.1).
* `AppState.clock` (`time::Clock`; tests use `FixedClock`), `time::format_ts` for the fixed RFC 3339 form,
  `time::STOCKHOLM`.

The OpenAPI document is generated with utoipa from the `#[utoipa::path]` annotations and the wire types in
`src/wire/`; `src/openapi.rs` lists the handlers and applies the document-wide rules. A handler change that alters
the wire contract makes `tests/openapi_contract.rs` fail against `contracts/openapi.yaml`.

## Seams for M3, M4 and M9 (SPEC §6.3, D-015)

* **Rate limit (M3):** `src/api/rate_limit.rs` returns the layer that `router.rs` attaches on the line marked
  `// M3: the rate limiter …`. In M2a it is the identity layer.
* **Background tasks (M4):** `src/tasks/mod.rs` has `pub async fn start(state: AppState) -> Result<(), AppError>`,
  called once by `serve` after migrations. In M2a it starts nothing.
* **Audit (`src/audit/mod.rs`, M4 implements, M3 and M9 call):**

  ```rust
  pub trait AuditWriter: Send + Sync + 'static {
      fn write<'a>(&'a self, conn: &'a mut SqliteConnection, event: AuditEvent)
          -> BoxFuture<'a, Result<Uuid, AppError>>;
  }
  ```

  `AuditEvent` carries entity type and id, action, source, actor user and device, `client_at`, `server_at`, and
  the wire object before (`None` for create) and after the change as JSON; the writer derives `changes` per SPEC
  §14.4.7 and inserts the row with a `server_version` from the caller's `BEGIN IMMEDIATE` transaction (`conn`).
  `AppState.audit` holds `NoopAuditWriter` until M4 replaces it.
* **Push (`src/push/mod.rs`, M4 implements, M3 calls):** `PushQueue::enqueue(&self, message: PushMessage)` with
  `PushMessage { push_type: PushType, entity_id: Option<Uuid>, actor_user_id: Uuid, count: u32 }` and the eight
  types of SPEC §14.6. It never blocks or fails; call it after commit. `AppState.push` holds `NoopPushQueue`.
* **Recurring dates (`kvitt-domain`, for M3's generation function and M4's scheduler):**
  `Period` (`YYYY-MM`, `FromStr`/`Display`, `next()`, `days()`, `clamped_date(day_of_month)`),
  `next_candidate_period(start_period, end_period, last_generated_period) -> Result<Option<Period>, RecurrenceError>`
  and `next_occurrence_date(&RecurrenceSchedule) -> Result<Option<String>, RecurrenceError>`.
* **Importer (M9):** `kvitt-import` already depends on `kvitt-domain` and `kvitt-server` (the library).

## Tests and the gate

From `server/`: `cargo fmt --check && cargo clippy --all-targets -- -D warnings && cargo test`.

* `crates/kvitt-domain/tests/vectors.rs`: every case of every file in `contracts/test-vectors/` (the two
  Kotlin-only analytics files are parsed and skipped).
* `crates/kvitt-server/tests/openapi_contract.rs`: the generated document equals `contracts/openapi.yaml` after
  the normalisations documented at the top of the file, plus self-tests that the comparison catches changes.
* `crates/kvitt-server/tests/skeleton/`: migration identity and pragmas, every route registered (501), E-1, E-2,
  protocol and token rules, error shapes against `contracts/examples/errors/`, wire types against every example in
  `contracts/examples/`.

M3 and M4 put their integration tests in `tests/core_*.rs`, `tests/sync_*.rs`, `tests/scheduler_*.rs`,
`tests/push_*.rs`. No `unwrap`/`expect` in non-test code (a crate-level `deny` enforces it under clippy).

## Docker image

```sh
docker build --platform linux/arm64 -f server/Dockerfile -t kvitt-server:dev server/
```

Build on the Mac, never on the Pi (`infra/dev/build.sh` does this for the dev stack). Stage 1 is
`rust:<pinned version>-bookworm`, building both binaries in release mode with `--locked`; stage 2 is
`gcr.io/distroless/cc-debian12:nonroot` pinned by digest, binaries in `/usr/local/bin/`, user 10001, entrypoint
`kvitt-server`, command `serve`. `--platform linux/amd64` also works (emulated on the Mac). The container needs only
`/data` writable and runs with a read-only root filesystem.