# rust-link-sidecar

Configuration reference and endpoint list. For what this component *is*, see the
[repo README](../README.md).

## Configuration

`sidecar.toml`, resolved in this order: `--config <PATH>`, else `$RUSTLINK_CONFIG`, else
`./sidecar.toml`. Environment variables override the file; the file overrides the defaults.

| Key | Env | Default | What it is |
|---|---|---|---|
| `[game].bind` | `RUSTLINK_GAME_BIND` | `127.0.0.1:7799` | Where the Oxide plugin dials in |
| `[game].server_id` | `RUSTLINK_SERVER_ID` | *(empty)* | Optional cross-check against the plugin's own `serverId` |
| `[web].bind` | `RUSTLINK_WEB_BIND` | `127.0.0.1:8090` | Where the website reaches this sidecar |
| `[web].auth_token` | `RUSTLINK_WEB_TOKEN` | *(generated)* | The shared secret the website presents |
| `[store].path` | `RUSTLINK_DB_PATH` | `rust-link.db` | SQLite file |
| `[store].retain_days` | `RUSTLINK_RETAIN_DAYS` | `14` | Days of event history to keep. `0` keeps everything |

Two things about those defaults are load-bearing:

- **`[game].bind` is loopback, and there is no token on that link.** The plugin and the sidecar
  share a host; `127.0.0.1` *is* the authentication. Binding it to a routable address puts an
  unauthenticated command channel on the network.
- **A relative `[store].path` resolves against the directory holding `sidecar.toml`**, not the
  working directory. A service manager's working directory must not decide where the database
  lands — on Windows that can be `%SystemRoot%\System32`, or a silently redirected VirtualStore
  copy.

`[game].server_id` is a **cross-check, not a second source of truth**. The plugin announces its own
`serverId` and that is the authority; when both are set and they disagree, the sidecar logs the
disagreement loudly and keeps the plugin's. Two game servers pointed at one sidecar by a copied
config is the mistake this catches, and it is silent in every other design.

### Reading the token back

```bash
rust-link-sidecar --print-config
```

Resolves the configuration exactly as a normal start would — writing the file and generating the
token if they are missing — and prints it as JSON on stdout, **including the token in clear text**.
That is the supported way for an installer to obtain it; the alternative is scraping a log.

## Endpoints

Everything except `/health` requires the token, as `Authorization: Bearer <t>`, `X-Api-Key: <t>`,
or `?token=<t>` (the last so browser WebSocket clients, which cannot set handshake headers, can
still authenticate). Every response carries `X-RustLink-Version`.

| Route | Backed by | Notes |
|---|---|---|
| `GET /health` | — | Unauthenticated, so monitoring can reach it |
| `GET /server` | store | The last `server.hello`. **`204` when the game has never connected** |
| `GET /boards` | store | Every board, keyed by kind. `200` with an empty object when there are none |
| `GET /events?kind=&wipe=&limit=` | store | Newest first; `limit` clamped to 1–1000. For a human |
| `GET /feed?since=&limit=` | store | **Oldest first, from a cursor.** For a consumer that must not miss a row. Omitting `since` asks where the end is |
| `GET /status` | plugin (RPC) | A live round trip. `503` with no plugin, `504` on no reply |
| `GET /ws` | broadcast | The live feed. Sends `ws.hello` on connect |

The split is the point: the store-backed reads answer while the game is off, which is what lets the
website render a server list during a wipe or a restart. `/status` is the one route that fails when
the game is down, because "what is it doing right now" has no stale answer worth giving.

`/server` answers `204`, not `200` with a null, when the game has never connected. "We have never
heard from this server" and "this server reports nothing" are different answers, and a client that
cannot tell them apart renders a server that does not exist.

## The protocol

Newline-delimited JSON over TCP, both directions. Outbound frames (plugin → sidecar) carry `kind`;
inbound frames (sidecar → plugin) carry `cmd`. Lines are capped at 1 MiB; an over-long line is
discarded and the connection stays up.

**This process files a frame by its `type`, and never by its `kind`** — which is what keeps it a
dumb forwarder while the catalogue grows. Ten new event kinds are no change here at all.

| `type` | Kept | Broadcast | Example |
|---|---|---|---|
| `event` | appended to the history | yes | `player.death` |
| `snapshot` | **replaces** the board of that kind | yes | `players.online` |
| `reply` | no | no | `server.status`, routed by `reqId` |
| `control` | no | yes | `pong`, `link.down` |

A frame with no `type` this build knows is **dropped and counted**, never guessed at, and the count
is on `/health` as `untyped_frames`. The game link has no version handshake, so a plugin and a
sidecar on different protocol versions show up there and nowhere else.

| Frame | Direction | Purpose |
|---|---|---|
| `server.hello` | plugin → sidecar | A board. Sent on **every connect**, not once at server start — this process restarts independently of the game. Carries `serverId`, `bootId` and `wipeId` |
| `players.online` | plugin → sidecar | The other board: who is connected, re-sent on connect and every 60s |
| `ping` / `pong` | sidecar → plugin → sidecar | The heartbeat, every 30s. A `pong` is never persisted; it only moves `last_event` |
| `server.status` | sidecar → plugin → sidecar | The one request/reply verb, correlated by `reqId` |
| the read path | plugin → sidecar | Presence, deaths, chat, tallies, moderation, the wipe — the catalogue is `PROTOCOL.md` §8.4 |

`bootId` is how a game restart is told apart from a sidecar reconnect — the distinction the event
system's `reconcile` hangs off later. `wipeId` is how a wipe splits the history instead of ending
it; the plugin derives it, and every frame carries it.

**History is bounded, boards are not.** `[store].retain_days` (default 14) prunes events hourly; a
board is one row per kind holding what is true now, and pruning it would make a server the site has
rendered for weeks look like one that has never connected. The permanent record is the website's.

**The RPC reply timeout (`rpc::REPLY_TIMEOUT`, 10s) is a ceiling every later command budget sits
under.** Core classifies a budget overrun as retryable unconditionally, because it cannot ask the
game while the action is still awaiting a socket. An action whose `budgetMs` exceeds this can never
report `retry: false`.

## Checks

```bash
cargo fmt --all -- --check
cargo clippy --all-targets -- -D warnings
cargo test
```