Rust-Link/sidecar

rust-link-sidecar

Configuration reference and endpoint list. For what this component is, see the repo README.

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

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

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