Module-Rust/server/sidecarClient.js

// ── The near end of a call whose far end is a Rust server ─────────────────
//
// Every other file in this module reads its own tables. This one is different in
// kind: it is the only place that leaves the process.
//
// **The website process never opens a connection to a game server**
// (MODULE_API.md §2.7). It opens one to a `rust-link` sidecar, which owns the
// socket to the game, persists what the game says before forwarding it, and
// answers reads from that store. `test/noGameConnection.test.js` enforces the
// decidable half of that rule and names this file as the one that may reach the
// network:
//
//     const MAY_OPEN_SOCKETS = new Set(['sidecarClient.js'])
//
// ── One client per configured server ──────────────────────────────────────
//
// R8: the bridge is one game server to one sidecar. So this file takes the
// server row as an argument rather than holding a single configured endpoint —
// six servers is six base URLs and six tokens, and core never learns there is
// more than one.
//
// ── TIMEOUT_MS is not a tuning knob. It is half of a rule. ────────────────
//
// An event action declares `budgetMs`, and core's dispatcher enforces it: when
// the budget expires it stops waiting and classifies the failure as **retry**,
// unconditionally, without asking the action — it cannot ask, the action is still
// awaiting a socket. So if core's deadline is shorter than this one, an action
// never gets to classify its own failure and `{ ok: false, retry: false }` is
// unreachable code. `budgetMs` must EXCEED this.
//
// It is also bounded from the other side: the sidecar's own RPC reply timeout is
// ten seconds, so a value below that would give up while the sidecar is still
// legitimately waiting for the game. The ordering is
// `sidecar RPC timeout  <  TIMEOUT_MS  <  budgetMs`, and every one of the three
// is written down somewhere the other two can be checked against.
//
// ── This file never throws ────────────────────────────────────────────────
//
// Every call answers `{ ok, status, data }`. A module that let a socket failure
// escape into a controller would hand an exception to a page whose whole job is
// to render while the game is off. The public site degrades; it does not 500.

const core = require('./core')

const log = core.logger('sidecar')

/** How long this client waits before giving up on a sidecar. See the header. */
const TIMEOUT_MS = 12000

/**
 * The wire version this module speaks. Declared in FOUR places that must agree:
 * here, `PROTOCOL_VERSION` in the sidecar, `ProtocolVersion` in the bridge
 * plugin, and `protocol` in its `overlay.toml`.
 *
 * **2 — the read path.** The bump lands here in the same change as the emitters,
 * even though this module does not yet consume any of the new frames: the
 * sidecar refuses a client declaring a different version with a `409`, so a
 * module left on 1 would stop being able to read the server board it has been
 * reading all along. A constant that lags the deployment is not a safe default;
 * it is an outage with a version number on it.
 *
 * It is sent on every request as `X-RustLink-Version`, which turns a mismatched
 * deployment into a `409` naming both numbers instead of a parse failure three
 * layers further in.
 */
const PROTOCOL_VERSION = 2

/** What a caller gets back. Shaped once so every call site reads the same. */
function reply(ok, status, data = null) {
  return { ok, status, data }
}

/**
 * Normalises a configured base URL into something `new URL(path, base)` will not
 * surprise anybody with.
 *
 * A trailing slash on the base and a leading slash on the path is the classic
 * way to lose a path segment, and an operator pasting a URL out of a terminal
 * supplies the trailing slash about half the time.
 */
function joinUrl(baseUrl, path) {
  return `${String(baseUrl).replace(/\/+$/, '')}${path}`
}

/**
 * One request to one sidecar.
 *
 * @param {object} server              a `rust_servers` row, token already decrypted
 * @param {string} server.baseUrl
 * @param {string|null} server.token
 * @param {string} path                e.g. `/server`
 * @param {object} [options]
 * @param {string} [options.method]
 * @param {object} [options.body]
 */
async function request(server, path, { method = 'GET', body = null } = {}) {
  if (!server || !server.baseUrl) return reply(false, 'not-configured')

  // A sidecar with auth off does not exist — it generates and persists a token on
  // first start — so a missing token here is a half-finished admin form, not a
  // sidecar to try unauthenticated. Saying so beats a 401 the operator has to
  // interpret.
  if (!server.token) return reply(false, 'no-token')

  const controller = new AbortController()
  const timer = setTimeout(() => controller.abort(), TIMEOUT_MS)

  try {
    const res = await fetch(joinUrl(server.baseUrl, path), {
      method,
      signal: controller.signal,
      headers: {
        Authorization: `Bearer ${server.token}`,
        'X-RustLink-Version': String(PROTOCOL_VERSION),
        ...(body ? { 'Content-Type': 'application/json' } : {}),
      },
      ...(body ? { body: JSON.stringify(body) } : {}),
    })

    // A protocol mismatch is a deployment fault and deserves its own status, not
    // to be folded into "the sidecar said no". The operator's fix is an upgrade
    // of one component, and the message has to be able to say which.
    if (res.status === 409) {
      const detail = await safeJson(res)
      log.warn('protocol mismatch', {
        server: server.id,
        module: PROTOCOL_VERSION,
        sidecar: detail && detail.sidecar_protocol,
      })
      return reply(false, 'protocol-mismatch', detail)
    }

    if (res.status === 401) return reply(false, 'unauthorized')

    // 204 is an ANSWER, not an absence of one: the sidecar is up and reports that
    // the game has never connected. Collapsing it into a failure would make a
    // freshly installed server indistinguishable from an unreachable one.
    if (res.status === 204) return reply(true, 'empty', null)

    if (!res.ok) return reply(false, `http-${res.status}`)

    return reply(true, 'ok', await safeJson(res))
  } catch (err) {
    // `AbortError` is this client's own deadline firing, and it is worth telling
    // apart from a refused connection: one means the sidecar is slow or the game
    // is not answering, the other means nothing is listening.
    const status = err && err.name === 'AbortError' ? 'timeout' : 'transport-error'
    log.warn('sidecar request failed', { server: server.id, path, status, error: err.message })
    return reply(false, status)
  } finally {
    clearTimeout(timer)
  }
}

async function safeJson(res) {
  try {
    return await res.json()
  } catch {
    // A sidecar that answered 200 with something that is not JSON is a sidecar
    // this module cannot use, but it is not a reason to throw at a page.
    return null
  }
}

/** Liveness, the protocol version, and whether the plugin is connected. Unauthenticated at the far end, but sent authenticated anyway so one code path covers every call. */
const health = (server) => request(server, '/health')

/** The last `server.hello` the sidecar stored. Answers while the game is off. */
const serverBoard = (server) => request(server, '/server')

/** A live round trip through the sidecar to the game. Fails when the game is down, by design. */
const liveStatus = (server) => request(server, '/status')

/** Every board at once: what is true now, before following what happens next. */
const boards = (server) => request(server, '/boards')

/**
 * The ingest cursor: events after `since`, oldest first.
 *
 * **`since` is required here, unlike on the wire.** The sidecar treats an omitted
 * cursor as "tell me where the end is", which is a genuinely useful question and
 * a catastrophic default for an ingest loop that would silently store nothing
 * and advance past everything. So the question is asked explicitly, by name, and
 * a caller cannot get it by forgetting an argument.
 */
const feed = (server, since, limit = 200) =>
  request(server, `/feed?since=${encodeURIComponent(since)}&limit=${encodeURIComponent(limit)}`)

/** Where the sidecar's history currently ends. What a new server's cursor starts at. */
const feedTail = (server) => request(server, '/feed')

module.exports = {
  TIMEOUT_MS,
  PROTOCOL_VERSION,
  request,
  health,
  serverBoard,
  liveStatus,
  boards,
  feed,
  feedTail,
  joinUrl,
}