cellos_server/

lib.rs

//! CellOS HTTP control plane API library surface.
//!
//! Exposes the router builder and core types so that integration tests
//! (and future embedders) can drive the server without spawning a real
//! TCP listener. See `src/main.rs` for the production wiring.

pub mod auth;
pub mod error;
pub mod jetstream;
pub mod routes;
pub mod state;
pub mod ws;

use axum::extract::DefaultBodyLimit;
use axum::http::{header, Method};
use axum::{
    middleware::map_response,
    routing::{delete, get, post},
    Router,
};
use tower_http::cors::{Any, CorsLayer};
use tower_http::trace::TraceLayer;

use crate::error::{normalize_problem_response, problem_response, AppErrorKind};

pub use state::{AppState, CellRecord, CellState, FormationRecord, FormationStatus};

/// Per-route ceiling on `POST /v1/formations` body bytes. axum
/// defaults to 2 MiB; that is ~100x the size of any realistic formation
/// document we have observed (~12 KiB for a 64-cell formation).
/// Lowering this surfaces a 413 Payload Too Large rather than burning
/// CPU on serde parsing a 2 MiB document at the admission gate.
const FORMATIONS_POST_MAX_BYTES: usize = 64 * 1024;

/// Build the full axum router with all routes mounted at their
/// canonical paths. `AppState` is cloned per request via axum's
/// `with_state`.
///
/// ADR-0017 §D2: `cellos-server` is API-only. The static bundle moved
/// to `cellctl` and is served by `cellctl webui`. There is no
/// `ServeDir` fallback here — unmatched paths return 404.
///
/// ADR-0016 (read-only browser boundary): CORS is restricted to
/// `GET` + `OPTIONS` so a misbehaving browser context (XSS, malicious
/// extension, or a hostile in-page script that slipped past the
/// `cellctl webui` proxy) cannot mutate state via a cross-origin
/// `POST /v1/formations`. The localhost proxy makes browser origins a
/// non-issue in practice, but we enforce the read-only shape
/// structurally so the boundary survives a proxy bug.
pub fn router(state: AppState) -> Router {
    Router::new()
        .route(
            "/v1/formations",
            post(routes::formations::create_formation)
                .layer(DefaultBodyLimit::max(FORMATIONS_POST_MAX_BYTES)),
        )
        .route("/v1/formations", get(routes::formations::list_formations))
        // NOTE: axum 0.8 ships matchit 0.8 which uses the brace
        // `{id}` capture syntax (the old `:id` form was removed). The
        // `{id}` segment matches a single path segment and is decoded
        // into the handler's `Path<…>` extractor.
        .route(
            "/v1/formations/{id}",
            get(routes::formations::get_formation),
        )
        .route(
            "/v1/formations/{id}",
            delete(routes::formations::delete_formation),
        )
        // CTL-002 (E2E report): name-addressed counterparts of the
        // UUID routes above. The literal `/by-name/` segment is matched
        // before `{id}` because axum's matchit prefers literal segments
        // over captures at the same depth, so `/v1/formations/by-name/foo`
        // never tries to parse `by-name` as a UUID.
        .route(
            "/v1/formations/by-name/{name}",
            get(routes::formations::get_formation_by_name),
        )
        .route(
            "/v1/formations/by-name/{name}",
            delete(routes::formations::delete_formation_by_name),
        )
        .route(
            "/v1/formations/{id}/status",
            post(routes::formations::update_formation_status),
        )
        .route("/v1/cells", get(routes::cells::list_cells))
        .route("/v1/cells/{id}", get(routes::cells::get_cell))
        // E2E report SRV-001: `cellctl version` is the day-1 reachability
        // probe a fresh operator types first. Returns build metadata
        // (crate version, optional short git SHA, build profile, API
        // version) behind the same Bearer gate as every other route.
        .route("/v1/version", get(routes::meta::get_version))
        // EVT-001: one-shot snapshot of recent events. The `--follow`
        // path stays on `/ws/events`; this exists for environments
        // where WebSocket isn't viable (corporate proxies, kubectl-
        // style scripted pulls). See `routes/events.rs` for the
        // contract and the WS-envelope wire compatibility note.
        .route("/v1/events", get(routes::events::list_events))
        .route("/ws/events", get(ws::ws_events))
        // FUZZ-WAVE-1 MED-2: unmatched paths used to return 404 with an
        // empty body and no Content-Type. RFC 9457 says every error
        // response should carry problem+json; adopters parse `type` to
        // distinguish a missing route from an authentication failure.
        .fallback(not_found_handler)
        // FUZZ-WAVE-1 MED-2: wrong-method-on-existing-path used to
        // return 405 with empty body. axum's method router still sets
        // the `Allow` header on its own response; the
        // `normalize_problem_response` middleware below preserves Allow
        // when it rewrites the body.
        .method_not_allowed_fallback(method_not_allowed_handler)
        .layer(TraceLayer::new_for_http())
        .layer(
            CorsLayer::new()
                // Origin is left open because the only legitimate
                // browser client is the cellctl localhost proxy — the
                // method restriction below is the structural gate, not
                // the origin list.
                .allow_origin(Any)
                .allow_methods([Method::GET, Method::OPTIONS])
                .allow_headers([header::AUTHORIZATION, header::CONTENT_TYPE]),
        )
        // FUZZ-WAVE-1 MED-1: outermost response-mapping layer normalises
        // every 4xx that isn't already problem+json (axum's built-in
        // JsonRejection / PathRejection / QueryRejection / BodyLimit
        // rejections emit text/plain). Placed AFTER CorsLayer so CORS
        // preflight 200s aren't touched, and outside TraceLayer so
        // tracing sees the original status.
        .layer(map_response(normalize_problem_response))
        .with_state(state)
}

/// FUZZ-WAVE-1 MED-2: 404 fallback for unmatched paths. Returns
/// `application/problem+json` so adopters can distinguish a missing
/// route (`/problems/not-found`) from an authentication failure
/// (`/problems/unauthorized`) without sniffing the body shape.
async fn not_found_handler(req: axum::extract::Request) -> axum::response::Response {
    let path = req.uri().path().to_string();
    // Keep the detail terse — we don't want to echo a 4 KiB attacker
    // URL verbatim into the error body. The leading slash plus first
    // 200 bytes is enough for an operator to debug.
    let truncated: String = path.chars().take(200).collect();
    problem_response(
        AppErrorKind::NotFound,
        format!("no route matched '{truncated}'"),
    )
}

/// FUZZ-WAVE-1 MED-2: 405 fallback for wrong-method-on-known-path.
/// axum's method router still attaches the `Allow` header to the
/// underlying response before this handler runs; the
/// `normalize_problem_response` layer copies it through to the
/// rewritten body. RFC 9110 §15.5.6 requires Allow on every 405.
async fn method_not_allowed_handler(req: axum::extract::Request) -> axum::response::Response {
    let method = req.method().as_str().to_string();
    let path: String = req.uri().path().chars().take(200).collect();
    problem_response(
        AppErrorKind::MethodNotAllowed,
        format!("method '{method}' not allowed for '{path}' — see Allow header"),
    )
}

#[cfg(test)]
mod cors_tests {
    use super::*;
    use axum::body::Body;
    use axum::http::{header, Method, Request, StatusCode};
    use tower::ServiceExt;

    /// ADR-0016 structural enforcement: a cross-origin browser MUST
    /// NOT be able to mutate state. The CORS preflight for
    /// `POST /v1/formations` is the gate — we assert the server's
    /// `Access-Control-Allow-Methods` response *omits* `POST`. With
    /// the strict layer in `router()`, the preflight advertises only
    /// the safe methods; a compliant browser then refuses to send the
    /// actual POST.
    #[tokio::test]
    async fn cors_preflight_for_post_does_not_allow_post() {
        let state = AppState::new(None, "test-token");
        let app = router(state);

        let req = Request::builder()
            .method(Method::OPTIONS)
            .uri("/v1/formations")
            .header(header::ORIGIN, "http://attacker.example")
            .header(header::ACCESS_CONTROL_REQUEST_METHOD, "POST")
            .header(header::ACCESS_CONTROL_REQUEST_HEADERS, "authorization")
            .body(Body::empty())
            .unwrap();

        let resp = app.oneshot(req).await.expect("router response");
        // CORS preflight itself succeeds at the HTTP layer; the gate is
        // in the Access-Control-Allow-Methods header.
        assert_eq!(resp.status(), StatusCode::OK);

        let allow_methods = resp
            .headers()
            .get(header::ACCESS_CONTROL_ALLOW_METHODS)
            .and_then(|v| v.to_str().ok())
            .unwrap_or_default()
            .to_ascii_uppercase();

        assert!(
            !allow_methods.contains("POST"),
            "POST must not appear in Access-Control-Allow-Methods (got {allow_methods:?})",
        );
        assert!(
            allow_methods.contains("GET"),
            "GET must appear in Access-Control-Allow-Methods (got {allow_methods:?})",
        );
    }

    /// And the safe preflight (GET) is allowed — sanity check we
    /// didn't accidentally lock the whole API down.
    #[tokio::test]
    async fn cors_preflight_for_get_is_allowed() {
        let state = AppState::new(None, "test-token");
        let app = router(state);

        let req = Request::builder()
            .method(Method::OPTIONS)
            .uri("/v1/formations")
            .header(header::ORIGIN, "http://localhost:9999")
            .header(header::ACCESS_CONTROL_REQUEST_METHOD, "GET")
            .header(header::ACCESS_CONTROL_REQUEST_HEADERS, "authorization")
            .body(Body::empty())
            .unwrap();

        let resp = app.oneshot(req).await.expect("router response");
        assert_eq!(resp.status(), StatusCode::OK);

        let allow_methods = resp
            .headers()
            .get(header::ACCESS_CONTROL_ALLOW_METHODS)
            .and_then(|v| v.to_str().ok())
            .unwrap_or_default()
            .to_ascii_uppercase();
        assert!(
            allow_methods.contains("GET"),
            "GET must be in Access-Control-Allow-Methods (got {allow_methods:?})",
        );
    }
}