fix(node): bound the request body the signature middleware buffers before it verifies

crates/gitlawb-node/src/auth/mod.rs

@@ -34,6 +34,17 @@ use gitlawb_core::http_sig::{
 };
 use gitlawb_core::identity::verify;
 
+/// Per-route-group ceiling on how much request body [`require_signature`] will
+/// buffer BEFORE it has authenticated anything.
+///
+/// This is middleware state rather than a constant because a single number cannot
+/// serve both a 2 GB git push and a 2 MB profile update: the git write group
+/// passes `GITLAWB_MAX_PACK_BYTES`, every other signed group passes
+/// [`crate::server::SIGNED_BODY_LIMIT`]. Making it a required piece of state means
+/// a new signed route group cannot be wired up without choosing a limit.
+#[derive(Clone, Copy, Debug)]
+pub struct SignatureBodyLimit(pub usize);
+
 /// Axum middleware that enforces HTTP Signature authentication (RFC 9421).
 ///
 /// Every write request must carry:
@@ -48,20 +59,52 @@ use gitlawb_core::identity::verify;
 ///   4. Resolves the did:key to an Ed25519 VerifyingKey
 ///   5. Rebuilds the signing string and verifies the Ed25519 signature
 ///   6. Verifies Content-Digest matches the request body
-pub async fn require_signature(request: Request, next: Next) -> Response {
-    // Buffer the body so we can verify content-digest and pass it downstream
+pub async fn require_signature(
+    State(SignatureBodyLimit(limit)): State<SignatureBodyLimit>,
+    request: Request,
+    next: Next,
+) -> Response {
+    verify_signature(limit, request, next).await
+}
+
+/// The signature check itself, shared by [`require_signature`] and the optional
+/// variant. `limit` bounds the pre-auth buffer; see [`SignatureBodyLimit`].
+async fn verify_signature(limit: usize, request: Request, next: Next) -> Response {
+    // Buffer the body so we can verify content-digest and pass it downstream.
+    //
+    // The buffer is bounded, because this runs BEFORE any identity check: an
+    // unauthenticated caller with no DID, no signature and no repo reaches this
+    // line. Nothing upstream supplies the bound. On the git write routes
+    // `RequestBodyLimitLayer` sits on the inner router, and a later `.layer()` is
+    // the OUTER service, so this middleware runs first and sees the raw body. On
+    // every other signed group axum's 2 MB `DefaultBodyLimit` is enforced by the
+    // `Bytes`/`Json` extractors through a request extension, which collecting the
+    // body here bypasses. `Limited` stops reading at the limit rather than reading
+    // everything and then measuring it, which is the property that matters.
     let (parts, body) = request.into_parts();
-    let body_bytes =
-        match body.collect().await {
-            Ok(collected) => collected.to_bytes(),
-            Err(_) => return (
+    let body_bytes = match http_body_util::Limited::new(body, limit).collect().await {
+        Ok(collected) => collected.to_bytes(),
+        // Over the limit: a distinct status from the 401 an unsigned request gets
+        // and the 400 below, so a client can tell "too big" from "not authenticated"
+        // and from "your body did not arrive".
+        Err(e) if e.is::<http_body_util::LengthLimitError>() => return (
+            StatusCode::PAYLOAD_TOO_LARGE,
+            Json(json!({
+                "error": "body_too_large",
+                "message": format!("request body exceeds the {limit}-byte limit for this route"),
+            })),
+        )
+            .into_response(),
+        Err(_) => {
+            return (
                 StatusCode::BAD_REQUEST,
                 Json(
                     json!({ "error": "unreadable_body", "message": "could not read request body" }),
                 ),
             )
-                .into_response(),
-        };
+                .into_response()
+        }
+    };
 
     let sig_input = parts
         .headers
@@ -248,11 +291,17 @@ pub async fn require_signature(request: Request, next: Next) -> Response {
 /// Optional variant for rolling upgrades: verify and inject `AuthenticatedDid` when
 /// RFC 9421 signature headers are present, but allow legacy unsigned requests to
 /// continue when no signature attempt was made.
-pub async fn optional_signature(request: Request, next: Next) -> Response {
+pub async fn optional_signature(
+    State(SignatureBodyLimit(limit)): State<SignatureBodyLimit>,
+    request: Request,
+    next: Next,
+) -> Response {
     let has_signature_headers = request.headers().contains_key("signature-input")
         || request.headers().contains_key("signature");
     if has_signature_headers {
-        return require_signature(request, next).await;
+        // Same pre-auth buffer, same bound: presenting signature headers is not
+        // authentication, so this path is as reachable as the required one.
+        return verify_signature(limit, request, next).await;
     }
     next.run(request).await
 }

crates/gitlawb-node/src/server.rs

@@ -42,17 +42,37 @@ async fn graphql_playground() -> impl IntoResponse {
     ))
 }
 
+/// Pre-auth body-buffer ceiling for every signed route group except the git write
+/// routes. Deliberately equal to axum's `DefaultBodyLimit` (2 MB), which is what
+/// these groups' `Bytes`/`Json` extractors already enforce: that default works
+/// through a request extension the extractors consult, and `require_signature`
+/// collects the raw body itself, so it never saw the cap. Matching the number
+/// keeps this change behavior-preserving on the response path (nothing that used
+/// to be accepted starts failing) and purely a memory fix.
+pub const SIGNED_BODY_LIMIT: usize = 2 * 1024 * 1024;
+
 /// Applies the standard auth middleware pair to a router: HTTP Signature verification
 /// followed by UCAN chain validation. The two layers run in this order for every
 /// matched request: `require_signature` first (sets `AuthenticatedDid`), then
 /// `require_ucan_chain` (reads it).
-fn add_auth_layers(router: Router<AppState>, state: AppState) -> Router<AppState> {
+///
+/// `body_limit` bounds the request body `require_signature` buffers before it has
+/// authenticated anything (see [`auth::SignatureBodyLimit`]): `max_pack_bytes` for
+/// the git write group, [`SIGNED_BODY_LIMIT`] for every other group.
+fn add_auth_layers(
+    router: Router<AppState>,
+    state: AppState,
+    body_limit: usize,
+) -> Router<AppState> {
     router
         .layer(middleware::from_fn_with_state(
             state,
             auth::require_ucan_chain,
         ))
-        .layer(middleware::from_fn(auth::require_signature))
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(body_limit),
+            auth::require_signature,
+        ))
 }
 
 pub fn build_router(state: AppState) -> Router {
@@ -63,7 +83,10 @@ pub fn build_router(state: AppState) -> Router {
         // Attach the verified DID to /graphql when a signature is present. The
         // layer covers only routes added before it, so /graphql/ws (added after,
         // read-only subscriptions) stays open.
-        .layer(middleware::from_fn(auth::optional_signature))
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(SIGNED_BODY_LIMIT),
+            auth::optional_signature,
+        ))
         .route_service("/graphql/ws", GraphQLSubscription::new(schema));
 
     // ── Task routes (write — require HTTP Signature) ───────────────────────
@@ -74,6 +97,7 @@ pub fn build_router(state: AppState) -> Router {
             .route("/api/v1/tasks/{id}/complete", post(tasks::complete_task))
             .route("/api/v1/tasks/{id}/fail", post(tasks::fail_task)),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     );
 
     // ── Task routes (read — open) ──────────────────────────────────────────
@@ -107,6 +131,7 @@ pub fn build_router(state: AppState) -> Router {
             .layer(middleware::from_fn(rate_limit::rate_limit_by_did))
             .layer(axum::Extension(limiter)),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     )
     .layer(middleware::from_fn(rate_limit::rate_limit_by_ip))
     .layer(axum::Extension(create_ip_limiter));
@@ -181,6 +206,7 @@ pub fn build_router(state: AppState) -> Router {
                 axum::routing::delete(agents::deregister_agent),
             ),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     );
 
     // Body limit is raised to GITLAWB_MAX_PACK_BYTES (default 2 GB) for git
@@ -205,6 +231,7 @@ pub fn build_router(state: AppState) -> Router {
             .layer(DefaultBodyLimit::disable())
             .layer(RequestBodyLimitLayer::new(pack_limit)),
         state.clone(),
+        pack_limit,
     )
     .layer(middleware::from_fn(rate_limit::rate_limit_by_ip))
     .layer(axum::Extension(push_limiter));
@@ -216,7 +243,10 @@ pub fn build_router(state: AppState) -> Router {
     // stays unsigned — gating the pin index is tracked separately (#121).
     let ipfs_routes = Router::new()
         .route("/ipfs/{cid}", get(ipfs::get_by_cid))
-        .layer(middleware::from_fn(auth::optional_signature))
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(SIGNED_BODY_LIMIT),
+            auth::optional_signature,
+        ))
         .merge(Router::new().route("/api/v1/ipfs/pins", get(ipfs::list_pins)));
 
     // ── Arweave permanent anchors ──────────────────────────────────────────
@@ -247,6 +277,7 @@ pub fn build_router(state: AppState) -> Router {
                 post(bounties::dispute_bounty),
             ),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     );
 
     // ── Bounty routes (read — open) ──────────────────────────────────────
@@ -262,12 +293,16 @@ pub fn build_router(state: AppState) -> Router {
             "/api/v1/agents/{did}/bounties",
             get(bounties::agent_bounty_stats),
         )
-        .layer(middleware::from_fn(auth::optional_signature));
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(SIGNED_BODY_LIMIT),
+            auth::optional_signature,
+        ));
 
     // ── Profile routes (write — require HTTP Signature) ─────────────────
     let profile_write_routes = add_auth_layers(
         Router::new().route("/api/v1/profile", axum::routing::put(profiles::set_profile)),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     );
 
     // ── Issue routes (write — require HTTP Signature, no rate limit) ─────
@@ -282,6 +317,7 @@ pub fn build_router(state: AppState) -> Router {
                 post(issues::create_issue_comment),
             ),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     );
 
     // ── Peer discovery routes ─────────────────────────────────────────────
@@ -300,6 +336,7 @@ pub fn build_router(state: AppState) -> Router {
     let sync_trigger_routes = add_auth_layers(
         Router::new().route("/api/v1/sync/trigger", post(peers::trigger_sync)),
         state.clone(),
+        SIGNED_BODY_LIMIT,
     )
     .layer(middleware::from_fn(rate_limit::rate_limit_by_ip))
     .layer(axum::Extension(rate_limit::IpRateLimiter {
@@ -316,9 +353,12 @@ pub fn build_router(state: AppState) -> Router {
         .route("/api/v1/peers/announce", post(peers::announce))
         .route("/api/v1/sync/notify", post(peers::notify_sync));
     peer_write_routes = if state.config.require_signed_peer_writes {
-        add_auth_layers(peer_write_routes, state.clone())
+        add_auth_layers(peer_write_routes, state.clone(), SIGNED_BODY_LIMIT)
     } else {
-        peer_write_routes.layer(middleware::from_fn(auth::optional_signature))
+        peer_write_routes.layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(SIGNED_BODY_LIMIT),
+            auth::optional_signature,
+        ))
     };
     let peer_write_routes = peer_write_routes
         .layer(middleware::from_fn(rate_limit::rate_limit_by_ip))
@@ -417,7 +457,10 @@ pub fn build_router(state: AppState) -> Router {
             "/api/v1/repos/{owner}/{repo}/replicas",
             get(replicas::list_replicas),
         )
-        .layer(middleware::from_fn(auth::optional_signature));
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(SIGNED_BODY_LIMIT),
+            auth::optional_signature,
+        ));
 
     // git-upload-pack (clone/fetch) — same raised body limit as receive-pack so
     // large pack responses from the server don't get truncated on the client side.
@@ -449,7 +492,13 @@ pub fn build_router(state: AppState) -> Router {
         )
         .layer(DefaultBodyLimit::disable())
         .layer(RequestBodyLimitLayer::new(pack_limit))
-        .layer(middleware::from_fn(auth::optional_signature));
+        // `pack_limit`, not SIGNED_BODY_LIMIT: git-upload-pack POSTs live here and
+        // the group has deliberately raised its ceiling, so the pre-auth buffer for
+        // a signed fetch negotiation must match rather than narrow it.
+        .layer(middleware::from_fn_with_state(
+            auth::SignatureBodyLimit(pack_limit),
+            auth::optional_signature,
+        ));
 
     // ── Meta ──────────────────────────────────────────────────────────────
     let meta_routes = Router::new()