From 4af7780c3ef9d697a6640c8fe5d87fc811e522a0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Wed, 24 Jun 2026 10:49:50 -0300
Subject: [PATCH 1/2] feat(rpc): add GET /lean/v0/config/spec

---
 crates/net/rpc/src/lib.rs  |  2 +
 crates/net/rpc/src/spec.rs | 77 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 crates/net/rpc/src/spec.rs

diff --git a/crates/net/rpc/src/lib.rs b/crates/net/rpc/src/lib.rs
index 09268765..5e3907a0 100644
--- a/crates/net/rpc/src/lib.rs
+++ b/crates/net/rpc/src/lib.rs
@@ -14,6 +14,7 @@ mod blocks;
 mod fork_choice;
 mod heap_profiling;
 pub mod metrics;
+mod spec;
 pub mod test_driver;
 
 pub(crate) use base::json_response;
@@ -100,6 +101,7 @@ fn build_api_router(store: Store) -> Router {
         .merge(blocks::routes())
         .merge(fork_choice::routes())
         .merge(admin::routes())
+        .merge(spec::routes())
         .with_state(store)
 }
 
diff --git a/crates/net/rpc/src/spec.rs b/crates/net/rpc/src/spec.rs
new file mode 100644
index 00000000..5a5ec0b9
--- /dev/null
+++ b/crates/net/rpc/src/spec.rs
@@ -0,0 +1,77 @@
+use axum::{Router, response::IntoResponse, routing::get};
+use ethlambda_blockchain::{INTERVALS_PER_SLOT, MILLISECONDS_PER_INTERVAL, MILLISECONDS_PER_SLOT};
+use ethlambda_storage::Store;
+use ethlambda_types::state::HISTORICAL_ROOTS_LIMIT;
+use serde::Serialize;
+
+use crate::json_response;
+
+// Dummy fork digest; keep in sync with ethlambda_p2p::gossipsub::messages::FORK_DIGEST until it's centralized in a shared crate.
+const FORK_DIGEST: &str = "12345678";
+
+#[derive(Serialize)]
+struct SpecResponse {
+    #[serde(rename = "MILLISECONDS_PER_SLOT")]
+    ms_per_slot: u64,
+    #[serde(rename = "INTERVALS_PER_SLOT")]
+    intervals_per_slot: u64,
+    #[serde(rename = "MILLISECONDS_PER_INTERVAL")]
+    ms_per_interval: u64,
+    #[serde(rename = "HISTORICAL_ROOTS_LIMIT")]
+    historical_roots_limit: u64,
+    #[serde(rename = "FORK_DIGEST")]
+    fork_digest: String,
+}
+
+async fn get_spec() -> impl IntoResponse {
+    json_response(SpecResponse {
+        ms_per_slot: MILLISECONDS_PER_SLOT,
+        intervals_per_slot: INTERVALS_PER_SLOT,
+        ms_per_interval: MILLISECONDS_PER_INTERVAL,
+        historical_roots_limit: HISTORICAL_ROOTS_LIMIT as u64,
+        fork_digest: FORK_DIGEST.to_string(),
+    })
+}
+
+pub(crate) fn routes() -> Router<Store> {
+    Router::new().route("/lean/v0/config/spec", get(get_spec))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::FORK_DIGEST;
+    use crate::test_utils::create_test_state;
+    use axum::{
+        body::Body,
+        http::{Request, StatusCode},
+    };
+    use ethlambda_blockchain::{
+        INTERVALS_PER_SLOT, MILLISECONDS_PER_INTERVAL, MILLISECONDS_PER_SLOT,
+    };
+    use ethlambda_storage::{Store, backend::InMemoryBackend};
+    use http_body_util::BodyExt;
+    use std::sync::Arc;
+    use tower::ServiceExt;
+
+    #[tokio::test]
+    async fn spec_returns_lean_constants() {
+        let store = Store::from_anchor_state(Arc::new(InMemoryBackend::new()), create_test_state());
+        let app = crate::build_api_router(store);
+        let resp = app
+            .oneshot(
+                Request::builder()
+                    .uri("/lean/v0/config/spec")
+                    .body(Body::empty())
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+        let body = resp.into_body().collect().await.unwrap().to_bytes();
+        let json: serde_json::Value = serde_json::from_slice(&body).unwrap();
+        assert_eq!(json["MILLISECONDS_PER_SLOT"], MILLISECONDS_PER_SLOT);
+        assert_eq!(json["INTERVALS_PER_SLOT"], INTERVALS_PER_SLOT);
+        assert_eq!(json["MILLISECONDS_PER_INTERVAL"], MILLISECONDS_PER_INTERVAL);
+        assert_eq!(json["FORK_DIGEST"], FORK_DIGEST);
+    }
+}

From 72216912320df30d4f9c15ea9cd3e8237f62c494 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Wed, 24 Jun 2026 15:38:06 -0300
Subject: [PATCH 2/2] fix(rpc): address review feedback on config/spec (test
 assertion, static fork_digest)

---
 crates/net/rpc/src/spec.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/crates/net/rpc/src/spec.rs b/crates/net/rpc/src/spec.rs
index 5a5ec0b9..27fb4cb1 100644
--- a/crates/net/rpc/src/spec.rs
+++ b/crates/net/rpc/src/spec.rs
@@ -20,7 +20,7 @@ struct SpecResponse {
     #[serde(rename = "HISTORICAL_ROOTS_LIMIT")]
     historical_roots_limit: u64,
     #[serde(rename = "FORK_DIGEST")]
-    fork_digest: String,
+    fork_digest: &'static str,
 }
 
 async fn get_spec() -> impl IntoResponse {
@@ -29,7 +29,7 @@ async fn get_spec() -> impl IntoResponse {
         intervals_per_slot: INTERVALS_PER_SLOT,
         ms_per_interval: MILLISECONDS_PER_INTERVAL,
         historical_roots_limit: HISTORICAL_ROOTS_LIMIT as u64,
-        fork_digest: FORK_DIGEST.to_string(),
+        fork_digest: FORK_DIGEST,
     })
 }
 
@@ -49,6 +49,7 @@ mod tests {
         INTERVALS_PER_SLOT, MILLISECONDS_PER_INTERVAL, MILLISECONDS_PER_SLOT,
     };
     use ethlambda_storage::{Store, backend::InMemoryBackend};
+    use ethlambda_types::state::HISTORICAL_ROOTS_LIMIT;
     use http_body_util::BodyExt;
     use std::sync::Arc;
     use tower::ServiceExt;
@@ -72,6 +73,10 @@ mod tests {
         assert_eq!(json["MILLISECONDS_PER_SLOT"], MILLISECONDS_PER_SLOT);
         assert_eq!(json["INTERVALS_PER_SLOT"], INTERVALS_PER_SLOT);
         assert_eq!(json["MILLISECONDS_PER_INTERVAL"], MILLISECONDS_PER_INTERVAL);
+        assert_eq!(
+            json["HISTORICAL_ROOTS_LIMIT"],
+            HISTORICAL_ROOTS_LIMIT as u64
+        );
         assert_eq!(json["FORK_DIGEST"], FORK_DIGEST);
     }
 }