From d5e47e1b4306ab448d185d254621cdea36e36849 Mon Sep 17 00:00:00 2001
From: Nico Flaig <nflaig@protonmail.com>
Date: Sat, 2 Dec 2023 14:31:49 +0100
Subject: [PATCH] fix: set consensus version header in state and block response
 (#6152)

---
 packages/api/src/beacon/server/beacon.ts | 23 ++++++++++++++++++++++-
 packages/api/src/beacon/server/debug.ts  | 21 ++++++++++++++++++++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/packages/api/src/beacon/server/beacon.ts b/packages/api/src/beacon/server/beacon.ts
index da5a0997a0d8..c71decd1ac8e 100644
--- a/packages/api/src/beacon/server/beacon.ts
+++ b/packages/api/src/beacon/server/beacon.ts
@@ -1,4 +1,5 @@
 import {ChainForkConfig} from "@lodestar/config";
+import {ssz} from "@lodestar/types";
 import {Api, ReqTypes, routesData, getReturnTypes, getReqSerializers} from "../routes/beacon/index.js";
 import {ServerRoutes, getGenericJsonServer} from "../../utils/server/index.js";
 import {ServerApi} from "../../interfaces.js";
@@ -30,15 +31,35 @@ export function getRoutes(config: ChainForkConfig, api: ServerApi<Api>): ServerR
     },
     getBlockV2: {
       ...serverRoutes.getBlockV2,
-      handler: async (req) => {
+      handler: async (req, res) => {
         const response = await api.getBlockV2(...reqSerializers.getBlockV2.parseReq(req));
         if (response instanceof Uint8Array) {
+          const slot = extractSlotFromBlockBytes(response);
+          const version = config.getForkName(slot);
+          void res.header("Eth-Consensus-Version", version);
           // Fastify 3.x.x will automatically add header `Content-Type: application/octet-stream` if Buffer
           return Buffer.from(response);
         } else {
+          void res.header("Eth-Consensus-Version", response.version);
           return returnTypes.getBlockV2.toJson(response);
         }
       },
     },
   };
 }
+
+function extractSlotFromBlockBytes(block: Uint8Array): number {
+  const {signature} = ssz.phase0.SignedBeaconBlock.fields;
+  /**
+   * class SignedBeaconBlock(Container):
+   *   message: BeaconBlock                 [offset - 4 bytes]
+   *   signature: BLSSignature              [fixed - 96 bytes]
+   *
+   * class BeaconBlock(Container):
+   *   slot: Slot                           [fixed - 8 bytes]
+   *   ...
+   */
+  const offset = 4 + signature.lengthBytes;
+  const bytes = block.subarray(offset, offset + ssz.Slot.byteLength);
+  return ssz.Slot.deserialize(bytes);
+}
diff --git a/packages/api/src/beacon/server/debug.ts b/packages/api/src/beacon/server/debug.ts
index 7dd767d4a2fd..fd9de661edd2 100644
--- a/packages/api/src/beacon/server/debug.ts
+++ b/packages/api/src/beacon/server/debug.ts
@@ -1,4 +1,5 @@
 import {ChainForkConfig} from "@lodestar/config";
+import {ssz} from "@lodestar/types";
 import {Api, ReqTypes, routesData, getReturnTypes, getReqSerializers} from "../routes/debug.js";
 import {ServerRoutes, getGenericJsonServer} from "../../utils/server/index.js";
 import {ServerApi} from "../../interfaces.js";
@@ -31,15 +32,33 @@ export function getRoutes(config: ChainForkConfig, api: ServerApi<Api>): ServerR
     },
     getStateV2: {
       ...serverRoutes.getStateV2,
-      handler: async (req) => {
+      handler: async (req, res) => {
         const response = await api.getStateV2(...reqSerializers.getStateV2.parseReq(req));
         if (response instanceof Uint8Array) {
+          const slot = extractSlotFromStateBytes(response);
+          const version = config.getForkName(slot);
+          void res.header("Eth-Consensus-Version", version);
           // Fastify 3.x.x will automatically add header `Content-Type: application/octet-stream` if Buffer
           return Buffer.from(response);
         } else {
+          void res.header("Eth-Consensus-Version", response.version);
           return returnTypes.getStateV2.toJson(response);
         }
       },
     },
   };
 }
+
+function extractSlotFromStateBytes(state: Uint8Array): number {
+  const {genesisTime, genesisValidatorsRoot} = ssz.phase0.BeaconState.fields;
+  /**
+   * class BeaconState(Container):
+   *   genesisTime: BeaconBlock             [offset - 4 bytes]
+   *   genesisValidatorsRoot: BLSSignature  [fixed - 96 bytes]
+   *   slot: Slot                           [fixed - 8 bytes]
+   *   ...
+   */
+  const offset = genesisTime.byteLength + genesisValidatorsRoot.lengthBytes;
+  const bytes = state.subarray(offset, offset + ssz.Slot.byteLength);
+  return ssz.Slot.deserialize(bytes);
+}