feat: add proposer duties v2 endpoint (#8597)

Adds proposer duties v2 endpoint which works the same as v1 but uses
previous epoch to determine dependent root to account for deterministic
proposer lookahead changes in fulu.

ethereum/beacon-APIs#563

Author: nflaig

packages/api/src/beacon/routes/validator.ts

@@ -285,6 +285,33 @@ export type Endpoints = {
     ExecutionOptimisticAndDependentRootMeta
   >;
 
+  /**
+   * Get block proposers duties
+   * Request beacon node to provide all validators that are scheduled to propose a block in the given epoch.
+   * Duties should only need to be checked once per epoch, however a chain reorganization could occur that results in a change of duties.
+   * For full safety, you should monitor head events and confirm the dependent root in this response matches. After Fulu, different checks
+   * need to be performed as the dependent root changes due to deterministic proposer lookahead.
+   *
+   * Before Fulu:
+   *  - event.current_duty_dependent_root when `compute_epoch_at_slot(event.slot) == epoch`
+   *  - event.block otherwise
+   *  - dependent_root value is `get_block_root_at_slot(state, compute_start_slot_at_epoch(epoch) - 1)`
+   *
+   * After Fulu:
+   * - event.previous_duty_dependent_root when `compute_epoch_at_slot(event.slot) == epoch`
+   * - event.block otherwise
+   * - dependent_root value is `get_block_root_at_slot(state, compute_start_slot_at_epoch(epoch - 1) - 1)`
+   *
+   * The dependent_root value is the genesis block root in the case of underflow."
+   */
+  getProposerDutiesV2: Endpoint<
+    "GET",
+    {epoch: Epoch},
+    {params: {epoch: Epoch}},
+    ProposerDutyList,
+    ExecutionOptimisticAndDependentRootMeta
+  >;
+
   getSyncCommitteeDuties: Endpoint<
     "POST",
     {
@@ -565,6 +592,21 @@ export function getDefinitions(config: ChainForkConfig): RouteDefinitions<Endpoi
         meta: ExecutionOptimisticAndDependentRootCodec,
       },
     },
+    getProposerDutiesV2: {
+      url: "/eth/v2/validator/duties/proposer/{epoch}",
+      method: "GET",
+      req: {
+        writeReq: ({epoch}) => ({params: {epoch}}),
+        parseReq: ({params}) => ({epoch: params.epoch}),
+        schema: {
+          params: {epoch: Schema.UintRequired},
+        },
+      },
+      resp: {
+        data: ProposerDutyListType,
+        meta: ExecutionOptimisticAndDependentRootCodec,
+      },
+    },
     getSyncCommitteeDuties: {
       url: "/eth/v1/validator/duties/sync/{epoch}",
       method: "POST",

packages/api/test/unit/beacon/testData/validator.ts

@@ -35,6 +35,13 @@ export const testData: GenericServerTestCases<Endpoints> = {
       meta: {executionOptimistic: true, dependentRoot: ZERO_HASH_HEX},
     },
   },
+  getProposerDutiesV2: {
+    args: {epoch: 1000},
+    res: {
+      data: [{slot: 1, validatorIndex: 2, pubkey: new Uint8Array(48).fill(3)}],
+      meta: {executionOptimistic: true, dependentRoot: ZERO_HASH_HEX},
+    },
+  },
   getSyncCommitteeDuties: {
     args: {epoch: 1000, indices: [1, 2, 3]},
     res: {

packages/beacon-node/src/api/impl/validator/index.ts

@@ -1002,7 +1002,7 @@ export function getValidatorApi(
       return {data: contribution};
     },
 
-    async getProposerDuties({epoch}) {
+    async getProposerDuties({epoch}, _context, opts?: {v2?: boolean}) {
       notWhileSyncing();
 
       // Early check that epoch is no more than current_epoch + 1, or allow for pre-genesis
@@ -1106,7 +1106,10 @@ export function getValidatorApi(
 
       // Returns `null` on the one-off scenario where the genesis block decides its own shuffling.
       // It should be set to the latest block applied to `self` or the genesis block root.
-      const dependentRoot = proposerShufflingDecisionRoot(state) || (await getGenesisBlockRoot(state));
+      const dependentRoot =
+        // In v2 the dependent root is different after fulu due to deterministic proposer lookahead
+        proposerShufflingDecisionRoot(opts?.v2 ? config.getForkName(startSlot) : ForkName.phase0, state) ||
+        (await getGenesisBlockRoot(state));
 
       return {
         data: duties,
@@ -1117,6 +1120,10 @@ export function getValidatorApi(
       };
     },
 
+    async getProposerDutiesV2(args, context) {
+      return this.getProposerDuties(args, context, {v2: true});
+    },
+
     async getAttesterDuties({epoch, indices}) {
       notWhileSyncing();
 

packages/state-transition/src/util/shufflingDecisionRoot.ts

@@ -1,3 +1,4 @@
+import {ForkName, isForkPostFulu} from "@lodestar/params";
 import {Epoch, Root, Slot} from "@lodestar/types";
 import {CachedBeaconStateAllForks} from "../types.js";
 import {getBlockRootAtSlot} from "./blockRoot.js";
@@ -10,8 +11,8 @@ import {computeStartSlotAtEpoch} from "./epoch.js";
  * Returns `null` on the one-off scenario where the genesis block decides its own shuffling.
  * It should be set to the latest block applied to this `state` or the genesis block root.
  */
-export function proposerShufflingDecisionRoot(state: CachedBeaconStateAllForks): Root | null {
-  const decisionSlot = proposerShufflingDecisionSlot(state);
+export function proposerShufflingDecisionRoot(fork: ForkName, state: CachedBeaconStateAllForks): Root | null {
+  const decisionSlot = proposerShufflingDecisionSlot(fork, state);
   if (state.slot === decisionSlot) {
     return null;
   }
@@ -22,8 +23,10 @@ export function proposerShufflingDecisionRoot(state: CachedBeaconStateAllForks):
  * Returns the slot at which the proposer shuffling was decided. The block root at this slot
  * can be used to key the proposer shuffling for the current epoch.
  */
-function proposerShufflingDecisionSlot(state: CachedBeaconStateAllForks): Slot {
-  const startSlot = computeStartSlotAtEpoch(state.epochCtx.epoch);
+function proposerShufflingDecisionSlot(fork: ForkName, state: CachedBeaconStateAllForks): Slot {
+  // After fulu, the decision slot is in previous epoch due to deterministic proposer lookahead
+  const epoch = isForkPostFulu(fork) ? state.epochCtx.epoch - 1 : state.epochCtx.epoch;
+  const startSlot = computeStartSlotAtEpoch(epoch);
   return Math.max(startSlot - 1, 0);
 }