Proposer duties backwards compat (#8335)

The beacon API spec wasn't updated to use the Fulu definition of `dependent_root` for the proposer duties endpoint. No other client updated their logic, so to retain backwards compatibility the decision has been made to continue using the block root at the end of epoch `N - 1`, and introduce a new v2 endpoint down the track to use the correct dependent root.

Eth R&D discussion: https://discord.com/channels/595666850260713488/598292067260825641/1433036715848765562


  Change the behaviour of the v1 endpoint back to using the last slot of `N - 1` rather than the last slot of `N - 2`. This introduces the possibility of dependent root false positives (the root can change without changing the shuffling), but causes the least compatibility issues with other clients.


Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

beacon_node/http_api/src/proposer_duties.rs

@@ -60,13 +60,13 @@ pub fn proposer_duties<T: BeaconChainTypes>(
             .safe_add(1)
             .map_err(warp_utils::reject::arith_error)?
     {
-        let (proposers, dependent_root, execution_status, _fork) =
+        let (proposers, _dependent_root, legacy_dependent_root, execution_status, _fork) =
             compute_proposer_duties_from_head(request_epoch, chain)
                 .map_err(warp_utils::reject::unhandled_error)?;
         convert_to_api_response(
             chain,
             request_epoch,
-            dependent_root,
+            legacy_dependent_root,
             execution_status.is_optimistic_or_invalid(),
             proposers,
         )
@@ -116,6 +116,11 @@ fn try_proposer_duties_from_cache<T: BeaconChainTypes>(
         .beacon_state
         .proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root, &chain.spec)
         .map_err(warp_utils::reject::beacon_state_error)?;
+    let legacy_dependent_root = head
+        .snapshot
+        .beacon_state
+        .legacy_proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root)
+        .map_err(warp_utils::reject::beacon_state_error)?;
     let execution_optimistic = chain
         .is_optimistic_or_invalid_head_block(head_block)
         .map_err(warp_utils::reject::unhandled_error)?;
@@ -129,7 +134,7 @@ fn try_proposer_duties_from_cache<T: BeaconChainTypes>(
             convert_to_api_response(
                 chain,
                 request_epoch,
-                head_decision_root,
+                legacy_dependent_root,
                 execution_optimistic,
                 indices.to_vec(),
             )
@@ -151,7 +156,7 @@ fn compute_and_cache_proposer_duties<T: BeaconChainTypes>(
     current_epoch: Epoch,
     chain: &BeaconChain<T>,
 ) -> Result<ApiDuties, warp::reject::Rejection> {
-    let (indices, dependent_root, execution_status, fork) =
+    let (indices, dependent_root, legacy_dependent_root, execution_status, fork) =
         compute_proposer_duties_from_head(current_epoch, chain)
             .map_err(warp_utils::reject::unhandled_error)?;
 
@@ -166,7 +171,7 @@ fn compute_and_cache_proposer_duties<T: BeaconChainTypes>(
     convert_to_api_response(
         chain,
         current_epoch,
-        dependent_root,
+        legacy_dependent_root,
         execution_status.is_optimistic_or_invalid(),
         indices,
     )
@@ -229,12 +234,18 @@ fn compute_historic_proposer_duties<T: BeaconChainTypes>(
 
     // We can supply the genesis block root as the block root since we know that the only block that
     // decides its own root is the genesis block.
-    let dependent_root = state
-        .proposer_shuffling_decision_root(chain.genesis_block_root, &chain.spec)
+    let legacy_dependent_root = state
+        .legacy_proposer_shuffling_decision_root_at_epoch(epoch, chain.genesis_block_root)
         .map_err(BeaconChainError::from)
         .map_err(warp_utils::reject::unhandled_error)?;
 
-    convert_to_api_response(chain, epoch, dependent_root, execution_optimistic, indices)
+    convert_to_api_response(
+        chain,
+        epoch,
+        legacy_dependent_root,
+        execution_optimistic,
+        indices,
+    )
 }
 
 /// Converts the internal representation of proposer duties into one that is compatible with the

beacon_node/http_api/tests/interactive_tests.rs

@@ -1017,10 +1017,9 @@ async fn proposer_duties_with_gossip_tolerance() {
     assert_eq!(
         proposer_duties_tolerant_current_epoch.dependent_root,
         head_state
-            .proposer_shuffling_decision_root_at_epoch(
+            .legacy_proposer_shuffling_decision_root_at_epoch(
                 tolerant_current_epoch,
                 head_block_root,
-                spec
             )
             .unwrap()
     );