Enforce Optimistic Sync Conditions & CLI Tests (v2) (#3050)

## Description

This PR adds a single, trivial commit (f5d2b27d78) atop #2986 to resolve a tests compile error. The original author (@ethDreamer) is AFK so I'm getting this one merged ☺️ 

Please see #2986 for more information about the other, significant changes in this PR.


Co-authored-by: Mark Mackey <mark@sigmaprime.io>
Co-authored-by: ethDreamer <37123614+ethDreamer@users.noreply.github.com>

beacon_node/beacon_chain/src/block_verification.rs

@@ -312,6 +312,8 @@ pub enum ExecutionPayloadError {
     ///
     /// The peer is not necessarily invalid.
     PoWParentMissing(ExecutionBlockHash),
+    /// The execution node is syncing but we fail the conditions for optimistic sync
+    UnverifiedNonOptimisticCandidate,
 }
 
 impl From<execution_layer::Error> for ExecutionPayloadError {
@@ -1128,6 +1130,29 @@ impl<'a, T: BeaconChainTypes> FullyVerifiedBlock<'a, T> {
         // `randao` may change.
         let payload_verification_status = notify_new_payload(chain, &state, block.message())?;
 
+        // If the payload did not validate or invalidate the block, check to see if this block is
+        // valid for optimistic import.
+        if payload_verification_status == PayloadVerificationStatus::NotVerified {
+            let current_slot = chain
+                .slot_clock
+                .now()
+                .ok_or(BeaconChainError::UnableToReadSlot)?;
+
+            if !chain
+                .fork_choice
+                .read()
+                .is_optimistic_candidate_block(
+                    current_slot,
+                    block.slot(),
+                    &block.parent_root(),
+                    &chain.spec,
+                )
+                .map_err(BeaconChainError::from)?
+            {
+                return Err(ExecutionPayloadError::UnverifiedNonOptimisticCandidate.into());
+            }
+        }
+
         // If the block is sufficiently recent, notify the validator monitor.
         if let Some(slot) = chain.slot_clock.now() {
             let epoch = slot.epoch(T::EthSpec::slots_per_epoch());

beacon_node/beacon_chain/src/execution_payload.rs

@@ -141,13 +141,25 @@ pub fn validate_merge_block<T: BeaconChainTypes>(
         }
         .into()),
         None => {
-            debug!(
-                chain.log,
-                "Optimistically accepting terminal block";
-                "block_hash" => ?execution_payload.parent_hash,
-                "msg" => "the terminal block/parent was unavailable"
-            );
-            Ok(())
+            let current_slot = chain
+                .slot_clock
+                .now()
+                .ok_or(BeaconChainError::UnableToReadSlot)?;
+            // Check the optimistic sync conditions. Note that because this is the merge block,
+            // the justified checkpoint can't have execution enabled so we only need to check the
+            // current slot is at least SAFE_SLOTS_TO_IMPORT_OPTIMISTICALLY ahead of the block
+            // https://github.com/ethereum/consensus-specs/blob/v1.1.9/sync/optimistic.md#when-to-optimistically-import-blocks
+            if block.slot() + chain.spec.safe_slots_to_import_optimistically <= current_slot {
+                debug!(
+                    chain.log,
+                    "Optimistically accepting terminal block";
+                    "block_hash" => ?execution_payload.parent_hash,
+                    "msg" => "the terminal block/parent was unavailable"
+                );
+                Ok(())
+            } else {
+                Err(ExecutionPayloadError::UnverifiedNonOptimisticCandidate.into())
+            }
         }
     }
 }

beacon_node/network/src/beacon_processor/worker/gossip_methods.rs

@@ -772,6 +772,7 @@ impl<T: BeaconChainTypes> Worker<T> {
             }
             // TODO(merge): reconsider peer scoring for this event.
             Err(e @BlockError::ExecutionPayloadError(ExecutionPayloadError::RequestFailed(_)))
+            | Err(e @ BlockError::ExecutionPayloadError(ExecutionPayloadError::UnverifiedNonOptimisticCandidate))
             | Err(e @BlockError::ExecutionPayloadError(ExecutionPayloadError::NoExecutionConnection)) => {
                 debug!(self.log, "Could not verify block for gossip, ignoring the block";
                             "error" => %e);