Implement sync_committee_rewards API (per-validator reward) (#3903)

[#3661](https://github.com/sigp/lighthouse/issues/3661)

`/eth/v1/beacon/rewards/sync_committee/{block_id}`

```
{
  "execution_optimistic": false,
  "finalized": false,
  "data": [
    {
      "validator_index": "0",
      "reward": "2000"
    }
  ]
}
```

The issue contains the implementation of three per-validator reward APIs:
* `sync_committee_rewards`
* [`attestation_rewards`](https://github.com/sigp/lighthouse/pull/3822)
* `block_rewards`

This PR only implements the `sync_committe_rewards `.

The endpoints can be viewed in the Ethereum Beacon nodes API browser: [https://ethereum.github.io/beacon-APIs/?urls.primaryName=dev#/Rewards](https://ethereum.github.io/beacon-APIs/?urls.primaryName=dev#/Rewards)

The implementation of [consensus client reward APIs](https://github.com/eth-protocol-fellows/cohort-three/blob/master/projects/project-ideas.md#consensus-client-reward-apis) is part of the [EPF](https://github.com/eth-protocol-fellows/cohort-three).

Co-authored-by: navie <naviechan@gmail.com>
Co-authored-by: kevinbogner <kevbogner@gmail.com>

beacon_node/beacon_chain/src/errors.rs

@@ -162,6 +162,7 @@ pub enum BeaconChainError {
     BlockRewardSlotError,
     BlockRewardAttestationError,
     BlockRewardSyncError,
+    SyncCommitteeRewardsSyncError,
     HeadMissingFromForkChoice(Hash256),
     FinalizedBlockMissingFromForkChoice(Hash256),
     HeadBlockMissingFromForkChoice(Hash256),

beacon_node/beacon_chain/src/lib.rs

@@ -43,6 +43,7 @@ pub mod schema_change;
 mod shuffling_cache;
 mod snapshot_cache;
 pub mod state_advance_timer;
+pub mod sync_committee_rewards;
 pub mod sync_committee_verification;
 pub mod test_utils;
 mod timeout_rw_lock;

beacon_node/beacon_chain/src/sync_committee_rewards.rs

@@ -0,0 +1,87 @@
+use crate::{BeaconChain, BeaconChainError, BeaconChainTypes};
+
+use eth2::lighthouse::SyncCommitteeReward;
+use safe_arith::SafeArith;
+use slog::error;
+use state_processing::per_block_processing::altair::sync_committee::compute_sync_aggregate_rewards;
+use std::collections::HashMap;
+use store::RelativeEpoch;
+use types::{BeaconBlockRef, BeaconState, ExecPayload};
+
+impl<T: BeaconChainTypes> BeaconChain<T> {
+    pub fn compute_sync_committee_rewards<Payload: ExecPayload<T::EthSpec>>(
+        &self,
+        block: BeaconBlockRef<'_, T::EthSpec, Payload>,
+        state: &mut BeaconState<T::EthSpec>,
+    ) -> Result<Vec<SyncCommitteeReward>, BeaconChainError> {
+        if block.slot() != state.slot() {
+            return Err(BeaconChainError::BlockRewardSlotError);
+        }
+
+        let spec = &self.spec;
+
+        state.build_committee_cache(RelativeEpoch::Current, spec)?;
+
+        let sync_aggregate = block.body().sync_aggregate()?;
+
+        let sync_committee = state.current_sync_committee()?.clone();
+
+        let sync_committee_indices = state.get_sync_committee_indices(&sync_committee)?;
+
+        let (participant_reward_value, proposer_reward_per_bit) =
+            compute_sync_aggregate_rewards(state, spec).map_err(|e| {
+                error!(
+                    self.log, "Error calculating sync aggregate rewards";
+                    "error" => ?e
+                );
+                BeaconChainError::SyncCommitteeRewardsSyncError
+            })?;
+
+        let mut balances = HashMap::<usize, u64>::new();
+
+        let mut total_proposer_rewards = 0;
+        let proposer_index = state.get_beacon_proposer_index(block.slot(), spec)?;
+
+        // Apply rewards to participant balances. Keep track of proposer rewards
+        for (validator_index, participant_bit) in sync_committee_indices
+            .iter()
+            .zip(sync_aggregate.sync_committee_bits.iter())
+        {
+            let participant_balance = balances
+                .entry(*validator_index)
+                .or_insert_with(|| state.balances()[*validator_index]);
+
+            if participant_bit {
+                participant_balance.safe_add_assign(participant_reward_value)?;
+
+                balances
+                    .entry(proposer_index)
+                    .or_insert_with(|| state.balances()[proposer_index])
+                    .safe_add_assign(proposer_reward_per_bit)?;
+
+                total_proposer_rewards.safe_add_assign(proposer_reward_per_bit)?;
+            } else {
+                *participant_balance = participant_balance.saturating_sub(participant_reward_value);
+            }
+        }
+
+        Ok(balances
+            .iter()
+            .filter_map(|(i, new_balance)| {
+                let reward = if *i != proposer_index {
+                    *new_balance as i64 - state.balances()[*i] as i64
+                } else if sync_committee_indices.contains(i) {
+                    *new_balance as i64
+                        - state.balances()[*i] as i64
+                        - total_proposer_rewards as i64
+                } else {
+                    return None;
+                };
+                Some(SyncCommitteeReward {
+                    validator_index: *i as u64,
+                    reward,
+                })
+            })
+            .collect())
+    }
+}

beacon_node/beacon_chain/src/test_utils.rs

@@ -2,6 +2,7 @@ pub use crate::persisted_beacon_chain::PersistedBeaconChain;
 pub use crate::{
     beacon_chain::{BEACON_CHAIN_DB_KEY, ETH1_CACHE_DB_KEY, FORK_CHOICE_DB_KEY, OP_POOL_DB_KEY},
     migrate::MigratorConfig,
+    sync_committee_verification::Error as SyncCommitteeError,
     validator_monitor::DEFAULT_INDIVIDUAL_TRACKING_THRESHOLD,
     BeaconChainError, NotifyExecutionLayer, ProduceBlockVerification,
 };
@@ -2079,6 +2080,30 @@ where
 
         (honest_head, faulty_head)
     }
+
+    pub fn process_sync_contributions(
+        &self,
+        sync_contributions: HarnessSyncContributions<E>,
+    ) -> Result<(), SyncCommitteeError> {
+        let mut verified_contributions = Vec::with_capacity(sync_contributions.len());
+
+        for (_, contribution_and_proof) in sync_contributions {
+            let signed_contribution_and_proof = contribution_and_proof.unwrap();
+
+            let verified_contribution = self
+                .chain
+                .verify_sync_contribution_for_gossip(signed_contribution_and_proof)?;
+
+            verified_contributions.push(verified_contribution);
+        }
+
+        for verified_contribution in verified_contributions {
+            self.chain
+                .add_contribution_to_block_inclusion_pool(verified_contribution)?;
+        }
+
+        Ok(())
+    }
 }
 
 // Junk `Debug` impl to satistfy certain trait bounds during testing.