From 73c3272d1ce2c219ad279fffe76e3e77a569c617 Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Wed, 21 Jul 2021 11:55:27 -0700
Subject: [PATCH] Feature/UpdateHeadTimely: cache finalized checkpoint when
 initial sync (#9244)

(cherry picked from commit b667d30d3f3949f98581b5f26d1444b39bbcd6a2)
---
 beacon-chain/blockchain/process_block.go      |  4 ++
 beacon-chain/blockchain/receive_block_test.go | 58 +++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/beacon-chain/blockchain/process_block.go b/beacon-chain/blockchain/process_block.go
index f4de74206afa..f2514add4d1d 100644
--- a/beacon-chain/blockchain/process_block.go
+++ b/beacon-chain/blockchain/process_block.go
@@ -309,6 +309,10 @@ func (s *Service) handleBlockAfterBatchVerify(ctx context.Context, signed interf
 		if err := s.updateFinalized(ctx, fCheckpoint); err != nil {
 			return err
 		}
+		if featureconfig.Get().UpdateHeadTimely {
+			s.prevFinalizedCheckpt = s.finalizedCheckpt
+			s.finalizedCheckpt = fCheckpoint
+		}
 	}
 	return nil
 }
diff --git a/beacon-chain/blockchain/receive_block_test.go b/beacon-chain/blockchain/receive_block_test.go
index f0b8c9612fa4..fd659a725346 100644
--- a/beacon-chain/blockchain/receive_block_test.go
+++ b/beacon-chain/blockchain/receive_block_test.go
@@ -8,6 +8,7 @@ import (
 
 	types "github.com/prysmaticlabs/eth2-types"
 	blockchainTesting "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/state"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
@@ -17,6 +18,7 @@ import (
 	"github.com/prysmaticlabs/prysm/proto/eth/v1alpha1/wrapper"
 	"github.com/prysmaticlabs/prysm/proto/interfaces"
 	"github.com/prysmaticlabs/prysm/shared/bytesutil"
+	"github.com/prysmaticlabs/prysm/shared/featureconfig"
 	"github.com/prysmaticlabs/prysm/shared/params"
 	"github.com/prysmaticlabs/prysm/shared/testutil"
 	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
@@ -283,6 +285,62 @@ func TestService_ReceiveBlockBatch(t *testing.T) {
 	}
 }
 
+func TestService_ReceiveBlockBatch_UpdateFinalizedCheckpoint(t *testing.T) {
+	// Must enable head timely feature flag to test this.
+	resetCfg := featureconfig.InitWithReset(&featureconfig.Flags{
+		UpdateHeadTimely: true,
+	})
+	defer resetCfg()
+
+	ctx := context.Background()
+	genesis, keys := testutil.DeterministicGenesisState(t, 64)
+
+	// Generate 5 epochs worth of blocks.
+	var blks []interfaces.SignedBeaconBlock
+	var roots [][32]byte
+	copied := genesis.Copy()
+	for i := types.Slot(1); i < params.BeaconConfig().SlotsPerEpoch*5; i++ {
+		b, err := testutil.GenerateFullBlock(copied, keys, testutil.DefaultBlockGenConfig(), i)
+		assert.NoError(t, err)
+		copied, err = state.ExecuteStateTransition(context.Background(), copied, wrapper.WrappedPhase0SignedBeaconBlock(b))
+		assert.NoError(t, err)
+		r, err := b.Block.HashTreeRoot()
+		require.NoError(t, err)
+		blks = append(blks, wrapper.WrappedPhase0SignedBeaconBlock(b))
+		roots = append(roots, r)
+	}
+
+	beaconDB := testDB.SetupDB(t)
+	genesisBlockRoot, err := genesis.HashTreeRoot(ctx)
+	require.NoError(t, err)
+	cfg := &Config{
+		BeaconDB: beaconDB,
+		ForkChoiceStore: protoarray.New(
+			0, // justifiedEpoch
+			0, // finalizedEpoch
+			genesisBlockRoot,
+		),
+		StateNotifier: &blockchainTesting.MockStateNotifier{RecordEvents: false},
+		StateGen:      stategen.New(beaconDB),
+	}
+	s, err := NewService(ctx, cfg)
+	require.NoError(t, err)
+	err = s.saveGenesisData(ctx, genesis)
+	require.NoError(t, err)
+	gBlk, err := s.cfg.BeaconDB.GenesisBlock(ctx)
+	require.NoError(t, err)
+
+	gRoot, err := gBlk.Block().HashTreeRoot()
+	require.NoError(t, err)
+	s.finalizedCheckpt = &ethpb.Checkpoint{Root: gRoot[:]}
+
+	// Process 5 epochs worth of blocks.
+	require.NoError(t, s.ReceiveBlockBatch(ctx, blks, roots))
+
+	// Finalized epoch must be updated.
+	require.Equal(t, types.Epoch(2), s.finalizedCheckpt.Epoch)
+}
+
 func TestService_HasInitSyncBlock(t *testing.T) {
 	s, err := NewService(context.Background(), &Config{StateNotifier: &blockchainTesting.MockStateNotifier{}})
 	require.NoError(t, err)