From cbe54fe3f97ed1e721fea19d3a46515ddfd02061 Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Wed, 13 Apr 2022 19:47:04 -0700
Subject: [PATCH] Handle nil execution block response when logging TTD (#10502)

---
 .../powchain/check_transition_config.go       | 11 +++++--
 .../powchain/check_transition_config_test.go  | 32 +++++++++++++++++++
 .../engine/v1/json_marshal_unmarshal_test.go  |  8 +++++
 3 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/beacon-chain/powchain/check_transition_config.go b/beacon-chain/powchain/check_transition_config.go
index 959457506..aebc38985 100644
--- a/beacon-chain/powchain/check_transition_config.go
+++ b/beacon-chain/powchain/check_transition_config.go
@@ -120,11 +120,16 @@ func (s *Service) handleExchangeConfigurationError(err error) {
 // Logs the terminal total difficulty status.
 func (s *Service) logTtdStatus(ctx context.Context, ttd *uint256.Int) (bool, error) {
 	latest, err := s.LatestExecutionBlock(ctx)
-	if err != nil {
+	switch {
+	case errors.Is(err, hexutil.ErrEmptyString):
+		return false, nil
+	case err != nil:
 		return false, err
-	}
-	if latest == nil {
+	case latest == nil:
 		return false, errors.New("latest block is nil")
+	case latest.TotalDifficulty == "":
+		return false, nil
+	default:
 	}
 	latestTtd, err := hexutil.DecodeBig(latest.TotalDifficulty)
 	if err != nil {
diff --git a/beacon-chain/powchain/check_transition_config_test.go b/beacon-chain/powchain/check_transition_config_test.go
index 5eac36bfc..659584ff9 100644
--- a/beacon-chain/powchain/check_transition_config_test.go
+++ b/beacon-chain/powchain/check_transition_config_test.go
@@ -190,6 +190,38 @@ func TestService_logTtdStatus(t *testing.T) {
 	require.Equal(t, false, reached)
 }
 
+func TestService_logTtdStatus_NotSyncedClient(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		defer func() {
+			require.NoError(t, r.Body.Close())
+		}()
+
+		resp := (*pb.ExecutionBlock)(nil) // Nil response when a client is not synced
+		respJSON := map[string]interface{}{
+			"jsonrpc": "2.0",
+			"id":      1,
+			"result":  resp,
+		}
+		require.NoError(t, json.NewEncoder(w).Encode(respJSON))
+	}))
+	defer srv.Close()
+
+	rpcClient, err := rpc.DialHTTP(srv.URL)
+	require.NoError(t, err)
+	defer rpcClient.Close()
+
+	service := &Service{
+		cfg: &config{},
+	}
+	service.rpcClient = rpcClient
+
+	ttd := new(uint256.Int)
+	reached, err := service.logTtdStatus(context.Background(), ttd.SetUint64(24343))
+	require.NoError(t, err)
+	require.Equal(t, false, reached)
+}
+
 func emptyPayload() *pb.ExecutionPayload {
 	return &pb.ExecutionPayload{
 		ParentHash:    make([]byte, fieldparams.RootLength),
diff --git a/proto/engine/v1/json_marshal_unmarshal_test.go b/proto/engine/v1/json_marshal_unmarshal_test.go
index e8a4cd5f3..927e3f170 100644
--- a/proto/engine/v1/json_marshal_unmarshal_test.go
+++ b/proto/engine/v1/json_marshal_unmarshal_test.go
@@ -5,6 +5,7 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
 	"github.com/prysmaticlabs/prysm/config/params"
 	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
@@ -173,6 +174,13 @@ func TestJsonMarshalUnmarshal(t *testing.T) {
 		require.DeepEqual(t, [][]byte{[]byte("hi")}, payloadPb.Transactions)
 		require.DeepEqual(t, [][]byte{[]byte("bye")}, payloadPb.Uncles)
 	})
+	t.Run("nil execution block", func(t *testing.T) {
+		jsonPayload := (*enginev1.ExecutionBlock)(nil)
+		enc, err := json.Marshal(jsonPayload)
+		require.NoError(t, err)
+		payloadPb := &enginev1.ExecutionBlock{}
+		require.ErrorIs(t, hexutil.ErrEmptyString, json.Unmarshal(enc, payloadPb))
+	})
 }
 
 func TestPayloadIDBytes_MarshalUnmarshalJSON(t *testing.T) {