Listens For State Initialized Event

beacon-chain/rpc/validator/server.go

@@ -189,6 +189,19 @@ func (vs *Server) WaitForChainStart(req *ptypes.Empty, stream ethpb.BeaconNodeVa
 				}
 				return stream.Send(res)
 			}
+			// Handle race condition in the event the blockchain
+			// service isn't initialized in time and the saved head state is nil.
+			if event.Type == statefeed.Initialized {
+				data, ok := event.Data.(*statefeed.InitializedData)
+				if !ok {
+					return errors.New("event data is not type *statefeed.InitializedData")
+				}
+				res := &ethpb.ChainStartResponse{
+					Started:     true,
+					GenesisTime: uint64(data.StartTime.Unix()),
+				}
+				return stream.Send(res)
+			}
 		case <-stateSub.Err():
 			return status.Error(codes.Aborted, "Subscriber closed, exiting goroutine")
 		case <-vs.Ctx.Done():

beacon-chain/rpc/validator/server_test.go

@@ -2,6 +2,7 @@ package validator
 
 import (
 	"context"
+	"sync"
 	"testing"
 	"time"
 
@@ -337,6 +338,44 @@ func TestWaitForChainStart_AlreadyStarted(t *testing.T) {
 	assert.NoError(t, Server.WaitForChainStart(&ptypes.Empty{}, mockStream), "Could not call RPC method")
 }
 
+func TestWaitForChainStart_HeadStateDoesNotExist(t *testing.T) {
+	db, _ := dbutil.SetupDB(t)
+	genesisValidatorRoot := [32]byte{0x01, 0x02}
+
+	// Set head state to nil
+	chainService := &mockChain.ChainService{State: nil}
+	notifier := chainService.StateNotifier()
+	Server := &Server{
+		Ctx: context.Background(),
+		ChainStartFetcher: &mockPOW.POWChain{
+			ChainFeed: new(event.Feed),
+		},
+		BeaconDB:      db,
+		StateNotifier: chainService.StateNotifier(),
+		HeadFetcher:   chainService,
+	}
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	mockStream := mock.NewMockBeaconNodeValidator_WaitForChainStartServer(ctrl)
+
+	wg := new(sync.WaitGroup)
+	wg.Add(1)
+	go func() {
+		assert.NoError(t, Server.WaitForChainStart(&ptypes.Empty{}, mockStream), "Could not call RPC method")
+		wg.Done()
+	}()
+	// Simulate a late state initialization event, so that
+	// method is able to handle race condition here.
+	notifier.StateFeed().Send(&feed.Event{
+		Type: statefeed.Initialized,
+		Data: &statefeed.InitializedData{
+			StartTime:             time.Unix(0, 0),
+			GenesisValidatorsRoot: genesisValidatorRoot[:],
+		},
+	})
+	testutil.WaitTimeout(wg, time.Second)
+}
+
 func TestWaitForChainStart_NotStartedThenLogFired(t *testing.T) {
 	db, _ := dbutil.SetupDB(t)