fix(core/fetcher): resubscribe if consensus node goes offline (#4096)

Author: vgonkivs

Diff for: core/fetcher.go

@@ -13,6 +13,7 @@ import (
 	coregrpc "github.com/tendermint/tendermint/rpc/grpc"
 	"github.com/tendermint/tendermint/types"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/status"
 
 	libhead "github.com/celestiaorg/go-header"
 )
@@ -173,9 +174,12 @@ func (f *BlockFetcher) SubscribeNewBlockEvent(ctx context.Context) (<-chan types
 
 	subscription, err := f.client.SubscribeNewHeights(ctx, &coregrpc.SubscribeNewHeightsRequest{})
 	if err != nil {
+		close(f.doneCh)
+		f.isListeningForBlocks.Store(false)
 		return nil, err
 	}
 
+	log.Debug("created a subscription. Start listening for new blocks...")
 	signedBlockCh := make(chan types.EventDataSignedBlock)
 	go func() {
 		defer close(f.doneCh)
@@ -189,6 +193,12 @@ func (f *BlockFetcher) SubscribeNewBlockEvent(ctx context.Context) (<-chan types
 				resp, err := subscription.Recv()
 				if err != nil {
 					log.Errorw("fetcher: error receiving new height", "err", err.Error())
+					_, ok := status.FromError(err) // parsing the gRPC error
+					if ok {
+						// ok means that err contains a gRPC status error.
+						// move on another round of resubscribing.
+						return
+					}
 					continue
 				}
 				withTimeout, ctxCancel := context.WithTimeout(ctx, 10*time.Second)

Diff for: core/fetcher_test.go

@@ -2,12 +2,15 @@ package core
 
 import (
 	"context"
+	"errors"
 	"net"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	coregrpc "github.com/tendermint/tendermint/rpc/grpc"
+	"google.golang.org/grpc"
 )
 
 func TestBlockFetcher_GetBlock_and_SubscribeNewBlockEvent(t *testing.T) {
@@ -40,3 +43,130 @@ func TestBlockFetcher_GetBlock_and_SubscribeNewBlockEvent(t *testing.T) {
 	}
 	require.NoError(t, fetcher.Stop(ctx))
 }
+
+type mockAPIService struct {
+	coregrpc.UnimplementedBlockAPIServer
+
+	grpcServer *grpc.Server
+	fetcher    *BlockFetcher
+}
+
+func (m *mockAPIService) SubscribeNewHeights(
+	_ *coregrpc.SubscribeNewHeightsRequest,
+	srv coregrpc.BlockAPI_SubscribeNewHeightsServer,
+) error {
+	for i := 0; i < 20; i++ {
+		b, err := m.fetcher.GetBlock(context.Background(), int64(i))
+		if err != nil {
+			return err
+		}
+		err = srv.Send(&coregrpc.NewHeightEvent{Height: b.Header.Height, Hash: b.Header.Hash()})
+		if err != nil {
+			return err
+		}
+		time.Sleep(time.Second)
+	}
+	return nil
+}
+
+func (m *mockAPIService) BlockByHeight(
+	req *coregrpc.BlockByHeightRequest,
+	srv coregrpc.BlockAPI_BlockByHeightServer,
+) error {
+	b, err := m.fetcher.client.BlockByHeight(context.Background(), &coregrpc.BlockByHeightRequest{Height: req.Height})
+	if err != nil {
+		return err
+	}
+	data, err := b.Recv()
+	if err != nil {
+		return err
+	}
+	err = srv.Send(data)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (m *mockAPIService) Start() error {
+	listener, err := net.Listen("tcp", ":50051")
+	if err != nil {
+		return err
+	}
+
+	grpcServer := grpc.NewServer()
+	m.grpcServer = grpcServer
+	coregrpc.RegisterBlockAPIServer(grpcServer, m)
+	go func() {
+		err = grpcServer.Serve(listener)
+		if err != nil && !errors.Is(err, grpc.ErrServerStopped) {
+			panic(err)
+		}
+	}()
+	return nil
+}
+
+func (m *mockAPIService) Stop() error {
+	m.grpcServer.Stop()
+	return nil
+}
+
+func (m *mockAPIService) generateBlocksWithHeights(ctx context.Context, t *testing.T) {
+	cfg := DefaultTestConfig()
+	fetcher, cctx := createCoreFetcher(t, cfg)
+	m.fetcher = fetcher
+	generateNonEmptyBlocks(t, ctx, fetcher, cfg, cctx)
+	require.NoError(t, fetcher.Stop(ctx))
+}
+
+// TestStart_SubscribeNewBlockEvent_Resubscription ensures that subscription will not stuck in case
+// gRPC server was stopped.
+func TestStart_SubscribeNewBlockEvent_Resubscription(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
+	t.Cleanup(cancel)
+	m := &mockAPIService{}
+	m.generateBlocksWithHeights(ctx, t)
+
+	require.NoError(t, m.Start())
+
+	client := newTestClient(t, "localhost", "50051")
+
+	fetcher, err := NewBlockFetcher(client)
+	require.NoError(t, err)
+	// subscribe to block event to get blocks
+	newBlockChan, err := fetcher.SubscribeNewBlockEvent(ctx)
+	require.NoError(t, err)
+
+	select {
+	case newBlockFromChan := <-newBlockChan:
+		h := newBlockFromChan.Header.Height
+		_, err := fetcher.GetSignedBlock(ctx, h)
+		require.NoError(t, err)
+	case <-ctx.Done():
+		require.NoError(t, ctx.Err())
+	}
+
+	require.NoError(t, m.Stop())
+
+	// stopping the server sends an error with the status code
+	// to client, so the subscription loop will be finished.
+	// check that newBlockChan was closed
+	_, ok := <-newBlockChan
+	require.False(t, ok)
+
+	// start server and try to get a new subscription
+	require.NoError(t, m.Start())
+	newBlockChan, err = fetcher.SubscribeNewBlockEvent(ctx)
+	require.NoError(t, err)
+	select {
+	case newBlockFromChan := <-newBlockChan:
+		h := newBlockFromChan.Header.Height
+		_, err := fetcher.GetSignedBlock(ctx, h)
+		require.NoError(t, err)
+	case <-ctx.Done():
+		require.NoError(t, ctx.Err())
+	}
+	require.NoError(t, m.Stop())
+	require.NoError(t, m.fetcher.Stop(ctx))
+	require.NoError(t, fetcher.Stop(ctx))
+}