log-backup: added more robust error handling for log backup advancer

br/pkg/streamhelper/advancer.go

@@ -262,14 +262,16 @@ func (c *CheckpointAdvancer) StartTaskListener(ctx context.Context) {
 				return
 			case e, ok := <-ch:
 				if !ok {
+					log.Info("[log backup advancer] Task watcher exits due to stream ends.")
 					return
 				}
-				log.Info("meet task event", zap.Stringer("event", &e))
+				log.Info("[log backup advancer] Meet task event", zap.Stringer("event", &e))
 				if err := c.onTaskEvent(ctx, e); err != nil {
 					if errors.Cause(e.Err) != context.Canceled {
 						log.Error("listen task meet error, would reopen.", logutil.ShortError(err))
 						time.AfterFunc(c.cfg.BackoffTime, func() { c.StartTaskListener(ctx) })
 					}
+					log.Info("[log backup advancer] Task watcher exits due to some error.", logutil.ShortError(err))
 					return
 				}
 			}

br/pkg/streamhelper/advancer_cliext.go

@@ -7,10 +7,12 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"io"
 	"strings"
 
 	"github.com/golang/protobuf/proto"
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	backuppb "github.com/pingcap/kvproto/pkg/brpb"
 	"github.com/pingcap/log"
 	berrors "github.com/pingcap/tidb/br/pkg/errors"
@@ -94,6 +96,9 @@ func (t AdvancerExt) toTaskEvent(ctx context.Context, event *clientv3.Event) (Ta
 
 func (t AdvancerExt) eventFromWatch(ctx context.Context, resp clientv3.WatchResponse) ([]TaskEvent, error) {
 	result := make([]TaskEvent, 0, len(resp.Events))
+	if err := resp.Err(); err != nil {
+		return nil, err
+	}
 	for _, event := range resp.Events {
 		te, err := t.toTaskEvent(ctx, event)
 		if err != nil {
@@ -118,33 +123,42 @@ func (t AdvancerExt) startListen(ctx context.Context, rev int64, ch chan<- TaskE
 		}
 		return true
 	}
+	collectRemaining := func() {
+		for {
+			select {
+			case resp, ok := <-c:
+				if !ok {
+					return
+				}
+				if !handleResponse(resp) {
+					return
+				}
+			default:
+				return
+			}
+		}
+	}
 
 	go func() {
 		defer close(ch)
 		for {
 			select {
 			case resp, ok := <-c:
+				failpoint.Inject("advancer_close_channel", func() {
+					// We cannot really close the channel, just simulating it.
+					ok = false
+				})
 				if !ok {
+					ch <- errorEvent(io.EOF)
 					return
 				}
 				if !handleResponse(resp) {
 					return
 				}
 			case <-ctx.Done():
-				// drain the remain event from channel.
-				for {
-					select {
-					case resp, ok := <-c:
-						if !ok {
-							return
-						}
-						if !handleResponse(resp) {
-							return
-						}
-					default:
-						return
-					}
-				}
+				collectRemaining()
+				ch <- errorEvent(ctx.Err())
+				return
 			}
 		}
 	}()

br/pkg/streamhelper/integration_test.go

@@ -7,12 +7,14 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"io"
 	"net"
 	"net/url"
 	"path"
 	"testing"
 
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	backuppb "github.com/pingcap/kvproto/pkg/brpb"
 	"github.com/pingcap/log"
 	berrors "github.com/pingcap/tidb/br/pkg/errors"
@@ -143,6 +145,7 @@ func TestIntegration(t *testing.T) {
 	t.Run("TestStreamListening", func(t *testing.T) { testStreamListening(t, streamhelper.AdvancerExt{MetaDataClient: metaCli}) })
 	t.Run("TestStreamCheckpoint", func(t *testing.T) { testStreamCheckpoint(t, streamhelper.AdvancerExt{MetaDataClient: metaCli}) })
 	t.Run("testStoptask", func(t *testing.T) { testStoptask(t, streamhelper.AdvancerExt{MetaDataClient: metaCli}) })
+	t.Run("TestStreamClose", func(t *testing.T) { testStreamClose(t, streamhelper.AdvancerExt{MetaDataClient: metaCli}) })
 }
 
 func TestChecking(t *testing.T) {
@@ -295,6 +298,7 @@ func testStreamListening(t *testing.T, metaCli streamhelper.AdvancerExt) {
 	taskInfo2 := simpleTask(taskName2, 4)
 	require.NoError(t, metaCli.PutTask(ctx, taskInfo2))
 	require.NoError(t, metaCli.DeleteTask(ctx, taskName2))
+
 	first := <-ch
 	require.Equal(t, first.Type, streamhelper.EventAdd)
 	require.Equal(t, first.Name, taskName)
@@ -310,8 +314,44 @@ func testStreamListening(t *testing.T, metaCli streamhelper.AdvancerExt) {
 	require.Equal(t, forth.Type, streamhelper.EventDel)
 	require.Equal(t, forth.Name, taskName2)
 	cancel()
-	_, ok := <-ch
-	require.False(t, ok)
+	fifth, ok := <-ch
+	require.True(t, ok)
+	require.Equal(t, fifth.Type, streamhelper.EventErr)
+	require.Error(t, fifth.Err, context.Canceled)
+	item, ok := <-ch
+	require.False(t, ok, "%v", item)
+}
+
+func testStreamClose(t *testing.T, metaCli streamhelper.AdvancerExt) {
+	ctx := context.Background()
+	taskName := "close_simple"
+	taskInfo := simpleTask(taskName, 4)
+
+	require.NoError(t, metaCli.PutTask(ctx, taskInfo))
+	ch := make(chan streamhelper.TaskEvent, 1024)
+	require.NoError(t, metaCli.Begin(ctx, ch))
+	require.NoError(t, metaCli.DeleteTask(ctx, taskName))
+	first := <-ch
+	require.Equal(t, first.Type, streamhelper.EventAdd)
+	require.Equal(t, first.Name, taskName)
+	require.ElementsMatch(t, first.Ranges, simpleRanges(4))
+	second := <-ch
+	require.Equal(t, second.Type, streamhelper.EventDel, "%s", second)
+	require.Equal(t, second.Name, taskName, "%s", second)
+
+	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/br/pkg/streamhelper/advancer_close_channel", "return"))
+	defer failpoint.Disable("github.com/pingcap/tidb/br/pkg/streamhelper/advancer_close_channel")
+	// We need to make the channel file some events hence we can simulate the closed channel.
+	taskName2 := "close_simple2"
+	taskInfo2 := simpleTask(taskName2, 4)
+	require.NoError(t, metaCli.PutTask(ctx, taskInfo2))
+	require.NoError(t, metaCli.DeleteTask(ctx, taskName2))
+
+	third := <-ch
+	require.Equal(t, third.Type, streamhelper.EventErr)
+	require.Error(t, third.Err, io.EOF)
+	item, ok := <-ch
+	require.False(t, ok, "%#v", item)
 }
 
 func testStreamCheckpoint(t *testing.T, metaCli streamhelper.AdvancerExt) {