address comment

dm/relay/binlog_writer.go

@@ -21,7 +21,6 @@ import (
 	"path/filepath"
 	"sync"
 
-	"github.com/pingcap/errors"
 	"github.com/pingcap/tiflow/dm/pkg/log"
 	"github.com/pingcap/tiflow/dm/pkg/terror"
 	"go.uber.org/atomic"
@@ -93,7 +92,7 @@ func (w *BinlogWriter) run() {
 		}
 
 		if w.file == nil {
-			w.err.CompareAndSwap(nilErr, terror.ErrRelayWriterNotOpened.Delegate(errors.New("file not opened")))
+			w.err.CompareAndSwap(nilErr, terror.ErrRelayWriterNotOpened.Generate())
 			errOccurs = true
 			return
 		}
@@ -186,7 +185,7 @@ func (w *BinlogWriter) Close() error {
 
 func (w *BinlogWriter) Write(rawData []byte) error {
 	if w.file == nil {
-		return terror.ErrRelayWriterNotOpened.Delegate(errors.New("file not opened"))
+		return terror.ErrRelayWriterNotOpened.Generate()
 	}
 	w.input <- rawData
 	w.offset.Add(int64(len(rawData)))

dm/relay/binlog_writer_test.go

@@ -61,7 +61,7 @@ func (t *testBinlogWriterSuite) TestWrite() {
 		// not opened
 		w := NewBinlogWriter(log.L(), dir)
 		err := w.Write(data1)
-		require.Contains(t.T(), err.Error(), "not opened")
+		require.Contains(t.T(), err.Error(), "no underlying writer opened")
 
 		// open non exist dir
 		err = w.Open("not-exist-uuid", "bin.000001")

dm/relay/relay_writer.go

@@ -154,7 +154,7 @@ func (w *FileWriter) handleFormatDescriptionEvent(ev *replication.BinlogEvent) (
 		}
 		err = w.Flush()
 		if err != nil {
-			return WResult{}, terror.Annotatef(err, "write binlog file header for %s", fullName)
+			return WResult{}, terror.Annotatef(err, "flush binlog file for %s", fullName)
 		}
 	}
 

dm/relay/relay_writer_test.go

@@ -237,7 +237,7 @@ func (t *testFileWriterSuite) TestRotateEventWithFormatDescriptionEvent(c *check
 	defer w1.Close()
 	w1.Init(uuid, filename)
 	_, err = w1.WriteEvent(rotateEv)
-	c.Assert(err, check.ErrorMatches, ".*file not opened.*")
+	c.Assert(err, check.ErrorMatches, ".*no underlying writer opened")
 
 	// 2. fake RotateEvent before FormatDescriptionEvent
 	relayDir = c.MkDir() // use a new relay directory