rafthttp: stop printing log when attaching stream with the same term

There is no need to print log when attaching stream with the same
term because the stream is installed back immediately.

This happens a lot when etcd 2.1 connects to etcd 2.0, so we make
the change.

rafthttp/streamer.go

@@ -76,9 +76,12 @@ func (s *stream) attach(sw *streamWriter) error {
 		// ignore lower-term streaming request
 		if sw.term < s.w.term {
 			return fmt.Errorf("cannot attach out of data stream server [%d / %d]", sw.term, s.w.term)
-		}
+		} else if sw.term == s.w.term {
+			s.w.stopWithoutLog()
+		} else {
 			s.w.stop()
 		}
+	}
 	s.w = sw
 	return nil
 }
@@ -156,6 +159,7 @@ type streamWriter struct {
 	fs       *stats.FollowerStats
 	q        chan []raftpb.Entry
 	done     chan struct{}
+	printLog bool
 }
 
 // newStreamWriter starts and returns a new unstarted stream writer.
@@ -166,6 +170,7 @@ func newStreamWriter(to types.ID, term uint64) *streamWriter {
 		term:     term,
 		q:        make(chan []raftpb.Entry, streamBufSize),
 		done:     make(chan struct{}),
+		printLog: true,
 	}
 	return s
 }
@@ -188,7 +193,9 @@ func (s *streamWriter) send(ents []raftpb.Entry) error {
 func (s *streamWriter) handle(w WriteFlusher) {
 	defer func() {
 		close(s.done)
+		if s.printLog {
 			log.Printf("rafthttp: server streaming to %s at term %d has been stopped", s.to, s.term)
+		}
 	}()
 
 	ew := newEntryWriter(w, s.to)
@@ -215,6 +222,11 @@ func (s *streamWriter) stop() {
 	<-s.done
 }
 
+func (s *streamWriter) stopWithoutLog() {
+	s.printLog = false
+	s.stop()
+}
+
 func (s *streamWriter) stopNotify() <-chan struct{} { return s.done }
 
 // TODO: move the raft interface out of the reader.