fix a race in the stream code

stream.go

@@ -64,7 +64,7 @@ func (s *streamKey) generateID(now time.Time) string {
 		next = fmt.Sprintf("%d-%d", last[0], last[1]+1)
 	}
 
-	lastID := s.lastID()
+	lastID := s.lastIDUnlocked()
 	if streamCmp(lastID, next) >= 0 {
 		last, _ := parseStreamID(lastID)
 		next = fmt.Sprintf("%d-%d", last[0], last[1]+1)
@@ -74,8 +74,16 @@ func (s *streamKey) generateID(now time.Time) string {
 	return next
 }
 
-// lastID doesn't lock the mutex
+// lastID locks the mutex
 func (s *streamKey) lastID() string {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	return s.lastIDUnlocked()
+}
+
+// lastID doesn't lock the mutex
+func (s *streamKey) lastIDUnlocked() string {
 	if len(s.entries) == 0 {
 		return "0-0"
 	}
@@ -209,7 +217,7 @@ func (s *streamKey) createGroup(group, id string) error {
 	}
 
 	if id == "$" {
-		id = s.lastID()
+		id = s.lastIDUnlocked()
 	}
 	s.groups[group] = &streamGroup{
 		stream:    s,
@@ -237,7 +245,7 @@ func (s *streamKey) add(entryID string, values []string, now time.Time) (string,
 	if entryID == "0-0" {
 		return "", errors.New(msgStreamIDZero)
 	}
-	if streamCmp(s.lastID(), entryID) != -1 {
+	if streamCmp(s.lastIDUnlocked(), entryID) != -1 {
 		return "", errors.New(msgStreamIDTooSmall)
 	}