fix wrong logic in event.go

store/event.go

@@ -140,19 +140,18 @@ func (eh *EventHistory) scan(prefix string, index uint64) (*Event, error) {
 	eh.rwl.RLock()
 	defer eh.rwl.RUnlock()
 
-	start := index - eh.StartIndex + eh.DupCnt
+	start := index - eh.StartIndex
 
 	// the index should locate after the event history's StartIndex
-	// and before its size
-
 	if start < 0 {
-		// TODO: Add error type
 		return nil,
 			etcdErr.NewError(etcdErr.EcodeEventIndexCleared,
-				fmt.Sprintf("prefix:%v index:%v", prefix, index))
+				fmt.Sprintf("the requested history has been cleared [%v/%v]",
+					eh.StartIndex, index))
 	}
 
-	if start >= uint64(eh.Queue.Size) {
+	// the index should locate before the size of the queue minus the duplicate count
+	if start >= (uint64(eh.Queue.Size) - eh.DupCnt) { // future index
 		return nil, nil
 	}
 
@@ -160,14 +159,13 @@ func (eh *EventHistory) scan(prefix string, index uint64) (*Event, error) {
 
 	for {
 		e := eh.Queue.Events[i]
-		if strings.HasPrefix(e.Key, prefix) {
+		if strings.HasPrefix(e.Key, prefix) && index <= e.Index { // make sure we bypass the smaller one
 			return e, nil
 		}
 
 		i = (i + 1) % eh.Queue.Capacity
 
-		if i == eh.Queue.back() {
-			// TODO: Add error type
+		if i == eh.Queue.back() { // find nothing, return and watch from current index
 			return nil, nil
 		}
 	}