eth/filters: fix race in NewVotes and NewFinalizedHeaders (#3689)

Author: zlacfzy

eth/filters/api.go

@@ -246,18 +246,20 @@ func (api *FilterAPI) NewVotes(ctx context.Context) (*rpc.Subscription, error) {
 		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
 	}
 
-	rpcSub := notifier.CreateSubscription()
+	var (
+		rpcSub  = notifier.CreateSubscription()
+		votes   = make(chan *types.VoteEnvelope, 128)
+		voteSub = api.events.SubscribeNewVotes(votes)
+	)
 
 	gopool.Submit(func() {
-		votes := make(chan *types.VoteEnvelope, 128)
-		voteSub := api.events.SubscribeNewVotes(votes)
+		defer voteSub.Unsubscribe()
 
 		for {
 			select {
 			case vote := <-votes:
 				notifier.Notify(rpcSub.ID, vote)
 			case <-rpcSub.Err():
-				voteSub.Unsubscribe()
 				return
 			}
 		}
@@ -366,18 +368,20 @@ func (api *FilterAPI) NewFinalizedHeaders(ctx context.Context) (*rpc.Subscriptio
 		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
 	}
 
-	rpcSub := notifier.CreateSubscription()
+	var (
+		rpcSub     = notifier.CreateSubscription()
+		headers    = make(chan *types.Header)
+		headersSub = api.events.SubscribeNewFinalizedHeaders(headers)
+	)
 
 	gopool.Submit(func() {
-		headers := make(chan *types.Header)
-		headersSub := api.events.SubscribeNewFinalizedHeaders(headers)
+		defer headersSub.Unsubscribe()
 
 		for {
 			select {
 			case h := <-headers:
 				notifier.Notify(rpcSub.ID, h)
 			case <-rpcSub.Err():
-				headersSub.Unsubscribe()
 				return
 			}
 		}