Merge pull request #3532 from nspcc-dev/fix/ws-client-subscription-panic

rpcclient/WS: fix data race on concurrent (un)subscription

pkg/rpcclient/wsclient.go

@@ -960,6 +960,14 @@ func (c *WSClient) UnsubscribeAll() error {
 // after WS RPC unsubscription request is completed. Until then the subscriber channel
 // may still receive WS notifications.
 func (c *WSClient) performUnsubscription(id string) error {
+	c.subscriptionsLock.RLock()
+	rcvrWas, ok := c.subscriptions[id]
+	c.subscriptionsLock.RUnlock()
+
+	if !ok {
+		return errors.New("no subscription with this ID")
+	}
+
 	var resp bool
 	if err := c.performRequest("unsubscribe", []any{id}, &resp); err != nil {
 		return err
@@ -975,6 +983,15 @@ func (c *WSClient) performUnsubscription(id string) error {
 	if !ok {
 		return errors.New("no subscription with this ID")
 	}
+
+	cleanUpSubscriptions := true
+	if rcvrWas.Receiver() != rcvr.Receiver() {
+		// concurrent subscription has been done and been overwritten; this
+		// is not this routine's subscription, cleanup only receivers map
+		rcvr = rcvrWas
+		cleanUpSubscriptions = false
+	}
+
 	ch := rcvr.Receiver()
 	ids := c.receivers[ch]
 	for i, rcvrID := range ids {
@@ -988,7 +1005,9 @@ func (c *WSClient) performUnsubscription(id string) error {
 	} else {
 		c.receivers[ch] = ids
 	}
-	delete(c.subscriptions, id)
+	if cleanUpSubscriptions {
+		delete(c.subscriptions, id)
+	}
 	return nil
 }