[#1560] morph/client: Perform RPC switch and restore in one step

Otherwise we could switch infinitely if subscription restore has failed.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/morph/client/client.go

@@ -54,9 +54,11 @@ type Client struct {
 
 	cfg cfg
 
-	endpoints *endpoints
+	endpoints endpoints
 
-	// switching between rpc endpoint lock
+	// switchLock protects endpoints, inactive, and subscription-related fields.
+	// It is taken exclusively during endpoint switch and locked in shared mode
+	// on every normal call.
 	switchLock *sync.RWMutex
 
 	// channel for ws notifications

pkg/morph/client/constructor.go

@@ -111,7 +111,7 @@ func New(key *keys.PrivateKey, endpoint string, opts ...Option) (*Client, error)
 		// they will be used in switch process, otherwise
 		// inactive mode will be enabled
 		cli.client = cfg.singleCli
-		cli.endpoints = newEndpoints(cfg.extraEndpoints)
+		cli.endpoints.init(cfg.extraEndpoints)
 	} else {
 		ws, err := newWSClient(*cfg, endpoint)
 		if err != nil {
@@ -124,7 +124,7 @@ func New(key *keys.PrivateKey, endpoint string, opts ...Option) (*Client, error)
 		}
 
 		cli.client = ws
-		cli.endpoints = newEndpoints(append([]string{endpoint}, cfg.extraEndpoints...))
+		cli.endpoints.init(append([]string{endpoint}, cfg.extraEndpoints...))
 	}
 
 	go cli.notificationLoop()

pkg/morph/client/multi.go

@@ -9,11 +9,9 @@ type endpoints struct {
 	list []string
 }
 
-func newEndpoints(ee []string) *endpoints {
-	return &endpoints{
-		curr: 0,
-		list: ee,
-	}
+func (e *endpoints) init(ee []string) {
+	e.curr = 0
+	e.list = ee
 }
 
 // next returns the next endpoint and its index
@@ -90,6 +88,19 @@ func (c *Client) switchRPC() bool {
 		c.cache.invalidate()
 		c.client = cli
 
+		c.logger.Info("connection to the new RPC node has been established",
+			zap.String("endpoint", newEndpoint))
+
+		if !c.restoreSubscriptions(newEndpoint) {
+			// new WS client does not allow
+			// restoring subscription, client
+			// could not work correctly =>
+			// closing connection to RPC node
+			// to switch to another one
+			cli.Close()
+			continue
+		}
+
 		return true
 	}
 }
@@ -133,21 +144,6 @@ func (c *Client) notificationLoop() {
 					return
 				}
 
-				newEndpoint, _ := c.endpoints.current()
-
-				c.logger.Warn("connection to the new RPC node has been established",
-					zap.String("endpoint", newEndpoint),
-				)
-
-				if !c.restoreSubscriptions() {
-					// new WS client does not allow
-					// restoring subscription, client
-					// could not work correctly =>
-					// closing connection to RPC node
-					// to switch to another one
-					c.client.Close()
-				}
-
 				// TODO(@carpawell): call here some callback retrieved in constructor
 				// of the client to allow checking chain state since during switch
 				// process some notification could be lost

pkg/morph/client/notifications.go

@@ -204,16 +204,12 @@ func (c *Client) UnsubscribeAll() error {
 
 // restoreSubscriptions restores subscriptions according to
 // cached information about them.
-func (c *Client) restoreSubscriptions() bool {
+func (c *Client) restoreSubscriptions(endpoint string) bool {
 	var (
-		err         error
-		id          string
-		endpoint, _ = c.endpoints.current()
+		err error
+		id  string
 	)
 
-	c.switchLock.Lock()
-	defer c.switchLock.Unlock()
-
 	// new block events restoration
 	if c.subscribedToNewBlocks {
 		_, err = c.client.SubscribeForNewBlocks(nil)