[#337] morph: Move subscription logic to subscriber

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/morph/client/client.go

@@ -69,9 +69,6 @@ type Client struct {
 	// on every normal call.
 	switchLock *sync.RWMutex
 
-	notifications chan rpcclient.Notification
-	subsInfo      // protected with switchLock
-
 	// channel for internal stop
 	closeChan chan struct{}
 
@@ -566,26 +563,11 @@ func (c *Client) IsValidScript(script []byte, signers []transaction.Signer) (val
 
 // NotificationChannel returns channel than receives subscribed
 // notification from the connected RPC node.
-// Channel is closed when connection to the RPC node has been
+// Channel is closed when connection to the RPC node is lost.
-// lost without the possibility of recovery.
 func (c *Client) NotificationChannel() <-chan rpcclient.Notification {
-	return c.notifications
+	c.switchLock.RLock()
-}
+	defer c.switchLock.RUnlock()
-
+	return c.client.Notifications //lint:ignore SA1019 waits for neo-go v0.102.0 https://github.com/nspcc-dev/neo-go/pull/2980
-// inactiveMode switches Client to an inactive mode:
-// - notification channel is closed;
-// - all the new RPC request would return ErrConnectionLost;
-// - inactiveModeCb is called if not nil.
-func (c *Client) inactiveMode() {
-	c.switchLock.Lock()
-	defer c.switchLock.Unlock()
-
-	close(c.notifications)
-	c.inactive = true
-
-	if c.cfg.inactiveModeCb != nil {
-		c.cfg.inactiveModeCb()
-	}
 }
 
 func (c *Client) setActor(act *actor.Actor) {

pkg/morph/client/constructor.go

@@ -10,11 +10,8 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
 	lru "github.com/hashicorp/golang-lru/v2"
-	"github.com/nspcc-dev/neo-go/pkg/core/block"
-	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
 	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
 	"github.com/nspcc-dev/neo-go/pkg/rpcclient/actor"
 	"github.com/nspcc-dev/neo-go/pkg/util"
@@ -108,21 +105,13 @@ func New(ctx context.Context, key *keys.PrivateKey, opts ...Option) (*Client, er
 	}
 
 	cli := &Client{
-		cache:         newClientCache(),
+		cache:      newClientCache(),
-		logger:        cfg.logger,
+		logger:     cfg.logger,
-		acc:           acc,
+		acc:        acc,
-		accAddr:       accAddr,
+		accAddr:    accAddr,
-		cfg:           *cfg,
+		cfg:        *cfg,
-		switchLock:    &sync.RWMutex{},
+		switchLock: &sync.RWMutex{},
-		notifications: make(chan rpcclient.Notification),
+		closeChan:  make(chan struct{}),
-		subsInfo: subsInfo{
-			blockRcv:               make(chan *block.Block),
-			notificationRcv:        make(chan *state.ContainedNotificationEvent),
-			notaryReqRcv:           make(chan *result.NotaryRequestEvent),
-			subscribedEvents:       make(map[util.Uint160]string),
-			subscribedNotaryEvents: make(map[util.Uint160]string),
-		},
-		closeChan: make(chan struct{}),
 	}
 
 	cli.endpoints.init(cfg.endpoints)
@@ -162,7 +151,7 @@ func New(ctx context.Context, key *keys.PrivateKey, opts ...Option) (*Client, er
 	}
 	cli.setActor(act)
 
-	go cli.notificationLoop(ctx)
+	go cli.closeWaiter(ctx)
 
 	return cli, nil
 }

pkg/morph/client/multi.go

@@ -6,11 +6,6 @@ import (
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
-	"github.com/nspcc-dev/neo-go/pkg/core/block"
-	"github.com/nspcc-dev/neo-go/pkg/core/state"
-	"github.com/nspcc-dev/neo-go/pkg/neorpc"
-	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
-	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
 	"go.uber.org/zap"
 )
 
@@ -34,7 +29,8 @@ func (e *endpoints) init(ee []Endpoint) {
 	e.list = ee
 }
 
-func (c *Client) switchRPC(ctx context.Context) bool {
+// SwitchRPC performs reconnection and returns true if it was successful.
+func (c *Client) SwitchRPC(ctx context.Context) bool {
 	c.switchLock.Lock()
 	defer c.switchLock.Unlock()
 
@@ -58,20 +54,8 @@ func (c *Client) switchRPC(ctx context.Context) bool {
 		c.logger.Info(logs.ClientConnectionToTheNewRPCNodeHasBeenEstablished,
 			zap.String("endpoint", newEndpoint))
 
-		subs, ok := c.restoreSubscriptions(ctx, cli, newEndpoint, false)
-		if !ok {
-			// 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
-		}
-
 		c.client = cli
 		c.setActor(act)
-		c.subsInfo = subs
 
 		if c.cfg.switchInterval != 0 && !c.switchIsActive.Load() &&
 			c.endpoints.list[c.endpoints.curr].Priority != c.endpoints.list[0].Priority {
@@ -82,97 +66,21 @@ func (c *Client) switchRPC(ctx context.Context) bool {
 		return true
 	}
 
+	c.inactive = true
+
+	if c.cfg.inactiveModeCb != nil {
+		c.cfg.inactiveModeCb()
+	}
 	return false
 }
 
-func (c *Client) notificationLoop(ctx context.Context) {
+func (c *Client) closeWaiter(ctx context.Context) {
-	var e any
-	var ok bool
-
-	for {
-		c.switchLock.RLock()
-		bChan := c.blockRcv
-		nChan := c.notificationRcv
-		nrChan := c.notaryReqRcv
-		c.switchLock.RUnlock()
-
-		select {
-		case <-ctx.Done():
-			_ = c.UnsubscribeAll()
-			c.close()
-
-			return
-		case <-c.closeChan:
-			_ = c.UnsubscribeAll()
-			c.close()
-
-			return
-		case e, ok = <-bChan:
-		case e, ok = <-nChan:
-		case e, ok = <-nrChan:
-		}
-
-		if ok {
-			c.routeEvent(ctx, e)
-			continue
-		}
-
-		if !c.reconnect(ctx) {
-			return
-		}
-	}
-}
-
-func (c *Client) routeEvent(ctx context.Context, e any) {
-	typedNotification := rpcclient.Notification{Value: e}
-
-	switch e.(type) {
-	case *block.Block:
-		typedNotification.Type = neorpc.BlockEventID
-	case *state.ContainedNotificationEvent:
-		typedNotification.Type = neorpc.NotificationEventID
-	case *result.NotaryRequestEvent:
-		typedNotification.Type = neorpc.NotaryRequestEventID
-	}
-
 	select {
-	case c.notifications <- typedNotification:
 	case <-ctx.Done():
-		_ = c.UnsubscribeAll()
-		c.close()
 	case <-c.closeChan:
-		_ = c.UnsubscribeAll()
-		c.close()
 	}
-}
+	_ = c.UnsubscribeAll()
-
+	c.close()
-func (c *Client) reconnect(ctx context.Context) bool {
-	if closeErr := c.client.GetError(); closeErr != nil {
-		c.logger.Warn(logs.ClientSwitchingToTheNextRPCNode,
-			zap.String("reason", closeErr.Error()),
-		)
-	} else {
-		// neo-go client was closed by calling `Close`
-		// method, that happens only when a client has
-		// switched to the more prioritized RPC
-		return true
-	}
-
-	if !c.switchRPC(ctx) {
-		c.logger.Error(logs.ClientCouldNotEstablishConnectionToAnyRPCNode)
-
-		// could not connect to all endpoints =>
-		// switch client to inactive mode
-		c.inactiveMode()
-
-		return false
-	}
-
-	// 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
-
-	return true
 }
 
 func (c *Client) switchToMostPrioritized(ctx context.Context) {
@@ -218,36 +126,28 @@ mainLoop:
 					continue
 				}
 
-				if subs, ok := c.restoreSubscriptions(ctx, cli, tryE, true); ok {
+				c.switchLock.Lock()
-					c.switchLock.Lock()
-
-					// higher priority node could have been
-					// connected in the other goroutine
-					if e.Priority >= c.endpoints.list[c.endpoints.curr].Priority {
-						cli.Close()
-						c.switchLock.Unlock()
-						return
-					}
-
-					c.client.Close()
-					c.cache.invalidate()
-					c.client = cli
-					c.setActor(act)
-					c.subsInfo = subs
-					c.endpoints.curr = i
 
+				// higher priority node could have been
+				// connected in the other goroutine
+				if e.Priority >= c.endpoints.list[c.endpoints.curr].Priority {
+					cli.Close()
 					c.switchLock.Unlock()
-
-					c.logger.Info(logs.ClientSwitchedToTheHigherPriorityRPC,
-						zap.String("endpoint", tryE))
-
 					return
 				}
 
-				c.logger.Warn(logs.ClientCouldNotRestoreSideChainSubscriptionsUsingNode,
+				c.client.Close()
-					zap.String("endpoint", tryE),
+				c.cache.invalidate()
-					zap.Error(err),
+				c.client = cli
-				)
+				c.setActor(act)
+				c.endpoints.curr = i
+
+				c.switchLock.Unlock()
+
+				c.logger.Info(logs.ClientSwitchedToTheHigherPriorityRPC,
+					zap.String("endpoint", tryE))
+
+				return
 			}
 		}
 	}
@@ -255,6 +155,7 @@ mainLoop:
 
 // close closes notification channel and wrapped WS client.
 func (c *Client) close() {
-	close(c.notifications)
+	c.switchLock.RLock()
+	defer c.switchLock.RUnlock()
 	c.client.Close()
 }

pkg/morph/client/notifications.go

@@ -1,16 +1,11 @@
 package client
 
 import (
-	"context"
-
-	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
 	"github.com/nspcc-dev/neo-go/pkg/core/block"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/neorpc"
 	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
-	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
 	"github.com/nspcc-dev/neo-go/pkg/util"
-	"go.uber.org/zap"
 )
 
 // Close closes connection to the remote side making
@@ -24,71 +19,46 @@ func (c *Client) Close() {
 	close(c.closeChan)
 }
 
-// SubscribeForExecutionNotifications adds subscription for notifications
+// ReceiveExecutionNotifications performs subscription for notifications
-// generated during contract transaction execution to this instance of client.
+// generated during contract execution. Events are sent to the specified channel.
 //
 // Returns ErrConnectionLost if client has not been able to establish
 // connection to any of passed RPC endpoints.
-func (c *Client) SubscribeForExecutionNotifications(contract util.Uint160) error {
+func (c *Client) ReceiveExecutionNotifications(contract util.Uint160, ch chan<- *state.ContainedNotificationEvent) (string, error) {
 	c.switchLock.Lock()
 	defer c.switchLock.Unlock()
 
 	if c.inactive {
-		return ErrConnectionLost
+		return "", ErrConnectionLost
 	}
 
-	_, subscribed := c.subscribedEvents[contract]
+	return c.client.ReceiveExecutionNotifications(&neorpc.NotificationFilter{Contract: &contract}, ch)
-	if subscribed {
-		// no need to subscribe one more time
-		return nil
-	}
-
-	id, err := c.client.ReceiveExecutionNotifications(&neorpc.NotificationFilter{Contract: &contract}, c.notificationRcv)
-	if err != nil {
-		return err
-	}
-
-	c.subscribedEvents[contract] = id
-
-	return nil
 }
 
-// SubscribeForNewBlocks adds subscription for new block events to this
+// ReceiveBlocks performs subscription for new block events. Events are sent
-// instance of client.
+// to the specified channel.
 //
 // Returns ErrConnectionLost if client has not been able to establish
 // connection to any of passed RPC endpoints.
-func (c *Client) SubscribeForNewBlocks() error {
+func (c *Client) ReceiveBlocks(ch chan<- *block.Block) (string, error) {
 	c.switchLock.Lock()
 	defer c.switchLock.Unlock()
 
 	if c.inactive {
-		return ErrConnectionLost
+		return "", ErrConnectionLost
 	}
 
-	if c.subscribedToBlocks {
+	return c.client.ReceiveBlocks(nil, ch)
-		// no need to subscribe one more time
-		return nil
-	}
-
-	_, err := c.client.ReceiveBlocks(nil, c.blockRcv)
-	if err != nil {
-		return err
-	}
-
-	c.subscribedToBlocks = true
-
-	return nil
 }
 
-// SubscribeForNotaryRequests adds subscription for notary request payloads
+// ReceiveNotaryRequests performsn subscription for notary request payloads
 // addition or removal events to this instance of client. Passed txSigner is
 // used as filter: subscription is only for the notary requests that must be
-// signed by txSigner.
+// signed by txSigner. Events are sent to the specified channel.
 //
 // Returns ErrConnectionLost if client has not been able to establish
 // connection to any of passed RPC endpoints.
-func (c *Client) SubscribeForNotaryRequests(txSigner util.Uint160) error {
+func (c *Client) ReceiveNotaryRequests(txSigner util.Uint160, ch chan<- *result.NotaryRequestEvent) (string, error) {
 	if c.notary == nil {
 		panic(notaryNotEnabledPanicMsg)
 	}
@@ -97,30 +67,17 @@ func (c *Client) SubscribeForNotaryRequests(txSigner util.Uint160) error {
 	defer c.switchLock.Unlock()
 
 	if c.inactive {
-		return ErrConnectionLost
+		return "", ErrConnectionLost
 	}
 
-	_, subscribed := c.subscribedNotaryEvents[txSigner]
+	return c.client.ReceiveNotaryRequests(&neorpc.TxFilter{Signer: &txSigner}, ch)
-	if subscribed {
-		// no need to subscribe one more time
-		return nil
-	}
-
-	id, err := c.client.ReceiveNotaryRequests(&neorpc.TxFilter{Signer: &txSigner}, c.notaryReqRcv)
-	if err != nil {
-		return err
-	}
-
-	c.subscribedNotaryEvents[txSigner] = id
-
-	return nil
 }
 
-// UnsubscribeContract removes subscription for given contract event stream.
+// Unsubscribe performs unsubscription for the given subscription ID.
 //
 // Returns ErrConnectionLost if client has not been able to establish
 // connection to any of passed RPC endpoints.
-func (c *Client) UnsubscribeContract(contract util.Uint160) error {
+func (c *Client) Unsubscribe(subID string) error {
 	c.switchLock.Lock()
 	defer c.switchLock.Unlock()
 
@@ -128,55 +85,7 @@ func (c *Client) UnsubscribeContract(contract util.Uint160) error {
 		return ErrConnectionLost
 	}
 
-	_, subscribed := c.subscribedEvents[contract]
+	return c.client.Unsubscribe(subID)
-	if !subscribed {
-		// no need to unsubscribe contract
-		// without subscription
-		return nil
-	}
-
-	err := c.client.Unsubscribe(c.subscribedEvents[contract])
-	if err != nil {
-		return err
-	}
-
-	delete(c.subscribedEvents, contract)
-
-	return nil
-}
-
-// UnsubscribeNotaryRequest removes subscription for given notary requests
-// signer.
-//
-// Returns ErrConnectionLost if client has not been able to establish
-// connection to any of passed RPC endpoints.
-func (c *Client) UnsubscribeNotaryRequest(signer util.Uint160) error {
-	if c.notary == nil {
-		panic(notaryNotEnabledPanicMsg)
-	}
-
-	c.switchLock.Lock()
-	defer c.switchLock.Unlock()
-
-	if c.inactive {
-		return ErrConnectionLost
-	}
-
-	_, subscribed := c.subscribedNotaryEvents[signer]
-	if !subscribed {
-		// no need to unsubscribe signer's
-		// requests without subscription
-		return nil
-	}
-
-	err := c.client.Unsubscribe(c.subscribedNotaryEvents[signer])
-	if err != nil {
-		return err
-	}
-
-	delete(c.subscribedNotaryEvents, signer)
-
-	return nil
 }
 
 // UnsubscribeAll removes all active subscriptions of current client.
@@ -191,163 +100,10 @@ func (c *Client) UnsubscribeAll() error {
 		return ErrConnectionLost
 	}
 
-	// no need to unsubscribe if there are
-	// no active subscriptions
-	if len(c.subscribedEvents) == 0 && len(c.subscribedNotaryEvents) == 0 &&
-		!c.subscribedToBlocks {
-		return nil
-	}
-
 	err := c.client.UnsubscribeAll()
 	if err != nil {
 		return err
 	}
 
-	c.subscribedEvents = make(map[util.Uint160]string)
-	c.subscribedNotaryEvents = make(map[util.Uint160]string)
-	c.subscribedToBlocks = false
-
 	return nil
 }
-
-// subsInfo includes channels for ws notifications;
-// cached subscription information.
-type subsInfo struct {
-	blockRcv        chan *block.Block
-	notificationRcv chan *state.ContainedNotificationEvent
-	notaryReqRcv    chan *result.NotaryRequestEvent
-
-	subscribedToBlocks     bool
-	subscribedEvents       map[util.Uint160]string
-	subscribedNotaryEvents map[util.Uint160]string
-}
-
-// restoreSubscriptions restores subscriptions according to cached
-// information about them.
-//
-// If it is NOT a background operation switchLock MUST be held.
-// Returns a pair: the second is a restoration status and the first
-// one contains subscription information applied to the passed cli
-// and receivers for the updated subscriptions.
-// Does not change Client instance.
-func (c *Client) restoreSubscriptions(ctx context.Context, cli *rpcclient.WSClient, endpoint string, background bool) (si subsInfo, ok bool) {
-	var (
-		err error
-		id  string
-	)
-
-	stopCh := make(chan struct{})
-	defer close(stopCh)
-
-	blockRcv := make(chan *block.Block)
-	notificationRcv := make(chan *state.ContainedNotificationEvent)
-	notaryReqRcv := make(chan *result.NotaryRequestEvent)
-
-	c.startListen(ctx, stopCh, blockRcv, notificationRcv, notaryReqRcv, background)
-
-	if background {
-		c.switchLock.RLock()
-		defer c.switchLock.RUnlock()
-	}
-
-	si.subscribedToBlocks = c.subscribedToBlocks
-	si.subscribedEvents = copySubsMap(c.subscribedEvents)
-	si.subscribedNotaryEvents = copySubsMap(c.subscribedNotaryEvents)
-	si.blockRcv = blockRcv
-	si.notificationRcv = notificationRcv
-	si.notaryReqRcv = notaryReqRcv
-
-	// new block events restoration
-	if si.subscribedToBlocks {
-		_, err = cli.ReceiveBlocks(nil, blockRcv)
-		if err != nil {
-			c.logger.Error(logs.ClientCouldNotRestoreBlockSubscriptionAfterRPCSwitch,
-				zap.String("endpoint", endpoint),
-				zap.Error(err),
-			)
-
-			return
-		}
-	}
-
-	// notification events restoration
-	for contract := range si.subscribedEvents {
-		contract := contract // See https://github.com/nspcc-dev/neo-go/issues/2890
-		id, err = cli.ReceiveExecutionNotifications(&neorpc.NotificationFilter{Contract: &contract}, notificationRcv)
-		if err != nil {
-			c.logger.Error(logs.ClientCouldNotRestoreNotificationSubscriptionAfterRPCSwitch,
-				zap.String("endpoint", endpoint),
-				zap.Error(err),
-			)
-
-			return
-		}
-
-		si.subscribedEvents[contract] = id
-	}
-
-	// notary notification events restoration
-	if c.notary != nil {
-		for signer := range si.subscribedNotaryEvents {
-			signer := signer // See https://github.com/nspcc-dev/neo-go/issues/2890
-			id, err = cli.ReceiveNotaryRequests(&neorpc.TxFilter{Signer: &signer}, notaryReqRcv)
-			if err != nil {
-				c.logger.Error(logs.ClientCouldNotRestoreNotaryNotificationSubscriptionAfterRPCSwitch,
-					zap.String("endpoint", endpoint),
-					zap.Error(err),
-				)
-
-				return
-			}
-
-			si.subscribedNotaryEvents[signer] = id
-		}
-	}
-
-	return si, true
-}
-
-func (c *Client) startListen(ctx context.Context, stopCh <-chan struct{}, blockRcv <-chan *block.Block,
-	notificationRcv <-chan *state.ContainedNotificationEvent, notaryReqRcv <-chan *result.NotaryRequestEvent, background bool) {
-	// neo-go WS client says to _always_ read notifications
-	// from its channel. Subscribing to any notification
-	// while not reading them in another goroutine may
-	// lead to a dead-lock, thus that async side notification
-	// listening while restoring subscriptions
-
-	go func() {
-		var e any
-		var ok bool
-
-		for {
-			select {
-			case <-stopCh:
-				return
-			case e, ok = <-blockRcv:
-			case e, ok = <-notificationRcv:
-			case e, ok = <-notaryReqRcv:
-			}
-
-			if !ok {
-				return
-			}
-
-			if background {
-				// background client (test) switch, no need to send
-				// any notification, just preventing dead-lock
-				continue
-			}
-
-			c.routeEvent(ctx, e)
-		}
-	}()
-}
-
-func copySubsMap(m map[util.Uint160]string) map[util.Uint160]string {
-	newM := make(map[util.Uint160]string, len(m))
-	for k, v := range m {
-		newM[k] = v
-	}
-
-	return newM
-}

pkg/morph/subscriber/subscriber.go

@@ -11,8 +11,8 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
 	"github.com/nspcc-dev/neo-go/pkg/core/block"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
-	"github.com/nspcc-dev/neo-go/pkg/neorpc"
 	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
+	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"go.uber.org/zap"
 )
@@ -35,16 +35,27 @@ type (
 		Close()
 	}
 
+	subChannels struct {
+		NotifyChan chan *state.ContainedNotificationEvent
+		BlockChan  chan *block.Block
+		NotaryChan chan *result.NotaryRequestEvent
+	}
+
 	subscriber struct {
 		*sync.RWMutex
 		log    *logger.Logger
 		client *client.Client
 
 		notifyChan chan *state.ContainedNotificationEvent
-
+		blockChan  chan *block.Block
-		blockChan chan *block.Block
-
 		notaryChan chan *result.NotaryRequestEvent
+
+		current subChannels
+
+		// cached subscription information
+		subscribedEvents       map[util.Uint160]bool
+		subscribedNotaryEvents map[util.Uint160]bool
+		subscribedToNewBlocks  bool
 	}
 
 	// Params is a group of Subscriber constructor parameters.
@@ -75,22 +86,28 @@ func (s *subscriber) SubscribeForNotification(contracts ...util.Uint160) error {
 	s.Lock()
 	defer s.Unlock()
 
-	notifyIDs := make(map[util.Uint160]struct{}, len(contracts))
+	notifyIDs := make([]string, 0, len(contracts))
 
 	for i := range contracts {
+		if s.subscribedEvents[contracts[i]] {
+			continue
+		}
 		// subscribe to contract notifications
-		err := s.client.SubscribeForExecutionNotifications(contracts[i])
+		id, err := s.client.ReceiveExecutionNotifications(contracts[i], s.current.NotifyChan)
 		if err != nil {
 			// if there is some error, undo all subscriptions and return error
-			for hash := range notifyIDs {
+			for _, id := range notifyIDs {
-				_ = s.client.UnsubscribeContract(hash)
+				_ = s.client.Unsubscribe(id)
 			}
 
 			return err
 		}
 
 		// save notification id
-		notifyIDs[contracts[i]] = struct{}{}
+		notifyIDs = append(notifyIDs, id)
+	}
+	for i := range contracts {
+		s.subscribedEvents[contracts[i]] = true
 	}
 
 	return nil
@@ -101,82 +118,34 @@ func (s *subscriber) Close() {
 }
 
 func (s *subscriber) BlockNotifications() error {
-	if err := s.client.SubscribeForNewBlocks(); err != nil {
+	s.Lock()
+	defer s.Unlock()
+	if s.subscribedToNewBlocks {
+		return nil
+	}
+	if _, err := s.client.ReceiveBlocks(s.current.BlockChan); err != nil {
 		return fmt.Errorf("could not subscribe for new block events: %w", err)
 	}
 
+	s.subscribedToNewBlocks = true
+
 	return nil
 }
 
 func (s *subscriber) SubscribeForNotaryRequests(mainTXSigner util.Uint160) error {
-	if err := s.client.SubscribeForNotaryRequests(mainTXSigner); err != nil {
+	s.Lock()
+	defer s.Unlock()
+	if s.subscribedNotaryEvents[mainTXSigner] {
+		return nil
+	}
+	if _, err := s.client.ReceiveNotaryRequests(mainTXSigner, s.current.NotaryChan); err != nil {
 		return fmt.Errorf("could not subscribe for notary request events: %w", err)
 	}
 
+	s.subscribedNotaryEvents[mainTXSigner] = true
 	return nil
 }
 
-func (s *subscriber) routeNotifications(ctx context.Context) {
-	notificationChan := s.client.NotificationChannel()
-
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case notification, ok := <-notificationChan:
-			if !ok {
-				s.log.Warn(logs.SubscriberRemoteNotificationChannelHasBeenClosed)
-				close(s.notifyChan)
-				close(s.blockChan)
-				close(s.notaryChan)
-
-				return
-			}
-
-			switch notification.Type {
-			case neorpc.NotificationEventID:
-				notifyEvent, ok := notification.Value.(*state.ContainedNotificationEvent)
-				if !ok {
-					s.log.Error(logs.SubscriberCantCastNotifyEventValueToTheNotifyStruct,
-						zap.String("received type", fmt.Sprintf("%T", notification.Value)),
-					)
-					continue
-				}
-
-				s.log.Debug(logs.SubscriberNewNotificationEventFromSidechain,
-					zap.String("name", notifyEvent.Name),
-				)
-
-				s.notifyChan <- notifyEvent
-			case neorpc.BlockEventID:
-				b, ok := notification.Value.(*block.Block)
-				if !ok {
-					s.log.Error(logs.SubscriberCantCastBlockEventValueToBlock,
-						zap.String("received type", fmt.Sprintf("%T", notification.Value)),
-					)
-					continue
-				}
-
-				s.blockChan <- b
-			case neorpc.NotaryRequestEventID:
-				notaryRequest, ok := notification.Value.(*result.NotaryRequestEvent)
-				if !ok {
-					s.log.Error(logs.SubscriberCantCastNotifyEventValueToTheNotaryRequestStruct,
-						zap.String("received type", fmt.Sprintf("%T", notification.Value)),
-					)
-					continue
-				}
-
-				s.notaryChan <- notaryRequest
-			default:
-				s.log.Debug(logs.SubscriberUnsupportedNotificationFromTheChain,
-					zap.Uint8("type", uint8(notification.Type)),
-				)
-			}
-		}
-	}
-}
-
 // New is a constructs Neo:Morph event listener and returns Subscriber interface.
 func New(ctx context.Context, p *Params) (Subscriber, error) {
 	switch {
@@ -200,16 +169,170 @@ func New(ctx context.Context, p *Params) (Subscriber, error) {
 		notifyChan: make(chan *state.ContainedNotificationEvent),
 		blockChan:  make(chan *block.Block),
 		notaryChan: make(chan *result.NotaryRequestEvent),
-	}
 
-	// Worker listens all events from neo-go websocket and puts them
+		current: newSubChannels(),
-	// into corresponding channel. It may be notifications, transactions,
+
-	// new blocks. For now only notifications.
+		subscribedEvents:       make(map[util.Uint160]bool),
+		subscribedNotaryEvents: make(map[util.Uint160]bool),
+	}
+	// Worker listens all events from temporary NeoGo channel and puts them
+	// into corresponding permanent channels.
 	go sub.routeNotifications(ctx)
 
 	return sub, nil
 }
 
+func (s *subscriber) routeNotifications(ctx context.Context) {
+	var (
+		// TODO: not needed after nspcc-dev/neo-go#2980.
+		cliCh             = s.client.NotificationChannel()
+		restoreCh         = make(chan bool)
+		restoreInProgress bool
+	)
+
+routeloop:
+	for {
+		var connLost bool
+		s.RLock()
+		curr := s.current
+		s.RUnlock()
+		select {
+		case <-ctx.Done():
+			break routeloop
+		case ev, ok := <-curr.NotifyChan:
+			if ok {
+				s.notifyChan <- ev
+			} else {
+				connLost = true
+			}
+		case ev, ok := <-curr.BlockChan:
+			if ok {
+				s.blockChan <- ev
+			} else {
+				connLost = true
+			}
+		case ev, ok := <-curr.NotaryChan:
+			if ok {
+				s.notaryChan <- ev
+			} else {
+				connLost = true
+			}
+		case _, ok := <-cliCh:
+			connLost = !ok
+		case ok := <-restoreCh:
+			restoreInProgress = false
+			if !ok {
+				connLost = true
+			}
+		}
+		if connLost {
+			if !restoreInProgress {
+				restoreInProgress, cliCh = s.switchEndpoint(ctx, restoreCh)
+				if !restoreInProgress {
+					break routeloop
+				}
+				curr.drain()
+			} else { // Avoid getting additional !ok events.
+				s.Lock()
+				s.current.NotifyChan = nil
+				s.current.BlockChan = nil
+				s.current.NotaryChan = nil
+				s.Unlock()
+			}
+		}
+	}
+	close(s.notifyChan)
+	close(s.blockChan)
+	close(s.notaryChan)
+}
+
+func (s *subscriber) switchEndpoint(ctx context.Context, finishCh chan<- bool) (bool, <-chan rpcclient.Notification) {
+	s.log.Info("RPC connection lost, attempting reconnect")
+	if !s.client.SwitchRPC(ctx) {
+		s.log.Error("can't switch RPC node")
+		return false, nil
+	}
+
+	cliCh := s.client.NotificationChannel()
+
+	s.Lock()
+	chs := newSubChannels()
+	go func() {
+		finishCh <- s.restoreSubscriptions(chs.NotifyChan, chs.BlockChan, chs.NotaryChan)
+	}()
+	s.current = chs
+	s.Unlock()
+
+	return true, cliCh
+}
+
+func newSubChannels() subChannels {
+	return subChannels{
+		NotifyChan: make(chan *state.ContainedNotificationEvent),
+		BlockChan:  make(chan *block.Block),
+		NotaryChan: make(chan *result.NotaryRequestEvent),
+	}
+}
+
+func (s *subChannels) drain() {
+drainloop:
+	for {
+		select {
+		case _, ok := <-s.NotifyChan:
+			if !ok {
+				s.NotifyChan = nil
+			}
+		case _, ok := <-s.BlockChan:
+			if !ok {
+				s.BlockChan = nil
+			}
+		case _, ok := <-s.NotaryChan:
+			if !ok {
+				s.NotaryChan = nil
+			}
+		default:
+			break drainloop
+		}
+	}
+}
+
+// restoreSubscriptions restores subscriptions according to
+// cached information about them.
+func (s *subscriber) restoreSubscriptions(notifCh chan<- *state.ContainedNotificationEvent,
+	blCh chan<- *block.Block, notaryCh chan<- *result.NotaryRequestEvent) bool {
+	var err error
+
+	// new block events restoration
+	if s.subscribedToNewBlocks {
+		_, err = s.client.ReceiveBlocks(blCh)
+		if err != nil {
+			s.log.Error(logs.ClientCouldNotRestoreBlockSubscriptionAfterRPCSwitch, zap.Error(err))
+			return false
+		}
+	}
+
+	// notification events restoration
+	for contract := range s.subscribedEvents {
+		contract := contract // See https://github.com/nspcc-dev/neo-go/issues/2890
+		_, err = s.client.ReceiveExecutionNotifications(contract, notifCh)
+		if err != nil {
+			s.log.Error(logs.ClientCouldNotRestoreNotificationSubscriptionAfterRPCSwitch, zap.Error(err))
+			return false
+		}
+	}
+
+	// notary notification events restoration
+	for signer := range s.subscribedNotaryEvents {
+		signer := signer // See https://github.com/nspcc-dev/neo-go/issues/2890
+		_, err = s.client.ReceiveNotaryRequests(signer, notaryCh)
+		if err != nil {
+			s.log.Error(logs.ClientCouldNotRestoreNotaryNotificationSubscriptionAfterRPCSwitch, zap.Error(err))
+			return false
+		}
+	}
+	return true
+}
+
 // awaitHeight checks if remote client has least expected block height and
 // returns error if it is not reached that height after timeout duration.
 // This function is required to avoid connections to unsynced RPC nodes, because