[relay] Refactor initial Relay connection (#2800)

Can support firewalls with restricted WS rules

allow to run engine without Relay servers
keep up to date Relay address changes

client/internal/connect.go

@@ -232,6 +232,7 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, probes *ProbeHold
 
 		relayURLs, token := parseRelayInfo(loginResp)
 		relayManager := relayClient.NewManager(engineCtx, relayURLs, myPrivateKey.PublicKey().String())
+		c.statusRecorder.SetRelayMgr(relayManager)
 		if len(relayURLs) > 0 {
 			if token != nil {
 				if err := relayManager.UpdateToken(token); err != nil {
@@ -242,9 +243,7 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, probes *ProbeHold
 			log.Infof("connecting to the Relay service(s): %s", strings.Join(relayURLs, ", "))
 			if err = relayManager.Serve(); err != nil {
 				log.Error(err)
-				return wrapErr(err)
 			}
-			c.statusRecorder.SetRelayMgr(relayManager)
 		}
 
 		peerConfig := loginResp.GetPeerConfig()

client/internal/engine.go

@@ -538,6 +538,7 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 
 		relayMsg := wCfg.GetRelay()
 		if relayMsg != nil {
+			// when we receive token we expect valid address list too
 			c := &auth.Token{
 				Payload:   relayMsg.GetTokenPayload(),
 				Signature: relayMsg.GetTokenSignature(),
@@ -546,9 +547,16 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 				log.Errorf("failed to update relay token: %v", err)
 				return fmt.Errorf("update relay token: %w", err)
 			}
+
+			e.relayManager.UpdateServerURLs(relayMsg.Urls)
+
+			// Just in case the agent started with an MGM server where the relay was disabled but was later enabled.
+			// We can ignore all errors because the guard will manage the reconnection retries.
+			_ = e.relayManager.Serve()
+		} else {
+			e.relayManager.UpdateServerURLs(nil)
 		}
 
-		// todo update relay address in the relay manager
 		// todo update signal
 	}
 

client/internal/peer/status.go

@@ -676,25 +676,23 @@ func (d *Status) GetRelayStates() []relay.ProbeResult {
 	// extend the list of stun, turn servers with relay address
 	relayStates := slices.Clone(d.relayStates)
 
-	var relayState relay.ProbeResult
-
 	// if the server connection is not established then we will use the general address
 	// in case of connection we will use the instance specific address
 	instanceAddr, err := d.relayMgr.RelayInstanceAddress()
 	if err != nil {
 		// TODO add their status
-		if errors.Is(err, relayClient.ErrRelayClientNotConnected) {
-			for _, r := range d.relayMgr.ServerURLs() {
-				relayStates = append(relayStates, relay.ProbeResult{
-					URI: r,
-				})
-			}
-			return relayStates
+		for _, r := range d.relayMgr.ServerURLs() {
+			relayStates = append(relayStates, relay.ProbeResult{
+				URI: r,
+				Err: err,
+			})
 		}
-		relayState.Err = err
+		return relayStates
 	}
 
-	relayState.URI = instanceAddr
+	relayState := relay.ProbeResult{
+		URI: instanceAddr,
+	}
 	return append(relayStates, relayState)
 }
 

client/internal/peer/worker_ice.go

@@ -46,8 +46,6 @@ type WorkerICE struct {
 	hasRelayOnLocally bool
 	conn              WorkerICECallbacks
 
-	selectedPriority ConnPriority
-
 	agent    *ice.Agent
 	muxAgent sync.Mutex
 
@@ -95,10 +93,8 @@ func (w *WorkerICE) OnNewOffer(remoteOfferAnswer *OfferAnswer) {
 
 	var preferredCandidateTypes []ice.CandidateType
 	if w.hasRelayOnLocally && remoteOfferAnswer.RelaySrvAddress != "" {
-		w.selectedPriority = connPriorityICEP2P
 		preferredCandidateTypes = icemaker.CandidateTypesP2P()
 	} else {
-		w.selectedPriority = connPriorityICETurn
 		preferredCandidateTypes = icemaker.CandidateTypes()
 	}
 
@@ -159,7 +155,7 @@ func (w *WorkerICE) OnNewOffer(remoteOfferAnswer *OfferAnswer) {
 		RelayedOnLocal:             isRelayCandidate(pair.Local),
 	}
 	w.log.Debugf("on ICE conn read to use ready")
-	go w.conn.OnConnReady(w.selectedPriority, ci)
+	go w.conn.OnConnReady(selectedPriority(pair), ci)
 }
 
 // OnRemoteCandidate Handles ICE connection Candidate provided by the remote peer.
@@ -394,3 +390,11 @@ func isRelayed(pair *ice.CandidatePair) bool {
 	}
 	return false
 }
+
+func selectedPriority(pair *ice.CandidatePair) ConnPriority {
+	if isRelayed(pair) {
+		return connPriorityICETurn
+	} else {
+		return connPriorityICEP2P
+	}
+}

relay/client/client.go

@@ -140,7 +140,7 @@ type Client struct {
 	instanceURL      *RelayAddr
 	muInstanceURL    sync.Mutex
 
-	onDisconnectListener func()
+	onDisconnectListener func(string)
 	onConnectedListener  func()
 	listenerMutex        sync.Mutex
 }
@@ -233,7 +233,7 @@ func (c *Client) ServerInstanceURL() (string, error) {
 }
 
 // SetOnDisconnectListener sets a function that will be called when the connection to the relay server is closed.
-func (c *Client) SetOnDisconnectListener(fn func()) {
+func (c *Client) SetOnDisconnectListener(fn func(string)) {
 	c.listenerMutex.Lock()
 	defer c.listenerMutex.Unlock()
 	c.onDisconnectListener = fn
@@ -554,7 +554,7 @@ func (c *Client) notifyDisconnected() {
 	if c.onDisconnectListener == nil {
 		return
 	}
-	go c.onDisconnectListener()
+	go c.onDisconnectListener(c.connectionURL)
 }
 
 func (c *Client) notifyConnected() {

relay/client/client_test.go

@@ -551,7 +551,7 @@ func TestCloseByServer(t *testing.T) {
 	}
 
 	disconnected := make(chan struct{})
-	relayClient.SetOnDisconnectListener(func() {
+	relayClient.SetOnDisconnectListener(func(_ string) {
 		log.Infof("client disconnected")
 		close(disconnected)
 	})

relay/client/guard.go

@@ -4,65 +4,120 @@ import (
 	"context"
 	"time"
 
+	"github.com/cenkalti/backoff/v4"
 	log "github.com/sirupsen/logrus"
 )
 
 var (
-	reconnectingTimeout = 5 * time.Second
+	reconnectingTimeout = 60 * time.Second
 )
 
 // Guard manage the reconnection tries to the Relay server in case of disconnection event.
 type Guard struct {
-	ctx         context.Context
-	relayClient *Client
+	// OnNewRelayClient is a channel that is used to notify the relay client about a new relay client instance.
+	OnNewRelayClient chan *Client
+	serverPicker     *ServerPicker
 }
 
 // NewGuard creates a new guard for the relay client.
-func NewGuard(context context.Context, relayClient *Client) *Guard {
+func NewGuard(sp *ServerPicker) *Guard {
 	g := &Guard{
-		ctx:         context,
-		relayClient: relayClient,
+		OnNewRelayClient: make(chan *Client, 1),
+		serverPicker:     sp,
 	}
 	return g
 }
 
-// OnDisconnected is called when the relay client is disconnected from the relay server. It will trigger the reconnection
+// StartReconnectTrys is called when the relay client is disconnected from the relay server.
+// It attempts to reconnect to the relay server. The function first tries a quick reconnect
+// to the same server that was used before, if the server URL is still valid. If the quick
+// reconnect fails, it starts a ticker to periodically attempt server picking until it
+// succeeds or the context is done.
+//
+// Parameters:
+// - ctx: The context to control the lifecycle of the reconnection attempts.
+// - relayClient: The relay client instance that was disconnected.
 // todo prevent multiple reconnection instances. In the current usage it should not happen, but it is better to prevent
-func (g *Guard) OnDisconnected() {
-	if g.quickReconnect() {
+func (g *Guard) StartReconnectTrys(ctx context.Context, relayClient *Client) {
+	if relayClient == nil {
+		goto RETRY
+	}
+	if g.isServerURLStillValid(relayClient) && g.quickReconnect(ctx, relayClient) {
 		return
 	}
 
-	ticker := time.NewTicker(reconnectingTimeout)
+RETRY:
+	ticker := exponentTicker(ctx)
 	defer ticker.Stop()
 
 	for {
 		select {
 		case <-ticker.C:
-			err := g.relayClient.Connect()
-			if err != nil {
-				log.Errorf("failed to reconnect to relay server: %s", err)
+			if err := g.retry(ctx); err != nil {
+				log.Errorf("failed to pick new Relay server: %s", err)
 				continue
 			}
 			return
-		case <-g.ctx.Done():
+		case <-ctx.Done():
 			return
 		}
 	}
 }
 
-func (g *Guard) quickReconnect() bool {
-	ctx, cancel := context.WithTimeout(g.ctx, 1500*time.Millisecond)
+func (g *Guard) retry(ctx context.Context) error {
+	log.Infof("try to pick up a new Relay server")
+	relayClient, err := g.serverPicker.PickServer(ctx)
+	if err != nil {
+		return err
+	}
+
+	// prevent to work with a deprecated Relay client instance
+	g.drainRelayClientChan()
+
+	g.OnNewRelayClient <- relayClient
+	return nil
+}
+
+func (g *Guard) quickReconnect(parentCtx context.Context, rc *Client) bool {
+	ctx, cancel := context.WithTimeout(parentCtx, 1500*time.Millisecond)
 	defer cancel()
 	<-ctx.Done()
 
-	if g.ctx.Err() != nil {
+	if parentCtx.Err() != nil {
 		return false
 	}
+	log.Infof("try to reconnect to Relay server: %s", rc.connectionURL)
 
-	if err := g.relayClient.Connect(); err != nil {
+	if err := rc.Connect(); err != nil {
 		log.Errorf("failed to reconnect to relay server: %s", err)
 		return false
 	}
 	return true
 }
+
+func (g *Guard) drainRelayClientChan() {
+	select {
+	case <-g.OnNewRelayClient:
+	default:
+	}
+}
+
+func (g *Guard) isServerURLStillValid(rc *Client) bool {
+	for _, url := range g.serverPicker.ServerURLs.Load().([]string) {
+		if url == rc.connectionURL {
+			return true
+		}
+	}
+	return false
+}
+
+func exponentTicker(ctx context.Context) *backoff.Ticker {
+	bo := backoff.WithContext(&backoff.ExponentialBackOff{
+		InitialInterval: 2 * time.Second,
+		Multiplier:      2,
+		MaxInterval:     reconnectingTimeout,
+		Clock:           backoff.SystemClock,
+	}, ctx)
+
+	return backoff.NewTicker(bo)
+}