[MM-50990] Fix potential rtcd client leak (#350)

* Fix client connection leak on version checking failure

* Skip check for master builds

* Abort reconnection if host is either missing or flagged

server/rtcd.go

@@ -88,10 +88,6 @@ func (p *Plugin) newRTCDClientManager(rtcdURL string) (m *rtcdClientManager, err
 			return nil, err
 		}
 
-		if err := m.versionCheck(client); err != nil {
-			return nil, fmt.Errorf("version compatibility check failed: %w", err)
-		}
-
 		if err := m.addHost(ip.String(), client); err != nil {
 			return nil, fmt.Errorf("failed to add host: %w", err)
 		}
@@ -143,10 +139,7 @@ func (m *rtcdClientManager) hostsChecker() {
 
 			// we look for newly advertised hosts we may not have a client for yet.
 			for ip := range ipsMap {
-				m.mut.RLock()
-				_, ok := m.hosts[ip]
-				m.mut.RUnlock()
-				if !ok {
+				if h := m.getHost(ip); h == nil {
 					// create new client
 
 					// We add some jitter to try and avoid multiple clients to attempt
@@ -160,11 +153,6 @@ func (m *rtcdClientManager) hostsChecker() {
 						continue
 					}
 
-					if err := m.versionCheck(client); err != nil {
-						m.ctx.LogError(fmt.Sprintf("version compatibility check failed: %s", err.Error()), "host", ip)
-						continue
-					}
-
 					if err := m.addHost(ip, client); err != nil {
 						m.ctx.LogError(fmt.Sprintf("failed to add host: %s", err.Error()), "host", ip)
 						continue
@@ -220,6 +208,12 @@ func (m *rtcdClientManager) addHost(host string, client *rtcd.Client) (err error
 	return nil
 }
 
+func (m *rtcdClientManager) getHost(ip string) *rtcdHost {
+	m.mut.RLock()
+	defer m.mut.RUnlock()
+	return m.hosts[ip]
+}
+
 // GetHostForNewCall returns the host to which a new call should be routed.
 // It performs a simple round-robin strategy based on number of calls.
 // New calls are routed to the non-flagged host with the smaller count.
@@ -264,12 +258,9 @@ func (m *rtcdClientManager) Send(msg rtcd.ClientMessage, callID string) error {
 	}
 	host := state.Call.RTCDHost
 
-	m.mut.RLock()
-	h := m.hosts[host]
-	m.mut.RUnlock()
-
 	var client *rtcd.Client
-	if h == nil {
+	if h := m.getHost(host); h == nil {
+		m.ctx.LogDebug("creating client for missing host on send", "host", host)
 		client, err = m.newRTCDClient(m.rtcdURL, host, getDialFn(host, m.rtcdPort))
 		if err != nil {
 			return fmt.Errorf("failed to create new client: %w", err)
@@ -332,7 +323,8 @@ func (m *rtcdClientManager) versionCheck(client *rtcd.Client) error {
 	}
 
 	// Always support dev builds.
-	if info.BuildVersion == "" || strings.HasPrefix(info.BuildVersion, "dev") {
+	if info.BuildVersion == "" || info.BuildVersion == "master" || strings.HasPrefix(info.BuildVersion, "dev") {
+		m.ctx.LogInfo("skipping version compatibility check", "buildVersion", info.BuildVersion)
 		return nil
 	}
 
@@ -365,6 +357,18 @@ func (m *rtcdClientManager) newRTCDClient(rtcdURL, host string, dialFn rtcd.Dial
 			return fmt.Errorf("max reconnection attempts reached, removing client")
 		}
 
+		h := m.getHost(host)
+		if h == nil {
+			return fmt.Errorf("host is missing")
+		}
+
+		if h.isFlagged() {
+			if err := m.removeHost(host); err != nil {
+				m.ctx.LogError("failed to remove rtcd client: %w", err)
+			}
+			return fmt.Errorf("host was flagged")
+		}
+
 		// On disconnect, it's possible the rtcd server restarted
 		// and cleared its stored credentials, so we attempt to connect and
 		// register again if that fails.
@@ -399,6 +403,13 @@ func (m *rtcdClientManager) newRTCDClient(rtcdURL, host string, dialFn rtcd.Dial
 		return nil, err
 	}
 
+	if err := m.versionCheck(client); err != nil {
+		if err := client.Close(); err != nil {
+			m.ctx.LogError(fmt.Sprintf("failed to close client: %s", err.Error()))
+		}
+		return nil, fmt.Errorf("version compatibility check failed: %w", err)
+	}
+
 	return client, nil
 }
 
@@ -641,3 +652,9 @@ func (m *rtcdClientManager) clientReader(client *rtcd.Client) {
 		}
 	}
 }
+
+func (h *rtcdHost) isFlagged() bool {
+	h.mut.RLock()
+	defer h.mut.RUnlock()
+	return h.flagged
+}