fix(connection): send fault if frontend disconnect

Author: JavierRibaldelRio

backend/cmd/setup_vehicle.go

@@ -64,6 +64,15 @@ func configureBroker(subloggers abstraction.SubloggersMap, loggerHandler *logger
 	pool := websocket.NewPool(connections, trace.Logger)
 	pool.SetOnDisconnect(func(count int) {
 		if count == 0 {
+			// Losing the last control-station GUI (closed, crashed or hung:
+			// heartbeats stop and the read deadline expires) must put the
+			// vehicle in a safe state, as required by competition rules.
+			trace.Warn().Msg("no clients connected, sending FAULT order")
+			faultOrder := &order_topic.Order{Id: 0, Fields: map[string]order_topic.Field{}}
+			if err := broker.UserPush(faultOrder); err != nil {
+				trace.Error().Err(err).Msg("failed to send fault order on client disconnect")
+			}
+
 			trace.Info().Msg("no clients connected, stopping logger")
 			loggerHandler.Stop()
 			if err := loggerTopic.NotifyStopped(); err != nil {

backend/pkg/websocket/client.go

@@ -9,6 +9,15 @@ import (
 	ws "github.com/gorilla/websocket"
 )
 
+// HeartbeatTopic is the liveness message every frontend sends once per
+// second. It is consumed by the websocket layer and never reaches the broker.
+const HeartbeatTopic = "connection/heartbeat"
+
+// heartbeatTimeout bounds how long a dead or frozen frontend goes undetected:
+// if no message (the heartbeat guarantees one per second) arrives within this
+// window, Read fails and the client is treated as disconnected.
+const heartbeatTimeout = 3 * time.Second
+
 type Client struct {
 	readMx    *sync.Mutex
 	writeMx   *sync.Mutex
@@ -26,6 +35,8 @@ func NewClient(conn *ws.Conn) *Client {
 		onClose:   func() {},
 	}
 
+	conn.SetReadDeadline(time.Now().Add(heartbeatTimeout))
+
 	return client
 }
 
@@ -46,6 +57,9 @@ func (client *Client) Read() (Message, error) {
 
 	var message Message
 	err := client.conn.ReadJSON(&message)
+	if err == nil {
+		client.conn.SetReadDeadline(time.Now().Add(heartbeatTimeout))
+	}
 	return message, err
 }
 

backend/pkg/websocket/pool.go

@@ -84,6 +84,13 @@ func (pool *Pool) handle(id ClientId, client *Client) {
 		}
 
 		clientLogger.Trace().Msg("read")
+
+		// Heartbeats only refresh the read deadline; they carry no payload
+		// for the broker.
+		if string(message.Topic) == HeartbeatTopic {
+			continue
+		}
+
 		pool.onMessage(id, &message)
 	}
 }

frontend/frontend-kit/core/src/websocket.ts

@@ -64,6 +64,11 @@ class SocketService {
    */
   private ws: WebSocketSubject<any> | null = null;
 
+  /**
+   * Handle of the interval that emits the liveness heartbeat while connected.
+   */
+  private heartbeatInterval: ReturnType<typeof setInterval> | null = null;
+
   /**
    * Connects to the WebSocket server by creating a new connection object and pushing it to `socketSource$`.
    * @param port - the port to connect to. Defaults to 4000.
@@ -81,6 +86,7 @@ class SocketService {
         next: () => {
           this.status$.next("connected");
           logger.core.log("WebSocket connected");
+          this.startHeartbeat();
         },
       },
     });
@@ -102,10 +108,30 @@ class SocketService {
     this.socketSource$.next(this.ws);
   }
 
+  /**
+   * Starts the periodic heartbeat that lets the backend detect a dead or
+   * frozen GUI. The backend expects one at least every 3 seconds and treats
+   * a missing heartbeat as a disconnection.
+   */
+  private startHeartbeat() {
+    this.stopHeartbeat();
+    this.heartbeatInterval = setInterval(() => {
+      this.ws?.next({ topic: "connection/heartbeat", payload: {} });
+    }, 1000);
+  }
+
+  private stopHeartbeat() {
+    if (this.heartbeatInterval !== null) {
+      clearInterval(this.heartbeatInterval);
+      this.heartbeatInterval = null;
+    }
+  }
+
   /**
    * Cleans up the WebSocket connection by setting the connection object to null and updating the status to "disconnected".
    */
   private cleanup() {
+    this.stopHeartbeat();
     this.ws = null;
     this.status$.next("disconnected");
   }