SignalR & Real-time

The Frontend API uses SignalR (backed by Azure SignalR Service) to provide real-time updates to connected clients. The CameraHub groups clients by camera ID and broadcasts image updates, activity logs, panorama images, and configuration changes.

CameraHub

Endpoint: /cameraHub
Protocol: WebSocket (wss://[hostname]/cameraHub)

Connection Flow

Hub Methods (Client → Server)

Method	Parameters	Description
JoinGroup	cameraId: string	Subscribe to updates for a specific camera. Adds the client's connection to the camera's SignalR group.
LeaveGroup	cameraId: string	Unsubscribe from a camera's updates. Removes the client from the group.

Broadcast Methods (Server → Group)

These methods send data to all clients in the specified camera group, excluding the sender.

Hub Method	Client Receive Event	Payload	Description
BroadcastImageToGroup	ReceiveImageBroadcast	SingleImageMetadataEntity	Broadcasts the latest captured image metadata for a camera
BroadcastActivityLogMessageToGroup	ReceiveActivityLogBroadcast	SingleImageMetadataEntity	Broadcasts activity log entries (PTZ moves, guard tour toggles, manual messages)
BroadcastPanoImageToGroup	ReceivePanoImageBroadcast	PanoImageMetadataEntity	Broadcasts the latest panorama image metadata
BroadcastCurrentConfigToGroup	ReceiveCurrentConfigBroadcast	string (JSON)	Broadcasts camera configuration changes

Deprecated Method

BroadcastSingleImageToGroup (client event: ReceiveBroadcast) is deprecated. Use BroadcastImageToGroup / ReceiveImageBroadcast instead.

Group Pattern

• Each camera has its own SignalR group identified by cameraId
• Clients can join multiple camera groups simultaneously
• Broadcasts are sent to all group members except the sender (Clients.GroupExcept)
• This prevents echo effects where the sender receives its own broadcast

---

BroadcastService (Server-Side)

The BroadcastService is a scoped service used by controllers to push activity log messages to SignalR groups from server-side operations (as opposed to client-initiated hub calls).

Method	Description
BroadcastActivityMessageToGroup(cameraId, message)	Sends an ActivityLogLatestByCamera record to all clients in the camera's group

Used by:

• ActivityLogController.AddMessage() — After inserting an activity log record, broadcasts it to the camera group
• CameraMovementController.ToggleGuardTour() — After toggling patrol mode, broadcasts the activity log entry
• CameraMovementController.MoveCameraHome() — After a home move completes, broadcasts the activity log entry
• FunctionEndpointsController.LeaseCameraAfterMove() — After the Image Acquisition callback processes a lease, broadcasts the activity log entry

---

Client Integration

Connecting to the Hub

// Example: JavaScript/TypeScript client connection
import { HubConnectionBuilder } from "@microsoft/signalr";

const connection = new HubConnectionBuilder()
  .withUrl("https://{api-hostname}/cameraHub")
  .withAutomaticReconnect()
  .build();

await connection.start();

Subscribing to Camera Updates

// Join a camera group
await connection.invoke("JoinGroup", "camera-001");

// Listen for image updates
connection.on("ReceiveImageBroadcast", (metadata) => {
  console.log("New image:", metadata.imageUrl);
});

// Listen for activity log updates
connection.on("ReceiveActivityLogBroadcast", (message) => {
  console.log("Activity:", message);
});

// Listen for panorama updates
connection.on("ReceivePanoImageBroadcast", (metadata) => {
  console.log("New panorama:", metadata.imageUrl);
});

// Listen for config changes
connection.on("ReceiveCurrentConfigBroadcast", (config) => {
  console.log("Config update:", config);
});

Leaving a Camera Group

await connection.invoke("LeaveGroup", "camera-001");

---

Configuration

SignalR is configured in ConfigureServices.cs and Program.cs:

// ConfigureServices.cs — Register SignalR with Azure backing
services.AddSignalR().AddAzureSignalR();

// Program.cs — Map the hub endpoint
app.MapHub<CameraHub>("/cameraHub");

The Azure SignalR Service connection string is loaded from Azure App Configuration / Key Vault. No local SignalR development server is needed — the Azure SignalR Service handles connection scaling in all environments.