SignalR Skill
Real-time communication in VanDaemon uses SignalR for WebSocket-based updates between the .NET API and Blazor WASM frontend. The hub at /hubs/telemetry broadcasts tank levels, control states, and alerts to subscribed client groups. Background services poll hardware every 5 seconds and push changes via IHubContext.
Quick Start
Server Hub Definition
csharp
// src/Backend/VanDaemon.Api/Hubs/TelemetryHub.cs
public class TelemetryHub : Hub
{
public async Task SubscribeToTanks()
{
await Groups.AddToGroupAsync(Context.ConnectionId, "tanks");
}
public async Task SubscribeToControls()
{
await Groups.AddToGroupAsync(Context.ConnectionId, "controls");
}
public async Task SubscribeToAlerts()
{
await Groups.AddToGroupAsync(Context.ConnectionId, "alerts");
}
}
Broadcasting from Background Service
csharp
// Inject IHubContext<TelemetryHub> in background service
await _hubContext.Clients.Group("tanks").SendAsync(
"TankLevelUpdated", tankId, currentLevel, tankName, cancellationToken);
Blazor Client Connection
csharp
// In Blazor component
_hubConnection = new HubConnectionBuilder()
.WithUrl($"{_apiBaseUrl}/hubs/telemetry")
.WithAutomaticReconnect()
.Build();
_hubConnection.On<Guid, double, string>("TankLevelUpdated", (id, level, name) =>
{
// Update UI state
InvokeAsync(StateHasChanged);
});
await _hubConnection.StartAsync();
await _hubConnection.InvokeAsync("SubscribeToTanks");
Key Concepts
| Concept | Usage | Example |
|---|---|---|
| Hub | Server endpoint for connections | TelemetryHub : Hub |
| Groups | Broadcast to subset of clients | Groups.AddToGroupAsync(connectionId, "tanks") |
| IHubContext | Broadcast from services | _hubContext.Clients.Group("tanks").SendAsync(...) |
| On<T> | Client-side event handler | _hubConnection.On<Guid, double>("TankLevelUpdated", ...) |
| WithAutomaticReconnect | Resilient connections | .WithAutomaticReconnect() |
Common Patterns
Group-Based Subscriptions
When: Different clients need different update types.
csharp
// Client subscribes only to what it needs
await _hubConnection.InvokeAsync("SubscribeToTanks");
await _hubConnection.InvokeAsync("SubscribeToControls");
// Server broadcasts to specific group
await _hubContext.Clients.Group("controls").SendAsync(
"ControlStateChanged", controlId, newState, controlName);
Connection State Handling
When: UI needs to reflect connection status.
csharp
_hubConnection.Closed += async (error) =>
{
_isConnected = false;
await InvokeAsync(StateHasChanged);
};
_hubConnection.Reconnected += async (connectionId) =>
{
_isConnected = true;
await _hubConnection.InvokeAsync("SubscribeToTanks");
await InvokeAsync(StateHasChanged);
};
See Also
- •patterns - Server and client implementation patterns
- •workflows - Setup, testing, and deployment workflows
Related Skills
- •See the aspnet-core skill for API and DI configuration
- •See the blazor skill for frontend integration patterns
- •See the docker skill for nginx WebSocket proxy configuration