Client Manager

ClientManager tracks all connected clients and enables server-to-client RPC from anywhere — controllers, background services, or other hubs. Inject it from DI as a singleton.

Inject ClientManager

public class NotificationService
{
    private readonly ClientManager _clients;

    public NotificationService(ClientManager clients) => _clients = clients;

    public void NotifyUser(string connectionId)
    {
        var methods = _clients.GetTypedMethods<IChatClient>(connectionId);
        methods.ReceiveMessage("System", "You have a new notification");
    }
}

Query clients

Method	Description
GetClientById(string id)	Get a single client by connection ID
GetAllClients()	All connected clients
GetAllClients(predicate)	Filter clients by a predicate
GetHARRRClients<T>()	Clients connected to a specific hub type
GetHARRRClients<T>(predicate)	Filter clients of a specific hub type

Examples

// Get all clients connected to the ChatHub
var chatClients = _clients.GetHARRRClients<ChatHub>();

// Find a specific user
var adminClients = _clients.GetAllClients(c =>
    c.User.IsInRole("Admin"));

// Filter by custom attributes
var mobileClients = _clients.GetAllClients()
    .WithAttribute("Platform", "iOS");

Typed extension methods

Extension methods on ClientManager combine client lookup and typed proxy creation in one step:

Method	Description
GetTypedMethods<T>(connectionId)	Typed proxy for a specific client
GetAllTypedMethods<T>()	(ClientContext, T) tuples for all clients
GetTypedMethodsForHub<T, THub>()	(ClientContext, T) tuples scoped to a hub type

// Call a single client by ID
var methods = _clients.GetTypedMethods<IChatClient>(connectionId);
methods.ReceiveMessage("System", "Hello!");

// Broadcast to all clients (typed)
foreach (var (ctx, methods) in _clients.GetAllTypedMethods<IChatClient>())
{
    methods.ReceiveMessage("System", $"Hello {ctx.Id}!");
}

// Broadcast scoped to a specific hub type
foreach (var (ctx, methods) in _clients.GetTypedMethodsForHub<IChatClient, AppHub>())
{
    methods.ReceiveMessage("System", "Hub-scoped broadcast");
}

Collection extensions on ClientContext

IEnumerable<ClientContext> has extension methods for batch invocations:

Method	Description
InvokeAllAsync<T>(method, args, ct)	Invoke method on all clients, await all results
InvokeOneAsync<T>(method, args, ct)	Invoke on clients until one succeeds
WithAttribute(key)	Filter by attribute existence
WithAttribute(key, value)	Filter by attribute key-value match

// Ask all clients with a specific attribute and get the first successful response
var result = await _clients.GetAllClients()
    .WithAttribute("Tag", "primary")
    .InvokeOneAsync<string>("GetStatus", Array.Empty<object>(), ct);
// result.ClientId — which client responded
// result.Value — the return value

Use in controllers

[ApiController]
[Route("api/[controller]")]
public class NotificationController : ControllerBase
{
    private readonly ClientManager _clients;

    public NotificationController(ClientManager clients) => _clients = clients;

    [HttpPost("broadcast")]
    public IActionResult Broadcast([FromBody] string message)
    {
        foreach (var (_, methods) in _clients.GetTypedMethodsForHub<IChatClient, AppHub>())
        {
            methods.ReceiveMessage("API", message);
        }
        return Ok();
    }
}

Use in background services

public class HeartbeatService : BackgroundService
{
    private readonly ClientManager _clients;

    public HeartbeatService(ClientManager clients) => _clients = clients;

    protected override async Task ExecuteAsync(CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            foreach (var (_, methods) in _clients.GetTypedMethodsForHub<IChatClient, AppHub>())
            {
                methods.ReceiveMessage("System", "heartbeat");
            }
            await Task.Delay(30_000, ct);
        }
    }
}

ClientContext properties

Each ClientContext provides detailed information about the connected client:

Property	Type	Description
Id	string	Connection ID
HARRRType	Type	Hub type the client is connected to
RemoteIp	IPAddress?	Client's IP address
User	ClaimsPrincipal	Authenticated user claims
ConnectedAt	DateTime	Connection timestamp
ReconnectedAt	List<DateTime>	Reconnection history
Attributes	ClientAttributes	Custom key-value storage
ConnectedTo	Uri	Hub URL

Custom client attributes

Clients can pass custom attributes via HTTP headers (prefixed with #) or query parameters (prefixed with @) during the initial handshake:

// Server: read custom attributes
var version = client.Attributes["AppVersion"];
var platform = client.Attributes["Platform"];

// Check attribute existence
bool hasPlatform = client.Attributes.Has("Platform");
bool isIOS = client.Attributes.Has("Platform", "iOS");

Next steps

• Server Methods — server-to-client calls inside the hub
• Authorization — filter clients by authentication state
• Connection Setup (.NET) — configure the .NET client