How to send message to only caller client in SignalR? - signalr

Question

Below is my SignalR Hub class code.
public class ChatHub : Hub
{
public void Send(string name, string message)
{
// Call the addNewMessageToPage method to update clients.
Clients.All.addNewMessageToPage(name, message);
}
public async void webAPIRequest()
{
HttpClient client = new HttpClient();
HttpResponseMessage response = await client.GetAsync("https://jsonplaceholder.typicode.com/posts");
//Clients.All.addWebAPIResponseToPage(response);
Clients.Caller.addWebAPIResponseToPage(response);
await Task.Delay(1000);
response = await client.GetAsync("http://www.google.com");
Clients.Caller.addWebAPIResponseToPage(response);
//Clients.All.addWebAPIResponseToPage(response);
await Task.Delay(1000);
response = await client.GetAsync("https://jsonplaceholder.typicode.com/posts?userId=1");
//Clients.All.addWebAPIResponseToPage(response);
Clients.Caller.addWebAPIResponseToPage(response);
}
}
As per my understanding ,
Clients.Caller.addWebAPIResponseToPage(response);
sends message only to caller client , whereas
Clients.All.addWebAPIResponseToPage(response);
sends the message to all the clients.
Is my understanding correct ?
If No , then what method needs to be called to send message only to caller client.

Answer 1

Yes your understanding is correct. Read it here
https://learn.microsoft.com/en-us/aspnet/signalr/overview/guide-to-the-api/hubs-api-guide-server#selectingclients
You can use caller, you can provide current user connection id and send message to that or I have seen a group called self in some places which keeps user logged in from various devices and send message to that.
For example if you are logged in on a desktop and on mobile as well then you will have two connection IDs but you are same user. You can add this user to a self_username_unique_group_name kind of group and then send a message to that group which will be sent to all devices where user is connected.
You can also manage connection IDs for a single user in a separate table and send message to all of those connection IDs if you want.
Too much flexibility and magic
Enjoy

Answer 2

I found this to work quite well where ConnectionMapping is described in https://learn.microsoft.com/en-us/aspnet/signalr/overview/guide-to-the-api/mapping-users-to-connections
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
services.AddScoped<SomeService>();
services.AddScoped<SessionService>();
services.AddScoped<ProgressHub>();
}
}
public class SomeService
{
ProgressHub _hub;
public SomeService(ProgressHub hub)
{
_hub = hub;
}
private async Task UpdateProgressT(T value)
{
_hub.Send(value);
}
}
public class ProgressHub : Hub
{
private readonly static ConnectionMapping<string> _connections = new ConnectionMapping<string>();
private readonly IHubContext<ProgressHub> _context;
private readonly SessionService _session;
public ProgressHub(IHubContext<ProgressHub> context, SessionService session)
{
_context = context;
_session = session;
}
public override Task OnConnectedAsync()
{
_connections.Add(_session.SiteId, Context.ConnectionId);
return base.OnConnectedAsync();
}
public override Task OnDisconnectedAsync(Exception exception)
{
_connections.Remove(_session.SiteId, Context.ConnectionId);
return base.OnDisconnectedAsync(exception);
}
public async Task Send(object data)
{
foreach (var connectionId in _connections.GetConnections(_session.SiteId))
{
await _context.Clients.Client(connectionId).SendAsync("Message", data);
}
}
}
public class SessionService
{
private readonly ISession _session;
public SessionService(IHttpContextAccessor accessor)
{
_session = accessor.HttpContext.Session;
if (_session == null) throw new ArgumentNullException("session");
}
public string SiteId
{
get => _session.GetString("SiteId");
set => _session.SetString("SiteId", value);
}
}