Mapping SignalR connections to users - asp.net

Question

Consider a web application like facebook, that can send realtime notifications to users.
What is the best way, using asp.net SignalR, to keep track of which connection ids belong to which user, even if the user disconnects, or reconnects later ?

Answer 1

Check out the following blog post:
Mapping ASP.NET SignalR Connections to Real Application Users
Briefly, you would be adding the connection ids to user on the OnConnected method and remove that connection on the OnDisconnected method. Keep in mind that an application user can have multiple connections. So, you need to have a one to many relationship between your user and the connection ids. The above linked post explains it in details with a sample.

Answer 2

I did this for an internal app. The way I did it is that when a user connects, I have the server ask the user to register themselves. This way I know that not only a user is connected and their signalR connnectionID, but they can also tell me any other information (like username or whatever).
When they reconnect I ask them to do it again.
SignalR will maintain the same connectionID per client even if they reconnect which is nice. A reconnection is not the same as an initial connection. New connections indicate a new client, but a reconnection is on the same client.
In my app I maintained a seperate threadsafe dictionary that I kept track of which user and which connectionID was doing what. This way I can say "oh, send message to user ABC" and look up their connectionID. Then act on the Hub's clients object in signalR for that connectionID. If you do it this way you can even have the same "user" in mutliple connections. Imagine user "abc" is open in two browser tabs. If you went strictly by connectionID they'd be technically two different users. But, by maintaining some sort of local collection grouping users and connections you can now have multiple connections for the same user.
I should mention that if you do it this way, you should make sure your site handles what happens when it restarts and loses all the connection information. For me, when someone reconnects I ask them to again re-identify themselves. This way I can re-build my local dictionary when the server comes online without worry. It does have more overhead because now you are asking all your clients to send information to you, but depending on your user case this could be staggered or bunched or otherwise distributed to help you handle load.
In general, however you get local information (whether by asking the user to supply it), or by http context session info, you need to track it yourself.

Answer 3

Well I used a different approach, I extended the ApplicationUser class like that:
// You can add profile data for the user by adding more properties to your ApplicationUser class, please visit http://go.microsoft.com/fwlink/?LinkID=317594 to learn more.
public class ApplicationUser : IdentityUser
{
//public int ApplicationUserId { get; set; }
//public string Name { get; set; }
//public string Address { get; set; }
//public string City { get; set; }
//public string State { get; set; }
//public string Zip { get; set; }
[Required]
public string Email { get; set; }
[Required]
public override string UserName { get; set; }
[NotMapped]
public string ConnectionId { get; set; }
[NotMapped]
public string ChattingUserConnectionId { get; set; }
//public string HomeTown { get; set; }
//public DateTime? BirthDate { get; set; }
}
And in my hub i'm doing something like that:
public class ChatHub : Hub
{
#region Data Members
private static ApplicationDbContext applicationDbContext = new ApplicationDbContext();
private static UserManager<ApplicationUser> userManager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(applicationDbContext));
private static List<ApplicationUser> connectedUsers = new List<ApplicationUser>();
And when a user connects to the chat, I get his ApplicationUser object by his user name and add it to the connectedUsers list. When he disconnects, I remove him.
I ran into some random exceptions with EF states and such which made me create the ApplicationDbContext and UserManager each time it is accessed instead of setting it in a static object:
private ApplicationUser GetCurrentUser()
{
ApplicationDbContext applicationDbContext = new ApplicationDbContext();
UserManager<ApplicationUser> userManager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(applicationDbContext));
var userName = Context.User.Identity.GetUserName();
var user = userManager.FindByName<ApplicationUser>(userName);
return user;
}
Edit:
The hub code has some problems loading child objects of the user. This code which is also used in the asp.net template will work better, ApplicationDBContext is not needed:
private ApplicationUserManager _userManager
{
get
{
return HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
}
}
var user = _userManager.FindByName<ApplicationUser, string>(userName);

Answer 4

There's a very good article on ASP.NET's SignalR tutorial section.
I've included the introductory paragraph below.
Mapping SignalR Users to Connections
Each client connecting to a hub passes a unique connection id. You can
retrieve this value in the Context.ConnectionId property of the hub
context. If your application needs to map a user to the connection id
and persist that mapping, you can use one of the following:
The User ID Provider (SignalR 2)
In-memory storage, such as a dictionary
SignalR group for each user
Permanent, external storage, such as a database table or Azure table
storage Each of these implementations is shown in this topic. You use
the OnConnected, OnDisconnected, and OnReconnected methods of the Hub
class to track the user connection status.
UserID Provider
If you're using ASP.NET's standard membership provider (IPrincipal.Identity.Name) you can just do the following to access a client based on a user account. If you have your own user system you can create your own provider.
public class MyHub : Hub
{
public void Send(string userId, string message)
{
Clients.User(userId).send(message);
}
}