Tracking SignalR connection ids to see if they really exist - asp.net

Question

Currently, I am storing all connected user's connection ids inside my database by mapping them to actual application users. What I do is pretty simple here: I add the connection id to the database when OnConnected event is fired. Then, I remove that connection from the database when OnDisconnected event is fired.
However, at some cases (for example, when the process is terminated, etc.), I don't get the disconnect event. This makes my connection table unreliable because I cannot be sure if the user is connected on one or more clients. For example, here is a block of code on my OnDisconnected method:
HubConnection hubConnection = _hubConnectionRepository.GetAll()
.FirstOrDefault(conn => conn.ConnectionId == connectionId);
if (hubConnection != null)
{
_hubConnectionRepository.Delete(hubConnection);
_hubConnectionRepository.Save();
}
if (!_hubConnectionRepository.GetAll().Any(conn => conn.UserId == user.Id))
{
Clients.Others.userDisconnected(username);
}
As you see, I check if there is any other connections associated to that user just after I remove his/her current connection. Depending on the case, I broadcast a message to all connected clients.
What I want here is something like this: to be able to poll the SignalR system with an array of connection ids and get back the disconnected ones so that I can remove them from my connection list inside the database. As far as I remember from my conversation with David Fowler, this's not possible today but what's the preferred approach on such cases?

Answer 1

This is just an idea.
On server:
Clients.All.ping()
On clients:
hub.client.ping = function() {
hub.server.pingResponse();
}
On Server:
void pingResponse()
{
Context.ConnectionId; //update database
}

Answer 2

This is what I did:
I have a class HubConnectionManager:
public class HubConnectionManager
{
static HubConnectionManager()
{
connections = new Dictionary<string, List<string>>();
users = new List<Login>();
}
#region Static Fields
private static Dictionary<string, List<string>> connections;
private static List<Login> users;
#endregion
#region Public Properties
public static Dictionary<string, List<string>> Connections
{
get
{
return connections;
}
}
#endregion
#region Public Methods and Operators
public static void AddConnection(Login login, string connectionId)
{
if (!connections.ContainsKey(login.LoginName))
{
connections.Add(login.LoginName, new List<string>());
if (!users.Contains(login))
{
users.Add(login);
}
}
// add with new connection id
connections[login.LoginName].Add(connectionId);
}
public static bool IsOnline(string connectionId)
{
return connections.Any(x => !string.IsNullOrEmpty(x.Value.FirstOrDefault(y => y == connectionId)));
}
public static void RemoveConnection(string user, string connectionId)
{
if (connections.ContainsKey(user))
{
connections[user].Remove(connectionId);
if (connections[user].Count == 0)
{
connections.Remove(user);
// remove user
users.RemoveAll(x => x.LoginName == user);
}
}
}
public static int GetAllConnectionsCount()
{
return connections.Keys.Sum(user => connections[user].Count);
}
public static Login GetUser(string connectionId)
{
string userName = connections.FirstOrDefault(x => x.Value.Any(y => y == connectionId)).Key;
return users.FirstOrDefault(x => x.LoginName == userName);
}
#endregion
}
I'm using a dictionary that holds UserName and it's list of connections (this is because like you said sometimes OnDisconnected doesn't fire properly:
connections = new Dictionary<string, List<string>>();
Then in your hub, you can check if a connection is still "connected"/ valid:
public class TaskActionStatus : Hub
{
public void SendMessage()
{
if (HubConnectionManager.IsOnline(Context.ConnectionId))
{
this.Clients.Client(Context.ConnectionId).actionInit("test");
}
}
...
}