SignalR: Wire-up the ConnectionId with a user instance

While working on a RPG game prototype based on ASP.NET I started experimenting with SignalR. This library was a perfect fit as it allows pushing data from server to clients in a very easy way (read: with just a few lines of code) and of course server method invocations from clients through JavaScript.

Unfortunately SignalR is not providing a direct and intuitive way of gluing together application specific (server side) objects with the SignalR internal connections. This means that at any time you know how many clients are connected but you have absolutely no idea who they are. A client is basically a connection. A connection has a unique connectionId so you can distinguish clients but that's about it. Even worse, each time a client reconnects it gets a new connection id.

In real world applications you have a bunch high level objects like: users, accounts, players etc. that are required to be in sync with client connections. So the problem is how to wire up a particular client with a well known object instance, say a Player object instance.

SignalR has few extension points that allow us to change the default behavior. One of those is a IConnectionIdGenerator. This interface is in charge of generating connection Id's and we will replace the built in behavior with a new one. The bellow implementation relies upon the fact that all clients must authenticate and during the authentication their playerId is stored in the tickets UserData.

public class ConnectionFactory : IConnectionIdGenerator
    {
        public string GenerateConnectionId( IRequest request )
        {
            if ( request.Cookies[FormsAuthentication.FormsCookieName] != null )
            {
                FormsAuthenticationTicket ticket = FormsAuthentication.Decrypt( request.Cookies[FormsAuthentication.FormsCookieName].Value );
                
                int playerId;
                if ( int.TryParse( ticket.UserData, out playerId ) )
                {                    
                    return ticket.UserData;
                }
            }

            throw new InvalidOperationException( "No cookie" );
        }
    }

To tell the SignalR framework to use our connection generator instead the build-in we simply point to our class at a convenient place like Application_Start:

void Application_Start( object sender, EventArgs e )
{
   GlobalHost.DependencyResolver.Register( typeof( IConnectionIdGenerator ), () => new ConnectionFactory() );
}

Now all clients will get the connection id based on their player Id, even better if a client disconnects and reconnects again it will get the very same connection id!