ict.ken.be

Real-time Web & Push Services with Hubs
by Christian Weyer (christian.weyer@thinktecture.com)
Developers of SignalR on https://jabbr.net

Push Services pattern (models a service that) 

• accepts incoming connections from callers
• is able to push data down to callers
• abstracts from communication nitty-gritty details
• consumers send to push service
• push service notifies consumers
• external events (Db, Message Queue, ...) trigger push service

HTTP is the protocol

• Periodic Polling
• Long Polling (http streaming/comet) -> server only responds when there is data
• Forever Frame (connection within an iframe)
• Server-Sent Events (SSE)
• Web Sockets (only Windows 8/Server 2012, network considerations/blockings)

Hubs

• public methods are callable from the outside
• send messages to clients by invoking client-side methods
• [HubName("chat")]
• Context holds connection- and request-specific information
• ConnectionId, Request, Headers, RequestCookies, QueryString, User
• First register the hubs and then add your other routes.
• Target method with parameters is dynamically 'injected' into code path, serialized, and embedded into protocol response
• Groups are not persisted on the server
• We need to keep track of what connections are in chat groups
• No automatic group count 

Clients.Caller.newMessage(message);
Clients.Client(Context.ConnectionId).newMessage(message);
Clients.All.newMessage(message);
Clients.Others.newMessage(message);
Clients.AllExcept(Context.ConnectionId).newMessage(message);

Groups.Add(Context.ConnectionId, room);
Clients.Group(room).newMessage(msg);

public override Task OnConnected() {}
public override Task OnDisconnected() {}
public override Task OnReconnected() {}

// Sending data from outside a hub, retrieve hub context via dependency resolver
private void SendMonitorData(string eventType, string connection)
{
 var context = GlobalHost.ConnectionManager.GetHubContext<MonitorHub>();
 context.Clients.All.newEvent(eventType, connection); 
}

Clients

• .NET4.0+, WinRT, Windows Phone 8, Silverlight 5, jQuery, C++, iOS native, iOS via Mono, Android via Mono
• /signalr/hubs is the dynamic proxy contract
• use signalr.exe ghp /url:http://localhost:31373 tool to create a static proxy

Javascript with proxy

 $.connection.hub.logging = true;
 chat = $.connection.chat
 $.connection.hub.start({ transport:'longPolling' });
 $.connection.hub.connectionSlow = onConnectionSlow;

Javascript without proxy

var connection = $.hubConnection();
 var proxy = connection.createHubProxy('chat');
 proxy.on('newMessage', onNewMessage);
 connection.start();
 proxy.invoke('sendMessage', $('#message').val());

.Net

var hubConnection = new HubConnection("http://localhost/ps");
 var chat = hubConnection.CreateHubProxy("chat");
 chat.On<string>("newMessage", msg => messages.Invoke(new Action(() => messages.Items.Add(msg));
 hubConnection.Start().Wait();
// Opened, Closed, Error, Received, Reconnected, Reconnecting, StateChanged

Hosting

OWIN (Open Web Server Interface for .Net) - http://owin.org
Katana project - http://katanaproject.codeplex.com

• Application delegate (AppFunc) var AppFunc = Func<IDictionary<string, object>, Task>;
• Environment dictionary
• ASP.Net hosting sits on top of OWIN
• Self-hosting
• Microsoft.Owin.Hosting aka Katana
• Microsoft.Owin.Host.HttpListener

// process user needs http.sys permissions on the url namespace
 public void Configuration(IAppBuilder app)
 {
   var a = Assembly.LoadFrom("Services.dll");
   app.MapHubs(new HubConfiguration { EnableCrossDomain = true });
 }
 
 using(WebApplication.Start<Startup>("http://localhost:6789") 
 {
   Console.WriteLine("Hubs running...");
   Console.ReadLine(); 
 }

// jQuery client needs to explicitly set connection url
$.connection.hub.url = "http://localhost:6789/signalr";

Azure

• Which server instance handles the client request?
• Which instance pushes?

Other aspects

• Use SignalR message bus
• SignalR extensible architecture
• Persistent connections
• Scale-Out
• WebApi Integration
• Security