WebSockets - How to create different messages?

Question

I am creating a websocket chat application and I managed to relay chat messages to other browsers connected. I have a console application listening on one port.

My question is... If one person logs on to the system I want everybody to know that, how can I do that? I'm using Linq to map the DB but if the logging is ok how do I send that message, that user X has logged in?

FINALLY I was able to create a chatroom using websockets, here is the final product, thanks for the orientation!

http://ukchatpoint.no-ip.org/Chatpoint/Pages/Uklobby.aspx

Answer 1

First make sure you're sending messages as JSON (JavaScript Object Notation) as this allows structured data to be sent back and forth, and client & server can differentiate between a chat message and an instruction (eg someone new logged in). For instance on the client:

mySocket.onmessage = function(event) {
    var command = JSON.parse(event.data);

    if(command.type === 'message') {
        var message = command.message;
        // handle chat message
    }
    else if (command.type === 'newUser') {
        var username = command.username;
        // handle new user
    }
};

On the server in ASP.NET C# you'd send them as:

public class ChatHandler : WebSocketHandler
{
    private JavaScriptSerializer serializer = new JavaScriptSerializer();
    private static WebSocketCollection chatapp = new WebSocketCollection();

    public override void OnMessage(string message)
    {
        var m = serializer.Deserialize<Message>(message);

        switch (m.Type)
        {
            case MessageType.NewUser:
                chatapp.Broadcast(serializer.Serialize(new
                {
                    type = "newUser",
                    username = m.username
                }));

                break;
            case MessageType.Message:
                chatapp.Broadcast(serializer.Serialize(new
                {
                    type = "message",
                    message = m.message
                }));

                break;
            default:
                return;
        }
    }
}

As Hightechrider says, you'll need to keep track of a list of connected clients, that's what WebSocketCollection class does in the code listing above.

Check out Paul Batum's WebSocket chat example on github here ( https://github.com/paulbatum/BUILD-2011-WebSocket-Chat-Samples/blob/master/BasicAspNetChat/ChatHandler.cs )

Also he did a presentation at the recent MS BUILD conference here ( http://channel9.msdn.com/Events/BUILD/BUILD2011/SAC-807T )

Answer 2

You would need to track the connections at the application level so you can send to all of them. But take a look at SignalR instead where a lot of the work involved with webSockets and long polling is being written for you. With SignalR you can use GetClients to get all the clients connected to a Hub .

Answer 3

使用PostgreSQL时，可以在数据库中使用NOTIFY来通知应用程序层，该应用程序层可以生成通过WebSockets发送的消息。