Using WebSocket in .NET 4.5 (Part 2)

Introduction 

Part 1 gives an overview to WebSocket protocol and .NET WebSocket support. 

Inthis article, I will demonstrate how to host a WebSocket server in atraditionalASP.NETorMVC 4 web application using HttpContext.AcceptWebSocketRequest. I will show JavaScript code in client-side web page. I will also show a client-side application to communicate with the same server using theClientWebSocketclass in the System.Net.WebSockets namespace. 

WSChat.zip contains the code sample for traditional ASP.NET. 

Mvc4WSChat.zip contains the code sample for MVC 4.  

Preparation

To enable WebSocket on the server side, please refer to Part 1.

Traditional ASP.NET 

To host a WebSocket server, I create a custom HTTP handler to accept client WebSocket connection requests and communicate with the client.

public class WSHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        if (context.IsWebSocketRequest)
        {
            context.AcceptWebSocketRequest(ProcessWSChat);
        }
    }

    public bool IsReusable { get { return false; } }

    private async Task ProcessWSChat(AspNetWebSocketContext context)
    {
        WebSocket socket = context.WebSocket;
        while (true)
        {
            ArraySegment buffer = new ArraySegment(new byte[1024]);
            WebSocketReceiveResult result = await socket.ReceiveAsync(
                buffer, CancellationToken.None);
            if (socket.State == WebSocketState.Open)
            {
                string userMessage = Encoding.UTF8.GetString(
                    buffer.Array, 0, result.Count);
                userMessage = "You sent: " + userMessage + " at " + 
                    DateTime.Now.ToLongTimeString();
                buffer = new ArraySegment(
                    Encoding.UTF8.GetBytes(userMessage));
                await socket.SendAsync(
                    buffer, WebSocketMessageType.Text, true, CancellationToken.None);
            }
            else
            {
                break;
            }
        }
    }
}

In the ProcessRequestmethod, I check whether  HttpContext.IsWebSocketRequest is true. True means the request is an AspNetWebSocket ( System.Web.WebSockets) request. Then I call HttpContext.AcceptWebSocketRequest to accept the request and establish the connection. I pass in a method as the argument. This method contains code to do the duplex communication through AspNetWebSocketContext.WebSocket. Here I just echo what the client has sent to the server.

Don’t forget to register the HTTP handler in web.config:

In web page, I write JavaScript code to communicate with theserver:

    
    
    


    
    

    
    

    (display)

The code of the standalone client application looks like:

class Program
{
    private static async Task ChatWithServer()
    {
        using (ClientWebSocket ws = new ClientWebSocket())
        {
            Uri serverUri = new Uri("ws://localhost/WSChat/WSHandler.ashx");
            await ws.ConnectAsync(serverUri, CancellationToken.None);
            while (true)
            {
                Console.Write("Input message ('exit' to exit): ");
                string msg = Console.ReadLine();
                if (msg == "exit")
                {
                    break;
                }
                ArraySegment bytesToSend = new ArraySegment(
                    Encoding.UTF8.GetBytes(msg));
                await ws.SendAsync(
                    bytesToSend, WebSocketMessageType.Text, 
                    true, CancellationToken.None);
                ArraySegment bytesReceived = new ArraySegment(new byte[1024]);
                WebSocketReceiveResult result = await ws.ReceiveAsync(
                    bytesReceived, CancellationToken.None);
                Console.WriteLine(Encoding.UTF8.GetString(
                    bytesReceived.Array, 0, result.Count));
                if (ws.State != WebSocketState.Open)
                {
                    break;
                }
            }
        }
    }

    static void Main(string[] args)
    {
        Task t = ChatWithServer();
        t.Wait();
    }
}  

ClientWebSocket ( System.Net.WebSockets ) plays the role to communicate with the WebSocket server hosted in IIS. Both  ClientWebSocket and AspNetWebSocket are inherited from System.Net.WebSockets.WebSocket . So the usage is consistent. Note that the client application can only work on Windows 8, Windows Server 2012 and above.

MVC 4  

Iimplement the same echo function in a MVC 4 web application. I create an ApiControllerto handle WebSocket requests. In the Get method, I still useHttpContext.AcceptWebSocketRequest to accept and establish connections: 

public class WSChatController : ApiController
{
    public HttpResponseMessage Get()
    {
        if (HttpContext.Current.IsWebSocketRequest)
        {
            HttpContext.Current.AcceptWebSocketRequest(ProcessWSChat);
        }
        return new HttpResponseMessage(HttpStatusCode.SwitchingProtocols);
    }
    private async Task ProcessWSChat(AspNetWebSocketContext context)
    {
        WebSocket socket = context.WebSocket;
        while (true)
        {
            ArraySegment buffer = new ArraySegment(new byte[1024]);
            WebSocketReceiveResult result = await socket.ReceiveAsync(
                buffer, CancellationToken.None);
            if (socket.State == WebSocketState.Open)
            {
                string userMessage = Encoding.UTF8.GetString(
                    buffer.Array, 0, result.Count);
                userMessage = "You sent: " + userMessage + " at " + 
                    DateTime.Now.ToLongTimeString();
                buffer = new ArraySegment(
                    Encoding.UTF8.GetBytes(userMessage));
                await socket.SendAsync(
                    buffer, WebSocketMessageType.Text, true, CancellationToken.None);
            }
            else
            {
                break;
            }
        }
    }
} 

The JavaScript code in my index.cshtmlis almost the same as the example I have shown before. The only difference is the URI used to send WebSocket connection request. It follows the MVC URI style:

@{
    Layout = null;
}



    
    
    
    


    
    

    
    

    (display)

Summary

Next in Part 3, I will demonstrate how to use WCF to host WebSocket server and how to communicate WebSocket WCF service using WCF client application or JavaScript in a web page. 

Related Links   

Using WebSocket in .NET 4.5:

• Part 1: Overview on WebSocket protocol and .NET support 
• Part 2: Using WebSocket in Traditional ASP.NET and MVC 4   
• Part 3: Using WCF support for WebSocket
• Part 4: Using Microsoft.WebSockets.dll