Introduction
Part 1 gives an overview to WebSocket protocol and .NET WebSocket support.
In
this article, I will demonstrate how to host a WebSocket server in a
traditional ASP.NET or MVC 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 the ClientWebSocket class in the System.Net.WebSockets
namespace.
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<byte> buffer = new ArraySegment<byte>(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<byte>(
Encoding.UTF8.GetBytes(userMessage));
await socket.SendAsync(
buffer, WebSocketMessageType.Text, true, CancellationToken.None);
}
else
{
break;
}
}
}
}In the ProcessRequest method, 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:
<system.webServer>
<handlers>
<add path="/WSChat/WSHandler.ashx" verb="*" name="WSHandler"
type="WSChat.WSHandler"/>
</handlers>
</system.webServer> In the web page, I write JavaScript code to communicate with the
server:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>WebSocket Chat</title>
<script type="text/javascript" src="Scripts/jquery-2.0.2.js"></script>
<script type="text/javascript">
var ws;
$().ready(function () {
$("#btnConnect").click(function () {
$("#spanStatus").text("connecting");
ws = new WebSocket("ws://" + window.location.hostname +
"/WSChat/WSHandler.ashx");
ws.onopen = function () {
$("#spanStatus").text("connected");
};
ws.onmessage = function (evt) {
$("#spanStatus").text(evt.data);
};
ws.onerror = function (evt) {
$("#spanStatus").text(evt.message);
};
ws.onclose = function () {
$("#spanStatus").text("disconnected");
};
});
$("#btnSend").click(function () {
if (ws.readyState == WebSocket.OPEN) {
ws.send($("#textInput").val());
}
else {
$("#spanStatus").text("Connection is closed");
}
});
$("#btnDisconnect").click(function () {
ws.close();
});
});
</script>
</head>
<body>
<input type="button" value="Connect" id="btnConnect" />
<input type="button" value="Disconnect" id="btnDisconnect" /><br />
<input type="text" id="textInput" />
<input type="button" value="Send" id="btnSend" /><br />
<span id="spanStatus">(display)</span>
</body>
</html>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<byte> bytesToSend = new ArraySegment<byte>(
Encoding.UTF8.GetBytes(msg));
await ws.SendAsync(
bytesToSend, WebSocketMessageType.Text,
true, CancellationToken.None);
ArraySegment<byte> bytesReceived = new ArraySegment<byte>(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
I
implement the same echo function in a MVC 4 web application. I create an
ApiController to handle WebSocket requests. In the Get method, I still use HttpContext.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<byte> buffer = new ArraySegment<byte>(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<byte>(
Encoding.UTF8.GetBytes(userMessage));
await socket.SendAsync(
buffer, WebSocketMessageType.Text, true, CancellationToken.None);
}
else
{
break;
}
}
}
}
The JavaScript code in my index.cshtml is 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;
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<title>Index</title>
<script type="text/javascript" src="Scripts/jquery-2.0.2.js"></script>
<script type="text/javascript">
var ws;
$().ready(function () {
$("#btnConnect").click(function () {
$("#spanStatus").text("connecting");
ws = new WebSocket("ws://" + window.location.hostname +
"/Mvc4WSChat/api/WSChat");
ws.onopen = function () {
$("#spanStatus").text("connected");
};
ws.onmessage = function (evt) {
$("#spanStatus").text(evt.data);
};
ws.onerror = function (evt) {
$("#spanStatus").text(evt.message);
};
ws.onclose = function () {
$("#spanStatus").text("disconnected");
};
});
$("#btnSend").click(function () {
if (ws.readyState == WebSocket.OPEN) {
ws.send($("#textInput").val());
}
else {
$("#spanStatus").text("Connection is closed");
}
});
$("#btnDisconnect").click(function () {
ws.close();
});
});
</script>
</head>
<body>
<input type="button" value="Connect" id="btnConnect" />
<input type="button" value="Disconnect" id="btnDisconnect" /><br />
<input type="text" id="textInput" />
<input type="button" value="Send" id="btnSend" /><br />
<span id="spanStatus">(display)</span>
</body>
</html>
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
