Using the Communication API and Web Sockets - HTML5 Programming for ASP.NET Developers - page 298

This code shows a generic handler— WebSocketGenericHandler —that triggers the Web Socket server.
The generic handler's ProcessRequest() method first checks whether the incoming request is a Web Socket
request. It does so by checking the IsWebSocketRequest property of the HttpContext object. This property
works hand in hand with the IIS 8.0 WebSocket module and returns true if an incoming request is a
WebSocket request. A WebSocket request is different than an ordinary HTTP request in that instead of
using the http:// protocol it uses the ws:// (WebSocket) protocol. For example, a WebSocket request to
this generic handler looks like this:
ws://localhost:49428/WebSocketGenericHandler.ashx
If IsWebSocketRequest returns true , the AcceptWebSocketRequest() method of the HttpContext is
called. This method takes one parameter—a user function—that supplies a function that listens and
responds to the client requests. In this case, the EchoServer function contains the logic to listen to the
incoming data and echo it to the client. The user function supplied to the AcceptWebSocketRequest()
method should be an asynchronous function, as shown in Listing 11-16.
Listing 11-16. EchoServer Asynchronous Function
public async Task EchoServer(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 EchoServer() method is marked as async , indicating that the code inside it runs in asynchronous
fashion. An async method is a convenient way to execute a long-running operation without blocking the
main thread. In this example, the Echo server is supposed to continuously listen for incoming requests—
that is, a long-running operation. EchoServer() returns a Task object. The Task class acts as a wrapper to
the asynchronous code. EchoServer() receives a parameter of type AspNetWebSocketContext . The
AspNetWebSocketContext class gives you access to the WebSocket through its WebSocket property. The
WebSocket class is the server-side counterpart of the HTML5 WebSocket object. An endless while loop is
then started so the Echo server can continuously listen to incoming requests.
To receive incoming data, you use the WebSocket class's ReceiveAsync() method. This method is
invoked along with the await operator. The await operator indicates that the execution of the calling