Michaels Blog | Silverlight 2 and System.Net.Sockets.Socket

The new beta of Silverlight 2^[1] introduces Sockets. The security model enforced by the System.Net.Sockets namespace in Silverlight 2 allows for a connection only back to the site or host of origin. So Silverlight 2 applications will be allowed to connect only to the host from which they were downloaded.

As the Web browser doesn't have a property of the IP address (as you may expect using sockets) there is a new endpoint class, the DnsEndPoint. To create a new instance of DnsEndPoint you have to specify the host name (as string e.g. from Application.Current.Host.Source.DnsSafeHost) and the port address.

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->string host = "mydomain.com";

DnsEndPoint endPoint = new DnsEndPoint(host, port);</div></pre>

All methods of the Socket class to connect, send or receive have to be used asynchronous. I've created a small helper class that wraps all the asynchronous operations. You can download the C# source here^[2].

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->using System;

using System.Net.Sockets; using System.Text; using System.Threading;

namespace Networking { internal sealed class SocketClient : IDisposable { private const int Receive = 1; private const int Send = 0;

private bool isConnected = false;

private Socket socket; private DnsEndPoint endPoint;

private static AutoResetEvent autoEvent = new AutoResetEvent(false); private static AutoResetEvent[] autoSendReceiveEvents = new AutoResetEvent[] { new AutoResetEvent(false), new AutoResetEvent(false) };

internal SocketClient(string host, int port) { endPoint = new DnsEndPoint(host, port); socket = new Socket(AddressFamily.InterNetwork / hostEndPoint.AddressFamily /, SocketType.Stream, ProtocolType.Tcp); }

internal void Connect() { SocketAsyncEventArgs args = new SocketAsyncEventArgs();

args.UserToken = socket; args.RemoteEndPoint = endPoint; args.Completed += new EventHandler<SocketAsyncEventArgs>(OnConnect);

socket.ConnectAsync(args); autoEvent.WaitOne();

if (args.SocketError != SocketError.Success) throw new SocketException((int)args.SocketError); }

internal void Disconnect() { socket.Close(); }

#region Events

private void OnConnect(object sender, SocketAsyncEventArgs e) { autoEvent.Set(); isConnected = (e.SocketError == SocketError.Success); }

private void OnReceive(object sender, SocketAsyncEventArgs e) { autoSendReceiveEvents[Send].Set(); }

private void OnSend(object sender, SocketAsyncEventArgs e) { autoSendReceiveEvents[Receive].Set();

if (e.SocketError SocketError.Success) { if (e.LastOperation SocketAsyncOperation.Send) { // Prepare receiving. Socket s = e.UserToken as Socket;

byte[] response = new byte[255]; e.SetBuffer(response, 0, response.Length); e.Completed += new EventHandler<SocketAsyncEventArgs>(OnReceive); s.ReceiveAsync(e); } } else { ProcessError(e); } }

#endregion

private void ProcessError(SocketAsyncEventArgs e) { Socket s = e.UserToken as Socket; if (s.Connected) { try { s.Shutdown(SocketShutdown.Both); } catch (Exception) { } finally { if (s.Connected) s.Close(); } }

throw new SocketException((int)e.SocketError); }

internal String SendReceive(string message) { if (isConnected) { Byte[] bytes = Encoding.UTF8.GetBytes(message);

SocketAsyncEventArgs args = new SocketAsyncEventArgs(); args.SetBuffer(bytes, 0, bytes.Length); args.UserToken = socket; args.RemoteEndPoint = endPoint; args.Completed += new EventHandler<SocketAsyncEventArgs>(OnSend);

socket.SendAsync(args);

AutoResetEvent.WaitAll(autoSendReceiveEvents);

return Encoding.UTF8.GetString(args.Buffer, args.Offset, args.BytesTransferred); } else throw new SocketException((int)SocketError.NotConnected); }

#region IDisposable Members

public void Dispose() { autoEvent.Close(); autoSendReceiveEvents[Send].Close(); autoSendReceiveEvents[Receive].Close(); if (socket.Connected) socket.Close(); }

#endregion } }</div></pre>