C# 4 and .NET 4

1350 ❘ ChaPTer 45 peer-tO-peer netwOrkinG
After you have built the application you can test it either by copying it to other computers in your local
network and running all instances, or by running multiple instances on one computer. If you choose the latter
option you must remember to change the port used for each instance by changing individual config files (copy
the contents of the Debug directory on your local computer and edit each config file in turn). The results will
be clearer in both ways of testing this application if you also change the username for each instance.
When the peer applications are running, you can use the Refresh button to obtain a list of peers asynchronously.
When you have located a peer you can send a default message by clicking the Message button for the peer.
Figure 45-7 shows this application in action with three instances running on one machine. In the figure, one
peer has just messaged another and this has resulted in a dialog box.
figure 45-7
Most of the work in this application takes place in the Window_Loaded() event handler for the Window1
window. This method starts by loading configuration information and setting the window title with the
username:
private void Window_Loaded(object sender, RoutedEventArgs e)
{
// Get configuration from app.config
string port = ConfigurationManager.AppSettings["port"];
string username = ConfigurationManager.AppSettings["username"];
string machineName = Environment.MachineName;
string serviceUrl = null;
// Set window title
this.Title = string.Format("P2P example — {0}", username);
code snippet Window1.xaml.cs
Next the peer host address is used along with the configured port to determine the endpoint on which to
host the WCF service. The service will use NetTcpBinding binding, so the URL of the endpoint uses the
net.tcp protocol:
// Get service url using IPv4 address and port from config file
foreach (IPAddress address in Dns.GetHostAddresses(Dns.GetHostName()))
{
if (address.AddressFamily ==
System.Net.Sockets.AddressFamily.InterNetwork)
{
serviceUrl = string.Format("net.tcp://{0}:{1}/P2PService",
address, port);
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