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CHAPTER 21 NETWORKING & WCF
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dataStream.Close(); myClient.Close(); All that remains for the client is the implementation of the HandleServerStream method, which will make use of the server calculator function. In Listing 21-8 you define two integer arrays, and you use a for loop to send a sequence of number pairs to the server using the StreamWriter and use the StreamReader to read the calculation results. To test these examples, you must first start the server and then the client. Here is the output from the server: Waiting for connection Connection accepted Server processed request: Server processed request: Server processed request: Server processed request: Server processed request: Press enter to finish
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And here is the output from the client: Writing message: 10 3 Got response: 13 Writing message: 20 6 Got response: 26 Writing message: 30 9 Got response: 39 Writing message: 40 3 Got response: 43 Writing message: 50 4 Got response: 54 Press enter to finish
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A serious limitation with the server in the previous section is that it only processes one client request at a time. One way of dealing with this is to use the Task Parallel Library, which is the topic of a later chapter. As a taste of things to come, Listing 21-9 demonstrates a parallel version of the calculator server which can provide service to multiple clients simultaneously. Listing 21-9. A Parallel Server using using using using using System; System.IO; System.Net; System.Net.Sockets; System.Threading.Tasks;
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CHAPTER 21 NETWORKING & WCF
class Listing 07 { static void Main(string[] args) { // create a new TcpListener object TcpListener myListener = new TcpListener(IPAddress.Any, 12000); // start accepting connections myListener.Start(); while (true) { // wait for a connection Console.WriteLine("Waiting for connection"); TcpClient theClient = myListener.AcceptTcpClient(); Console.WriteLine("Connection accepted"); Task.Factory.StartNew(() => { // get the Stream object Stream netStream = theClient.GetStream(); // handle the connection - use the result to // determine if we continue to accept connections HandleClientStream(netStream); // close the stream netStream.Close(); // close the network connection theClient.Close(); }); } // wait for input before exiting Console.WriteLine("Press enter to finish"); Console.ReadLine(); } private static bool HandleClientStream(Stream clientStream) { // create StreamReader and StreamWriter objects around the Stream StreamReader myReader = new StreamReader(clientStream); StreamWriter myWriter = new StreamWriter(clientStream); // define a string that will be used to read from the StreamReader string dataLine; // enter a loop to read lines from the client while ((dataLine = myReader.ReadLine()) != null) { // read a string from the StreamReader and split it on the space character string[] stringElements = dataLine.Split(' '); // parse the two integer values
CHAPTER 21 NETWORKING & WCF
int firstInt = int.Parse(stringElements[0]), secondInt = int.Parse(stringElements[1]); // compute the result int result = firstInt + secondInt; // print out the information locally Console.WriteLine("Task {3}: Server processed request: {0} + {1} = {2}", firstInt, secondInt, result, Task.CurrentId); // return the result of the calculation to the cliebt myWriter.WriteLine(result); // flush the writer to make sure that the data is flushed myWriter.Flush(); } // return true if you want to accept further connections, false otherwise return false; } } Be sure to read the Parallel Programming chapter before you use this example as the basis for your own programs. In particular, you should read the section on synchronization to avoid a frequently encountered set of problems associated with parallel programming.
The Windows Communication Foundation
The calculator client/server example in the previous example demonstrated how to use the TcpListener and TcpClient classes, but the result didn t really take advantage of the C# language features. The client could send any message to the server, not just the int values that the server was expecting. Extending the protocol between the client and the server is certainly possible but potentially troublesome, and you d still need to write some code to check for errors in processing messages from the client. An alternative approach is to use the Windows Commination Foundation (WCF), which is the .NET programming model for creating service-oriented applications, informally known as web services. The benefit of using WCF is that you get to work with C# objects, giving you the benefits of type safety, exception handling, and everything else that Part I of this book covered. The drawback of using WCF is complexity; WCF supports many different options and configurations. Getting started with WCF is reasonably simple, but mastering WCF especially for large-scale applications requires time and patience. There isn t space in this book to get deeply into WCF, but in the following sections I ll show you how to create basic a basic WCF server and client and demonstrate how to implement the simple calculator example from earlier in the chapter.
Note To use WCF you must add a reference to the System.ServiceModel assembly to your project. In the Visual Studio Solution Explorer, right click on the References folder, select the .NET tab, select System.ServiceModel from the list, and click OK.
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