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CHAPTER 21 NETWORKING & WCF
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Running the client also produces output from the server: Calculator Server ready Press enter to finish Addition Request: 10 + 20 Multiplcation Request: 20 Subtraction Request: 30 Division Request: 40 / 50
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= 30 * 30 = 600 40 = -10 = 0.8
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As you can see, with very little effort you have been able to create a server that publishes capabilities using C# interfaces, methods, and attributes and a client that can communicate with the server using C# objects and values without having to worry about the details of the network plumbing. This has been a crash course in WCF, but I hope that it demonstrates the basic capabilities and encourages you to look deeper into the functionality on offer.
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Other Useful Network Classes
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The .NET Framework class library contains a wide range of classes that can be used to perform many different kinds of network activity. In this section, I ll demonstrate three useful classes that can be used to create a simple web server, use connectionless IP networking, and perform lookups in the Domain Name System.
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Writing a Simple Web Server
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At the start of the chapter, I showed you how to make requests using the WebClient class, which is a useful convenience class for making HTTP requests. The .NET Framework library also provides support for implementing a simple HTTP server which you can use to deliver content to your clients. This support comes in the form of the System.Net.HttpListener class. There was a point back in the mid-1990s where every programmer wrote their own web server. I ended up writing about a dozen different ones to be embedded in different projects. Things are different now. The quality of the off-the-shelf servers has improved significantly and we have all realized that writing our own server can expose our projects to all kinds of security problems. That said, if you are going to write a simple web server, this is how you do it. Listing 21-15 provides a demonstration of using the HttpListener class. Listing 21-15. A simple Web Server using System; using System.IO; using System.Net; class Listing 15 { static void Main(string[] args) { // define the directory that will be used to load the images string baseDir = @"..\..\images\";
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CHAPTER 21 NETWORKING & WCF
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// create a new listener HttpListener myListener = new HttpListener(); // add the prefixes we will listen for myListener.Prefixes.Add("http://+:14000/demo/"); // start listening for client requests myListener.Start(); while (true) { // wait for a client request to arrive Console.WriteLine("Waiting for client request"); HttpListenerContext reqContext = myListener.GetContext(); // get the request and response objects from the context HttpListenerRequest clientRequest = reqContext.Request; HttpListenerResponse clientResponse = reqContext.Response; // get the file component from the URL string filename = clientRequest.Url.LocalPath; filename = string.Format("{0}{1}{2}", baseDir, '\\', filename.Substring(filename.LastIndexOf('/') + 1)); // see if the file exists if (File.Exists(filename)) { Console.WriteLine("Request for file: {0}", filename); // open a stream to the file and copy the contents to the response stream Stream filestream = File.Open(filename, FileMode.Open, FileAccess.Read); filestream.CopyTo(clientResponse.OutputStream); // close the input stream filestream.Close(); } else { // the file does not exist Console.WriteLine("Request for nonexistent file: {0}", filename); // set an error code for the client clientResponse.StatusCode = 404; } // close the response clientResponse.Close(); } // wait for input before exiting Console.WriteLine("Press enter to finish"); Console.ReadLine(); } } Listing 21-15 will serve files contained in a directory specified by the baseDir variable, set to be the images directory in the project directory (this is defined using a relative path from where the program
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CHAPTER 21 NETWORKING & WCF
will be started, which is either the bin\Debug or bin\Release directories). Requests for files which do not exist in this directory, or requests for anything else, will return a not found message to the client. Start by creating an HttpListener object and telling it what prefixes it should listen for. Here are the relevant statements from the example: HttpListener myListener = new HttpListener(); myListener.Prefixes.Add("http://+:14000/demo/"); The prefix used in the example tells the HttpListener object to listen to port 14000 and requests that start with /demo/. The plus sign (+) means that it should accept requests that contain any hostname. A single HttpListener can support more than one prefix, but let s keep things simple for this example. When you have added the prefixes you require to the HttpListener, you can start listening for requests by calling the Start method, like this:
myListener.Start();
Using HttpListener is very similar to using TcpListener, albeit HttpListener takes care of parsing client requests so that you get an HTTP-centric view of what is happening. You accept a request from a client by calling the GetContext method, which blocks until a client connects and returns an HttpListenerContext object when one does. The HttpListenerContext class defines a pair of properties that let you get details of the request from the client and the object used to return a response. These properties are described in Table 21-7. Table 21-7. HttpListenerContext Properties
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