C# in a Nutshell, Second Edition

Generic Request/Response Architecture

The request/response architecture is based on Uniform Resource Indicator (URI) and stream I/O, follows the factory design pattern, and makes good use of abstract types and interfaces. A factory method, WebRequest.Create( ), parses the URI and creates the appropriate protocol handler to fulfill the request.

Protocol handlers share a common abstract base type (WebRequest), which exposes properties that configure the request and methods used to retrieve the response.

Responses are also represented as types and share a common abstract base type (WebResponse), which exposes a NetworkStream, providing a simple streams-based I/O and easy integration into the rest of the FCL.

This example is a simple implementation of the popular Unix snarf utility. It demonstrates the use of the WebRequest and WebResponse classes to retrieve the contents of a URI and print them to the console:

// Snarf.cs // Run Snarf.exe <http-uri> to retrieve a web page // e.g. snarf.exe http://www.oreilly.com/catalog/csharpnut/ using System; using System.IO; using System.Net; using System.Text; class Snarf { static void Main(string[ ] args) { // Retrieve the data at the URL with a WebRequest instance WebRequest req = WebRequest.Create(args[0]); WebResponse resp = req.GetResponse( ); // Read in the data, performing ASCII->Unicode encoding Stream s = resp.GetResponseStream( ); StreamReader sr = new StreamReader(s, Encoding.ASCII); string doc = sr.ReadToEnd( ); Console.WriteLine(doc); ...