9.2 Generic RequestResponse Architecture

9.2 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); // Print result to console   } }