C# in a Nutshell, Second Edition

HTTP-Specific Support

The request/response architecture inherently supports protocol-specific extensions via the use of subtyping. Since WebRequest.Create( ) creates and returns the appropriate handler type based on the URI, accessing protocol-specific features is as easy as downcasting the returned WebRequest object to the appropriate protocol-specific handler and accessing the extended functionality.

The FCL includes specific support for the HTTP protocol, including the ability to easily access and control elements of an interactive web session, such as the HTTP headers, user-agent strings, proxy support, user credentials, authentication, keep-alives, pipelining, and more.

This example demonstrates the use of the HTTP-specific request/response classes to control the user-agent string for the request and retrieve the server type:

// ProbeSvr.cs
// Run ProbeSvr.exe <servername> to retrieve the server type
using System;
using System.Net;
class ProbeSvr {
  static void Main(string[ ] args) {
  
    // Get instance of WebRequest ABC, convert to HttpWebRequest
    WebRequest req = WebRequest.Create(args[0]);
    req.Method = "HEAD"; // we're just looking at headers
    HttpWebRequest httpReq = (HttpWebRequest)req;
  
    // Access HTTP-specific features such as User-Agent
    httpReq.UserAgent = "CSPRProbe/1.0";
  
    // Retrieve response and print to console
    WebResponse resp = req.GetResponse( );
    HttpWebResponse httpResp = (HttpWebResponse)resp;
    Console.WriteLine(httpResp.Server);

  }
}