C# 4 and .NET 4

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Although the WebClient class is very simple to use, it has very limited features. In particular, you cannot
use it to supply authentication credentials — a particular problem with uploading data is that not many sites
will accept uploaded files without authentication! It is possible to add header information to requests and to
examine any headers in the response, but only in a very generic sense — there is no specific support for any
one protocol. This is because WebClient is a very general-purpose class designed to work with any protocol
for sending a request and receiving a response (such as HTTP or FTP). It cannot handle any features specific
to any one protocol, such as cookies, which are specific to HTTP. To take advantage of these features, you
need to use a family of classes based on two other classes in the System.Net namespace: WebRequest and
WebResponse.
WebrequesT and WebresPonse Classes
The WebRequest class represents the request for information to send to a particular URI. The URI is passed
as a parameter to the Create() method. A WebResponse represents the data you retrieve from the server.
By calling the WebRequest.GetResponse() method, you actually send the request to the web server and
create a WebResponse object to examine the return data. As with the WebClient object, you can obtain a
stream to represent the data, but in this case you use the WebResponse.GetResponseStream() method.
This section briefly discusses a few of the other areas supported by WebRequest, WebResponse, and other
related classes.
You start off by downloading a web page using these classes, which is the same example as before, but using
WebRequest and WebResponse. In the process, you uncover the class hierarchy involved, and then see how
to take advantage of extra HTTP features that are supported by this hierarchy.
The following code shows the modifications you need to make to the BasicWebClient sample to use the
WebRequest and WebResponse classes:
public Form1()
{
InitializeComponent();
}
WebRequest wrq = WebRequest.Create("http://www.reuters.com");
WebResponse wrs = wrq.GetResponse();
Stream strm = wrs.GetResponseStream();
StreamReader sr = new StreamReader(strm);
string line;
while ( (line = sr.ReadLine()) != null)
{
listBox1.Items.Add(line);
}
strm.Close();
In the code example, you start by instantiating an object representing a web request. You don’t do this using
a constructor, but instead call the static method WebRequest.Create(). As you learn in more detail later
in this chapter (see “The Web Request and Web Response Hierarchy” section), the WebRequest class is part
of a hierarchy of classes supporting different network protocols. To receive a reference to the correct object
for the request type, a factory mechanism is in place. The WebRequest.Create() method will create the
appropriate object for the given protocol.
An important part of the HTTP protocol is the ability to send extensive header information with both
request and response streams. This information can include cookies and the details of the particular
browser sending the request (the user agent). As you would expect, the .NET Framework provides full
support for accessing the most significant data. The WebRequest and WebResponse classes provide some
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