HttpWebRequest and HttpWebResponse reduce the otherwise complex task of submitting HTTP requests to Web servers and capturing the responses to a few simple lines of code. To submit a request, use the WebRequest class’s static Create method to create a request and then call GetResponse on the resulting HttpWebRequest object:

WebRequest request = WebRequest.Create ("http://www.wintellect.com");
WebResponse response = request.GetResponse ();

GetResponse returns an HttpWebResponse object encapsulating the response. Calling GetResponseStream on HttpWebResponse returns a Stream object that you can wrap a reader around to read the response. The following code echoes the text of the response to a console window:

StreamReader reader = new StreamReader (response.GetResponseStream ());
for (string line = reader.ReadLine (); line != null;
    line = reader.ReadLine ())
    Console.WriteLine (line);
reader.Close ();

It’s that simple. HttpWebRequest also contains methods named BeginGetResponse and EndGetResponse that you can use to submit asynchronous Web requests, which might be useful if you don’t want to wait around for large amounts of data to come back through a slow dial-up connection.

The LinkList application in Figure 3-5 uses the WebRequest, WebResponse, and Regex classses to list a Web page’s hyperlinks. Its input is the URL of a Web page; its output is a list of all the URLs accompanying Hrefs in the Web page. Fetching the Web page is easy thanks to WebRequest.GetResponse. Regex.Match simplifies the task of parsing the Hrefs out of the response. To see LinkList in action, as shown in Figure 3-6, compile it and type linklist followed by a URL at the command prompt:

linklist http://www.wintellect.com

LinkList also demonstrates that StreamReader objects can read from any kind of stream, not just file streams. Specifically, it uses a StreamReader to read the contents of the stream returned by WebResponse’s GetResponseStream method. This is abstraction at its finest and is the primary reason that the FCL’s architects decided to use readers and writers to abstract access to streams.

using System;
using System.IO;
using System.Net;
using System.Text.RegularExpressions;

class MyApp
{
    static void Main (string[] args)
    {
        if (args.Length == 0) {
            Console.WriteLine ("Error: Missing URL");
            return;
        }

        StreamReader reader = null;

        try {
            WebRequest request = WebRequest.Create (args[0]);
            WebResponse response = request.GetResponse ();
            reader = new StreamReader (response.GetResponseStream ());
            string content = reader.ReadToEnd ();

            Regex regex = new Regex ("href\\s*=\\s*\"([^\"]*)\"",
                RegexOptions.IgnoreCase);

            MatchCollection matches = regex.Matches (content);
            foreach (Match match in matches)

                Console.WriteLine (match.Groups[1]);
        }
        catch (Exception e) {
            Console.WriteLine (e.Message);
        }
        finally {
            if (reader != null)
                reader.Close ();
        }
    }
}

Figure 3-6

LinkList output.

Want to send e-mail from a .NET Framework application? You could do it the hard way by using sockets to establish a connection to a mail server and then transmit a mail message using Simple Mail Transfer Protocol (SMTP). Or you could do it the easy way and rely on classes in the System.Web.Mail namespace. System.Web.Mail provides a simple managed interface to SMTP. The core classes are MailMessage, which represents e-mail messages; MailAttachment, which represents attachments; and SmtpMail, which places a friendly wrapper around the host system’s SMTP mail service.

Here’s how easy it is to send e-mail from a managed application:

using System.Web.Mail;
  .
  .
  .
MailMessage message = new MailMessage ();
message.From = "webmaster@wintellect.com";
message.To = "Everyone@wintellect.com";
message.Subject = "Scheduled Power Outage";
message.Body = "Our servers will be down tonight.";
SmtpMail.SmtpServer = "localhost";
SmtpMail.Send (message);

Having the capability to send e-mail programmatically can come in handy in countless ways. For example, you might want to send e-mail confirmations to customers who purchase merchandise from your Web site, or you might write your own software to transmit electronic newsletters to clients. Whatever your motivation, it doesn’t get much easier than this.

Figure 3-7 contains the source code for a simple e-mail client named SendMail, built around the MailMessage and SmtpMail classes. To spice things up just a bit, and to serve as a preview of things to come, SendMail isn’t a console application—it’s a Web application. Specifically, it’s an ASP.NET Web form. (See Figure 3-8.) Clicking the Send Mail button activates the OnSend method, which composes an e-mail message from the user’s input and sends it to the recipient. To run the application, copy SendMail.aspx to the \Inetpub\wwwroot directory of a PC that has ASP.NET and Internet Information Services installed on it. Then open a browser and type http://localhost/sendmail.aspx in the address bar. Once the Web form appears, fill in the fields and click the Send Mail button to send an e-mail message.

Some machines require a bit of reconfiguring to allow ASP.NET applications to send mail. If SendMail.aspx throws an exception when you click the Send Mail button, here’s what to do. First make sure your machine’s SMTP service is running. You can do that in the IIS configuration manager or in the Services Control Panel applet. Second, make sure the SMTP service is configured to allow relaying from localhost. To do that, open the IIS configuration manager (you’ll find it in Administrative Tools), right-click Default SMTP Virtual Server, select Properties, click the Access tab, click the Relay button, select Only The List Below, and use the Add button to add 127.0.0.1 to the list of computers allowed to relay.

<%@ Import Namespace="System.Web.Mail" %>

<html>
  <body>
    <h1>Simple SMTP E-Mail Client</h1>
    <form runat="server">
      <hr>
      <table cellspacing="8">
        <tr>
          <td align="right" valign="bottom">From:</td>
          <td><asp:TextBox ID="Sender" RunAt="server" /></td>
        </tr>

        <tr>
          <td align="right" valign="bottom">To:</td>
          <td><asp:TextBox ID="Receiver" RunAt="server" /></td>
        </tr>
        <tr>
          <td align="right" valign="bottom">Subject:</td>
          <td><asp:TextBox ID="Subject" RunAt="server" /></td>
        </tr>
        <tr>
          <td align="right" valign="top">Message:</td>
          <td><asp:TextBox ID="Body" TextMode="MultiLine" Rows="5"
            Columns="40" RunAt="server" /></td>
        </tr>
      </table>
      <hr>
      <asp:Button Text="Send Mail" OnClick="OnSend" RunAt="server" />
    </form>
  </body>
</html>

<script language="C#" runat="server">
  void OnSend (Object sender, EventArgs e)
  {
      MailMessage message = new MailMessage ();
      message.From = Sender.Text;
      message.To = Receiver.Text;
      message.Subject = Subject.Text;
      message.Body = Body.Text;
      SmtpMail.SmtpServer = "localhost";
      SmtpMail.Send (message);
  }
</script>

Figure 3-8

The SendMail application.