Chapter 35: Accessing the Internet

Overview

Chapters 32 through 34 as well as Chapter 36 discuss how you can use C# to write powerful, efficient, and dynamic Web pages using ASP.NET and XML Web services. For the most part, the clients accessing ASP.NET pages will be users running Internet Explorer or other Web browsers such as Opera or FireFox. However, you might want to add Web-browsing features to your own application, or need your applications to programmatically obtain information from a Web site. In this latter case, it is usually better for the site to implement a Web service. However, if you are accessing public Internet sites, you might not have any control over how the site is implemented.

This chapter covers facilities provided through the .NET base classes for using various network protocols, particularly HTTP and TCP, to access networks and the Internet as a client. In particular, this chapter covers:

• Downloading files from the World Wide Web

• Using the new Web Browser control in a Windows Forms application

• Manipulating IP addresses and performing DNS lookups

• Socket programming with TCP, UDP, and socket classes

The two namespaces of most interest for networking are System.Net and System.Net.Sockets. The System.Net namespace is generally concerned with higher-level operations, for example, down-loading and uploading files, and making Web requests using HTTP and other protocols, whereas System.Net.Sockets contains classes to perform lower-level operations. You will find these classes useful when you want to work directly with sockets or protocols such as TCP/IP. The methods in these classes closely mimic the Windows socket (Winsock) API functions derived from the Berkeley sockets interface.

This chapter takes a fairly practical approach, mixing examples with a discussion of the relevant theory and networking concepts as appropriate. This chapter is not a guide to computer networking but an introduction to using the .NET Framework for network communication.

You also take a look at using the new WebBrowser control in a Windows Forms environment and how it can make accomplishing some specific Internet access tasks easier for you to accomplish.

However, the chapter starts with the simplest case, sending a request to a server and storing the information sent back in the response. (As is the case with the other chapters, you can download the sample code for this chapter from the Wrox Web site at www.wrox.com.)