Network Programming Concept
Network applications are everywhere. Any time you browse the Web, send an email message, or pop up an X window, you are using a network application. Interestingly, all network applications are based on the same basic programming model, have similar overall logical structures, and rely on the same programming interface. Network applications rely on many of the concepts that you have already learned in our study of systems. For example, processes, signals, byte ordering, memory mapping, and dynamic storage allocation all play important roles. There are new concepts to master as well. We will need to understand the basic clientserver programming model and how to write client-server programs that use the services provided by the Internet. At the end, we will tie all of these ideas together by developing a small but functional Web server that can serve both static and dynamic content with text and graphics to real Web browsers.
The Client-Server Programming Model
Every network application is based on the client-server model. With this model, an application consists of a server process and one or more client processes. A server manages some resource, and it provides some service for its clients by manipulating that resource. For example, a Web server manages a set of disk files that it retrieves and executes on behalf of clients. An FTP server manages a set of disk files that it stores and retrieves for clients. Similarly, an email server manages a spool file that it reads and updates for clients.
The fundamental operation in the client-server model is the transaction (Figure 12.1). A client-server transaction consists of four steps:
1. When a client needs service, it initiates a transaction by sending a request to the server. For example, when a Web browser needs a file, it sends a request to a Web server.
2. The server receives the request, interprets it, and manipulates its resources in the appropriate way. For example, when a Web server receives a request from a browser, it reads a disk file.
3. The server sends a response to the client, and then waits for the next request. For example, a Web server sends the file back to a client.
4. The client receives the response and manipulates it. For example, after aWeb browser receives a page from the server, it displays it on the screen.
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Tags: networking, security, TCP/IP, UDP
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