Programming PHP, 4th Edition

Chapter 8. Web Techniques

PHP was designed as a web-scripting language and, although it is possible to use it in purely command-line and GUI scripts, the web accounts for the vast majority of PHP uses. A dynamic website may have forms, sessions, and sometimes redirection, and this chapter explains how to implement those elements in PHP. You’ll learn how PHP provides access to form parameters and uploaded files, how to send cookies and redirect the browser, how to use PHP sessions, and more.

HTTP Basics

The web runs on HTTP, or Hypertext Transfer Protocol. This protocol governs how web browsers request files from web servers and how the servers send the files back. To understand the various techniques we’ll show you in this chapter, you need to have a basic understanding of HTTP. For a more thorough discussion of HTTP, see the HTTP Pocket Reference (O’Reilly) by Clinton Wong.

When a web browser requests a web page, it sends an HTTP request message to a web server. The request message always includes some header information, and it sometimes also includes a body. The web server responds with a reply message, which always includes header information and usually contains a body. The first line of an HTTP request looks like this:

GET /index.html HTTP/1.1

This line specifies an HTTP command, called a method, followed by the address of a document and the version of the HTTP protocol being used. In this case, the request is using the GET method to ask for the index.html document using ...