Web Database Applications with PHP and MySQL, 2nd Edition

Hypertext Transfer Protocol

As discussed in Chapter 1, HTTP is the standard that allows documents to be communicated and shared over the Web. From a network perspective, HTTP is an application-layer protocol that is built on top of TCP/IP. Since the original version, HTTP/0.9, there have only been two revisions of the HTTP standard. HTTP/1.0 was released as RFC-1945^[1] in May 1996 and HTTP/1.1 as RFC-2616 in June 1999.

In Chapter 1, we told you that HTTP is very simple: a client—most conspicuously a web browser—sends a request for some resource to a web (HTTP) server, and the server sends back a response. The HTTP response carries the resource—the HTML document or image or whatever—as its payload back to the client.

Continuing our analogy from the previous section, HTTP is a kind of cover letter—like a fax cover sheet—that is stored in an envelope and tells the receiver what language the document is in, instructions on how to read the letter, and how to reply.

Uniform Resource Locators

Uniform resource locators—more commonly known as URLs—are used as the primary naming and addressing method of the Web. URLs belong to the larger class of uniform resource identifiers ; both identify resources, but URLs include specific host details that allow connection to a server that holds the resource.

A URL can be broken into three basic parts: first, the protocol identifier; second, the host and service identifier; and, last, a resource identifier that contains a path with optional ...