27.1 Chapter 27 WWW and HTTP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ARCHITECTURE The WWW today is a distributed client/server service, in which a client using a browser can access a service using a server. However, the service provided is distributed over many locations called sites. Client (Browser) Server Uniform Resource Locator Cookies Topics discussed in this section:

27.3 Figure 27.1 Architecture of WWW

27.4 Figure 27.2 Browser

27.5 Figure 27.3 URL ftp:// 80 by default

The WWW was originally designed as a stateless entity. Cookies are needed for extending functionalities of the Web, such as: To remember past client in order to show a customized webpage Cookies

When a server receives a request from a client, it stores information about the client in a file or a string. The server includes the cookie in the response that it sends to the client. When the client receives the response, the browser stores the cookie in the cookie directory Cookies: Creation and storage

WEB DOCUMENTS The documents in the WWW can be grouped into three broad categories: static, dynamic, and active. The category is based on the time at which the contents of the document are determined. Static Documents Dynamic Documents Active Documents Topics discussed in this section:

27.9 Figure 27.4 Static document Uses the Hypertext Markup Language (HTML)

27.10 Figure 27.5 Boldface tags

27.11 Figure 27.7 Beginning and ending tags Example: Chapter3-part3

27.12 Figure 27.8 Dynamic document using CGI

27.13 Figure 27.9 Dynamic document using server-site script

27.14 Dynamic documents are sometimes referred to as server-site dynamic documents. Note

27.15 Figure Active document using Java applet

27.16 Figure Active document using client-site script

27.17 Active documents are sometimes referred to as client-site dynamic documents. Note

HTTP The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. HTTP Transaction Persistent Versus Nonpersistent Connection Topics discussed in this section:

27.19 Figure HTTP transaction HTTP uses the services of TCP on well- known port 80.

27.20 Figure Request and response messages (all in Plain Text)

27.21 Table 27.1 Methods

27.22 Table 27.2 Status codes

27.23 Table 27.2 Status codes (continued)

27.24 Figure Header format

27.25 Table 27.3 General headers

27.26 Table 27.4 Request headers

27.27 Table 27.5 Response headers

27.28 Table 27.6 Entity headers

27.29 Figure Example 27.1

27.30 Figure Example 27.2 (client sends data to server)

27.31 Example 27.3 (continued)

Trying out HTTP (client side) for yourself 1. Telnet to your favorite Web server: Opens TCP connection to port 80 (default HTTP server port) at cs.ucf.edu. Anything typed in sent to port 80 at telnet Type in a GET HTTP request: GET /~czou/CNT3004/example.html HTTP/1.1 Host: By typing this in (hit carriage return twice), you send this minimal (but complete) GET request to HTTP server 3. Look at response message sent by HTTP server! 27.32

Web Browser’s Operation First, get the basis static HTML file /~czou/CNT3004/example.html Second, interpret HTML to find all contained “objects” Images, java applets, flash,…. Third, get those objects via HTTP 27.33

Let’s look at HTTP in action Telnet example “GET” must be Capital letters! Must have “host” header! For web proxy reason A proxy can know where to forward the GET request What if type in “HTTP/1.0” ? Wireshark example 27.34

27.35 HTTP version 1.1 specifies a persistent connection by default. Note

Persistent vs Nonpersistent Connection In a nonpersistent connection, one TCP connection is made for each request/response. In a persistent connection, the server leaves the connection open for more requests after sending a response. The server can close the connection at the request of a client or if a time-out has been reached Wireshark example