27.1

Chapter 27

WWW and HTTP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

27.2

27-1 ARCHITECTURE27-1 ARCHITECTURE

The The WWWWWW today is a distributed client/server service, today is a distributed client/server service, in which a client using a browser can access a service in which a client using a browser can access a service using a server. However, the service provided is using a server. However, the service provided is distributed over many locations called sites.distributed over many locations called sites.

Client (Browser)ServerUniform Resource LocatorCookies

Topics discussed in this section:Topics discussed in this section:

27.3

Figure 27.1 Architecture of WWW

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Figure 27.2 Browser

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Figure 27.3 URL

http://https://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.

27.6

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.

27.7

Cookies: Creation and storage

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27-2 WEB DOCUMENTS27-2 WEB DOCUMENTS

The documents in the WWW can be grouped into three The documents in the WWW can be grouped into three broad categories: broad categories: staticstatic, , dynamicdynamic, and , and activeactive. The . The category is based on the time at which the contents of category is based on the time at which the contents of the document are determined.the document are determined.

Static DocumentsDynamic DocumentsActive Documents

Topics discussed in this section:Topics discussed in this section:

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Figure 27.4 Static document

Uses the Hypertext Markup Language (HTML)

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Figure 27.5 Boldface tags

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Figure 27.7 Beginning and ending tags

Example: <a href="Chapter3-part3.ppt">Chapter3-

part3</a> <img src="../images/smallUCF.gif" width="200"

border="0" height="76">

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Figure 27.8 Dynamic document using CGI

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Figure 27.9 Dynamic document using server-site script

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Dynamic documents are sometimes referred to as server-site dynamic

documents.

Note

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Figure 27.10 Active document using Java applet

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Figure 27.11 Active document using client-site script

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Active documents are sometimes referred to as client-site dynamic

documents.

Note

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27-3 HTTP27-3 HTTP

The Hypertext Transfer Protocol (HTTP) is a protocol The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. used mainly to access data on the World Wide Web.

HTTP TransactionPersistent Versus Nonpersistent Connection

Topics discussed in this section:Topics discussed in this section:

27.19

Figure 27.12 HTTP transaction

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

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Figure 27.13 Request and response messages (all in Plain Text)

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Table 27.1 Methods

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Table 27.2 Status codes

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Table 27.2 Status codes (continued)

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Figure 27.15 Header format

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Table 27.3 General headers

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Table 27.4 Request headers

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Table 27.5 Response headers

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Table 27.6 Entity headers

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Figure 27.16 Example 27.1

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Figure 27.17 Example 27.2 (client sends data to server)

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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 www.cs.ucf.edu

telnet www.cs.ucf.edu 80

2. Type in a GET HTTP request:GET /~czou/CNT3004/example.html HTTP/1.1Host: www.cs.ucf.edu

By typing this in (hit carriagereturn twice), you sendthis minimal (but complete) GET request to HTTP server

3. Look at response message sent by HTTP server!

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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,….

<img src="../images/smallUCF.gif“ > <img

src=“http://upload.wikimedia.org/wikipedia/commons/6/63/Wikipedia-logo.png” >

Third, get those objects via HTTP

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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

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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.

27.36 Wireshark example