INFT132 093 03 Web Concepts

Dr Michael Rees

School of Information Technology

[email protected]

INFT11/71-132

Web Applications

Web Concepts

Web Applications 2

• Internet is the basic infrastructure

• The Web provides a linked, information structure – web pages

• Uses Hypertext Transfer Protocol (HTTP) to transfer web pages

• Web pages use a document structure called Hypertext Markup Language (HTML)

• HTML contains tags that define the content and layout of the web pages

Internet v Web

© 2009 Michael Rees

Web Applications 3

Web Software Technology

• Web server:– Software that serves web pages and related

files (entities)– Supports HTTP

• Web client (browser):– Internet host machine running client

application – Initiates HTTP requests to designated web

server to retrieve web pages and other files (entities)

– Displays (or saves or executes) retrieved entities

© 2009 Michael Rees

Retrieving a Web Page

© 2009 Michael Rees Web Applications 4

1. Browser acquires a URL

2. Browser uses DNS to determine the IP address of the web server

3. Using HTTP protocol, browser sends a request to the web server at that IP address for the named web page

4. Web server received request via HTTP, locates the file requested and transmits HTML content back to the browser via HTTP

5. The browser interprets the HTML and displays the page on the screen

This is the request-response cycle

HTTP Request–Response cycle


4. Response + [Entity]

Web Server

Web Browser(Client)

3. Check Request• syntax• existence• authentication

5. Interpret & Display6. Close TCP Connection

1. Open TCPConnection2. Request + [Entity]

Uniform Resource Identifier - URI

• Two types of URI:– Uniform Resource Name - URN

• Used to identify resources with unique names, such as books (which have unique ISBN’s)

• Scheme is urn• Example: urn:foo:a123,456

– Uniform Resource Locator - URL• Specifies location at which a resource can be

found• http scheme, others are https, ftp, mailto, and

file• Example:

http://www.bond.edu.au/bondit/index.htm

© 2009 Michael Rees 6Web Applications

ftp://ftp.rfc-editor.org/in-notes/rfc2141.txt


HTTP

• Implemented over a TCP connection

• 80 is the standard port number used

• Request:– Command line– Additional header lines– Blank line– Optional content

• Response:– Status code– Additional header lines– Blank line– Optional content


More details on HTTP

http://www.tutorialspoint.com/cgi-bin/printversion.cgi?tutorial=http&file=what_is_http.htm

HTTP Example

• To acquire: http://www.somehost.com/path/file.html

• Request

GET /path/file.html HTTP/1.0From: [email protected]: HTTPTool/1.0[blank line here]

• Response

HTTP/1.0 200 OKDate: Fri, 31 Dec 1999 23:59:59 GMTContent-Type: text/htmlContent-Length: 1354

<html><body><h1>Happy New Millennium!</h1>

(more file contents) . . .</body></html>


Multipurpose Internet Mail Extensions

• Abbreviated to MIME

• Convention for specifying content type of a message– In HTTP, typically used to specify content

type of the body of the response

• MIME content type syntax:– top-level type / subtype

• Examples: text/html, image/jpeg



Secure Servers

• HTTP messages typically travel over a public network

• Private information (such as credit card numbers) should be encrypted to prevent eavesdropping

• https URL scheme tells browser to use encryption

• Common encryption standards:– Secure Socket Layer (SSL)– Transport Layer Security (TLS)



Secure Servers

BrowserWeb

Server

I’d like to talk securely to you (over port 443)

Here’s my certificate and encryption data

Here’s an encrypted HTTP request

Here’s an encrypted HTTP response

Here’s an encrypted HTTP request

Here’s an encrypted HTTP response

TLS/SSL

TLS/SSL

HTTPRequests

HTTPResponses

HTTPRequests

HTTPResponses


Resources

• Read Sections 1.1 through 1.8 of textbook


Education

INFT132 093 03 Web Concepts