• Web Clients ! Basic Browser Functions ! URLs ! User-Controllable Features ! Additional Functionality

S Prabhavathi AP/IT

1

Web Clients •  A web client is a software that accesses a web server by

sending an HTTP request message and processing the resulting HTTP response.

•  Examples of web client software

" Web browsers " text-only browsers " browsers running on cell phones " software robots used to automatically crawl the Web and

download information for use by search engines (and, unfortunately, e-mail spammers).

•  Any web client that is designed to directly support user access to web servers is known as a user agent.

2

Web Browsers

•  First graphical browser running on general-purpose platforms: Mosaic (1993)

•  Microsoft Internet Explorer (IE) browser, which was originally

based on Mosaic. •  Other browsers: Mozilla(open source)- runs on linux,

Windows, Macintosh. Firefox, Opera, Safari, Chrome. 3

Web Browsers

4

5

Web Browsers

6

•  Primary tasks: – Convert web addresses (URL’s) to HTTP requests – Use DNS to get IP address – Establish TCP connection – Communicate with web servers(HTTP request) via

HTTP – Render (appropriately display) documents returned

by a server

HTTP URL’s

7

•  Browser uses authority to connect via TCP •  Request-URI included in start line (/ used for path if none

supplied) •  The query portion of a URL was to pass search terms to a web

server. •  If both the path and query are missing from a URL, then the

Request-URI must be set to /, which is known as the root path. •  Fragment identifier not sent to server (used to scroll browser

client area)

8

•  Browser would send a HTTP request for the above URL as

•  GET /a/b/c.txt?t=win&s=chess HTTP/1.1 •  ... •  Host: www.example.org:56789 •  ...

User-Controllable Features

9

•  Graphical browsers also provide many user-controllable features, including:

•  Standard features –  Save web page to disk –  Find string in page –  Fill forms automatically (passwords, billing address, …) –  Set preferences (language, character set, cache and HTTP

parameters) –  Modify display style (e.g., increase font sizes) –  Display raw HTML and HTTP header info (e.g., Last-

Modified) –  Choose browser themes (skins) –  View history of web addresses visited –  Bookmark favorite pages for easy return

10

Set Preferences

Additional functionality

11

•  Automatic URL completion •  Script execution(programs for validating data) •  Event handling (mouse clicks) •  Management of form GUI (text, buttons) •  Secure communication(encodes sensitive

information) •  Plug-in execution (non html documents-pdf)

Automatic URL Completion

12

13

End of Web Clients