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7. WWW and HTPP

28/02/23

MoodlePDF

The Word Wide Web and URLs​

  • WWW - Is a distributed system for publishing and accessing resources across the internet
  • It is a client server system, web browsers are the commonest client
  • Based on a request-response protocol (HTTP)

Web Protocols​

  • HyperText Transfer Protocol (HTTP) - A transfer protocol that specifies how a browser interacts with a web server
  • Uniform Resource Locator (URL) - Representation standard that specifies the format of web page identifiers
  • HyperText Markup Language (HTML) - A representation standard that specifies the contents and layout of a web page

Browser: Handling a URL​

  1. Divides the URL into protocol, computer name & port, document name, parameters
  2. Use the protocol to decide which protocol to use
  3. Use the computer name and protocol port to form a TCP connection to the server on which the page resides
  4. Use the computer name, document name and parameters to request a specific page from the server using HTTP
  5. Displays the content (or error) received from the server

Browser: URLs and Navigation​

  • Each tab in a browser is displaying the content retrieved from one URL
  • URL can be changed by entering new url, hyperlink or code
  • AJAX can also be used to make a http request in the background

HTTP​

  • Primarily transfer protocol that a browser uses to interact with a web server.
  • HTTP is a request-response protocol

Methods​

  • GET - Requests a document; server sends a copy of the document
  • HEAD - Request status information; server sends status (headers) only for the request document
  • POST - Sends data to a server
  • PUT - Server replaces the data
  • DELETE - Request document be deleted

Response​

  • 200 - OK
  • 400 - Bad Request
  • 403 - Forbidden
  • 404 - Not Found
  • 301 - Moved
  • 307 - Redirect

HTML & Scripting​

  • Representation standard that specifies the syntax of a web page for display in a browser

Client-side scripting - Embedded JavaScript which is run in the browser. Handle user input events, make HTTP requests, dynamically update the HTML.

Server-side scripting - HTML the server receives could be static or dynamically generated. (generated on-the-fly by running code on the server to handle)