Web Review

Key Concepts

DNS

• translates domain names into IP addresses
• a domain name is separated by dots
  • TLDs
  • subdomains

URLS

• see Figure 9.1, page 247

• well-known ports: FTP (21), SSH (22), SMTP (25), HTTP (80), HTTPS (443)

HTML

• markup for web pages
• links and image tags are important because they contain references to other objects
• the browser interprets the HTML as a Document Object Model (DOM)

Scripts

• can manipulate the document object model (DOM)
• can be embedded or given in a URL
• page loading — see list on page 248
• pay attention to ways that JavaScript can run on a page
  • in script tags with or without URLs
  • in URLs for links
• JavaScript can set itself to run when the document is loaded or when an object is clicked

HTTP

• HTTP consists of request messages and responses messages
  • GET
  • POST
  • CONNECT
• see Figure 9.2, page 249
• open a web browser and user browser network tools to see live requests

Web forms

• sent in FORM elements
• may generate a new HTTP request
  • typically a POST request with data in the body
• may be handled by JavaScript

HTTP Proxies

• originally used as a gateway to the web, to simplify clients
• now also used for caching
• may be invisible (e.g. not requested by the client) for HTTP resources
• HTTP CONNECT method may be used to tunnel through a proxy / firewall

Browser redirection

• both HTTP and HTML allow a browser to be directed automatically to a new resource
• see list of redirect mechanisms, page 251

Summary

• walk through all the steps that occur when a browser visits a URL