Overview

• Web Pages consist of objects
• A web page is one base html page but with several referenced objects
• Files can be in 3 states
  • Static - no change
  • Dynamic - input from client
  • Active - program runs on client

URL - Uniform Resource Encoder

• URL Defines 4 things
  • Protocol; FTP, HTTP, HTTPS, TELNET
  • Host Computer
  • Port - optional
  • Path; location of the file server Protocol :// Host : Port / Path https://augusta.edu:443/login

HTTP Connections

• non-persistent HTTP
  • at most one object sent over TCP connection; connection then closes
  • downloading multiple objects required multiple connections
• persistent HTTP
  • many objects can be sent over a single TCP connection

HTTP Request Message

• Two types of HTTP messages, request and response
• General Format:
• method|URL|version|header field name|value
• Blank lines are the delimiter between the head and body

Uploading Form Input

• POST method
  • Web page often includes form inputs
  • input is uploaded to server in entity body
• GET
  • Loaded into the URL
  • Most common

Status Response Codes

• 200 OK
  • request succeeded. good
• 301 Moved Permanently
  • File has been moved, specified later in message
  • This is usually when you try to access HTTPS with HTTP
• 400 Bad Request
  • Request not understood by server
• 404 Not Found
  • Requested file does not exist
• 500 HTTP Version not supported

Cookies

• Many sites use cookies for:
  • cookie header line of http response message
  • cookie header line of http request
  • user’s cookie saved on host but managed by browser
  • back-end database at website
• Examples
  • When initial http request arrives at site, the site creates:
    • unique id’s
    • entry for back-end database
• Uses
  • authorization
  • shopping carts
  • recommendations
  • user session state

HTTP/2

• More use of pipe-lining/multiplexing for faster transfers
• Allows servers to push responses
• Header field now uses binary instead of plain text
• Moves encrypted data by default -> TLS