HTTP

Complete

Summary

HTTP status codes

200 Ok
301 Moved Permanently
304 Not Modified
403 Forbidden
404 Not Found
500 Internet Server Error

HTTP versions

Version	Features
`HTTP/1.0`	- TCP - 1 connection per object
`HTTP/1.1`	- TCP - persistent connection - pipelining
`HTTP/2`	- TCP - multiplexing
`HTTP/3`	- QUIC/UDP

Concept

HyperText Transfer Protocol(HTTP)

application layer protocol
apps request and recieve web resources, 1 request per resource
uses TCP in the transport layer

for cs2105 HTTP refers to HTTP/1 and HTTP/2 which use TCP, HTTP/3 uses UDP/QUIC

Uniform Resource Locator(URL)

addresses web objects, ie. html files, images

HTTP request

GET /~cs2105/demo.html HTTP/1.1\r\n
Host: www.comp.nus.edu.sg\r\n
User-Agent: Mozilla/5.0\r\n
Connection: close\r\n
\r\n
<body>

HTTP response

HTTP/1.1 200 OK
Date: Wed, 01 Jul 2015 08:47:52 GMT\r\n
Server: Apache/2.4.6 (Unix) OpenSSL/1.0.1m\r\n
Accept-Ranges: bytes\r\n
Connection: Keep-Alive\r\n
Content-Length: 73\r\n
Content-Type: text/html\r\n
Keep-Alive: timeout=5, max=100\r\n
\r\n
<!DOCTYPE html>
<html lang="en">
...

HTTP/1.0

single TCP connection for each resource

HTTP/1.1

Persistence

single TCP connection, with the server
removes overhead from RTT for every TCP connection
sequential: waits for response before sending next request

persistence is possible only if the hostname remains the same

Pipelining

requests are made before recieving responses from older requests
requires a persistent connection

HTTP/2

multiplexing
response can come back in any order, maybe even interleaved

Browser caching

Statefulness

HTTP is stateless, ie each HTTP session is standalone
use cookies to maintain state between sessions

Caching resources

images
scripts(JS)
CSS
use conditional get requests, check if cached versions are still up to date with the server’s version
avoid sending unecessary data