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HTTP

HyperText Transfer Protocol

Prof. Cesare Pautasso
http://www.pautasso.info
cesare.pautasso@usi.ch
@pautasso

HTTP Protocol

Test HTTP with Telnet

$telnet www.usi.ch 80
GET / HTTP/1.0
        	
HTTP/1.0 200 OK
        	
<html>...</html>

HTTP Request

GET /faculty/pautasso/ HTTP/1.1
Host: www.inf.usi.ch
User-Agent: User-Agent: Mozilla/5.0 (Mac OS X 10.6) Firefox/15.0
Accept: text/xml,application/xml,application/xhtml+xml,*/*
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

HTTP Response

HTTP/1.x 200 OK
Transfer-Encoding: chunked
Date: Tue, 18 Sep 2007 14:46:38 GMT
Server: Apache/2.0.52 (Red Hat)
Last-Modified: Sun, 16 Sep 2007 21:50:53 GMT
Etag: "e7198-7030-ae960940"
Accept-Ranges: bytes
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Content-Type: text/html

<html> <head> <title>Prof. Cesare Pautasso</title>
<style type="text/css"> …</style>
<script type="text/javascript"> <!-- … --> </script>
</head> <body> … </body> </html>

HTTP Status Codes

  • 1xx Informational
    • 100 Continue
  • 2xx Successful
    • 200 OK
    • 201 Created
    • 202 Accepted
  • 3xx Redirection
    • 301 Moved Permanently
    • 303 See Other
    • 307 Temporary Redirect
  • 4xx Client Error
    • 400 Bad Request
    • 401 Unauthorized
    • 403 Forbidden
    • 404 Not Found
    • 405 Method Not Allowed
    • 414 Request URI Too Long
  • 5xx Server Error
    • 500 Internal Server Error
    • 501 Not Implemented
    • 502 Bad Gateway
    • 503 Service Unavailable

HTTP Headers

https://addons.mozilla.org/en-US/firefox/addon/live-http-headers/

Content Type Negotiation

GET /time
Accept: text/html
HTTP/1.1 200 OK
Content-Type: text/html

MIME Types

application/json
application/octet-stream
application/pdf
application/soap+xml
application/xhtml+xml
application/zip
audio/mpeg
image/jpeg
image/png
multipart/form-data
text/css
text/html
text/plain
text/xml
video/quicktime

http://www.iana.org/assignments/media-types/

Caching

GET /faculty/pautasso/ HTTP/1.1
Host: www.inf.unisi.ch
If-Modified-Since: Sun, 16 Sep 2007 21:50:53 GMT
If-None-Match: "e7198-7030-ae960940" 
Cache-Control: max-age=0
HTTP/1.x 304 Not Modified 
Etag: "e7198-7030-ae960940" 
Date: Tue, 18 Sep 2007 14:50:12 GMT

        	

http://www.mnot.net/cache_docs/

HTTP Authentication

http://www.ietf.org/rfc/rfc2617.txt

HTTP Basic Authentication

HTTP/1.1 401 Unauthorized
WWW-Authenticate: Basic realm="USILU..."
Authorization: Basic QWxhZGRpbjpvcGVuIH...
        		

Base-64 encoding of username:password

HTTP Digest Authentication

HTTP/1.1 401 Unauthorized
WWW-Authenticate: Digest 
                  realm=“USI", 
                  qop="auth", 
                  nonce="dcd98...0bf093“
Authorization: Digest 
               username="student",
               nonce="dcd98...0bf093", 
               uri="/index.html", 
               qop="auth", 
               nc=00000001, 
               cnonce="0a4f113b", 
               response="6629fae49393a05..."

HTTP Properties

Standard

  • Communication Protocol between any Web browser and any Web server
  • Many (competing) server stacks and client libraries exists for all programming languags and operating system/hardware platforms
  • Firewalls are typically configures with HTTP Port 80 open by default

Synchronous

  • The Web server must be available to answer the request of the Web browser
  • The interaction completes only after the response has been received by the Web browser

Secure

  • Basic Authentication is not secure!
  • Use HTTP over SSL (HTTPS) for a secure communication channel

Stateless

  • In HTTP 1.0 every Request/Response pair requires to establish a new TPC/IP connection
  • Performance Optimization: existing connections can be kept-alive with HTTP 1.1
  • Every request is independent from all of the others and must contain all information needed by the Web server to answer it

References

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