Lecture 3 - Webapps - v1.1 - Chapter 3 Web Application...

Chapter 3: Web
Application
Service and Cloud Computing
(COMP 4442)
Dr. Lei Yang
[email protected]
3-1

Chapter 3: roadmap
3.1 What’s the HTTP?
3.2 What’s a HTTP Server
•
Sta±c web server
•
Dynamic web server
3.3 Java Web Applica±on
3.4 Summary
3-2

3.1 What’s the HTTP?
3-3

Internet protocol stack
•
applicaton: supportng neTwork
applicatons
•
F±P, SM±P, HTTP
•
TransporT: process-process daTa Transfer
•
±CP, UDP
•
neTwork: routng of daTagrams from source
To destnaton
•
IP, routng proTocols
•
link: daTa Transfer beTween neighboring
neTwork elemenTs
•
ETherneT, 802.111 (WiFi), PPP
•
physical: biTs “on The wire”
application
transport
network
link
physical
3-4

HyperText Transfer Protocol (HTTP)

An applicaton-layer proTocol for disTribuTed, collaboratve, hypermedia
informaton sysTems.

Providing fundamenTal means of exchanging informaton and requestng
services on web

On Top of The ±CP (±ransmission ConTrol ProTocol)

Capabilites

( H±±P 1.0 )

Allow messages in The MIME (Multpurpose InTerneT Mail ExTensions)
formaT

ConTain meTa-informaton abouT:
•
DaTa Transferred
•
ModiFers on The requesT/response semantcs

( H±±P 1.1 )

SupporT for hierarchical proxies, caching, persisTenT connectons, virTual
hosTs

DeTermine applicatons’ True capabilites

±exT-based ProTocol
3-5

HTTP overview
•
Web’s application layer
protocol
•
client/server model
•
client : browser that
requests, receives,
(using HTTP protocol)
and “displays” Web
objects
•
server: Web server
sends (using HTTP
protocol) objects in
response to requests
PC running
Firefox browser
server
running
Apache Web
server
iphone running
Safari browser
H
T
P
r
e
q
u
s
t
p
o
n
3-6

HTTP overview (contnued
)
uses TCP:
•
client initiates TCP
connection (creates
socket) to server, port
80
•
server accepts TCP
connection from client
•
HTTP messages
(application-layer
protocol messages)
exchanged between
browser (HTTP client)
and Web server (HTTP
server)
•
TCP connection closed
HTTP is “stateless”
•
server maintains
no information
about past client
requests
protocols that maintain
“state” are complex!

past history (state) must
be maintained

if server/client crashes,
their views of “state”
may be inconsistent,
must be reconciled
aside
3-7

Non-persistent HTTP
suppose user enters URL:
1a . HTTP client initiates TCP
connection to HTTP server
(process) at
on
port 80
2 . HTTP client sends HTTP
request message
(containing URL) into TCP
connection socket.
Message indicates that
client wants object
someDepartment/home.i
ndex
1b . HTTP server at host
waiting for TCP
connection at port 80.
“accepts” connection,
notifying client
3 . HTTP server receives
request message, forms
response message
containing requested
object, and sends
message into its socket
time
(contains text,
references to 10
jpeg images)
3-8

Non-persistent HTTP (cont.)
5
. HTTP client receives
response message containing
html fle, displays html.