Today we are going to learn about URI and HTTP
Uniform
Resource Identifier:
A Uniform
Resource Locator (URL) is used to address a document on the Web.
• The name that corresponds to an IP address in the
DNS is known as a URL
• A full Web address is like:
–
http://www.scss.tcd.ie/Owen.Conlan/php/xpath/index.html
• A URL usually follows these syntax rules:
–
scheme://host.domain.country_code:port/path/filename
Retrieving
a URL
TCP/IP
is a collection of communication protocols
that controls the way that information is broken up and posted over the Internet.
• HTTP takes
care of the communication between a web server and a web browser.
• To retrieve
a Web resource, the user either specifies
a URL in the Web browser’s address
or clicks on a hyperlink <a>
in a document.
HTTP
is used for sending requests from a web client (a browser) to a web server, returning web content (web pages) from the server back to the client.
• The Web
browser specifies the details of
the required Web page in a HTTP Request
message
• The Web
server receives this request and
after processing it completes the operation by returning either the
document or an error in the HTTP Response message.
HTTP
(HyperText Transfer Protocol):
It is one of the Application Layer Protocol. How
do applications interact with each
over a network or the internet?
Example:
HTTP(S) Websites and
Documents
FTP Files
SMTP,POP,IMAP E-Mail
HTTP is a protocol
for distributed hypertext and
hypermedia. Used by Web Client (browser)
and Web Server to communicate.
HTTP
REQUEST
Message indicating the client
wants to a piece of hypertext or hypermedia from the server
/*header
POST
/Login.php HTTP/1.1! //REQUEST TYPE(POST)
Host:
www.website.com!
User-Agent:
Mozilla/5.0 ! * header
Content-Length:
27!
*header
Content-Type:
application/x-www-form-urlencoded */
userid=joe&password=guessm! //body
REQUEST
TYPE:
·
GET: Received
document on URL"
·
POST: Send
information to server on
URL"
·
PUT: Replace
document on URL"
·
DELETE: Remove document on URL"
·
HEAD: Received headers from document on URL"
·
OPTIONS: Request options for this server"
REQUEST HEADER:
Content
Length: the length of the content
User-Agent:
Sending application
Date:
Date J
Host*:
Receiver.
Others…
HTTP
RESPONSE:
HTTP/1.1 200 OK! //Response Code
Date: Thu, 08 Apr 2004 18:24:33 GMT! /*
Server: Apache/1.3.29 (Unix) PHP/4.3.4! *
X-Powered-By: PHP/4.3.4! *
Content-Language: nl! *
Content-Type: text/html; * header
charset=iso-8859-1! *
X-Cache: MISS from wikipedia.org! *
Connection: close! *
Content-Length: 49! */
<html><head></head><body></body></html>
//body
RESPONSE
CODE!
1xx: informal message by server"
2xx: successful HTTP request"
3xx: redirection"
4xx: client error in HTTP request"
5xx: server error"
6xx: proxy error"
MOST
COMMON!
401 (unauthorized)
400 (bad request)
403 (forbidden)
404 (not found)
500(internal server error)
RESPONSE
HEADER:
Content Length: the length of the
content
Content Type: type of content
Server: Type of server
Date: Date
Host*: Receiver.
Others…
Hope, you will understand the HTTP protocol and its role on the internet.
Stay tuned for next discussion on HTML.
