PC WIZZ STUFF: ABOUT HTTP

ANSWER:-

What exactly happens when you type a URL(Uniform Resource Locator) in the
location bar of the browser? Well firstly the browser performs a DNS queiry
and converts the human readable domain name (like hotmail.com) into a machine
readable IP address. Once the browser gets the IP address of the host, it
connects to Port 80(The HTTP daemon by default runs on Port 80) of the remote
host and asks the host for a particular document or page with the help of HTTP
commands. HTTP or HyperText Transfer Protocol is the protocol used by browsers
to communicate with hosts i.e. to ask for a particular file at a specific URL
or to send or post data to the server.We are never aware of this process which
occurs in the background.

Now in this section we will learn to do manually what the browser does
automatically.When the browser asks for a file at a specific URL it is said to
'request' for information. Now before we move on, let's see what a typical
request
looks like. A typical HTTP request would be something like the below:

get url HTTP/1.1

Let's see what the specific parts of a typical request stands for.The first
word i.e. the 'get' part is called the method.There are 3 types of methods-:

The Get method:-

The 'get' method is the most common method which is widely used.It is with the
'get' method that the browsers request for pages or douments.In this kind of
method you are the client(browser) and request for a page from the server
which is the host you are connected to.

The Post Method:-

The 'post' method is used to upload files to the server.This kind of method is
used say when you upload your website by using not the FTP service but by
straightaway uploading files through a HTML page.In this method there is a
reversal of roles and now you become the server and the host you are connected
to becomes the client.

The Head Method:-

The 'head' method is the least popular method and not many people know about
it.Although not widely used, it is still a part of HTTP methods. You would use
the 'head' method say when you want to make sure that a particualar file
exists at a particular URL without downloading the entire file.This method
just downloads the header info of a particular file and not the entire file.

All this might seem a bit weird, but I suggest that you just understand the
basic difference between the various methods and then move on.

Anyway coming back to the various parts of a HTTP request.The first part as
you now know is the method, now the second part is the URL that you are
requesting.Say for example I want to request the contacts.htm file then the
HTTP request would look something like:

get /contacts.htm HTTP/1.1

Now you may ask where the first '/' has come from. Now to understand that you
need to look at the URL that you type into the Location bar of the browser.Say
for example, the HTML file that you are requesting is
http://www.microsoft.com/windows.htm then the URL would be what is left after
removing the http:// and the domain name i.e. www.microsoft.com. Hence the URL
is /windows.htm

Now what will the URL be if you want to request for Yahoo homepage? Normally
you write http://www.yahoo.com in the location bar to access Yahoo's homepage.
Now if we remove the http:// and also the domain name(www.yahoo.com) then what
is left?
Nothing. This means the URL of the HTTP request is '/'. Hence the HTTP request
now looks like.

get / HTTP/1.1

The third part of the HTTP request is pretty self explanatory.The HTTP/1.1
specifies the version of the HTTP service used by the browser.So say if a
server is running HTTP/1.1 and a browser which is running HTTP/1.0 requests a
page then the server will send the page in terms of HTTP/1.0 only removing the
enhancements of HTTP/1.1

So now that you know what a normal HTTP request sent by your browser looks,
let's find out how we can do this manually.This too requires Telnet.Now you
know how important the Telnet client is in a Hacker's armoury.So launch your
Telnet client and connect to Port 80(As the HTTP daemon runs on Port 80) of
any host.If the host you are trying to connect to does not have a website i.e
does not have Port 80 open, then you would get a Error Message.If the
connection is successful then the Title bar of your Telnet client will show
the host address you are connected to and it will be ready for user input.

The HTTP daemon is not as boring as it seems to be till now.Infact it is very
very interesting.Once telnet is ready for input just type h (or any other
letter) and hit enter twice.

NOTE:- After each HTTP command one has to press Enter Twice to send
the command to the server or to bring about a response from a server.It is
just how the HTTP protocol works.

Now as 'h' or any other command that you typed is not a valid HTTP command,
the server will give you an error message, something like the below:

HTTP/1.1 400 Bad Request
Server: Netscape-Enterprise/3.5.1

The server replies with the version of HTTP it is running(not so important),
it gives us an error message and the error code associated with it(again not
so important), but it also gives us the OS name and OS version, it is
running.Wow!!! It gives hackers who want to break into their server the
ultimate piece of information which they require.

Anyway now let's see what happens when we give a normal authentic request
requesting for the main page of Yahoo.So after I telnet to Port 80 of
www.yahoo.com I give the command:

get / http/1.1

(requesting for the Yahoo Homepage)

HTTP/1.0 200 OK
Content-Length: 12085
Content-Type: text/html

(No OS name,interesting, well Yahoo being a Top Web Company has configured
their server to not display the OS name and Version when an HTTP request is
encountered.)

<html><head><title>Yahoo!</title><base href=http://www.yahoo.com/><meta http-
equiv="PICS-Label" content='(PICS-1.1 "http://www.rsac.org/ratingsv01.html" l
gen true for "http://www.yahoo.com" r (n 0 s 0 v 0 l
0))'></head><body><center><form action=http://search.yahoo.com/bin/search><map
name=m><area coords="72,0,130,58" href=r/wn><area coords="131,0,189,58"
href=http://mail.yahoo.com><area coords="414,0,472,58" href=r/i1><area
coords="473,0,531,58" href=r/hw></map><img width=600 height=59 border=0
usemap="#m" src=http://a1.g.a.yimg.com/7/1/31/000/us.yimg.com/i/main4s3.gif
alt=Yahoo> <table border=0 cellspacing=0 cellpadding=4 width=600><tr><td
align=center width=160>
<a href="/homet/?http://auctions.yahoo.com">Yahoo!
Auctions</a> <a
href="/homet/?http://list.auctions.yahoo.com/27813-category.html">Pokemon</a>,
<a href="/homet/?http://list.auctions.yahoo.com/26360-category-
leaf.html">cars</a>, <a href="/homet/?http://list.auctions.yahoo.com/40291-
category-leaf.html">'N Sync</a></td><td align=center><a
href="
http://rd.yahoo.com/M=26036.208672.1462854.389576/S=2716149:NP/A=167764/?h
ttp://messenger.yahoo.com/" target="_top"><img width=230 height=33
src="
http://a32.g.a.yimg.com/7/32/31/000/us.yimg.com/a/ya/yahoopager/messenger/m
essengermail.gif" alt="Yahoo! Messenger" border=0></a></td><td align=center
width=160><a href="/homet/?http://mail.yahoo.com">Yahoo!
Mail</a> free
email for life</td></tr><tr><td colspan=3 align=center><input size=30 name=p>
<input type=submit value=Search> <a href=r/so>advanced
search</a></td></tr></table><table border=0 cellspacing=0 cellpadding=4
width=600><tr><td nowrap align=center><a href=r/sh>Shopping</a> -
<a href=r/os>Auctions</a> -
<a href=r/yp>Yellow Pages</a> -
<a href=r/ps>People Search</a> -
<a href=r/mp>Maps</a> -
<a href=r/ta>Travel</a> -
<a href=r/cf>Classifieds</a> -
<a href=r/pr>Personals</a> -
<a href=r/pl>Games</a> -
<a href=r/yc>Chat</a> -
<a href=r/ub>Clubs</a> <a href=http://mail.yahoo.com>Mail</a> -
<a href=r/ca>Calendar</a> -
<a href=r/pg>Messenger</a> -
<a href=r/cm>Companion</a> -
<a href=r/i2>My Yahoo!</a> -
<a href=r/dn>News</a> -
<a href=r/ys>Sports</a> -
<a href=r/wt>Weather</a> -
<a href=r/tg>TV</a> -
<a href=r/sq>Stock Quotes</a> -
<a href=r/xy>more...</a></td></tr><tr><td></td></tr></table><table
border=0 cellspacing=0 width=600><tr><td bgcolor=339933><table border=0
cellspacing=0 cellpadding=0><tr><td
height=2></td></tr></table></td></tr></table><table border=0 cellspacing=7
cellpadding=2><tr><td valign=top align=center>

<table cellspacing=0 cellpadding=3 border=0 width="100%"><tr><td align=center
bgcolor=99cc99><a href=r/s/1>Yahoo!
Shopping</a> - Thousands of stores.
Millions of products.<table cellspacing=0 cellpadding=2 border=0
width="100%"><tr><td align=center bgcolor=ffffff><table cellspacing=0 border=0
width="100%"><tr><td colspan=2>Departments</td><td>Stores</td><td>Products</td></tr><tr><td valign=top
width="22%">·
<a href=r/s/2>Apparel</a> ·
<a href=r/s/3>Bath/Beauty</a> ·
<a href=r/s/4>Computers</a> ·
<a href=r/s/5>Electronics</a></td><td valign=top
width="22%">·
<a href=r/s/10>Flowers</a> ·
<a href=r/s/11>Sports</a> ·
<a href=r/s/7>Music</a> ·
<a href=r/s/9>Video/DVD</a></td><td valign=top width="31%">
· <a href=r/s/eb>Eddie Bauer</a> 
· <a href=r/s/ash>Ashford</a> 
· <a href=r/s/toys>Toys R Us</a> 
· <a href=r/s/nord>Nordstrom</a> 
</td><td valign=top width="25%">
· <a href=r/s/nsync>'N Sync</a> 
· <a href=r/s/cam>Digital cameras</a> 
· <a href=r/s/poke>Pokemon</a> 
· <a href=r/s/mp3>MP3 players</a> 
</td></tr></table></td></tr></table></td></tr></table>

<table border=0 cellspacing=0 cellpadding=4><tr><td valign=top
nowrap><a href=r/ar>Arts &
Humanities</a> <a href=r/li>Literature</a>,
<a href=r/ph>Photography</a>... <a
href=r/bu>Business & Economy</a> <a href=r/co>Companies</a>,
<a href=r/fi>Finance</a>,
<a href=r/jo>Jobs</a>... <a
href=r/ci>Computers & Internet</a> <a href=r/in>Internet</a>,
<a href=r/ww>WWW</a>,
<a href=r/sf>Software</a>,
<a href=r/ga>Games</a>... <a
href=r/ed>Education</a> <a href=r/un>College and
University</a>,
<a href=r/k2>K-12</a>... <a
href=r/en>Entertainment</a> <a href=r/cl>Cool Links</a>,
<a href=r/mo>Movies</a>,
<a href=r/hu>Humor</a>,
<a href=r/mu>Music</a>... <a
href=r/go>Government</a> <a href=r/el>Elections</a>,
<a href=r/mi>Military</a>,
<a href=r/la>Law</a>,
<a href=r/tx>Taxes</a>... <a
href=r/he>Health</a> <a href=r/md>Medicine</a>,
<a href=r/ds>Diseases</a>,
<a href=r/dg>Drugs</a>,
<a href=r/ft>Fitness</a>...</td><td valign=top nowrap><font
size=3 face=arial><a href=r/nm>News & Media</a> <a
href=r/fc>Full Coverage</a>,
<a href=r/nw>Newspapers</a>,
<a href=r/tv>TV</a>... <a
href=r/rs>Recreation
& Sports</a> <a href=r/sp>Sports</a>,
<a href=r/tr>Travel</a>,
<a href=r/au>Autos</a>,
<a href=r/od>Outdoors</a>... <a
href=r/rf>Reference</a> <a href=r/lb>Libraries</a>,
<a href=r/dc>Dictionaries</a>,
<a href=r/qt>Quotations</a>... <a
href=r/re>Regional</a> <a href=r/ct>Countries</a>,
<a href=r/rg>Regions</a>,
<a href=r/us>US States</a>... <a
href=r/sc>Science</a> <a href=r/am>Animals</a>,
<a href=r/as>Astronomy</a>,
<a href=r/eg>Engineering</a>... <a
href=r/ss>Social Science</a> <a href=r/ac>Archaeology</a>,
<a href=r/ec>Economics</a>,
<a href=r/lg>Languages</a>... <a
href=r/cu>Society & Culture</a> <a href=r/pe>People</a>,
<a href=r/ev>Environment</a>,
<a href=r/rl>Religion</a>...</td></tr></table></td>
<td align=right valign=top bgcolor=dcdcdc width=155><table border=0
cellspacing=1 width="100%"><tr><td align=center bgcolor=ffffcc nowrap
colspan=2><table border=0 cellspacing=0 cellpadding=0 width=120><tr><td
align=center>In the
News</td></tr></table></td></tr><tr><td
valign=top>·</td><td><a
href="/homer/?http://fullcoverage.yahoo.com/fc/world/Elian_Gonzalez/">Reno
says
Elian to be returned to father</a></td></tr><tr><td
valign=top>·</td><td><a
href="/homer/?http://fullcoverage.yahoo.com/Full_Coverage/World/Zimbabwe/
">Zimba
bwe land seizures continue</a></td></tr><tr><td
valign=top>·</td><td><a
href="/homer/?http://sports.yahoo.com/pga/">The Masters</a>, <a
href="/homer/?http://sports.yahoo.com/mlb/">MLB</a>, <a
href="/homer/?http://sports.yahoo.com/nba/">NBA</a></td></tr><tr><td
align=right colspan=2><a href=r/xn>more...</a></td></tr><tr><td
align=center bgcolor=ffffcc colspan=2>Marketplace</td></tr><tr><td
valign=top>·</td><td><a
href="/homer/?http://taxes.yahoo.com/">Y! Tax Center</a> - tax guide, online
filing, and more</td></tr><tr><td
valign=top>·</td><td><a href=/homer/?http://b2b.yahoo.com
>Y!
Business Marketplace</a> - products for all
industries</td></tr><tr><td
valign=top>·</td><td>Free <a
href="/homer/?http://www.bluelight.com/isp.html">56K Internet
Access</a></td></tr><tr><td valign=top>·</td><td><a
href="/homer/?http://bills.yahoo.com/">Yahoo! Bill Pay</a> - free 3-month
trial
</td></tr><tr><td align=right colspan=2><a
href=r/xm>more...</a></td></tr><tr><td align=center
bgcolor=ffffcc colspan=2>Inside
Yahoo!</td></tr><tr><td valign=top>·</td><td><a
href="/homer/?http://movies.yahoo.com">Y! Movies</a> - showtimes, reviews,
info</td></tr><tr><td valign=top>·</td><td><a
href="/homer/?http://photos.yahoo.com/">Yahoo! Photos</a> - upload, share, and
print pictures</td></tr><tr><td
valign=top>·</td><td>Play free <a
href="/homer/?http://baseball.fantasysports.yahoo.com/baseball/">Fantasy
Baseball</a></td></tr><tr><td
valign=top>·</td><td><a
href="/homer/?http://geocities.yahoo.com/home/">Yahoo! GeoCities</a> - build
your free home page</td></tr><tr><td align=right colspan=2><a
href=r/xi>more...</a></td></tr></table></td></tr></table>
<table border=0 cellspacing=0 width=600><tr><td bgcolor=339933><table border=0
cellspacing=0 cellpadding=0><tr><td
height=2></td></tr></table></td></tr></table>
</form><form action=http://search.local.yahoo.com/zipsearch><table border=0
cellspacing=4 cellpadding=0><tr><td align=right valign=top
nowrap>World Yahoo!s</td><td></td><td valign=top
colspan=2>Europe :
<a href=r/dk>Denmark</a> -
<a href=r/fr>France</a> -
<a href=r/de>Germany</a> -
<a href=r/it>Italy</a> -
<a href=r/no>Norway</a> -
<a href=r/es>Spain</a> -
<a href=r/se>Sweden</a> -
<a href=r/uk>UK & Ireland</a> Pacific Rim :
<a href=r/ai>Asia</a> -
<a href=r/an>Australia & NZ</a> -
<a href=r/cc>China</a> -
<a href=r/cn>Chinese</a> -
<a href=r/hk>HK</a> -
<a href=r/jp>Japan</a> -
<a href=r/kr>Korea</a> -
<a href=r/sg>Singapore</a> -
<a href=r/tw>Taiwan</a> Americas :
<a href=r/ag>Argentina</a> -
<a href=r/br>Brazil</a> -
<a href=r/cd>Canada</a> -
<a href=r/mx>Mexico</a> -
<a href=r/ep>Spanish</a></td></tr><tr><td align=right
nowrap>Yahoo! Get Local</td><td></td><td
nowrap><a
href=r/lo>LA</a> -
<a href=r/ny>NYC</a> -
<a href=r/ba>SF Bay</a> -
<a href=r/ch>Chicago</a> -
<a href=r/mm>more...</a>   </td><td nowrap><input
name=q size=5 maxlength=5> <input type=submit value="Enter Zip
Code"></td></tr><tr><td align=right valign=top
nowrap>Other</td><td></td><td valign=top
colspan=2><a href=r/ya>Autos</a> -
<a href=r/em>Careers</a> -
<a href=r/di>Digital</a> -
<a href=r/ye>Entertainment</a> -
<a href=r/le>Event Guide</a> -
<a href=r/gr>Greetings</a> -
<a href=r/yh>Health</a> -
<a href=r/iv>Invites</a> -
<a href=r/ne>Net Events</a> <a href=r/ms>Message Boards</a> -
<a href=r/mv>Movies</a> -
<a href=r/rk>Music</a> -
<a href=r/yr>Real Estate</a> -
<a href=r/sb>Small Business</a> -
<a href=r/il>Y! Internet Life</a> -
<a href=r/yg>Yahooligans!</a></td></tr></table></form><table border=0
cellspacing=0 width=600><tr><td bgcolor=339933><table border=0 cellspacing=0
cellpadding=0><tr><td height=2></td></tr></table></td></tr></table><table
border=0 cellspacing=6 cellpadding=0><tr><td align=right><a
href=r/vs>Yahoo! prefers</a></td><td><a href=r/vs><img width=37
height=23 border=0
src=http://a1.g.a.yimg.com/7/1/31/000/us.yimg.com/a/vi/visa/sm.gif
></a></td></tr
></table><a href=r/ad>How to Suggest a Site</a> -
<a href=r/cp>Company Info</a> -
<a href=r/pv>Privacy Policy</a> -
<a href=r/ts>Terms of Service</a> -
<a href=r/cb>Contributors</a> -
<a href=r/hr>Openings at Yahoo!</a>Copyright © 2000 Yahoo! Inc. All
rights reserved. <a href=r/cy>Copyright
Policy</a></center></body></html>

The get method gives the HTML source of the document requested.It seems just
as if you are seeing the source by clicking View> Source.

Similiarly you can see what happens when you issue the 'PUT' and 'Head'
methods.Just replace 'Get' with the Method that you want to use.For

Example,

head / http/1.1 and put/ http/1.1

Let's go back to the response that we got from the HTTP daemon
once the HTTP Get method was okayed at Yahoo.The first line of the response
was:

HTTP/1.0 200 OK

Now what does this 200 signify? Well the '200' is called the status
code.Whenever you give the server a HTTP command, it processes the command and
accrodingly displays a status code.A status code is a 3 digit code in the form
of xxx. Status codes start from 1xx to 5xx.I am not sure what the 1xx series
signifies as they are rarely used.The 2xx series signify a succssful
completion of the HTTP command given.The 3xx series signify errors due to
moving of documents.The 4xx series signify errors caused at browser side and
finally the 5xx series signify errors at the server side.

The most common status code that you come across, but may not have ever see is
the 200 OK status code.Each time you are able to see a page on the browser
successfully, the browser has been sent this status code by the HTTP daemon.

The most common errors that you might come across and actually see would be
the 404 Error---Not Found. This error emssage means that the Url that you
tying to access is not found, it has either been moved or has been deleted or
the linking of the web pages itself has not been done properly.I can go to the
up directory to look for the exact new changed URL.

thank you :)

PC WIZZ STUFF

11 June 2012

ABOUT HTTP

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