2. Introduction
• Transfer protocol used throughout the
WWW
• is a request-response protocol
• it is stateless
• latest version is HTTP/1.1
• runs on top of TCP on the standardized
port 80
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3. conti…
• Specifies what messages client may send
to servers and what response they get
back
• Each interaction consists of one ASCII
request followed by one RFC 822 MIME
like response
• All client and servers must obey this
protocol
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4. connections
• In http 1.0, after the connection
established, a single request sent over
and a single response sent back
• It is efficient for normal web page
containing html text
• When web page contain large no of icons,
images etc, establishing a TCP connection
to transport a single icon become very
expensive
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5. Conti….
• HTTP 1.1 support persistent connections
• establish a TCP connection send a
request and get a response
• Then send additional requests and get
additional responses
• The relative overload due to TCP is much
less per request
• It is possible to pipeline the requests
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6. Methods
• Although HTTP was designed for use in
the Web, it has been intentionally made to
future object-oriented applications.
• so operations, called methods, other than
just requesting a Web page are supported
• Each request consists of one or more lines
of ASCII text, with first word on first line
being the name of the method requested.
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7. Conti…
• The names are case sensitive
• The methods are:
• GET method
requests the server to send the page.
page is suitably encoded in MIME.
vast majority of requests to Web servers are
GETs.
The usual form of GET is
GET filename HTTP/1.1
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8. conti…
• HEAD method:
asks for the message header, without the
actual page
used to get a page's time of last modification,
to collect information for indexing purposes
to test a URL for validity.
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9. Conti….
• PUT method:
reverse of GET
instead of reading the page, it writes the page
makes it possible to build a collection of Web
pages on a remote server
request contains the page
It may be encoded using MIME
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10. Conti….
• POST method:
PUT is similar to POST method.
bears a URL, but instead of replacing the
existing data, the new data is ''appended'' to it
neither PUT nor POST is used very much.
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11. Conti….
• DELETE method:
it removes the page.
authentication and permission play a major
role
There is no guarantee that DELETE succeeds
Because even if the remote HTTP server is
willing to delete the page, the underlying file
may have a mode that forbids the HTTP
server from modifying
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12. Conti….
• TRACE method:
for debugging
instructs the server to send back the request
useful when requests are not being
processed correctly and the client wants to
know what request the server actually got.
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13. Conti….
• CONNECT method:
reserved for future use.
• OPTIONS method:
provides a way for the client to query the
server about its properties or those of a
specific file
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14. The built-in HTTP request methods
Method Description
GET Request to read a Web page
HEAD Request to read a Web page’s header
PUT Request to store a Web page
POST Append to a named recourse
DELETE Remove the Web page
TRACE Echo the incoming request
CONNECT Reserved for future use
OPTIONS Query certain options
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15. Status lines
• Every request gets a response consisting
of a status line, and possibly additional
information
• It contains a three-digit status code telling
whether the request was satisfied, and if
not, why not
• first digit is used to divide the responses
into five major groups
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16. The status code response groups
Code Meaning Example
1xx Information 100=server agrees to handle clients
request
2xx Success 200=request succeeded;204=no
content present
3xx Redirection 301=page moved;304=cached page
still valid
4xx Client error 403=forbidden page;404=page not
found
5xx Server error 500=internal server error;503=try
again later
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17. Message Headers
• request line may be followed by additional
lines with more information called request
headers
• Responses may also have response
headers
• Some headers can be used in either
direction
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19. Conti….
• User-Agent header allows the client to
inform the server about its browser, os,
and other properties
• It is used by the client to provide the
server with the information
• four Accept headers tell the server what
the client is willing to accept in the event
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20. Conti….
• Accept header specifies the MIME types
that are welcome
• Accept-Charset header gives the
character set
• Accept-encode header deals with
compression methods
• Accept-Language header indicates a
natural language
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21. Conti….
• If the server has a choice of pages, it can
use this information to supply the one the
client is looking for
• If it is unable to satisfy the request, an
error code is returned and the request fails
• Host header names the server
• It is taken from the URL
• This header is mandatory
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22. Conti….
• It is used because some IP addresses
may serve multiple DNS names and the
server needs some way to tell which host
to hand the request to.
• Authorization header is needed for
pages that are protected
• client may have to prove it has a right to
see the page requested.
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23. Conti….
• Although cookies are dealt with in RFC
2109 rather than RFC 2616, they also
have two headers
• Cookie header is used by clients to return
to server a cookie that was previously sent
by some machine in server's domain
• Date header can be used in both
directions and contains the time and date
the message was sent
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24. Conti….
• Upgrade header is used to make it easier
to make the transition to a future version
of the HTTP protocol.
• It allows the client to announce what it can
support and the server to assert what it is
using.
• Server, allows the server to tell who it is
and some of its properties if it wishes.
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25. Conti….
• next four headers, all starting with
Content-, allow the server to describe
properties of page it is sending.
• Last-Modified header tells when the
page was last modified.
• This header plays an important role in
page caching.
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26. Conti….
• Location header can be used if the page
has moved or to allow multiple URLs to
refer to the same page
• If a page is very large, a small client may
not want it all at once
• Some servers will accept requests for byte
ranges, so page can be fetched in multiple
small units.
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27. Conti….
• Accept-Ranges header announces
server's willingness to handle this type of
partial page request.
• Set-Cookie, is how servers send cookies
to clients.
• client is expected to save the cookie and
return it on subsequent requests to the
server.
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