HyperText Transfer Protocol

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HyperText Transfer Protocol
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What is HTTP?

• HTTP or HyperText Transfer Protocol is the
  underlying protocol used by the World Wide Web.
  HTTP defines how messages are formatted and
  transmitted, and what actions Web servers and
  browsers should take in response to various
  commands.

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Stateless Protocol ?

• each command is executed independently, without
  any knowledge of the commands that came before it.

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Versions
Invented by Tim Berners-Lee

• HTTP 0.9
• HTTP 1.0
• HTTP 1.1
• HTTP 1.2 the future

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HTTP vs. FTP

• FTP transfers entire files from one machine
  (Server) to another (client)
• HTTP transfers the contents of a file to a web
  browser or client for interpretation.
• FTP usually requires a user to login
• HTTP does not.

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HTTP vs. FTP cond

• FTP is duplex
• HTTP is simplex

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Background

• Tim Berners-Lee invented the World Wide Web, and
  later wrote the first web client, server, and
  software for it.
• Part of this software was the HTTP protocol

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Important Groups and Acronyms

• IETF Internet Engineering Task Force Computer
  Professionals, Vendors and Researchers
• W3C World Wide Web Consortium Founded by the
  father of the internet to lead the internet to
  its full potential.
• RFCs Request For Comments An internet document
  deemed important by the IETF. If it gains enough
  interest it can become an internet standard.

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HTTP 1.1

• The Official Web standard for HTTP communication.
• Allows messages to be sent between clients and
  servers.
• Messages take the formatrequest method, URI, and
  protocol version followed by a MIME like message
  containing request modifiers, client information,
  possible body content and footers.

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HTTP 1.1 Clients MUST

• Include the Host header with each request
• Accept responses with chunked data
• Either support persistent connections, or include
  the "Connection close" header with each request
• Handle the "100 Continue" response

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HTTP 1.1 Clients MUST

• Require the Host header from HTTP 1.1 clients
• Accept absolute URL's in a request
• Accept requests with chunked data
• Either support persistent connections, or include
  the "Connection close" header with each response
  

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HTTP 1.1 Clients MUST

• Use the "100 Continue" response appropriately
• Include the Date header in each response
• Handle requests with If-Modified-Since or
  If-Unmodified-Since headers
• Support at least the GET and HEAD methods
• Support HTTP 1.0 requests

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How it all works (Caching)
Request chain ------------------------------------
--gt UA -----v----- A -----v----- B -----v----- C
-----v----- O lt-----------------------------------
-- Response chain
Request chain ----------gt UA -----v----- A
-----v----- B - - - - - - C - - - - - - O
lt--------- Response chain (machine B caching)
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How it all works

• Establishing the connection
• Making the request
• Sending the right headers
• Response
• Interpreting the response.

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How it all works
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How it all works
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How it all works
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How it all works

• Bad Requests
• How Browsers / User agents interpret Response
  Codes.

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How it all works
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How it all works

• 200 OK
• The request succeeded, and the resulting resource
  (e.g. file or script output) is returned in the
  message body.
• 404 Not Found
• The requested resource doesn't exist.
• 301 Moved Permanently 302 Moved Temporarily 303
  See Other (HTTP 1.1 only)
• The resource has moved to another URL (given by
  the Location response header), and should be
  automatically retrieved by the client. This is
  often used by a CGI script to redirect the
  browser to an existing file.
• 500 Server Error
• An unexpected server error. The most common cause
  is a server-side script that has bad syntax,
  fails, or otherwise can't run correctly.

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Conclusion

• HTTP - economical and widely used
• Disadvantage stateless applications have to
  create and manage the state data, integrity of
  data passed between it and the server.
• Overheads