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www and http services


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www and http services

  1. 1.  When a web address (or URL- Uniform Resource Locator) is typed into a web browser, the web browser establishes a connection to the web service running on the server using HTTP.  URLs and URIs (uniform resource identifiers) are the names most people associate with web addresses.
  2. 2.  The URL refers to a specific resource—a web page named index.html on a server identified as  Web browsers are the client applications computers use to connect to the World Wide Web and access resources stored on a web server.  As with most server processes, the web server runs as a background service and makes different types of files available.
  3. 3.  To access the content, web clients make connections to the server and request the desired resources.  The server replies with the resources and, upon receipt, the browser interprets the data and presents it to the user.  Browsers can interpret and present many data types, such as plain text or HTML, the language in which web pages are constructed.
  4. 4.  Other types of data, however, might require another service or program, typically referred to as a plug-in or add-on.  To help the browser determine what type of file it is receiving, the server specifies what kind of data the file contains.
  5. 5. consider the URL First, the browser interprets the three parts of the URL:  ■ http: The protocol or scheme ■ The server name ■ web-server.htm: The specific filename requested  The browser then checks with a name server to convert into a numeric address, which it uses to connect to the server.
  6. 6.  Using the HTTP requirements, the browser sends a GET request to the server and asks for the file web-server.htm.  The server in turn sends the HTML code for this web page to the browser.  Finally, the browser deciphers the HTML code and formats the page for the browser window.
  7. 7.  HTTP, one of the protocols in the TCP/IP suite, was originally developed to publish and retrieve HTML pages and is now used for distributed, collaborative information systems.  HTTP is used across the world wide web for data transfer and is one of the most used application protocols.
  8. 8.  HTTP specifies a request/response protocol. When a client, typically a web browser, sends a request message to a server, the HTTP protocol defines the message types the client uses to request the web page and the message types the server uses to respond.
  9. 9.  GET is a client request for data. A web browser sends the GET message to request pages from a web server.  When the server receives the GET request, it responds with a status line, such as HTTP/1.1 200 OK, and a message of its own, the body of which can be the requested file, an error message, or some other information.
  10. 10.  The are: three common message types ■ GET ■ POST ■ PUT
  11. 11.  POST and PUT are used to send messages that upload data to the web server.  For example, when the user enters data into a form embedded in a web page, POST includes the data in the message sent to the server.  PUT uploads resources or content to the web server.
  12. 12. Looks up phone book for the number Example Could have been also POST/phonebook.cgi.HTTP/1.0 achieved by Get Date: But in that case number User-Agent: would have been in the Accept Language: en-us Resource URL Content Length: 14 Which would have been 98490 55266 stored in the log
  13. 13.  Although it is remarkably flexible, HTTP is not a secure protocol.  The POST messages upload information to the server in plain text that can be intercepted and read.  Similarly, the server responses, typically HTML pages, are unencrypted.
  14. 14.  For secure communication across the Internet, the Secure HTTP (HTTPS) protocol is used for accessing and posting web server information. HTTPS can use authentication and encryption to secure data as it travels between the client and server.  HTTPS specifies additional rules for passing data between the application layer and the transport layer.
  15. 15. HTTP Protocol Using GET
  16. 16. Accessing Resources over the Web  <protocol>://<server>/<path> Communication Protocol between the client and the server Defines the address (Uniform Resource Locator)
  17. 17. Hypertext Transport Protocol (HTTP) characteristics  Request-response mechanism:  Resource Identification  Statelessness  Meta data support ◦ Transaction is initiated by a client sending a request to server ◦ Server generates a response ◦ Each HTTP request includes a URI (Uniform Resource Identifier) ◦ The server does not maintain any information about the transaction ◦ Metadata about information can be exchanged in the messages
  18. 18. HTTP Request Format Request Line Header Lines GET /index.html HTTP/1.0 Specifies resource via URI & meta data Host: Date: BBBBBBBBBBBB User-Agent: Mozilla/5.0 (en) (WINNT; U) Accept-Language: en-us Carriage Return/Line Feed Message Body Specifies request method Content-length: (Message Payload)
  19. 19. HTTP Response Format Status line Header Lines HTTP/1.0 200 OK Date: BBBBBBBBBBBB Server: Apache/1.3.12 (Unix) Last-Modified: (date) Content Type: text/html Carriage Return/Line Feed Message Body Content-length: (Message Payload) Status line with result code and phrase Specifies server & resource meta data
  20. 20. Result Code and Phrase      1xx: Informational – Not Done Yet 2xx: Success – You win 3xx:Redirection-You lose but try again 4xx:Client Error – You lose, your fault 5xx:Server Error – You lose, my bad 200 204 300 301 302 304 400 401 404 500 OK No Content Multiple Choices Moved Permanently Moved Temporarily Not Modified Bad Request Unauthorized Not Found Internal Server Error
  21. 21. Improvements in HTTP/1.1  Persistent connections ◦ Keeps the connection open after the server response ◦ Connection can be closed by either client or server  Request Pipelining ◦ Allows a client to send several requests without waiting for a response ◦ Server responds in the same order  Chunked Encoding ◦ Allows sender to break a message into arbitrary sized chunks ◦ Useful for dynamically created response messages
  22. 22. Cookies HTTP is stateless protocol Cookies manage state maintenance by shifting the burden to client • Cookies are transmitted in clear text (security issue) • • Server Client Usual HTTP Request 1st client request 2nd client request Usual HTTP Response, including header line Setcookie: <cookie> Usual HTTP Request, including header line Set-cookie: <cookie> Usual HTTP Response Client does not interpret the cookie string Server is presented with the previously returned state information
  23. 23. User Authentication • Users browser information remembers credentials and includes them in headers for subsequent requests • Browser typically deletes stored authentication credentials once browser is closed • HTTP allows various authentication mechanisms
  24. 24. Group 2  John Gabriel Javier  Jenica Salmorin  Enrefie Abuela  Marilou Villanueva