24-AL-HTTP - Web,HTTPandWebCaching 1 HTTPoverview

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1 Web, HTTP and Web Caching
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2 HTTP overview HTTP: hypertext transfer protocol Web’s application layer protocol client/server model client:  browser that requests,  receives, “displays” Web objects server:  Web server sends objects in  response to requests HTTP 1.0: RFC 1945 HTTP 1.1: RFC 2068 PC running Explorer Server  running Apache Web server Mac running Navigator HTTP request HTTP response
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3 HTTP overview (continued) Uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP messages (application-layer protocol messages) exchanged between  browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is “stateless” server maintains no information about past client requests
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4 Web Objects Web page  consists of  objects Object can be HTML file, JPEG image, Java applet, audio file,… Web page consists of  base HTML-file  which includes several referenced  objects Each object is addressable by a  URL Example URL: www.someschool.edu/someDept/pic.gif host name path name
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5 HTTP request message two types of HTTP messages:  request, response HTTP request message: ASCII (human-readable format) GET /somedir/page.html HTTP/1.1 Host: www.someschool.edu User-agent: Mozilla/4.0 Connection: close Accept-language:fr (extra carriage return, line feed) request line (GET, POST,  HEAD commands) header  lines Carriage return,  line feed  indicates end  of message
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6 HTTP request message: general format
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7 Uploading form input Post method: Web page often includes form  input Input is uploaded to server in  entity body URL method: Uses GET method Input is uploaded in URL  field of request line: www.somesite.com/animalsearch?monkeys&banana
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8 Request types HTTP/1.0 GET POST HEAD asks server to leave requested  object out of response HTTP/1.1 GET, POST, HEAD PUT uploads file in entity body to  path specified in URL field DELETE deletes file specified in the URL  field
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9 HTTP response message HTTP/1.1 200 OK Connection close Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …. ..
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24-AL-HTTP - Web,HTTPandWebCaching 1 HTTPoverview

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