class9.ppt - User-server state cookies Many major Web sites use cookies Four components 1 cookie header line in the HTTP response message 2 cookie

class9.ppt - User-server state cookies Many major Web sites...

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1 User-server state: cookies Many major Web sites use cookies Four components: 1) cookie header line in the HTTP response message 2) cookie header line in HTTP request message 3) cookie file kept on user’s host and managed by user’s browser 4) back-end database at Web site Example: o Susan access Internet always from same PC o She visits a specific e- commerce site for first time o When initial HTTP requests arrives at site, site creates a unique ID and creates an entry in backend database for ID
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Cookies: keeping “state” (cont.) client server usual http response msg usual http response msg cookie file one week later: usual http request msg cookie: 1678 cookie- specific action access ebay 8734 usual http request msg Amazon server creates ID 1678 for user create entry usual http response Set-cookie: 1678 ebay 8734 amazon 1678 usual http request msg cookie: 1678 cookie- specific action access ebay 8734 amazon 1678 backend database 2
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3 Cookies (continued) What cookies can bring: o shopping carts o recommendations o user session state (Web e-mail) Cookies and privacy: o cookies permit sites to learn a lot about you o you may supply name and e-mail to sites o search engines use redirection & cookies to learn yet more o advertising companies obtain info across sites aside
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4 Web caches (proxy server) o user sets browser: Web accesses via cache o browser sends all HTTP requests to cache o object in cache: cache returns object o else cache requests object from origin server, then returns object to client Goal: satisfy client request without involving origin server client Proxy server client HTTP request HTTP request HTTP respons e HTTP response HTTP request HTTP response origin server origin server
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5 More about Web caching o Cache acts as both client and server o Typically cache is
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