Web Services November 13, 2003Web HistoryWeb History (cont)Internet HostsWeb ServersWeb ContentStatic and Dynamic ContentURLsHow Clients and Servers Use URLsAnatomy of an HTTP TransactionHTTP RequestsHTTP Requests (cont)Slide 13HTTP ResponsesGET Request to Apache Server From IE BrowserGET Response From Apache ServerServing Dynamic ContentServing Dynamic Content (cont)Slide 19Issues in Serving Dynamic ContentCGIadd.com: THE Internet addition portal!The add.com ExperienceServing Dynamic Content With GETSlide 25Slide 26Slide 27Some CGI Environment VariablesSlide 29Slide 30Serving Dynamic Content With GETProxiesWhy Proxies?For More InformationWeb ServicesNovember 13, 2003Web ServicesNovember 13, 2003TopicsTopicsHTTPServing static contentServing dynamic content15-213“The course that gives CMU its Zip!”– 2 –15-213, F’03Web HistoryWeb History1945: 1945: Vannevar Bush, “As we may think”, Atlantic Monthly, July, 1945.Describes the idea of a distributed hypertext system.A “memex” that mimics the “web of trails” in our minds.1989:1989:Tim Berners-Lee (CERN) writes internal proposal to develop a distributed hypertext system.Connects “a web of notes with links.”Intended to help CERN physicists in large projects share and manage information 1990:1990:Tim BL writes a graphical browser for Next machines.– 3 –15-213, F’03Web History (cont)Web History (cont)19921992NCSA server released26 WWW servers worldwide19931993Marc Andreessen releases first version of NCSA Mosaic browserMosaic version released for (Windows, Mac, Unix).Web (port 80) traffic at 1% of NSFNET backbone traffic.Over 200 WWW servers worldwide.19941994Andreessen and colleagues leave NCSA to form "Mosaic Communications Corp" (now Netscape).– 4 –15-213, F’03Internet HostsInternet Hosts– 5 –15-213, F’03Web ServersWeb ServersWebserverHTTP requestHTTP response(content)Clients and servers Clients and servers communicate using the communicate using the HyperText Transfer HyperText Transfer Protocol (HTTP)Protocol (HTTP)Client and server establish TCP connectionClient requests contentServer responds with requested contentClient and server close connection (usually)Current version is HTTP/1.1Current version is HTTP/1.1RFC 2616, June, 1999. Webclient(browser)– 6 –15-213, F’03Web ContentWeb ContentWeb servers return Web servers return contentcontent to clients to clientscontent: a sequence of bytes with an associated MIME (Multipurpose Internet Mail Extensions) typeExample MIME typesExample MIME typestext/html HTML documenttext/plain Unformatted textapplication/postscript Postcript documentimage/gif Binary image encoded in GIF formatimage/jpeg Binary image encoded in JPEG format– 7 –15-213, F’03Static and Dynamic ContentStatic and Dynamic ContentThe content returned in HTTP responses can be either The content returned in HTTP responses can be either staticstatic or or dynamicdynamic..Static content: content stored in files and retrieved in response to an HTTP requestExamples: HTML files, images, audio clips.Dynamic content: content produced on-the-fly in response to an HTTP requestExample: content produced by a program executed by the server on behalf of the client.Bottom line: Bottom line: All Web content is associated with a file All Web content is associated with a file that is managed by the server.that is managed by the server.– 8 –15-213, F’03URLsURLsEach file managed by a server has a unique name called a Each file managed by a server has a unique name called a URL (Universal Resource Locator)URL (Universal Resource Locator)URLs for static content:URLs for static content:http://www.cs.cmu.edu:80/index.htmlhttp://www.cs.cmu.edu/index.htmlhttp://www.cs.cmu.eduIdentifies a file called index.html, managed by a Web server at www.cs.cmu.edu that is listening on port 80.URLs for dynamic content:URLs for dynamic content:http://www.cs.cmu.edu:8000/cgi-bin/adder?15000&213Identifies an executable file called adder, managed by a Web server at www.cs.cmu.edu that is listening on port 8000, that should be called with two argument strings: 15000 and 213.– 9 –15-213, F’03How Clients and Servers Use URLsHow Clients and Servers Use URLsExample URL: Example URL: http://www.aol.com:80http://www.aol.com:80/index.html/index.htmlClients use Clients use prefixprefix ((http://www.aol.com:80http://www.aol.com:80) to infer:) to infer:What kind of server to contact (Web server)Where the server is (www.aol.com)What port it is listening on (80)Servers use Servers use suffixsuffix ( (/index.html/index.html) to:) to:Determine if request is for static or dynamic content.No hard and fast rules for this.Convention: executables reside in cgi-bin directoryFind file on file system.Initial “/” in suffix denotes home directory for requested content.Minimal suffix is “/”, which all servers expand to some default home page (e.g., index.html).– 10 –15-213, F’03Anatomy of an HTTP TransactionAnatomy of an HTTP Transactionunix> telnet www.aol.com 80 Client: open connection to serverTrying 205.188.146.23... Telnet prints 3 lines to the terminalConnected to aol.com.Escape character is '^]'.GET / HTTP/1.1 Client: request linehost: www.aol.com Client: required HTTP/1.1 HOST header Client: empty line terminates headers.HTTP/1.0 200 OK Server: response lineMIME-Version: 1.0 Server: followed by five response headersDate: Mon, 08 Jan 2001 04:59:42 GMTServer: NaviServer/2.0 AOLserver/2.3.3Content-Type: text/html Server: expect HTML in the response bodyContent-Length: 42092 Server: expect 42,092 bytes in the resp body Server: empty line (“\r\n”) terminates hdrs<html> Server: first HTML line in response body... Server: 766 lines of HTML not shown.</html> Server: last HTML line in response bodyConnection closed by foreign host. Server: closes connectionunix> Client: closes connection and terminates– 11 –15-213, F’03HTTP RequestsHTTP RequestsHTTP request is a HTTP request is a request linerequest line, followed by zero or , followed by zero or more more request headersrequest headersRequest line: Request line:
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