Web services Nov 29, 2001Web historyWeb history (cont)Internet Domain Survey (www.isc.org)Web 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 ApacheServing dynamic contentSlide 18Slide 19Slide 20Issues in serving dynamic contentCGIadd.com: THE Internet addition portal!The add.com experienceServing dynamic content with GETSlide 26Slide 27Slide 28Some CGI environment variablesSlide 30Slide 31Serving dynamic content with GETFor more informationWeb services Nov 29, 2001Topics•HTTP•Serving static content•Serving dynamic contentclass27.ppt15-213“The course that gives CMU its Zip!”CS 213 F’01– 2 –class27.pptWeb history1945: •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:•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:•Tim BL writes a graphical browser for Next machines.CS 213 F’01– 3 –class27.pptWeb history (cont)1992•NCSA server released•26 WWW servers worldwide1993•Marc Andreessen releases first version of NCSA Mosaic browser•Mosaic version released for (Windows, Mac, Unix).•Web (port 80) traffic at 1% of NSFNET backbone traffic.•Over 200 WWW servers worldwide.1994•Andreessen and colleagues leave NCSA to form "Mosaic Communications Corp" (now Netscape).CS 213 F’01– 4 –class27.pptInternet Domain Survey(www.isc.org)1001,00010,000100,0001,000,00010,000,000100,000,000Internet hostsMosaicandNetscapeCS 213 F’01– 5 –class27.pptWeb serverswebserverHTTP requestHTTP response(content)Clients and servers communicate using the HyperText Transfer Protocol (HTTP)•client and server establish TCP connection•Client requests content•Server responds with requested content•client and server close connection (usually)Current version is HTTP/1.1•RFC 2616, June, 1999. webclient(browser)CS 213 F’01– 6 –class27.pptWeb contentWeb servers return content to clients•content: a sequence of bytes with an associated MIME (Multipurpose Internet Mail Extensions) typeExample MIME types•text/html HTML page•text/plain Unformatted text•application/postscript Postcript document•image/gif Binary image encoded in GIF format•image/jpg Binary image encoded in JPG formatCS 213 F’01– 7 –class27.pptStatic and dynamic contentThe content returned in HTTP responses can be either static or dynamic.•Static content: content stored in files and retrieved in response to an HTTP request–Examples: HTML files, images, audio clips.•Dynamic content: content produced on-the-fly in response to an HTTP request–Example: content produced by a program executed by the server on behalf of the client.Bottom line: all content is associated with a file managed by the server.CS 213 F’01– 8 –class27.pptURLsEach file managed by a server has a unique name called a URL (Universal Resource Locator)URLs for static content:•http://www.cs.cmu.edu:80/index.html•http://www.cs.cmu.edu/index.html•http://www.cs.cmu.edu–identifies 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:•http://www.cs.cmu.edu:8000/cgi-bin/adder?15000&213–identifies 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.CS 213 F’01– 9 –class27.pptHow clients and servers use URLsExample URL: http://www.aol.com:80/index.htmlClients use prefix (http://www.aol.com:80) 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 suffix (/index.html) to:•Determine if request is for static or dynamic content.–No hard and fast rules for this.–Convention: executables reside in cgi-bin directory•Find file on filesystem.–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).CS 213 F’01– 10 –class27.pptAnatomy 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 terminatesMCS 213 F’01– 11 –class27.pptHTTP requestsHTTP request is a request line, followed by zero or more request headersrequest line: <method> <uri> <version>•<version> is HTTP version of request (HTTP/1.0 or HTTP/1.1)•<uri> is typically URL for proxies, URL suffix for servers.•<method> is either GET, POST, OPTIONS, HEAD, PUT, DELETE, or TRACE.CS 213 F’01– 12 –class27.pptHTTP requests (cont)HTTP methods:•GET: retrieve static or dynamic content–arguments for dynamic content are in URI–workhorse method (99% of requests)•POST: retrieve dynamic content–arguments for dynamic content are in the request body•OPTIONS: get server or file attributes•HEAD: like GET but no data in response body•PUT: write a file to the server!•DELETE: delete a file on the server!•TRACE: echo request in response body–useful for debugging.CS 213 F’01– 13 –class27.pptHTTP
View Full Document