Web ServicesNovember 29, 2006Web ServicesNovember 29, 2006TopicsTopics HTTP Serving static content Serving dynamic content15-213“The course that gives CMU its Zip!”class24.ppt–2–15-213, F’06Web HistoryWeb History1945: 1945: Vannevar Bush, “As we may think”, Atlantic Monthly, July, 1945.z Describes the idea of a distributed hypertext system.z 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.z Connects “a web of notes with links.”z 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’06Web History (cont)Web History (cont)19921992 NCSA server released 26 WWW servers worldwide19931993 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.19941994 Andreessen and colleagues leave NCSA to form “Mosaic Communications Corp” (predecessor to Netscape). –4–15-213, F’06Internet HostsInternet Hosts How many of the 232IP addresses have registered names?–5–15-213, F’06Web ServersWeb ServersWebserverHTTP requestHTTP response(content)Clients and servers Clients and servers communicate using the communicate using the HyperTextHyperTextTransfer Transfer Protocol (HTTP)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/1.1Current version is HTTP/1.1 RFC 2616, June, 1999. Webclient(browser) http://www.w3.org/Protocols/rfc2616/rfc2616.htmlhttp://www.w3.org/Protocols/rfc2616/rfc2616.html–6–15-213, F’06Web ContentWeb ContentWeb servers return Web servers return contentcontentto clientsto clients content: a sequence of bytes with an associated MIME (Multipurpose Internet Mail Extensions) typeExample MIME typesExample MIME types text/html HTML document text/plain Unformatted text application/postscript Postcript document image/gif Binary image encoded in GIF format image/jpeg Binary image encoded in JPEGformat–7–15-213, F’06Static and Dynamic ContentStatic and Dynamic ContentThe content returned in HTTP responses can be either The content returned in HTTP responses can be either staticstaticor or dynamicdynamic.. Static content: content stored in files and retrieved in response to an HTTP requestz Examples: HTML files, images, audio clips. Dynamic content: content produced on-the-fly in response to an HTTP requestz Example: 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’06URLsURLsEach 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.html http://www.cs.cmu.edu/index.html http://www.cs.cmu.eduz 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:URLs for dynamic content: http://www.cs.cmu.edu:8000/cgi-bin/adder?15000&213z 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.–9–15-213, F’06How 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.htmlindex.html) to:) to: Determine if request is for static or dynamic content.z No hard and fast rules for this.z Convention: executables reside in cgi-bin directory Find file on file system.z Initial “/” in suffix denotes home directory for requested content.z Minimal suffix is “/”, which all servers expand to some default home page (e.g., index.html).–10–15-213, F’06Anatomy 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 headerClient: 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 bodyServer: 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’06HTTP 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: <method> <<method> <uriuri> <version>> <version> <version> is HTTP version of request (HTTP/1.0 or HTTP/1.1) <uri> is typically URL for proxies, URL suffix for servers.z A URL is a type of URI (Uniform Resource Identifier)z See http://www.ietf.org/rfc/rfc2396.txt <method> is either GET, POST, OPTIONS, HEAD, PUT, DELETE, or TRACE. –12–15-213, F’06HTTP Requests (cont)HTTP Requests (cont)HTTP methods:HTTP methods: GET: Retrieve static or dynamic contentz Arguments for dynamic content are in URIz Workhorse method (99% of requests) POST: Retrieve dynamic contentz Arguments for dynamic content are in the request
View Full Document