Web History 15 213 1945 The course that gives CMU its Zip Web Services November 29 2006 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 Topics Tim Berners Lee CERN writes internal proposal to develop a distributed hypertext system HTTP Serving static content Serving dynamic content z Connects a web of notes with links z Intended to help CERN physicists in large projects share and manage information 1990 Tim BL writes a graphical browser for Next machines 15 213 F 06 2 class24 ppt Web History cont Internet Hosts 1992 NCSA server released 26 WWW servers worldwide 1993 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 predecessor to Netscape 3 15 213 F 06 4 How many of the 232 IP addresses have registered names 15 213 F 06 Web Content Web Servers Web servers return content to clients Clients and servers communicate using the HyperText Transfer Protocol HTTP Client and server establish TCP connection Client requests content Example MIME types HTTP request Web client browser Server responds with requested content content a sequence of bytes with an associated MIME Multipurpose Internet Mail Extensions type Web server HTTP response content Client and server close connection usually text html HTML document text plain Unformatted text application postscript Postcript document image gif image jpeg Binary image encoded in GIF format Binary image encoded in JPEG format Current version is HTTP 1 1 RFC 2616 June 1999 http www w3 org Protocols rfc2616 rfc2616 html 15 213 F 06 5 Static and Dynamic Content URLs The content returned in HTTP responses can be either static or dynamic dynamic Each file managed by a server has a unique name called a URL Universal Resource Locator URLs for static content Static content content stored in files and retrieved in response to an HTTP request z Examples HTML files images audio clips 15 213 F 06 6 Dynamic content content produced on the fly in response to an HTTP request http www cs cmu edu 80 index html http www cs cmu edu index html http www cs cmu edu z Identifies a file called index html managed by a Web server at z Example content produced by a program executed by the www cs cmu edu that is listening on port 80 server on behalf of the client Bottom line All Web content is associated with a file that is managed by the server URLs for dynamic content http www cs cmu edu 8000 cgi bin adder 15000 213 z 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 7 15 213 F 06 8 15 213 F 06 How Clients and Servers Use URLs Example URL http www aol com 80 index html http www aol com 80 index html Clients use prefix http www aol com 80 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 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 unix telnet www aol com 80 Trying 205 188 146 23 Connected to aol com Escape character is GET HTTP 1 1 host www aol com Client open connection to server Telnet prints 3 lines to the terminal Client request line Client required HTTP 1 1 HOST header Client empty line terminates headers Server response line Server followed by five response headers HTTP 1 0 200 OK MIME Version 1 0 Date Mon 08 Jan 2001 04 59 42 GMT Server NaviServer 2 0 AOLserver 2 3 3 Content Type text html Server expect HTML in the response body Content 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 body Connection closed by foreign host Server closes connection unix Client closes connection and terminates Servers use suffix index html index html to Anatomy of an HTTP Transaction 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 15 213 F 06 9 15 213 F 06 10 HTTP Requests HTTP Requests cont HTTP request is a request line line followed by zero or more request headers HTTP methods GET Retrieve static or dynamic content z Arguments for dynamic content are in URI z Workhorse method 99 of requests Request line method uri version uri POST Retrieve dynamic content version is HTTP version of request HTTP 1 0 or HTTP 1 1 OPTIONS Get server or file attributes uri is typically URL for proxies URL suffix for servers 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 z Arguments for dynamic content are in the request body z A URL is a type of URI Uniform Resource Identifier z See http www ietf org rfc rfc2396 txt 11 method is either GET POST OPTIONS HEAD PUT DELETE or TRACE 15 213 F 06 z Useful for debugging 12 15 213 F 06 HTTP Requests cont HTTP Responses Request headers header name header data data Provide additional information to the server HTTP response is a response line followed by zero or more response headers headers Response line version status code status msg msg Major differences between HTTP 1 1 and HTTP 1 0 HTTP 1 0 uses a new connection for each transaction HTTP 1 1 also supports persistent connections z 200 z 403 z 404 z multiple transactions over the same connection z Connection Keep Alive HTTP 1 1 requires HOST header HTTP 1 1 supports chunked encoding described later z Transfer Encoding chunked HTTP 1 1 adds additional support for caching 15 213 F 06 13 OK Forbidden Not found Request was handled without error Server lacks permission to access file Server couldn t find the file Response headers header name header data z Host kittyhawk cmcl cs cmu edu version is HTTP version of the response status code is numeric status status msg is corresponding English text GET Request to Apache Server From IE Browser Provide additional information about response Content Type MIME type of content in response body Content Length Length of content in response body 15 213 F 06 14
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