Outline. Lecture 8: CGI (Common Gateway Interface ) Common Gateway Interface (CGI) CGI Overview

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1 Outline Lecture 8: CGI (Common Gateway Interface ) CGI Overview Between Client and Handler Between Web Server and Handler Wendy Liu CSC309F Fall Common Gateway Interface (CGI) CGI Overview Access to dynamic server-side content Services Data 3 4 1

2 Components of the CGI Model Clients Web browsers Web server Mediates communication between browsers and handler programs CGI Protocol Specifies interaction between Browser and handler programs Function call syntax Web server and handler programs Handler programs (or CGI scripts) Any executables residing on the web server Can be written in any language C, C++, Perl, VB, Python, SmallTalk, Assembly, Lisp, etc. 5 CGI Interaction (1) Client sends request with a URL+additional info Web server receives the request Web server identifies the request as a CGI request Web server locates the handler program 6 CGI Interaction (2) CGI Interaction (3) Web server starts up the handling program Heavy weight process creation Web server feeds request parameters to handler Through stdin or environment variables 7 Handler program executes Output of the handler is sent to the Web server via stdout Output is typically a web page Web server returns output to the requesting web browser 8 2

3 Handling CGI Process CGI Example in Perl Request for CGI1 Request for CGI2 Request for CGI1 Main Process CGI-based Web Server Child Process for CGI1 Child Process for CGI2 Child Process for CGI1 #!/local/bin/perl print "Content-type: text/html\n\n"; print "<html>\n"; print "<body>\n"; print "<h1>hello</h1>\n"; print "</body>\n"; print "</html>\n"; In Web page <a href= cgi-bin/hello.pl > Click to run CGI </a> Cause the execution of the Perl script hello.pl 9 10 Client - Handler Interaction Between Client and Handler Indirect interaction Clients request the execution of a handler program by specifying A request method (e.g., GET, POST) Universal Resource Locator (URL) Locates the handler Additional arguments Query string

4 Query String Encoding Query string is used to transmit data associated with a GET/POST request All arguments are packed into a single string Each argument is represented by a name-value pair as name=value Arguments are separated by ampersand, & name_1=value_1&name_2=value_2 Spaces in a name or value are replaced by a plus sign, + URLs cannot have spaces in them Other characters (=, &, +) are replaced by a percent sign (%) followed by a two-digit hexadecimal value GET HTTP Methods Query string attached to the URL after? As part of the URL URL may have a length restriction on the server side Limited amount of information can be passed Arguments appear in server logs POST Query string encoded in the HTTP request body Not part of the URL Arbitrarily long form data can be communicated Arguments usually do not appear in server logs On the Web page Forms Example: GET <form action= cgi-bin/login.pl method= get > <input type= text name= id /> <input type= text name= password /> Request sent to web server Assuming user enters: abc and 123 GET cgi-bin/login.pl?id=abc&password=123 HTTP/1.1 Forms Example: POST On the Web page <form action= cgi-bin/login.pl method= post > <input type= text name= id /> <input type= text name= password /> Request sent to web server Assuming user enters: abc and 123 POST cgi-bin/login.pl HTTP/1.1 <headers > id=abc&password=

5 Between Web Server and Handler Web Server - Handler Interaction Information about a request comes from Request line Header line Request-body (POST) Handler input Environment variables stdin (request body) Handler output stdout Environment Variables AUTH_TYPE CONTENT_LENGTH CONTENT_TYPE GATEWAY_INTERFACE PATH_INFO PATH_TRANSLATED QUERY_STRING REMOTE_ADDR REMOTE_HOST REMOTE_IDENT REMOTE_USER REQUEST_METHOD SCRIPT_NAME SERVER_NAME SERVER_PORT SERVER_PROTOCOL SERVER_SOFTWARE Example Perl Script #!/local/bin/perl print "Content-type: text/plain\n\n"; print = keys %ENV; # variable = values %ENV; # variable values while (@keys) { print pop(@keys), '=', pop(@values), "\n"; } $request_method = $ENV{'REQUEST_METHOD'}; if ($request_method eq "POST") { $formsize = $ENV{'CONTENT_LENGTH'}; read (STDIN, $form_info, $formsize); print "\nstdin\n" print $form_info; }

6 Example Web Page <body> <h3>get</h3> <form action="cgi-bin/stdin.pl" method="get"><p> Student Number: <input type="text" name="studentnum"/> <br /> Id: <input type="text" name="id"/> <br /> Password: <input type="password" name="password"/> <br /> Return Files: <input type="checkbox" name="returnfiles"/> <br /> <input type="submit" name="submit" /></p> <h3>post</h3> <form action="cgi-bin/stdin.pl" method="post"><p> Student Number: <input type="text" name="studentnum"/> <br /> Id: <input type="text" name="id"/> <br /> Password: <input type="password" name="password"/> <br /> Return Files: <input type="checkbox" name="returnfiles"/> <br /> <input type="submit" name="submit" /><p> </body> Example GET Request HTTP/ OK Date: Mon, 01 Oct :17:56 GMT Server: Apache/ (Unix) Last-Modified: Wed, 12 Sep :22:21 GMT Accept-Ranges: bytes Content-Length: 65 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/plain Environment SERVER_PORT=80 REQUEST_METHOD=GET QUERY_STRING=studentNum=a&id=b&password=234&returnFiles=on&submit =Submit Example POST Request HTTP/ OK Date: Mon, 01 Oct :17:56 GMT Server: Apache/ (Unix) Last-Modified: Wed, 12 Sep :32:21 GMT Accept-Ranges: bytes Content-Length: 65 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/plain Environment SERVER_PORT=80 REQUEST_METHOD=POST QUERY_STRING= STDIN studentnum=a&id=b&password=234&returnfiles=on&submit=submit Important Announcement Tuesday Oct 16, hr tutorial given in a CDF lab, BA3185 Thursday Oct 18, 2007 Midterm, BA2195 Starting Tuesday Oct 23, 2007 The official lecture room will be BA2185 on each Tuesday until the end of term No change to Thursdays classes (BA1240)

Forms, CGI. Cristian Bogdan 2D2052 / 2D1335 F5 1

Forms, CGI. Cristian Bogdan 2D2052 / 2D1335 F5 1 Forms, CGI Cristian Bogdan 2D2052 / 2D1335 F5 1 Objectives The basics of HTML forms How form content is submitted GET, POST Elements that you can have in forms Responding to forms Common Gateway Interface