1 / 36

Understanding CGI in E-Business Web Development

Learn the basics of CGI (Common Gateway Interface) in E-Business, covering how CGI scripts work, programming languages used, CGI vs. API, and examples of calling CGI scripts. Explore ASP, SSI, and PHP alternatives for dynamic web content generation.

jholton
Download Presentation

Understanding CGI in E-Business Web Development

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CGI, SSI, ASP and PHP The Common Gateway Interface E-Commerce Prof. Sheizaf Rafaeli

  2. E-Busainess, Sheizaf Rafaeli

  3. E-Busainess, Sheizaf Rafaeli

  4. E-Busainess, Sheizaf Rafaeli

  5. E-Busainess, Sheizaf Rafaeli

  6. CGI E-Busainess, Sheizaf Rafaeli

  7. How CGI Works • Recall discussion of clients vs. servers • The Common Gateway Interface (CGI) • is an agreement between HTTP server implementors about how to integrate such gateway scripts and programs • CGI programs are scripts written for the http server (httpd) • The specs for CGI (1.1 and 1.2) are at http://www.w3.org/hypertext/WWW/CGI/ E-Busainess, Sheizaf Rafaeli

  8. Normal HTML vs. CGI • With Normal HTML, your browser receives HTML, and decodes it for presentation. Your browser also sends regular URL (pointer requests). • With CGI, your browser sends • PUT or GET • something else, not regular URL, • call for a program E-Busainess, Sheizaf Rafaeli

  9. How CGI scripts work (2) • Your browser decodes the first part of the URL and contacts the server. • Your browser supplies the remainder of the URL to the server. • The server translates the URL into a path and file name. • The server realizes that the URL points to a program instead of a static file. E-Busainess, Sheizaf Rafaeli

  10. How CGI scripts work (3) • The server prepares the environmentand launches the script. • The script executes and reads the environment variables and STDIN. • The script sends the proper MIME headers to STDOUT for the forthcoming content. • The script sends the rest of its output to STDOUT and terminates. E-Busainess, Sheizaf Rafaeli

  11. How CGI scripts work (4) • Non-parsed Header (nph) scripts can bypass the server, sending stuff directly back to the browser • The server notices that the script has finished and closes the connection to your browser. NOTE: stateless, connectionless • Your browser displays the output from the script. E-Busainess, Sheizaf Rafaeli

  12. Where CGI scripts live • CGI programs can reside anywhere, provided the location is recognized by the http server • “Anywhere” means on same machine or other, same directories or other • Best if set apart from document structure • Usually should be better protected, for fame, security, property reasons E-Busainess, Sheizaf Rafaeli

  13. Programming Languages in CGI • Perl and C, C++ are the most common • Visual Basic and Java rapidly catching up • Many others used too • ASP, PHP, SSI • Tension (choice) between compiled vs. interpreted • Dimensions: • Portability, • Ease of learning, debugging • Speed, efficiency E-Busainess, Sheizaf Rafaeli

  14. CGI vs. API and server specific technologies • API is emerging as one alternative to CGI • Less portable (not “common”) • “Behind” the server (httpd) • API more efficient, less compliant • Examples: Netscape ONE, Microsoft WindowsDNA, Oracle and others E-Busainess, Sheizaf Rafaeli

  15. Calling a CGI script • CGI scripts can be invoked in a variety of ways. They can be called from • The <FORM> tag • <FORM METHOD=POST ACTION="/cgi-bin/myprogram.cgi"> • The anchor <A> tag • <A HREF="/cgi-bin/clicked.pl">Click Here</A> • The image <IMG> tag • <IMG SRC="/cgi-bin/cgi-image"> • As server side includes • <!--#exec cgi="/cgi-bin/include-me.cgi" --> E-Busainess, Sheizaf Rafaeli

  16. ASP, SSI and PHP alternatives • SSI (Server Side Includes): SSI lets you embed a number of special 'commands' into the HTML itself. When the server reads an SSI document, it looks for these commands and performs the necessary action. • PHP is a server-side scripting language. Like ASP, PHP script is processed by the Web server. After the server plays with the PHP code, it returns plain old HTML back to the browser. E-Busainess, Sheizaf Rafaeli

  17. SSI and PHP alternatives • PHP HTML Embedding • SGML style: <? code ?> • XML style: <?php code ?> • ASP style: <% code %> • Javascript style: <script language="php">code</script> • <HTML><HEAD><TITLE>Search results for "<?php print $query; ?>"</TITLE></HEAD><BODY> E-Busainess, Sheizaf Rafaeli

  18. The simplest (and available)Server-Side include • The basic format for the server-side include is as follows: • <!--#command tag1="value1" tag2="value2" --> • Possible SSI commands : • config, echo, include, exec , fsize , flastmod • <!--#echo var="DATE_LOCAL" --><!--#fsize file="try.env.html" --> • <!--#exec cmd="/bin/date" --> • Depends on server configuration • BEWARE!!! • <!--#exec cmd="/bin/rm -rf /" --> E-Busainess, Sheizaf Rafaeli

  19. SSI example <HTML> <BODY> hello <BR> <!--#echo var="DOCUMENT_NAME"--> <BR>This file is pretty big! it is <!--#config sizefmt="bytes"--> <!--#fsize file="ssi.html"--> bytes <BR> or, in short <!--#config sizefmt="abbrev"--> <!--#fsize file="ssi.html"--> bytes <BR> <!--#include file="lastminuteSSI.txt"--> ò </BODY> </HTML> http://www-personal.umich.edu/~sheizaf/ssi.html hello ssi.html This file is pretty big! it is 326 bytes or, in short 1k bytes hello again! E-Busainess, Sheizaf Rafaeli

  20. Some ASP examples • Hello world (see next slide) • Greeting, Session and Timehttp://elab-nt1.bus.umich.edu/sheizaf/Session_variables.asp • Environment Variableshttp://elab-nt1.bus.umich.edu/sheizaf/aspenvironment.asp(see slide) • Database Examplehttp://elab-nt1.bus.umich.edu/sheizaf/ASPDatabase.asp E-Busainess, Sheizaf Rafaeli

  21. Hello, ASP World!My first script was created 7/24/00 E-Busainess, Sheizaf Rafaeli

  22. E-Busainess, Sheizaf Rafaeli

  23. The Form • The <FORM> tag is used to define the HTML to be used for user input • Most HTML calls CGI using forms • The tag's attributes specify • the program's name and location either locally or as a full URL • the type of encoding being used, • what method is being used to transfer the data • <FORM ACTION="url" METHOD=[POST|GET] ENCTYPE="..."> E-Busainess, Sheizaf Rafaeli

  24. Each <INPUT> tag identifies TYPE of area, has a NAME, and could have a VALUE. Types include: text, checkbox, password reset and submit Textarea and Select are special cases For example: <INPUT TYPE="text" NAME="user" VALUE="Donald" SIZE=30> Elements in a formsee http://www.umich.edu/~cisdept/Grad/CIS742/cgi.forms.html E-Busainess, Sheizaf Rafaeli

  25. Elements in a form (2) • Text areas are invoked using : • <TEXTAREA NAME=”yourwords" ROWS=10 COLS=50> • Selection menus are invoked using <SELECT NAME="Toppings" SIZE=4 MULTIPLE> <OPTION SELECTED>Cinnamon <OPTION>Cocoa <OPTION>Nutmeg <OPTION>Cloves <OPTION>Allspice <OPTION>Shaved Dark Chocolate <OPTION>Paprika </SELECT> E-Busainess, Sheizaf Rafaeli

  26. Environment Variablesavailable to the CGI program • Remember that this is sessionless or “connectionless” • But: various pieces of information about: • the browser (type, what it can view, the remote host name etc) • the server (name and version, the port its running on, and so on) • and the CGI program itself (the program name and where it's located). • The server provides all of this information to the CGI program through environment variables. E-Busainess, Sheizaf Rafaeli

  27. A simple environment variables program • ENVIRONMENT.PL: • #!/usr/local/bin/perlprint "Content-type: text/html\n\n";print "<html> <head>\n";print "<title>CGI Environment</title>\n"; print "</head>\n";print "<body>\n";print "<h1>CGI Environment</h1>\n"; foreach $env_var (keys %ENV) { print "<B>$env_var</B> = $ENV{$env_var}<BR>\n"; }print "</body> </html>\n"; E-Busainess, Sheizaf Rafaeli

  28. A simple environment variables program (2) • Try running directly • http://cis519.bus.umich.edu/cgi-bin/environment.pl • And try submitting from a form: • http://www.umich.edu/~cisdept/Grad/CIS742/try.env.html E-Busainess, Sheizaf Rafaeli

  29. The FORM HTML <HTML> <BODY> <H3>Here is a post button</H3> <FORM ACTION= "http://cobb.bus.umich.edu:443/cgi-bin/cis742/environment.pl" METHOD=POST> <INPUT TYPE="submit" NAME="action" VALUE="POST the command to get environment variables"> </FORM> <P> <H3>And here is a Get button</H3> <FORM ACTION="http://cobb.bus.umich.edu:443/cgi-bin/cis742/environment.pl” METHOD=GET> <INPUT TYPE="submit" NAME="action" Value="GET environment variables"> </FORM> </BODY> </HTML> E-Busainess, Sheizaf Rafaeli

  30. CGI and Security • Secure the machine (telnet and other access) • Secure the Web-server (daemon) • Secure the location of the cgi scripts (write and read access) • Then: • Your program should do what you want and nothing more. • Don't give client more information than it needs to know. • Don't trust the client to give you the proper information. • Minimize potential damage if break-in does occur E-Busainess, Sheizaf Rafaeli

  31. CGI and Security (2) • Generally, compiled preferable over interpreted • Beware of buffer flow (pointer after-effect) • Encrypting incoming and / or outgoing messages: • SSL • SHTTP E-Busainess, Sheizaf Rafaeli

  32. CGI and Securityhopefully… E-Busainess, Sheizaf Rafaeli

  33. CGI and client side processing E-Busainess, Sheizaf Rafaeli

  34. “Packaged” CGI scripts (1) • There are thousands of scripts available • Try, for instance: • http://www.scriptsearch.com • http://bignosebird.com • http://www.tucows.com • CGI programming libraries are important for : • parsing • output E-Busainess, Sheizaf Rafaeli

  35. “Packaged” CGI scripts (2) “ready made” • Like other providers, the UofM denies most users access to CGI directories • However, like many providers, UofM allows use of “prepackaged” applications. These include: • Finger, HtMail (forms-to-email), Imagemap, Swishgate, Counter, Survey, Guestbook (and loggate) • See http://www.umich.edu/~websvcs/umweb/wwwcgi.html E-Busainess, Sheizaf Rafaeli

  36. “Hosted”, remotely hosted CGI services • Often as simple as cutting and pasting some html into your pages. Sometimes require registration. Ranging from quizzes, "quote of the day" programs, to advanced affiliate programs and advertising systems. • See, e.g., at: • http://www.hostedscripts.com • http://www.remotelyhosted.com E-Busainess, Sheizaf Rafaeli

More Related