cgi programming languages web based software development july 21, 2005 song, jaeha
TRANSCRIPT
CGI Programming Languages
Web Based Software DevelopmentJuly 21, 2005Song, JaeHa
Agenda
Introduction CGI Mechanism CGI Languages Alternatives Conclusion
Introduction: Definition
CGI: Common Gateway Interface A simple interface for running gateways In an information server In Platform-independent manner
Gateway: a program that provides path into internal applications or resources, such as database or file system
Introduction: Conceptual diagram
Script: The software that is invoked by the server according to this interface.
Server: The application program that invokes the script in order to service requests from the client.
Meta-variable: A named parameter which carries information from the server to the script.
Client Server ScriptsInternal services
HTTP RequestCGI RequestMeta-variable Internal Request
HTTP Response CGI Response Internal Response
CGI Mechanisms: Server
As an Application gateway Receive request from client Select CGI script to handle request Convert client request to CGI request Execute script Convert CGI response into response for client
Authentication and security handling Manages special directory such as /cgi-bin CGI time-out handling Error page handling
CGI Mechanisms: CGI request
Request meta-variables sources
Environment variables STDIN Command line arguments
CONTENT_TYPE REQUEST_METHOD QUERY_STRING CONTENT_LENGTH …
Request message body For POST method
CGI Mechanisms: CGI response Response header fields
CGI-field Content-Type Location Status
Other-field Protocol-specific header fields Extension header fields
Response message body STDOUT
CGI Mechanisms: Interface ports Input
STDIN POST method with 0 < CONTENT_LENGTH
Environment variables Request meta-variables
Command line argument ISINDEX query
Output STDOUT
CGI Languages: Only Perl ?
Almost written in Perl But, CGI needs only
environment variables STDIN/STDOUT command line arguments
CGI Languages: Others
C/C++ Fortran TCL Unix shells Visual Basic Apple scripts Ruby Etc.
CGI Languages: Choosing Others Perl is always best ? Concerns
Productivity Learning curve Execution overhead Etc.
CGI Languages: CGI in C
C for CGI Programming Well known: Short Learning Curve Low execution overhead inconvenient in String handling
CGI Languages: CGI Output in C
#include <stdio.h>void main() {
/** Print the CGI response header, required for all HTML output.**/
/** Note the extra \n, to send the blank line. **/printf("Content-type: text/html\n\n") ;
/** Print the HTML response page to STDOUT. **/ printf("<html>\n") ;printf("<head><title>CGI Output</title></head>\n") ; printf("<body>\n") ;printf("<h1>Hello, world.</h1>\n") ;printf("</body>\n") ;printf("</html>\n") ;exit(0) ;
}
CGI Languages: CGI I/O in C
#include <stdio.h>…main(int argc, char *argv[]) {
entry entries[MAX_ENTRIES];register int x,m=0;int cl;printf("Content-type: text/html%c%c",10,10);if(strcmp(getenv("REQUEST_METHOD"),"POST")) {
…}if(strcmp(getenv("CONTENT_TYPE"),"application/x-www-form-urlencoded")) {
printf("This script can only be used to decode form results. \n");exit(1);
}cl = atoi(getenv("CONTENT_LENGTH"));for(x=0;cl && (!feof(stdin));x++) {
…}…
}
CGI Languages: CGI in Ruby
Ruby for CGI Programming Packages for Productivity improvement
CGICGI::CookieCGI::HtmlExtensionCGI::QueryExtensionCGI::SessionCGI::Session::FileStoreCGI::Session::MemoryStoreCGI::Session::PStore
Stylish Under development Small user group
CGI Languages: CGI in Ruby
#!/usr/bin/env rubyprint "HTTP/1.0 200 OK\r\n“print "Content-type: text/html\r\n\r\n“print "<html><body>Hello World!</body></html>\r\n"
…
require "cgi“
cgi = CGI.newvalue = cgi['field_name']fields = cgi.keyscgi.has_key?('field_name') cgi.include?('field_name') …
Alternatives: SSI/Servlets/Server API
SSI Server Side Includes Simple interface for basic dynamic content Non-standard
Servlets an alternative API for JAVA overcomes the limitation of JAVA not supporting environ
ment variables Server API
Generally the most powerful and most complex option Non portable Varies from server to server
Alternatives: Servlets/JSP Kinds of CGI scripts
Scripts: … It need not be a standalone program, but could be a dynamically loaded or shared library or even a subroutine in the server.
Servlets: Thread instead of process Lightweight : less overhead in execution Sharing states: i.e. session information Crash propagation Cold deploy
JSP: reversion between hosts and guests Contents oriented instead of control oriented Less ‘ ” ’ Easy to read Hot deploy
Alternatives: CGI Pros and Cons Advantages
Separation of concerns Server for client request handling Scripts for application issues
Simple
Drawbacks Performance Scalability Maintainability Security
Conclusion
Common Gateway Interface A simple interface for information server
extension
For simple dynamic web programming
Any languages are possible when they supports minimum set of mechanisms STDIN/STDOUT Environment variables Able to invoke in Information server
Mainly in Perl
References
CGI Programming RFC Page: http://www.faqs.org/rfcs/rfc3875.html
W3C’s CGI Pages: http://www.w3.org/CGI
CGI FAQ http://www.htmlhelp.com/faq/cgifaq.1.html
Another CGI FAQ: http://www.webthing.com/tutorials/cgifaq.html
Dynamic Programming Language Choice Criteria: http://www.apacheweek.com/features/dynamicpages
Ruby CGI: http://www.ruby-doc.org/stdlib/libdoc/cgi/rdoc/
Web Programming Languages Introduction: http://www.freelance-help.com/web-programming.ph
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