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Day #2Serving Dynamic Content with CGI
Wildan [email protected]
http://workshop.openthinklabs.com
#6
Overview
● How the CGI protocol works● How to configure Apache to run CGI scripts, on
both Unix and Windows● How to troubleshoot common errors
Common Gateway Interface
Source : http://viu.eng.rpi.edu/
CGI Protocol
CERN HTTPd Server NCSA HTTPd Server
Both provided mechanisms to invoke externalprograms and scripts to create dynamic content but incompatible
The Solution
The CGI 1.1 specification
CGI Operation
● Apache receives a request and determines that it needs to be served by the CGI program
● Apache starts an instance of the CGI program● Apache passes information about the request to the
CGI● Apache receives the response from the CGI, optionally
processes its headers and contents, and sends it to the client
● The CGI program finishes and all resources associated with it are recalled by the operating system
CGI Environment VariablesVariable Name Variable Description
SERVER_NAME Hostname or IP address of the server
REQUEST_METHOD HTTP request method: HEAD, GET, POST, and so on
REMOTE_ADDR Client IP address
CONTENT_TYPE MIME type of any client data being passed by a POST or PUT request
CONTENT_LENGTH Size of the client data
CGI Response
● Location: Instructs Apache that the CGI is not going to answer the request and that the client should be redirected to the specified URL.
● Status: This is not a valid HTTP header and it is not transmitted back to the client, but it indicates the HTTP status code for the request to Apache.
● Content-Type: Specifies the type of data returned in the request. For example, if you are returning a Web page, the header value should be text/html.
Advantages and Disadvantages of CGI Scripts
● Portability● Simplicity● Existing Code● Source Hiding● Memory Leaks
● Performance● Code and
Presentation
Configuring Apache
Configuring ApacheCGI Content
ScriptAlias
ScriptAlias /usr/local/apache2/cgi-bin/ /cgi-bin/
Configuring ApacheFine-Grained Control
SetHandler Directive
# Any files accessed thru the /cgi-bin/ url will execute as CGI scripts.<Location “/cgi-bin/”> Options +ExecCGI SetHandler cgi-script<Location>
Associating CGI Processing with File Extensions
# Any files ending in .pl will be executed as CGI scripts<Files *.pl> Options +ExecCGI SetHandler cgi-script</Files># Any files ending in .cgi in the /usr/local/apache2/htdocs/scripts # will be executed as CGI scriptsAddHandler cgi-script .cgi
<Directory “/usr/local/apache2/htdocs/scripts”> Options +ExecCGI</Directory>
Configuring ApacheAction and Script
Action image/gif /cgi-bin/process.cgiScript PUT /cgi-bin/upload.cgi
Configuring ApacheCGI Security
● Non Parse Headers (NPH) Scripts● nph-example.cgi
● Debugging CGI Execution● ScriptLog● ScriptLogLength● ScriptLogBuffer
Unix ConfigurationTesting Shell Script CGIs
Unix ConfigurationPerl Installation
● Preinstalled Perl#which perlperl -v
● Installing Binaries● Linux
– Redhat : rpm -i perl*.rpm– Ubuntu : sudo apt-get install perl
● Installing from Sourcehttp://www.perl.com/pub/a/language/info/software.html#sourcecode
Unix ConfigurationTesting Perl CGI Scripts
Windows Configuration
● Testing Batch File CGIs● Perl on Windows
● http://www.activestate.com
● Testing Perl Scripts
Common CGI Problems● Forbidden Error
● Filesystem Permissions● CGI Execute Permissions
● Internal Server Error● Program Permissions● Interpreter Location● Malformed Headers
● Other Causes● Source Code in the Browser
Q&Ahttp://workshop.openthinklabs.com/resources
Reference
● Daniel Lopez Ridruezo; SAMS Teach Yourself Apache2 in 24 Hours, SAMS Publishing, 2002 (Buy this book on Amazon)
