Use Apache Filter In Windows

In this tutorial we will use Apache’s mod_ext_filter module. To put simply, it allows you to easily process your content through an external program before it’s passed onto the user’s web browser.

System Info

• Windows 7 – 64 bit
• Apache 2.4
• PHP 5.3

Requirements

PHP should be runnable in the command line. To check if this is possible, open command prompt and enter: php –version. It should return information about php.

Configure Apache

1. Open Apache’s main configuration file, httpd.conf. Mine is found in D:/webserver/apache24/conf/. Enable mod_ext_filter by uncommenting this line:

   LoadModule ext_filter_module modules/mod_ext_filter.so

2. Next Add the ExtFilterDefine directives at the bottom of httpd.conf:

   ExtFilterDefine html_changer mode=output intype=text/html cmd="D:/webserver/phpfilter.cmd"

   The ExtFilterDefine directive defines the characteristics of an external filter, including the program to run and its arguments.

   • html_changer – is the filtername. This name can then be used in SetOutputFilter directives.
   • mode=output – tells Apache to process the response.
   • intype=text/html – specifies the internet media type (i.e., MIME type) of documents which should be filtered.
   • cmd=”D:/webserver/phpfilter.cmd” – cmd specifies the external command to run. Here it is pointing to a command line script that we will create below.
3. Next add SetOutputFilter directive:

   SetOutputFilter html_changer

   This directive activates the html_filter which we have defined using ExtFilterDefine.

4. Save and restart Apache

Create a Windows Batch File

5. Create a file named phpfilter.cmd. Inside it put this code:

   @php "D:/webserver/filterscript.php"

   All it does is call php from the command line and run the script at D:/webserver/filterscript.php. The @ character means to suppress output.

Create the Filtering Script

6. Create a php file and name it filterscript.php. Save it to where you point the windows batch file to. Mine is in D:/webserver/filterscript.php. Inside it place this code:

   <?php
   $f = fopen( 'php://stdin', 'r' );
   
   while( $line = fgets( $f ) ) {
       $line = str_replace('</body>','<div style="background:#428bca; position:fixed; left:0; bottom:0; padding:2px 5px; font-size:12px; color:#fff">'.$_SERVER['REMOTE_ADDR'].'</div>', $line);
       echo $line;
   }
   
   fclose( $f );

   As you can see this is a just a php script. What you don’t see often is the line:

   $f = fopen( 'php://stdin', 'r' );

   All it does is to read the input stream passed by Apache to PHP.

   while( $line = fgets( $f ) ) {

   This tells php to loop thru each line of input.

   $line = str_replace('</body>','<div style="background:#428bca; position:fixed; left:0; bottom:0; padding:2px 5px; font-size:12px; color:#fff">'.$_SERVER['REMOTE_ADDR'].'</div></body>', $line);

   This line is a rudimentary way of prepending a custom div to a body tag. The custom div has inline styles attached to it. It also shows the current IP address.

   echo $line;

   Returns the output line by line. The output is passed on to Apache to be served later on.

   fclose( $f );

   Closes the stream.

   That’s it, save the file.

7. Finally test if the filter is working by going to http://localhost/ using your browser. You should see the inserted div at the bottom left:
   

   

Additional Resources

• http://httpd.apache.org/docs/2.4/mod/mod_ext_filter.html
• http://www.jamiebegin.com/mod_ext_filter-mod_rewrites-red-headed-step-sister/
• http://www.jamiebegin.com/using-apaches-mod_ext_filter-to-automatically-add-watermarks-to-website-images/