Author: wikimedia

Description:
MediaWiki 1.17.0
PHP 5.3.8-1~dotdeb.2 (cgi-fcgi)
MySQL 5.1.58-1~dotdeb.1

In /includes/Webstart.php, starting at line 132:

1. Initialise output buffering
2. Check that there is no previous output or previously set up buffers, because
3. that would cause us to potentially mix gzip and non-gzip output, creating a
4. big mess.

if ( !defined( 'MW_NO_OUTPUT_BUFFER' ) && ob_get_level() == 0 ) {

		require_once( "$IP/includes/OutputHandler.php" );
		ob_start( 'wfOutputHandler' );

}

The output handler is not initialized if ob_get_level() != 0. As a consequence, gzip content encoding would not be enabled.

The problem is that ob_get_level() will always return 1 or more if you have output buffering enabled in php.ini (output_buffering is false by default, but PHP suggests a production value of 4096), which means that basically every PHP script starts with ob_start().

One solution to this problem would be to remove the default output buffer early when Mediawiki starts:

while(ob_get_level() > 0){

	   ob_end_clean();

}

If this is undesired, and if the conditional check in Webstart is not changed, at the least, mediawiki setup should show a warning notice that with the given output_buffering setting, its output handler (i.e. gzip handler) won't be executed.

Version: 1.21.x
Severity: normal