Dan Nesset reports in mediawiki-l that when serving files from ConfirmAccount, the response contains "Content-Encoding: , gzip", which "befuddles
some browsers, such as FF, IE and Safari and they fail to decompress the
file."
This comes as a combination of mod_deflate, PHP's ob_gzhandler and MediaWiki.
When serving files, mediawiki clears any gzipping layer, including its own one. You seem to have at php.ini output_handler=ob_gzhandler. When mediawiki detects that ob_gzhandler is active, performs ob_end_clean() and does header( 'Content-Encoding:' ); in order to clean the Content-Encoding field (otherwise you would get plain data with header saying it's in gzip).
Then, you also have mod_deflate into the mix. It detects an existing Content-Encoding header, and apr_table_mergen "merges" adding ', gzip' despite the header being empty.
Where is the bug?
mod_deflate shouldn't concatenate if the field is empty.
php could skip passing Content-Encoding to other modules if empty.
MediaWiki could use the header( 'Content-Encoding: identity' ); instead of header( 'Content-Encoding:' );
How can _you_ fix it right now?
You don't need having three compressing layers. I'd deactivate mod_deflate and output_handler=ob_gzhandler, letting mediawiki compress the pages automatically for you.
Just disabling mod_deflate or output_handler=ob_gzhandler would work too, but note that keeping mod_deflate with your current configuration will compress streamed files, which is likely to be inefficient.
rfc2616 section 14.11 defines Content-Encoding header as
"Content-Encoding" ":" 1#content-coding
The #rule (see section 2) requires at least one content-coding to be present, which MediaWiki is currently violating (yes, the empty header does arrive at the user browser).
Version: 1.18.x
Severity: normal
URL: http://thread.gmane.org/gmane.org.wikimedia.mediawiki/36969