#40325 [Asn->WFx]: Vary: header missing in gzip output handlers

ID: 40325 Updated by: mike@php.net Reported By: nicolas dot grekas+php at gmail dot com -Status: Assigned +Status: Wont fix -Bug Type: HTTP related +Bug Type: Zlib Related Operating System: All PHP Version: 5.2.0 Assigned To: mike New Comment: We can't fix this issue, due to the nature of PHP output handlers. Consider he following code snippet: <?php ob_start("ob_gzhandler"); ob_end_clean(); ?> We'll get a plain response plus the Vary header, not really better either. I'd suggest you to use mod_deflate or f.e. always send the Vary header yourself when using a zlib output handler: <?php header("Vary: Accept-Encoding"); ob_start("ob_gzhandler"); ?> Previous Comments: ------------------------------------------------------------------------ [2007-03-21 14:42:15] nicolas dot grekas+php at gmail dot com I'm sorry to insist, but this is for the good of PHP :) This bug is not bogus. Here is the related RFC2616 HTTP1.1-14.44 excerpt that is not honored by ob_gzhandler : "An HTTP/1.1 server SHOULD include a Vary header field with any cacheable response that is subject to server-driven negotiation.". In fact today, ob_gzhandler do send a "Vary: Accept-Encoding" header when the client accepts gzip or deflate. (This is the case for example for IE, Gecko, and many browsers.) BUT : the RFC says that the vary header should be send IF _a_negociation_occurs_. That means that the Vary header is not meant to be send based on the result of any negociation. The point is : if you negociate, then you should send a Vary header, whatever the result of the nego. What ob_gzhandler actually does is : negociate, then if gzip/deflate accepted, send a Vary What it should do is : send a Vary, then negociate. This but is in no way related to the bug of IE regarding vary headers : the current conditions requested by ob_gzhandler to send its vary header are always met by IE (accept gzip ? => yes). Hope it helps ------------------------------------------------------------------------ [2007-02-02 18:44:25] nicolas dot grekas+php at gmail dot com I knew this pb for IE, and the link of php_lists is worth reading. BUT it is NOT related to the bug I was submitting. IE's bug with Vary header is : IF (non-compressed-content + Vary-header) THEN IE-dont-cache-entity Here is my bug : IF a resource is negotiated for compression THEN we MUST send a Vary header. In fact, for IE, the negotiation made by ob_gzhandler DOES ALREADY send a Vary header. Because negotiation ends to : browser (IE) accepts gzipped content. So fixing this issue WONT CHANGE ANYTHING FOR IE, but will fix corrupted caches. Should I explain more deeply the issue ? Regards, Nicolas ------------------------------------------------------------------------ [2007-02-02 17:02:44] mike@php.net Thanks, awesome read. ------------------------------------------------------------------------ [2007-02-02 15:38:48] php_lists at realplain dot com Just thought I'd add this comment that IE doesn't handle these Vary: headers correctly (breaks caching that would usually be used). :-( See http://lists.over.net/pipermail/mod_gzip/2002-December/006826.html It's been awhile since I read the details, but maybe you'd want to use "Cache-Control: private" instead or in addition to Vary:? ------------------------------------------------------------------------ [2007-02-02 13:11:50] nicolas dot grekas+php at gmail dot com Oops : I've switched Expected and Actual results, sorry ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/40325 -- Edit this bug report at http://bugs.php.net/?id=40325&edit=1