I am trying to figure out why Safari (3.0.4) won't send If-Modified-Since headers for SWFs in some cases. I have observed that for some SWFs, Safari never sends the If-Modified-Since header, while it does for other content such as graphics and other SWFs. Also, IE and Firefox/Mozilla seem to handle these particular SWFs just fine. I did find mention of this issue from several years ago at http://www.codepoetry.net/archives/2003/11/07/safari_and_ifmodifiedsince.php . Are these SWFs not making into the Safari cache at all (this has been really hard to verify which is why I'm not sure), or is there some other reason that Safari does not send the If-Modified-Since header (maybe the HTTP headers applied by the server or something). I am looking for any information that will help in working around this issue, or some idea of when it might be fixed.
I suspect that this may be caused by a broken (empty) Cache-Control header in the server response: HTTP/1.1 200 OK Date: Tue, 18 Mar 2008 08:07:54 GMT Server: Apache/2.2.3 (Linux/SUSE) Last-Modified: Thu, 04 Oct 2007 22:27:30 GMT ETag: "18414b-51031-43bb24aae5880" Accept-Ranges: bytes Cache-Control: Expires: Tue, 18 Mar 2008 08:07:54 GMT Vary: Accept-Encoding Content-Encoding: gzip Pragma: Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Transfer-Encoding: chunked Content-Type: application/x-shockwave-flash Some experimentation would be needed to determine if this is indeed the cause. > Also, IE and Firefox/Mozilla seem to handle these particular SWFs just fine. Even though the response is malformed, this difference in behavior can be seen as a bug in system frameworks below WebKit, and thus needs to be filed at <http://bugreport.apple.com> for Apple engineers working on those to take a look.
Here are the response headers that are being sent with one of the SWFs that have the problem: HTTP/1.1 200 OK Date: Thu, 27 Mar 2008 05:42:33 GMT Server: Apache/2.2.4 (Win32) mod_scgi/1.12 PHP/5.2.2 Last-Modified: Mon, 24 Mar 2008 02:45:14 GMT ETag: "aaa55-168ce8-d3456280" Accept-Ranges: bytes Cache-Control: Expires: Thu, 27 Mar 2008 05:42:33 GMT Vary: Accept-Encoding Content-Encoding: gzip Pragma: Keep-Alive: timeout=5, max=80 Connection: Keep-Alive Transfer-Encoding: chunked Content-Type: application/x-shockwave-flash The Cache-Control header is empty. I will try setting this to something and see if it helps. The odd thing is that Safari is caching some SWFs correctly using these same response headers. If the problem is the empty Cache-Control, it seems like it would be consistently not caching everything and not sending the If-Modified-Since headers in every case.
I just changed the Cache-Control header to "must-revalidate" and I am still seeing the same issue. Maybe it has something to do with the file size. In any case, I am still seeing the same strange behavior where some resources like HTML, JS, image files, and other SWFs seem to cache correctly and send the If-Modified Since header, but another set of SWFs (mostly larger ones) never send the If-Modified-Since header.
The test file is over 300K in size, too large to be cached because of a bug - see bug 18972 for more details. *** This bug has been marked as a duplicate of 18972 ***