I'm generating dynamic content with PHP.
I'm sending the following HTTP-header:
HTTP/1.1 304 Not Modified
Date: Sun, 09 Dec 2012 17:24:41 GMT
Server: Apache
Connection: keep-alive, Keep-Alive
Keep-Alive: timeout=1, max=100
Etag: "237f43b800e655dbe6567f7d32d34c99"
Expires: Sun, 16 Dec 2012 17:24:41 GMT
Cache-Control: max-age=604800
Vary: Accept-Encoding
I later check for the Etag to send a header('HTTP/1.1 304 Not Modified') if it matches.
This works perfectly with Chrome and Firefox.
However, Safari (Version 6.0.2) does not send "If-Modified-Since" and "If-None-Match" headers.
This is the Request-Header sent by Safari on the second page hit:
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/536.26.17 (KHTML, like Gecko) Version/6.0.2 Safari/536.26.17
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Cache-Control: max-age=0
All other files linked on that page receive the right Request-Headers and Safari used cached files or 304 where appropriate.
Why doesn't send Safari the correct Request-Header? What could I change?
Thank you!
The notes of If-Modified-Since warn against using something different than the contents of the Last-Modified response header:
Note: If a client uses an arbitrary date in the If-Modified-Since header instead of a date taken from the Last-Modified header for the same request, the client should be aware of the fact that this date is interpreted in the server's understanding of time.
Your response doesn't contain a Last-Modified, but even if it did, nothing in the spec says that user agents MUST or SHOULD send If-Modified-Since, they just MAY.
As to why Safari doesn't send an If-None-Match beats me; your ETag looks valid.
Again in general nothing in the spec says you MUST cache, just that when you do, you MUST obey Cache-Control. So it's a bit of an asymmetric relation, you can enforce (transparent) caches to recheck with the origin server, but as an origin server, you can't enforce useragents to cache.
Safari is only partly free software. So nothing much, if adding a Last-Modified doesn't help.