Empty Expires: headers causes proxy cache to not cache the request #2406

Since I have my current internet connection I have been VERY frustrated by the fact, that on the demo, none of the assets are cached and always return 200. What happens, is that my internet provider proxy cache didn't honor the cache headers.

After researching the cause is that the Expires: header is empty.

Setting the Expires: header in the far future (as advised by Yahoo best practises) fixes the issue and causes the proxy cache they use to finally cache our assets.

Setting expires in the far future, means that the file will not even be requested at all, so that the browser will only request in the far future.

However it should work nicely for us, because we use a buster in the assets URLs so that when the assets change, the <.. src='...'> URL is also changed (good call on this one anthon ;)

See also #1887

Yahoo best practises Expires header

Should be ok in most cases. The only exception is the js/ proxy serving piwik.js which has no cache buster string.

(In [4642]) Fixes #2406

In c1703a107774db816b5a65717ee1d9de394cffa4: cache /js/ for 10 days rather than none. Refs #2406
From forum feedback: http://forum.piwik.org/read.php?2,112741