I have cacheable dynamic content made in PHP 5.1.0+. I already send the correct headers (including Last-Modified and ETag) to clients.
I now want my script to be able to answer
$_SERVER['HTTP_IF_NONE_MATCH'] when present. When the conditions matches, I want to answer a
HTTP 304 "Not Modified" to clients.
What are the correct conditions? When exactly I issue a 304 instead of the whole content?
The accepted answer in question How to know when to send a 304 Not Modified response seems to issue this correctly but I have hard times to port that code to PHP 5.