I'm implementing caching at the server application level, because my hosting doesn't provide Apache caching modules and it's not possible to use a reverse proxy there. Its cheap and fast hosting, so I don't want to change it.
Can I detect when the user presses F5 or Ctrl+F5, instead clicking on link to one page? I'm quite sure there are some special HTTP headers generated on request like this. Without it, the page will be always served from cache.
No. The browser will send the same information on a refresh as if the user had just come to that page, with the same referrer information. Hence the problem of double-POSTing if someone refreshes the destination page for a form.
What you could do is have a refresh button on the page (as Google Ads used to have before they removed it), which you could use to send a relevant GET or POST variable to the server which would trigger the update you were looking for.
Alternatively, you could use a cookie to determine if the user had seen that page was the last page that user had seen as treat a second request for that page as a refresh.
Browsers do send additional headers, but behavior different. This info in link a bit outdated: stackoverflow question
Looks like Cache-control:no-cache is the best solution, to check for Ctrl+F5, but better to check not the only one header.
Just checked on Firefox Ubuntu, F5 gives nothing, but Ctrl+F5 request contain this
Pragma no-cache
Cache-Control no-cache
Checked Chromium - same behavior, same two headers.
This headers may pass any proxy in the middle, and come to end - site server, as I known.
If-None-Matchheader if the response to the first load did contain anETagheader.