Thank you for your offer to look further into this matter. Meanwhile i searched for places where things could be cached. I found a cause. So I think your investigation service on my server is not needed.
In my apache setup there is a declaration
ExpiresActive On
ExpiresDefault "now plus 1 hour"
This tells the browser to cache all responses from the server 1 hour.
As my server setup is quite old I forgot completely about that. But it did not cause any problem until now, and because it reduces the responsetimes from the server quite a bit I would like to keep this setting.
Anyway, some googling around gives several options:
1. Set ExpiresActive Off. Which I would not like to do
2. Use ExpiresByType, to exclude the response from the scan from caching. Inspecting the response, it has mime type text/html. So the statement would be ExpiresByType text/html 0. This is possible a workable option, as it only impacts plain text files and not the majority of the files served.
3. Have the calling javascript include a dummy parameter with a sequence number or timestamp. This causes everytime a request by a new url, bypassing the cached response from previous requests. For me this looks like a work-around, not a definitive solution.
4. Include a header with the response to disable caching of the respons.
Option 4 would be my preferred solution. As a test I setup a second domain and made a copy of my joomla. In the file scan.php, I added in the function sendJsonResponse before the echo command:
header("Cache-Control: no-store, no-cache, must-revalidate");
On my test system rescanning tickets do not result in wrong replies anymore. Inspecting the return message in Chrome does indeed show the header line, disabling the cache as intended.
I would like some solution like this included in event booking, as it is not very wel possible to exclude caching specifically server-side. Option 2 would be the best I think.
Alternatively, i might use the altered scan.php on my production system. Unfortunately, i cannot find a way to override php files which are stored in the controller directory.
Regards Frans
