thanks for your reply.
This cache management header is only used for the local caching of any (wget) download. If you set the above header in the fetcher script it isn’t using any local caching mechanism and requests a fresh file download from the web server every time it’s triggered.
I’ve to investigate a bit more also to the fact that I’m using a caching proxy server inside my LAN. On the RPi I disabled proxy usage for local addresses, but it seems maybe something isn’t working correctly here.
The .ics file (calendar export from Lotus Domino client) has the same structure like other files (eg. from MS Outlook or Thunderbird). So, I guess this isn’t really a calendar file problem as more an OS related issue.
If I download this file from the web server with ‘wget’ on my RPi, I’m getting the same file version every time I try to download even if it has changed or not. If I manipulate the HTTP-header which wget is using, the download is working as expected. (see http://xmodulo.com/how-to-use-custom-http-headers-with-wget.html for example). Some about cache management can be found here: http://dev.mobify.com/blog/beginners-guide-to-http-cache-headers/
Currently I’m at work, but I’ll try to figure it out today evening. I’ll update this post with my findings.