I agree to the privacy violation problem for man-in-the-middle caching...
That's why I am not allowed to use it, that is the initial problem.
There must be a way to store in cache things like files which are hosted at some filehoster on the internet. But okay, at the moment this is just not possible (legal way).
>When we jump right ahead to discuss technical details, I would like
>someone to check out if we can easily control the cache to store our
>files, so that we don't have to manage our own one.
You could give squid a separated cache-dir for update-things.
Did you check the new "rock-storage" type of squid? It is really fast.
Also the newer versions of squid are multithreaded or at least multiple instanced.
So I recommend using squid's cache. It is well established over many years and very fast.
There just has to be a mapping for the files to query them from cache storage.
Squid has an internal mapping, if it would be possible to get into that API - the problem will be small.