I have several Linux virtual machines running on my home PC. One of the quirks of Linux is that every time you run a package manager, it wants to "refresh" the configured software repositories - which basically means it wants to download a file from the Internet. If I revert to an earlier snapshot of the VM, then next time I run the package manager it will re-download the exact same data again [since it no longer exists in the VM].

It seems a shame to waste bandwidth endlessly downloading the same data over and over again, so I was wondering if there's some way I can set up some kind of HTTP proxy server that caches downloaded files. I have no idea how you would do such a thing though. In particular, it needs to be set up so that the VMs don't need to "know" that the cache is there; it needs to be transparent. But I don't know how to do that.

Any suggestions on what software I'd need to use? It would be nice if I could run it under the Windows host OS, but running a small VM with a Linux guest is also possible...