Thanks for opening a pull request! We really appreciate your help.

I did a force push and added a new Tgz format that emulates [Gzip, Tar] and should give the correct error messages

If you don't mind, I did some small changes (added a comment here and created an extra variable there).

Was trying to remove some of the code repetition in the compress_files, but I realized it was not possible, but I committed the small changes anyways.