it seems the file cache does *not* have the ATTIC magic header (nor
does it have one in borg), so we don't need to edit the file - we just
copy it like a regular file.
while i'm here, simplify the cache conversion loop: it's no use
splitting the copy and the edition since the latter is so fast, just
do everything in one loop, which makes it much easier to read.
convert is too generic for the Attic conversion: we may have other
converters, from other, more foreign systems that will require
different options and different upgrade mechanisms that convert could
never cover appropriately. we are more likely to use an approach
similar to "git fast-import" instead here, and have the conversion
tools be external tool that feed standard data into borg during
conversion.
upgrade seems like a more natural fit: Attic could be considered like
a pre-historic version of Borg that requires invasive changes for borg
to be able to use the repository. we may require such changes in the
future of borg as well: if we make backwards-incompatible changes to
the repository layout or data format, it is possible that we require
such changes to be performed on the repository before it is usable
again. instead of scattering those conversions all over the code, we
should simply have assertions that check the layout is correct and
point the user to upgrade if it is not.
upgrade should eventually automatically detect the repository format
or version and perform appropriate conversions. Attic is only the
first one. we still need to implement an adequate API for
auto-detection and upgrade, only the seeds of that are present for now.
of course, changes to the upgrade command should be thoroughly
documented in the release notes and an eventual upgrade manual.
we separate the conversion and the copy in order to be able to copy
arbitrary files from attic without converting them. this allows us to
copy the config file cleanly without attempting to rewrite its magic
number
- issue #234: handle exception when config file is empty is really not a borg cache config
- there was a unused %s in the Exception string
- error msg was wrong when version check failed - this IS a borg cache, but not of expected version
note that we do not depend on attic to build borg, just to do those
tests. if attic goes away, we could eventually do this another way or
just stop testing this altogether.
