The use of catObjectStream is optimally fast. Although it might be
possible to combine this with git-annex branch merge to avoid some
redundant work.
Benchmarking, a git-annex branch that had 100000 files changed
took less than 1.88 seconds to run through this.
At this point the RepoSize database is getting populated, and it
all seems to be working correctly. Incremental updates still need to be
done to make it performant.
Including locking on creation, handling of permissions errors, and
setting repo sizes.
I'm confident that locking is not needed while using this database.
Since writes happen in a single transaction. When there are two writers
that are recording sizes based on different git-annex branch commits,
one will overwrite what the other one recorded. Which is fine, it's only
necessary that the database stays consistent with the content of a
git-annex branch commit.
Plan is to run this when populating Annex.reposizes on demand.
So Annex.reposizes will be up-to-date with the journal, including
crucially journal entries for private repositories. But also
anything that has been written to the journal by another process,
especially if the process was ran with annex.alwayscommit=false.
From there, Annex.reposizes can be kept up to date with changes made
by the running process.
This is very innefficient, it will need to be optimised not to
calculate the sizes of repos every time.
Also, fixed a bug in balancedPicker that caused it to pick a too high
index when some repos were excluded due to being full.
This deals with the possible security problem that someone could make an
unusually low UUID and generate keys that are all constructed to hash to
a number that, mod the number of repositories in the group, == 0.
So balanced preferred content would always put those keys in the
repository with the low UUID as long as the group contains the
number of repositories that the attacker anticipated.
Presumably the attacker than holds the data for ransom? Dunno.
Anyway, the partial solution is to use HMAC (sha256) with all the UUIDs
combined together as the "secret", and the key as the "message". Now any
change in the set of UUIDs in a group will invalidate the attacker's
constructed keys from hashing to anything in particular.
Given that there are plenty of other things someone can do if they can
write to the repository -- including modifying preferred content so only
their repository wants files, and numcopies so other repositories drom
them -- this seems like safeguard enough.
Note that, in balancedPicker, combineduuids is memoized.
This all works fine. But it doesn't check repository sizes yet, and
without repository size checking, once a repository gets full, there
will be no other repository that will want its files.
Use of sha2 seems unncessary, probably alder2 or md5 or crc would have
been enough. Possibly just summing up the bytes of the key mod the number
of repositories would have sufficed. But sha2 is there, and probably
hardware accellerated. I doubt very much there is any security benefit
to using it though. If someone wants to construct a key that will be
balanced onto a given repository, sha2 is certianly not going to stop
them.
This removes versionedExport, which was only used by the S3 special
remote. Instead, versionedexport=yes is a common way for remotes to
indicate that they are versioned.
This is not perfect because it does not handle versioned special
remotes, which should not be untrustworthy, but now are when proxied.
The implementation turned out to be easy, because the exporttree field
is a default field, so is available in RemoteConfig even for git
remotes.
This handles cases where a single key is used by multiple files in the
exported tree. When using `git-annex push`, the key's content gets
stored in the annexobjects location, and then when the branch is pushed,
it gets renamed from the annexobjects location to the first exported
file. For subsequent exported files, a copy of the content needs to be
made. This causes it to download the key from the remote in order to
upload another copy to it.
This is not needed when using `git push` followed by `git-annex copy --to`
the proxied remote, because the received key is stored at all export
locations then.
Also, fixed handling of the synced branch push, it was exporting master
when synced/master was pushed.
Note that currently, the first push to the remote does not see that it
is able to get a key from it in order to upload it back. It displays
"(not available)". The second push is able to. Since git-annex push
pushes first the synced branch and then the branch, this does end up
with a full export being made, but it is not quite right.
This is similar to git-annex copy --from --to, in that it downloads a
local copy, locks it for removal, uploads it, and drops it. Removal of
the temporary local copy is done without verifying numcopies for the
same reason as that command.
I do wonder, looking at this, if there's a race where the local copy
gets used as a copy to allow some other drop in the narrow window after
it is downloaded and before it gets locked for removal. That would need
some other repository to have an out of date location log that says the
repository contains a copy of the key, in order for it to try to use it
as a copy. If there is such a race, git-annex copy/move would also be
vulnerable to it. It would be better to lock it for removal before
starting to download it! That is possible in v10 repositories, which do
use a separate content lock file.
Note that, when the exported tree contains several files that use the
same key, it will be downloaded repeatedly, once per time needed to
upload it. It would be possible to avoid that extra work, but it would
complicate this since the local copy would need to be preserved, locked
for removal, until the end. Also, that would mean that interrupting the
export would leave possibly a lot of temporarily downloaded keys in the
local repository, while currently it can only leave one.
Since git-annex sync sends the sync branch first, and only displays the
output of the push to the sync branch, this makes git-annex
post-retrieve's output when updating the exported tree be visible when
syncing.
This also makes syncing with a non-bare repository still update the
exported tree, even when the checked out branch is not able to be
updated. The sync branch gets sent regardless.
When getting from a P2P HTTP remote, prompt for credentials when required,
instead of failing.
This feels like it might be a bug in servant-client. withClientM's type
suggests it would not throw a ClientError. But it does in this case.
