Making GITBUNDLE be in the backend list allows those keys to be
hashed to verify, both when git-remote-annex downloads them, and by other
transfers and by git fsck.
GITMANIFEST is not in the backend list, because those keys will never be
stored in .git/annex/objects and can't be verified in any case.
This does mean that git-annex version will include GITBUNDLE in the list
of backends.
Also documented these in backends.mdwn
Sponsored-by: Kevin Mueller on Patreon
Not quite there yet.
Also, changed the format of GITBUNDLE keys to use only one '-'
after the UUID. A sha256 does not contain that character, so can just
split at the last one.
Amusingly, the sha256 will probably not actually be verified. A git
bundle contains its own checksums that git uses to verify it. And if
someone wanted to replace the content of a GITBUNDLE object, they
could just edit the manifest to use a new one whose sha256 does verify.
Sponsored-by: Nicholas Golder-Manning
Changed the format of the url to use annex: rather than annex::
The reason is that in the future, might want to support an url that
includes an uriAuthority part, eg:
annex://foo@example.com:42/358ff77e-0bc3-11ef-bc49-872e6695c0e3?type=directory&encryption=none&directory=/mnt/foo/"
To parse that foo@example.com:42 as an uriAuthority it needs to start with
annex: rather than annex::
That would also need something to be done with uriAuthority, and also
the uriPath (the UUID) is prefixed with "/" in that example. So the
current parser won't handle that example currently. But this leaves the
possibility for expansion.
Sponsored-by: Joshua Antonishen on Patreon
The UUID is included in the GITMANIFEST in order to allow a single
key/value store to be used to store several special remotes, without any
namespacing. In that situation though, if the same ref is pushed to two
special remotes, it will result in git bundles with the same content.
Which is ok, until a re-push happens to one of the special remote.
At that point, the old git bundle will be deleted. That will prevent
fetching it from the other special remote, where the re-push has not
happened.
Adding the UUID avoids this problem.
And document remote.<name>.git-remote-annex-max-bundles which will
configure it.
datalad-annex uses a similar url format, but with some enhancements.
See https://github.com/datalad/datalad-next/blob/main/datalad_next/gitremotes/datalad_annex.py
I added the UUID to the URL, because it is needed in order to pick out which
manifest file to use. The design allows for a single key/value store to have
several special remotes all stored in it, and so the manifest includes
the UUID in its name.
While datalad-annex allows datalad-annex::<url>?, and allows referencing
peices of the url in the parameters, needing the UUID prevents
git-remote-annex from supporting that syntax. And anyway, it is a
complication and I want to keep things simple for now.
Sponsored-by: unqueued on Patreon
Added to git-annex_proxies todo because this is something OpenNeuro
would need in order to use the git-annex proxy.
Sponsored-by: Dartmouth College's OpenNeuro project
Rather than requiring the last listed bundle in the manifest include all
refs that are in the remote, build up refs from each bundle listed in
the manifest.
This fixes a bug where pushing first a new branch foo from one clone,
and then pushing a new branch bar from another clone, caused the second
push to lose branch foo. Now the second push will add a new bundle, but
the foo ref in the bundle from the first push will still be used.
Pushing a deletion of a ref now has to delete all bundles and push a new
bundle with only the remaining refs in it.
In a "list for-push", it now has to unbundle all bundles, in order for a
deletion repush to have available all objects. (And a non-deletion push
can also rely on refs/namespaces/mine/ being up-to-date.)
It would have been possible to fix the bug by only making it do that
unbundling in "list for-push", without changing what's stored in the
bundles. But I think I prefer to populate the bundles this way. For one
thing, deleting a pushed ref now really deletes all data relating to it,
rather than leaving it present in old bundles. For another, it's easier
to explain since there is no special case for the last bundle. And, it
will often result in smaller bundles.
Note that further efficiency gains are possible with respect to what
objects are included in an incremental bundle. Two XXX comments
document how to reduce excess objects. It didn't seem worth implementing
those optimisations in this proof of concept code.
Sponsored-by: Brock Spratlen on Patreon
In a situation where there are two repos that are diverged and each pushes
in turn to git-remote-annex, the first to push updates it. Then the second
push fails because it is not a fast-forward. The problem is, before git
push fails with "non-fast-forward", it actually calls git-remote-annex
with push.
So, to the user it appears as if the push failed, but it actually reached
the remote, and overwrote the other push!
The only solution to this seems to be for git-remote-annex push to notice
when a non-force-push would overwrite a ref stored in the remote, and
refuse to push that ref, returning an error to git. This seems strange,
why would git make remote helpers implement that when it later checks the
same thing itself?
With this fix, it's still possible for a race to overwrite a change to
the MANIFEST and lose work that was pushed from the other repo. But that
needs two pushes to be running at the same time. From the user's
perspective, that situation is the same as if one repo pushed new work,
then the other repo did a git push --force, overwriting the first repo's
push. In the first repo, another push will then fail as a non
fast-forward, and the user can recover as usual. But, a MANIFEST
overwrite will leave bundle files in the remote that are not listed in
the MANIFEST. It seems likely that git-annex will eventually be able to
detect that after the fact and clean it up. Eg, it can learn all bundles
that are stored in the remote using the location log, and compare them
to the MANIFEST to find bundles that got lost.
The race can also appear to the user as if they pushed a ref, but then
it got deleted from the remote. This happens when two two pushes are
pushing different ref names. This might be harder for the user to
notice; git fetch does not indicate that a remote ref got deleted.
They would have to use git fetch --prune to notice the deletion.
Once the user does notice, they can re-push their ref to recover.
Sponsored-by: Jack Hill on Patreon
This is a shell script, so not final code, and it does not use git-annex
at all, but it shows how to push to git bundles, listed in a MANIFEST,
the same as the git-remote-annex program will eventually do.
While developing this, I realized that the design needed to be changed
slightly regarding where refs are stored. Since a push can delete a ref
from a remote, storing each newly pushed ref in a bundle won't work,
because deleting a ref would then entail deleting all old bundles and
re-uploading from scratch. So instead, only the refs in the last bundle
listed in the MANIFEST are the active refs. Any refs in prior bundles
are just old refs that were stored previously (a reflog as it were).
That means that, in a situation where two different people are pushing
to the same special remote from different repos, whoever pushes last
wins. Any refs pushed by the other person earlier will be ignored. This
may not be desirable, and git-annex might be able use the git-annex
branch to detect such situations and rescue the refs that got lost. Even
without such a recovery process though, the refs that the other person
thought they pushed will be preserved in their refs/namespaces/mine, so
a pull followed by a push will generally resolve the situation.
Note that the use of refs/namespaces/mine in the bundle is not really
desirable, and it might be worth making a local clone of the repo in
order to set up the refs that will be put in the bundle. Which seems to
be the only way to avoid needing that. But it does need to maintain
the refs/namespaces/mine/ in the git repo in order to remember what refs
have been pushed to the remote before, in order to include them in the
next bundle pushed. A name that includes the remote uuid will be needed
in the final implementation.
Anyway, this shell script seems to fully work, including incremental
pushing, force pushing, and pushes that delete refs.
Sponsored-by: Brett Eisenberg on Patreon
