This solves the problem of sameas remotes trampling over per-remote
state. Used for:
* per-remote state, of course
* per-remote metadata, also of course
* per-remote content identifiers, because two remote implementations
could in theory generate the same content identifier for two different
peices of content
While chunk logs are per-remote data, they don't use this, because the
number and size of chunks stored is a common property across sameas
remotes.
External special remote had a complication, where it was theoretically
possible for a remote to send SETSTATE or GETSTATE during INITREMOTE or
EXPORTSUPPORTED. Since the uuid of the remote is typically generate in
Remote.setup, it would only be possible to pass a Maybe
RemoteStateHandle into it, and it would otherwise have to construct its
own. Rather than go that route, I decided to send an ERROR in this case.
It seems unlikely that any existing external special remote will be
affected. They would have to make up a git-annex key, and set state for
some reason during INITREMOTE. I can imagine such a hack, but it doesn't
seem worth complicating the code in such an ugly way to support it.
Unfortunately, both TestRemote and Annex.Import needed the Remote
to have a new field added that holds its RemoteStateHandle.
This avoids some extra work, but I don't think it was possible for two ssh
endpoint discoveries run concurrently to both prompt for the ssh password;
Annex.Ssh itself deals with concurrency.
This is mostly groundwork for http password prompting.
Using Logs.RemoteState for this means that if the same key gets uploaded
twice to a git-lfs remote, but somehow has different content the two
times (eg it's an URL key with non-stable content), the sha256/size of
the newer content uploaded will overwrite what was remembered before. That
seems ok; it just means that git-annex will request the newer version of
the content when downloading from git-lfs.
It will remember the sha256 and size if both are not known, or if only
the sha256 is not known but the size is known, it only remembers the
sha256, to avoid wasting space on the size. I did not add special case
for when the sha256 is known and the size is not, because it's been a
long time since git-annex created SHA256 keys without a size.
(See doc/upgrades/SHA_size.mdwn)
The protocol design allows the server to respond with some other object;
if a server for some reason a server did that, it would not be right for
git-annex to download its content. I don't think it would be a security
hole, since git-annex is downloading a specific key and will verify the
key's content. Seems like a good idea to belt-and-suspenders test for
such a misuse of the protocol.
This is a special remote and a git remote at the same time; git can pull
and push to it and git-annex can use it as a special remote.
Remote.Git has to check if it's configured as a git-lfs special remote
and sets it up as one if so.
Object methods not implemented yet.
