Useful for things like ipfs that don't use regular urls.
An external special remote can add a regular url to a key, and then
git-annex get will download it from the web. But for ipfs, we want to
instead tell git-annex that the uri uses OtherDownloader. Before this
change, the external special remote protocol lacked a way to do that.
This allows a remote to store a piece of arbitrary state associated with a
key. This is needed to support Tahoe, where the file-cap is calculated from
the data stored in it, and used to retrieve a key later. Glacier also would
be much improved by using this.
GETSTATE and SETSTATE are added to the external special remote protocol.
Note that the state is left as-is even when a key is removed from a remote.
It's up to the remote to decide when it wants to clear the state.
The remote state log, $KEY.log.rmt, is a UUID-based log. However,
rather than using the old UUID-based log format, I created a new variant
of that format. The new varient is more space efficient (since it lacks the
"timestamp=" hack, and easier to parse (and the parser doesn't mess with
whitespace in the value), and avoids compatability cruft in the old one.
This seemed worth cleaning up for these new files, since there could be a
lot of them, while before UUID-based logs were only used for a few log
files at the top of the git-annex branch. The transition code has also
been updated to handle these new UUID-based logs.
This commit was sponsored by Daniel Hofer.
This was unexpectedly difficult because of a depdenency cycle. To parse a
preferred content expression involves several things that need to operate
on the list of remotes. Which needs Remote.External. The only way to avoid
this cycle (I tried breaking it at several points) was to skip parsing the
expression in SETWANTED.
That's sorta ok, because git-annex already has to deal with unparsable
preferred content expressions being stored, in order to handle eg,
upgrades. But I'm still not very happy that I cannot check it.
I feel this is a strong indication that I need to beware of further
bloating the special remote protocol interface.
Changed protocol spec to make SETCONFIG only store it persistently when run
during INITREMOTE. I see no reason to support storing it persistently at
other times, and doing so would unnecessarily complicate the code.
Also, letting that be done would probably result in use for storing data that
doesn't really belong there, and special remote authors who don't
understand how the union merging works would probably be surprised the
results.
That complicated special remote programs, because they had to avoid making
PREPARE fail if some configuration is missing, because the remote might not
be initialized yet. Instead, complicate git-annex slightly by only sending
PREPARE immediately before some other request other than INITREMOTE (or
PREPARE of course).
This is mostly straightforward, but did turn out quite nicely stronly
typed, and with a quite nice automatic tokenization and parsing of received
messages.
Made a few minor changes to the protocol to clear up ambiguities and make
it easier to parse. Note particularly that setting remote configuration
is moved to a separate command, which allows a remote to set arbitrary data.
More complicated, but less asynchronous, which will make it easier for
special remote programs to use it, at the expense of some added complexity
in git-annex.
