This needs the content to be present in order to hash it. But it's not
possible for a module used by Backend.URL to call inAnnex because that
would entail a dependency loop. So instead, rely on the fact that
Command.Migrate calls inAnnex before performing a migration.
But, Command.ExamineKey calls fastMigrate and the key may or may not
exist, and it's not wanting to actually perform a migration in any case.
To handle that, had to add an additional value to fastMigrate to
indicate whether the content is inAnnex.
Factored generateEquivilantKey out of Remote.Web.
Note that migrateFromURLToVURL hardcodes use of the SHA256E backend.
It would have been difficult not to, given all the dependency loop
issues. But --backend and annex.backend are used to tell git-annex
migrate to use VURL in any case, so there's no config knob that
the user could expect to configure that.
Sponsored-by: Brock Spratlen on Patreon
git-annex fsck and some other commands that verify the content of a key
were using the non-incremental verification interface. But for VURL
urls, that interface is innefficient because when there are multiple
equivilant keys, it has to separately read and checksum for each key in
turn until one matches. It's more efficient for those to use the
incremental interface, since the file can be read a single time.
There's no real downside to using the incremental interface when available.
Note that more speedup could be had for VURL, if it was able to
calculate the checksum a single time and then compare with the
equivilant keys checksums. When the equivilant keys use the same type of
checksum.
Sponsored-by: k0ld on Patreon
VURL is now fully working, though needs more testing.
Still need to implement verifyKeyContentIncrementally but it works
without it.
Sponsored-by: Luke T. Shumaker on Patreon
Considerable difficulty to work around an import cycle. Had to move the
list of backends (except for VURL) to Backend.Variety to VURL could use
it.
Sponsored-by: Kevin Mueller on Patreon
When downloading a VURL from the web, make sure that the equivilant key
log is populated.
Unfortunately, this does not hash the content while it's being
downloaded from the web. There is not an interface in Backend currently
for incrementally hash generation, only for incremental verification of an
existing hash. So this might add a noticiable delay, and it has to show
a "(checksum...") message. This could stand to be improved.
But, that separate hashing step only has to happen on the first download
of new content from the web. Once the hash is known, the VURL key can have
its hash verified incrementally while downloading except when the
content in the web has changed. (Doesn't happen yet because
verifyKeyContentIncrementally is not implemented yet for VURL keys.)
Note that the equivilant key log file is formatted as a presence log.
This adds a tiny bit of overhead (eg "1 ") per line over just listing the
urls. The reason I chose to use that format is it seems possible that
there will need to be a way to remove an equivilant key at some point in
the future. I don't know why that would be necessary, but it seemed wise
to allow for the possibility.
Downloads of VURL keys from other special remotes that claim urls,
like bittorrent for example, does not popilate the equivilant key log.
So for now, no checksum verification will be done for those.
Sponsored-by: Nicholas Golder-Manning on Patreon
Not yet implemented is recording hashes on download from web and
verifying hashes.
addurl --verifiable option added with -V short option because I
expect a lot of people will want to use this.
It seems likely that --verifiable will become the default eventually,
and possibly rather soon. While old git-annex versions don't support
VURL, that doesn't prevent using them with keys that use VURL. Of
course, they won't verify the content on transfer, and fsck will warn
that it doesn't know about VURL. So there's not much problem with
starting to use VURL even when interoperating with old versions.
Sponsored-by: Joshua Antonishen on Patreon
