add remote state logs

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.

1 files changed, 33 insertions, 0 deletions

diff --git a/Logs/RemoteState.hs b/Logs/RemoteState.hs
new file mode 100644
index 000000000..95e51832e
--- /dev/null
+++ b/Logs/RemoteState.hs
@@ -0,0 +1,33 @@
+{- Remote state logs.
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Logs.RemoteState (
+	getRemoteState,
+	setRemoteState,
+) where
+
+import Common.Annex
+import Logs
+import Logs.UUIDBased
+import qualified Annex.Branch
+
+import qualified Data.Map as M
+import Data.Time.Clock.POSIX
+
+type RemoteState = String
+
+setRemoteState :: UUID -> Key -> RemoteState -> Annex ()
+setRemoteState u k s = do
+	ts <- liftIO getPOSIXTime
+	Annex.Branch.change (remoteStateLogFile k) $
+		showLogNew id . changeLog ts u s . parseLogNew Just
+
+getRemoteState :: UUID -> Key -> Annex (Maybe RemoteState)
+getRemoteState u k = extract . parseLogNew Just
+	<$> Annex.Branch.get (remoteStateLogFile k)
+  where
+	extract m = value <$> M.lookup u m