git-annex/Logs/Presence.hs
Joey Hess 05989556a2
start implementing hidden git-annex repositories
This adds a separate journal, which does not currently get committed to
an index, but is planned to be committed to .git/annex/index-private.

Changes that are regarding a UUID that is private will get written to
this journal, and so will not be published into the git-annex branch.

All log writing should have been made to indicate the UUID it's
regarding, though I've not verified this yet.

Currently, no UUIDs are treated as private yet, a way to configure that
is needed.

The implementation is careful to not add any additional IO work when
privateUUIDsKnown is False. It will skip looking at the private journal
at all. So this should be free, or nearly so, unless the feature is
used. When it is used, all branch reads will be about twice as expensive.

It is very lucky -- or very prudent design -- that Annex.Branch.change
and maybeChange are the only ways to change a file on the branch,
and Annex.Branch.set is only internal use. That let Annex.Branch.get
always yield any private information that has been recorded, without
the risk that Annex.Branch.set might be called, with a non-private UUID,
and end up leaking the private information into the git-annex branch.

And, this relies on the way git-annex union merges the git-annex branch.
When reading a file, there can be a public and a private version, and
they are just concacenated together. That will be handled the same as if
there were two diverged git-annex branches that got union merged.
2021-04-20 15:04:53 -04:00

71 lines
2.2 KiB
Haskell

{- git-annex presence log
-
- This is used to store presence information in the git-annex branch in
- a way that can be union merged.
-
- A line of the log will look like: "date N INFO"
- Where N=1 when the INFO is present, 0 otherwise.
-
- Copyright 2010-2014 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU AGPL version 3 or higher.
-}
module Logs.Presence (
module X,
addLog,
maybeAddLog,
readLog,
logNow,
currentLog,
currentLogInfo,
historicalLogInfo,
) where
import Logs.Presence.Pure as X
import Annex.Common
import Annex.VectorClock
import qualified Annex.Branch
import Git.Types (RefDate)
{- Adds a LogLine to the log, removing any LogLines that are obsoleted by
- adding it. -}
addLog :: Annex.Branch.RegardingUUID -> RawFilePath -> LogLine -> Annex ()
addLog ru file line = Annex.Branch.change ru file $ \b ->
buildLog $ compactLog (line : parseLog b)
{- When a LogLine already exists with the same status and info, but an
- older timestamp, that LogLine is preserved, rather than updating the log
- with a newer timestamp.
-}
maybeAddLog :: Annex.Branch.RegardingUUID -> RawFilePath -> LogLine -> Annex ()
maybeAddLog ru file line = Annex.Branch.maybeChange ru file $ \s -> do
m <- insertNewStatus line $ logMap $ parseLog s
return $ buildLog $ mapLog m
{- Reads a log file.
- Note that the LogLines returned may be in any order. -}
readLog :: RawFilePath -> Annex [LogLine]
readLog = parseLog <$$> Annex.Branch.get
{- Generates a new LogLine with the current time. -}
logNow :: LogStatus -> LogInfo -> Annex LogLine
logNow s i = do
c <- currentVectorClock
return $ LogLine c s i
{- Reads a log and returns only the info that is still in effect. -}
currentLogInfo :: RawFilePath -> Annex [LogInfo]
currentLogInfo file = map info <$> currentLog file
currentLog :: RawFilePath -> Annex [LogLine]
currentLog file = filterPresent <$> readLog file
{- Reads a historical version of a log and returns the info that was in
- effect at that time.
-
- The date is formatted as shown in gitrevisions man page.
-}
historicalLogInfo :: RefDate -> RawFilePath -> Annex [LogInfo]
historicalLogInfo refdate file = map info . filterPresent . parseLog
<$> Annex.Branch.getHistorical refdate file