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{- git-annex file replacing
-
- Copyright 2013 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Annex.ReplaceFile where
import Common.Annex
import Annex.Perms
{- Replaces a possibly already existing file with a new version,
- atomically, by running an action.
-
- The action is passed a temp file, which it can write to, and once
- done the temp file is moved into place.
-
- The action can throw an IO exception, in which case the temp file
- will be deleted, and the existing file will be preserved.
-
- Throws an IO exception when it was unable to replace the file.
-}
replaceFile :: FilePath -> (FilePath -> Annex ()) -> Annex ()
replaceFile file action = replaceFileOr file action (liftIO . nukeFile)
{- If unable to replace the file with the temp file, runs the
- rollback action, which is responsible for cleaning up the temp file. -}
replaceFileOr :: FilePath -> (FilePath -> Annex ()) -> (FilePath -> Annex ()) -> Annex ()
replaceFileOr file action rollback = do
tmpdir <- fromRepo gitAnnexTmpMiscDir
void $ createAnnexDirectory tmpdir
tmpfile <- liftIO $ setup tmpdir
go tmpfile `catchNonAsync` (const $ rollback tmpfile)
where
setup tmpdir = do
(tmpfile, h) <- openTempFileWithDefaultPermissions tmpdir "tmp"
hClose h
return tmpfile
go tmpfile = do
action tmpfile
liftIO $ replaceFileFrom tmpfile file
replaceFileFrom :: FilePath -> FilePath -> IO ()
replaceFileFrom src dest = go `catchIO` fallback
where
go = moveFile src dest
fallback _ = do
createDirectoryIfMissing True $ parentDir dest
go
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