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{- git-annex file replacing
-
- Copyright 2013-2015 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
{-# LANGUAGE CPP #-}
module Annex.ReplaceFile where
import Annex.Common
import Annex.Perms
import Utility.Tmp
{- Replaces a possibly already existing file with a new version,
- atomically, by running an action.
-
- The action is passed the name of temp file, in a temp directory,
- which it can write to, and once done the temp file is moved into place
- and anything else in the temp directory is deleted.
-
- The action can throw an exception, in which case the temp directory
- 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 = do
misctmpdir <- fromRepo gitAnnexTmpMiscDir
void $ createAnnexDirectory misctmpdir
#ifndef mingw32_HOST_OS
-- Use part of the filename as the template for the temp
-- directory. This does not need to be unique, but it
-- makes it more clear what this temp directory is for.
filemax <- liftIO $ fileNameLengthLimit misctmpdir
let basetmp = take (filemax `div` 2) (takeFileName file)
#else
-- Windows has limits on the whole path length, so keep
-- it short.
let basetmp = "t"
#endif
withTmpDirIn misctmpdir basetmp $ \tmpdir -> do
let tmpfile = tmpdir </> basetmp
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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