git-annex/Utility/FileMode.hs

{- File mode utilities.
 -
 - Copyright 2010-2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Utility.FileMode where

import Common

import Control.Exception (bracket)
import System.Posix.Types
import Foreign (complement)

{- Applies a conversion function to a file's mode. -}
modifyFileMode :: FilePath -> (FileMode -> FileMode) -> IO ()
modifyFileMode f convert = void $ modifyFileMode' f convert
modifyFileMode' :: FilePath -> (FileMode -> FileMode) -> IO FileMode
modifyFileMode' f convert = do
	s <- getFileStatus f
	let old = fileMode s
	let new = convert old
	when (new /= old) $
		setFileMode f new
	return old

{- Adds the specified FileModes to the input mode, leaving the rest
 - unchanged. -}
addModes :: [FileMode] -> FileMode -> FileMode
addModes ms m = combineModes (m:ms)

{- Removes the specified FileModes from the input mode. -}
removeModes :: [FileMode] -> FileMode -> FileMode
removeModes ms m = m `intersectFileModes` complement (combineModes ms)

{- Runs an action after changing a file's mode, then restores the old mode. -}
withModifiedFileMode :: FilePath -> (FileMode -> FileMode) -> IO a -> IO a
withModifiedFileMode file convert a = bracket setup cleanup go
	where
		setup = modifyFileMode' file convert
		cleanup oldmode = modifyFileMode file (const oldmode)
		go _ = a

writeModes :: [FileMode]
writeModes = [ownerWriteMode, groupWriteMode, otherWriteMode]

readModes :: [FileMode]
readModes = [ownerReadMode, groupReadMode, otherReadMode]

{- Removes the write bits from a file. -}
preventWrite :: FilePath -> IO ()
preventWrite f = modifyFileMode f $ removeModes writeModes

{- Turns a file's owner write bit back on. -}
allowWrite :: FilePath -> IO ()
allowWrite f = modifyFileMode f $ addModes [ownerWriteMode]

{- Allows owner and group to read and write to a file. -}
groupWriteRead :: FilePath -> IO ()
groupWriteRead f = modifyFileMode f $ addModes
	[ ownerWriteMode, groupWriteMode
	, ownerReadMode, groupReadMode
	]

checkMode :: FileMode -> FileMode -> Bool
checkMode checkfor mode = checkfor `intersectFileModes` mode == checkfor

{- Checks if a file mode indicates it's a symlink. -}
isSymLink :: FileMode -> Bool
isSymLink = checkMode symbolicLinkMode

{- Checks if a file has any executable bits set. -}
isExecutable :: FileMode -> Bool
isExecutable mode = combineModes ebits `intersectFileModes` mode /= 0
	where
		ebits = [ownerExecuteMode, groupExecuteMode, otherExecuteMode]

{- Runs an action without that pesky umask influencing it, unless the
 - passed FileMode is the standard one. -}
noUmask :: FileMode -> IO a -> IO a
noUmask mode a
	| mode == stdFileMode = a
	| otherwise = bracket setup cleanup go
	where
		setup = setFileCreationMask nullFileMode
		cleanup = setFileCreationMask
		go _ = a

combineModes :: [FileMode] -> FileMode
combineModes [] = undefined
combineModes [m] = m
combineModes (m:ms) = foldl unionFileModes m ms

stickyMode :: FileMode
stickyMode = 512

isSticky :: FileMode -> Bool
isSticky = checkMode stickyMode

setSticky :: FilePath -> IO ()
setSticky f = modifyFileMode f $ addModes [stickyMode]