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|
{- general purpose utility functions
-
- Copyright 2010-2011 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Utility (
hGetContentsStrict,
readFileStrict,
readMaybe,
viaTmp,
withTempFile,
dirContents,
myHomeDir,
catchBool,
inPath,
firstM,
anyM
) where
import IO (bracket)
import System.IO
import System.Posix.Process hiding (executeFile)
import System.Posix.User
import System.FilePath
import System.Directory
import Utility.Path
import Data.Maybe
import Control.Monad (liftM)
{- A version of hgetContents that is not lazy. Ensures file is
- all read before it gets closed. -}
hGetContentsStrict :: Handle -> IO String
hGetContentsStrict h = hGetContents h >>= \s -> length s `seq` return s
{- A version of readFile that is not lazy. -}
readFileStrict :: FilePath -> IO String
readFileStrict f = readFile f >>= \s -> length s `seq` return s
{- Attempts to read a value from a String. -}
readMaybe :: (Read a) => String -> Maybe a
readMaybe s = case reads s of
((x,_):_) -> Just x
_ -> Nothing
{- Runs an action like writeFile, writing to a tmp file first and
- then moving it into place. -}
viaTmp :: (FilePath -> String -> IO ()) -> FilePath -> String -> IO ()
viaTmp a file content = do
pid <- getProcessID
let tmpfile = file ++ ".tmp" ++ show pid
createDirectoryIfMissing True (parentDir file)
a tmpfile content
renameFile tmpfile file
{- Runs an action with a temp file, then removes the file. -}
withTempFile :: String -> (FilePath -> Handle -> IO a) -> IO a
withTempFile template a = bracket create remove use
where
create = do
tmpdir <- catch getTemporaryDirectory (const $ return ".")
openTempFile tmpdir template
remove (name, handle) = do
hClose handle
catchBool (removeFile name >> return True)
use (name, handle) = a name handle
{- Lists the contents of a directory.
- Unlike getDirectoryContents, paths are not relative to the directory. -}
dirContents :: FilePath -> IO [FilePath]
dirContents d = do
c <- getDirectoryContents d
return $ map (d </>) $ filter notcruft c
where
notcruft "." = False
notcruft ".." = False
notcruft _ = True
{- Current user's home directory. -}
myHomeDir :: IO FilePath
myHomeDir = do
uid <- getEffectiveUserID
u <- getUserEntryForID uid
return $ homeDirectory u
{- Catches IO errors and returns a Bool -}
catchBool :: IO Bool -> IO Bool
catchBool = flip catch (const $ return False)
{- Return the first value from a list, if any, satisfying the given
- predicate -}
firstM :: (Monad m) => (a -> m Bool) -> [a] -> m (Maybe a)
firstM _ [] = return Nothing
firstM p (x:xs) = do
q <- p x
if q
then return (Just x)
else firstM p xs
{- Returns true if any value in the list satisfies the preducate,
- stopping once one is found. -}
anyM :: (Monad m) => (a -> m Bool) -> [a] -> m Bool
anyM p = liftM isJust . firstM p
{- Checks if a command is available in PATH. -}
inPath :: String -> IO Bool
inPath command = getSearchPath >>= anyM indir
where
indir d = doesFileExist $ d </> command
|
