File.hs

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE CPP                 #-}
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-- | A module containing various file utility functions
module Hakyll.Core.Util.File
    ( makeDirectories
    , getRecursiveContents
    , removeDirectory
    , withPermissions
    ) where


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import           Control.Exception   (throw)
import           Control.Monad       (filterM, forM)
import           System.Directory    (createDirectoryIfMissing, doesPathExist,
                                      doesDirectoryExist, getDirectoryContents)
import           System.FilePath     (takeDirectory, (</>))
import           System.IO.Error     (catchIOError, isPermissionError)
#ifndef mingw32_HOST_OS
import           Control.Monad       (when)
import           System.Directory    (removeDirectoryRecursive)
#else
import           Control.Concurrent  (threadDelay)
import           Control.Exception   (SomeException, catch)
import           System.Directory    (removePathForcibly)
#endif


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-- | Given a path to a file, try to make the path writable by making
--   all directories on the path.
makeDirectories :: FilePath -> IO ()
makeDirectories = createDirectoryIfMissing True . takeDirectory


--------------------------------------------------------------------------------
-- | Get all contents of a directory.
--
-- If a directory is encountered for which you do not have
-- permission, the directory will be skipped instead of
-- an exception being thrown.
--
-- If a dangling\/broken symbolic link is encountered, then it will
-- be skipped (since returning it may cause callers to throw exceptions).
getRecursiveContents :: (FilePath -> IO Bool)  -- ^ Ignore this file/directory
                     -> FilePath               -- ^ Directory to search
                     -> IO [FilePath]          -- ^ List of files found for which you have permissions
getRecursiveContents ignore top = go ""
  where
    isProper x
        | x `elem` [".", ".."] = return False
        | otherwise            = not <$> ignore x

    getProperDirectoryContents absDir =
        filterM isProper =<< withPermissions (getDirectoryContents absDir) []

    go relDir = do
        let absDir = top </> relDir
        dirExists <- doesDirectoryExist absDir
        if not dirExists
            then return []
            else do
                names <- getProperDirectoryContents absDir
                fmap concat . forM names $ \name -> do
                    let relPath = relDir </> name
                        absPath = top </> relPath
                    isDirectory <- doesDirectoryExist absPath
                    if isDirectory
                        then go relPath
                        else do
                            pathExists <- doesPathExist absPath
                            return $ if pathExists then [relPath] else []


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removeDirectory :: FilePath -> IO ()
#ifndef mingw32_HOST_OS
removeDirectory fp = do
    e <- doesDirectoryExist fp
    when e $ removeDirectoryRecursive fp
#else
-- Deleting files on Windows is unreliable. If a file/directory is open by a program (e.g. antivirus),
-- then removing related directories *quickly* may fail with strange messages.
-- See here for discussions:
--      https://github.com/haskell/directory/issues/96
--      https://github.com/haskell/win32/pull/129
--
-- The hacky solution is to retry deleting directories a few times,
-- with a delay, on Windows only.
removeDirectory = retryWithDelay 10 . removePathForcibly

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-- | Retry an operation at most /n/ times (/n/ must be positive).
--   If the operation fails the /n/th time it will throw that final exception.
--   A delay of 100ms is introduced between every retry.
retryWithDelay :: Int -> IO a -> IO a
retryWithDelay i x
    | i <= 0    = error "Hakyll.Core.Util.File.retry: retry count must be 1 or more"
    | i == 1    = x
    | otherwise = catch x $ \(_::SomeException) -> threadDelay 100 >> retryWithDelay (i-1) x
#endif

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-- | Perform an IO action, catching any permission errors and returning
--   a default value in their place.  All other exceptions are rethrown.
withPermissions :: IO a
                -> a  -- ^ Default value to return in case of a permission error
                -> IO a
withPermissions act onError
    = act `catchIOError` \e ->
        if isPermissionError e
            then pure onError
            else throw e