356 lines
9.9 KiB
Haskell
356 lines
9.9 KiB
Haskell
-- |
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-- Module : HPath.IO.Errors
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-- Copyright : © 2016 Julian Ospald
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-- License : BSD3
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--
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-- Maintainer : Julian Ospald <hasufell@posteo.de>
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-- Stability : experimental
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-- Portability : portable
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--
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-- Provides error handling.
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{-# LANGUAGE ScopedTypeVariables #-}
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module HPath.IO.Errors
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(
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-- * Types
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HPathIOException(..)
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, RecursiveFailureHint(..)
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-- * Exception identifiers
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, isSameFile
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, isDestinationInSource
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, isRecursiveFailure
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, isReadContentsFailed
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, isCreateDirFailed
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, isCopyFileFailed
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, isRecreateSymlinkFailed
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-- * Path based functions
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, throwFileDoesExist
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, throwDirDoesExist
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, throwSameFile
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, sameFile
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, throwDestinationInSource
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, doesFileExist
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, doesDirectoryExist
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, isWritable
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, canOpenDirectory
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-- * Error handling functions
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, catchErrno
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, rethrowErrnoAs
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, handleIOError
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, bracketeer
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, reactOnError
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)
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where
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import Control.Applicative
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(
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(<$>)
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)
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import Control.Exception
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import Control.Monad
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(
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forM
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, when
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)
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import Control.Monad.IfElse
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(
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whenM
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)
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import Data.ByteString
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(
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ByteString
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)
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import Data.ByteString.UTF8
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(
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toString
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)
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import Data.Typeable
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(
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Typeable
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)
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import Foreign.C.Error
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(
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getErrno
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, Errno
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)
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import GHC.IO.Exception
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(
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IOErrorType
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)
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import HPath
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import {-# SOURCE #-} HPath.IO
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(
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canonicalizePath
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)
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import System.IO.Error
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(
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alreadyExistsErrorType
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, catchIOError
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, ioeGetErrorType
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, mkIOError
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)
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import qualified System.Posix.Directory.ByteString as PFD
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import System.Posix.Files.ByteString
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(
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fileAccess
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, getFileStatus
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)
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import qualified System.Posix.Files.ByteString as PF
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-- |Additional generic IO exceptions that the posix functions
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-- do not provide.
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data HPathIOException = SameFile ByteString ByteString
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| DestinationInSource ByteString ByteString
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| RecursiveFailure [(RecursiveFailureHint, IOException)]
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deriving (Eq, Show, Typeable)
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-- |A type for giving failure hints on recursive failure, which allows
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-- to programmatically make choices without examining
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-- the weakly typed I/O error attributes (like `ioeGetFileName`).
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--
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-- The first argument to the data constructor is always the
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-- source and the second the destination.
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data RecursiveFailureHint = ReadContentsFailed (Path Abs) (Path Abs)
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| CreateDirFailed (Path Abs) (Path Abs)
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| CopyFileFailed (Path Abs) (Path Abs)
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| RecreateSymlinkFailed (Path Abs) (Path Abs)
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deriving (Eq, Show)
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instance Exception HPathIOException
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toConstr :: HPathIOException -> String
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toConstr SameFile {} = "SameFile"
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toConstr DestinationInSource {} = "DestinationInSource"
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toConstr RecursiveFailure {} = "RecursiveFailure"
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-----------------------------
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--[ Exception identifiers ]--
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-----------------------------
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isSameFile, isDestinationInSource, isRecursiveFailure :: HPathIOException -> Bool
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isSameFile ex = toConstr (ex :: HPathIOException) == toConstr SameFile{}
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isDestinationInSource ex = toConstr (ex :: HPathIOException) == toConstr DestinationInSource{}
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isRecursiveFailure ex = toConstr (ex :: HPathIOException) == toConstr RecursiveFailure{}
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isReadContentsFailed, isCreateDirFailed, isCopyFileFailed, isRecreateSymlinkFailed ::RecursiveFailureHint -> Bool
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isReadContentsFailed ReadContentsFailed{} = True
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isReadContentsFailed _ = False
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isCreateDirFailed CreateDirFailed{} = True
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isCreateDirFailed _ = False
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isCopyFileFailed CopyFileFailed{} = True
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isCopyFileFailed _ = False
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isRecreateSymlinkFailed RecreateSymlinkFailed{} = True
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isRecreateSymlinkFailed _ = False
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----------------------------
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--[ Path based functions ]--
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----------------------------
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-- |Throws `AlreadyExists` `IOError` if file exists.
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throwFileDoesExist :: Path Abs -> IO ()
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throwFileDoesExist fp =
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whenM (doesFileExist fp)
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(ioError . mkIOError
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alreadyExistsErrorType
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"File already exists"
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Nothing
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$ (Just (toString $ fromAbs fp))
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)
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-- |Throws `AlreadyExists` `IOError` if directory exists.
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throwDirDoesExist :: Path Abs -> IO ()
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throwDirDoesExist fp =
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whenM (doesDirectoryExist fp)
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(ioError . mkIOError
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alreadyExistsErrorType
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"Directory already exists"
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Nothing
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$ (Just (toString $ fromAbs fp))
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)
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-- |Uses `isSameFile` and throws `SameFile` if it returns True.
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throwSameFile :: Path Abs
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-> Path Abs
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-> IO ()
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throwSameFile fp1 fp2 =
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whenM (sameFile fp1 fp2)
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(throwIO $ SameFile (fromAbs fp1) (fromAbs fp2))
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-- |Check if the files are the same by examining device and file id.
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-- This follows symbolic links.
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sameFile :: Path Abs -> Path Abs -> IO Bool
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sameFile fp1 fp2 =
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withAbsPath fp1 $ \fp1' -> withAbsPath fp2 $ \fp2' ->
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handleIOError (\_ -> return False) $ do
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fs1 <- getFileStatus fp1'
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fs2 <- getFileStatus fp2'
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if ((PF.deviceID fs1, PF.fileID fs1) ==
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(PF.deviceID fs2, PF.fileID fs2))
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then return True
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else return False
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-- TODO: make this more robust when destination does not exist
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-- |Checks whether the destination directory is contained
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-- within the source directory by comparing the device+file ID of the
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-- source directory with all device+file IDs of the parent directories
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-- of the destination.
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throwDestinationInSource :: Path Abs -- ^ source dir
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-> Path Abs -- ^ full destination, @dirname dest@
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-- must exist
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-> IO ()
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throwDestinationInSource source dest = do
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dest' <- (\x -> maybe x (\y -> x </> y) $ basename dest)
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<$> (canonicalizePath $ dirname dest)
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dids <- forM (getAllParents dest') $ \p -> do
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fs <- PF.getSymbolicLinkStatus (fromAbs p)
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return (PF.deviceID fs, PF.fileID fs)
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sid <- fmap (\x -> (PF.deviceID x, PF.fileID x))
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$ PF.getFileStatus (fromAbs source)
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when (elem sid dids)
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(throwIO $ DestinationInSource (fromAbs dest)
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(fromAbs source))
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-- |Checks if the given file exists and is not a directory.
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-- Does not follow symlinks.
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doesFileExist :: Path Abs -> IO Bool
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doesFileExist fp =
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handleIOError (\_ -> return False) $ do
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fs <- PF.getSymbolicLinkStatus (fromAbs fp)
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return $ not . PF.isDirectory $ fs
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-- |Checks if the given file exists and is a directory.
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-- Does not follow symlinks.
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doesDirectoryExist :: Path Abs -> IO Bool
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doesDirectoryExist fp =
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handleIOError (\_ -> return False) $ do
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fs <- PF.getSymbolicLinkStatus (fromAbs fp)
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return $ PF.isDirectory fs
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-- |Checks whether a file or folder is writable.
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isWritable :: Path Abs -> IO Bool
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isWritable fp =
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handleIOError (\_ -> return False) $
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fileAccess (fromAbs fp) False True False
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-- |Checks whether the directory at the given path exists and can be
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-- opened. This invokes `openDirStream` which follows symlinks.
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canOpenDirectory :: Path Abs -> IO Bool
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canOpenDirectory fp =
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handleIOError (\_ -> return False) $ do
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bracket (PFD.openDirStream . fromAbs $ fp)
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PFD.closeDirStream
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(\_ -> return ())
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return True
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--------------------------------
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--[ Error handling functions ]--
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--------------------------------
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-- |Carries out an action, then checks if there is an IOException and
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-- a specific errno. If so, then it carries out another action, otherwise
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-- it rethrows the error.
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catchErrno :: [Errno] -- ^ errno to catch
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-> IO a -- ^ action to try, which can raise an IOException
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-> IO a -- ^ action to carry out in case of an IOException and
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-- if errno matches
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-> IO a
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catchErrno en a1 a2 =
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catchIOError a1 $ \e -> do
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errno <- getErrno
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if errno `elem` en
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then a2
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else ioError e
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-- |Execute the given action and retrow IO exceptions as a new Exception
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-- that have the given errno. If errno does not match the exception is rethrown
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-- as is.
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rethrowErrnoAs :: Exception e
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=> [Errno] -- ^ errno to catch
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-> e -- ^ rethrow as if errno matches
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-> IO a -- ^ action to try
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-> IO a
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rethrowErrnoAs en fmex action = catchErrno en action (throwIO fmex)
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-- |Like `catchIOError`, with arguments swapped.
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handleIOError :: (IOError -> IO a) -> IO a -> IO a
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handleIOError = flip catchIOError
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-- |Like `bracket`, but allows to have different clean-up
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-- actions depending on whether the in-between computation
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-- has raised an exception or not.
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bracketeer :: IO a -- ^ computation to run first
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-> (a -> IO b) -- ^ computation to run last, when
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-- no exception was raised
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-> (a -> IO b) -- ^ computation to run last,
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-- when an exception was raised
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-> (a -> IO c) -- ^ computation to run in-between
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-> IO c
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bracketeer before after afterEx thing =
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mask $ \restore -> do
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a <- before
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r <- restore (thing a) `onException` afterEx a
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_ <- after a
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return r
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reactOnError :: IO a
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-> [(IOErrorType, IO a)] -- ^ reaction on IO errors
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-> [(HPathIOException, IO a)] -- ^ reaction on HPathIOException
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-> IO a
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reactOnError a ios fmios =
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a `catches` [iohandler, fmiohandler]
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where
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iohandler = Handler $
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\(ex :: IOException) ->
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foldr (\(t, a') y -> if ioeGetErrorType ex == t
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then a'
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else y)
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(throwIO ex)
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ios
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fmiohandler = Handler $
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\(ex :: HPathIOException) ->
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foldr (\(t, a') y -> if toConstr ex == toConstr t
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then a'
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else y)
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(throwIO ex)
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fmios
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