96 lines
3 KiB
Haskell
96 lines
3 KiB
Haskell
{- Temporary files.
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-
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- Copyright 2010-2020 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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{-# LANGUAGE CPP #-}
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{-# OPTIONS_GHC -fno-warn-tabs #-}
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module Utility.Tmp (
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Template,
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viaTmp,
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withTmpFile,
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withTmpFileIn,
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relatedTemplate,
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) where
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import System.IO
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import System.FilePath
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import System.Directory
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import Control.Monad.IO.Class
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import System.PosixCompat.Files
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import Utility.Exception
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import Utility.FileSystemEncoding
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import Utility.FileMode
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type Template = String
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{- Runs an action like writeFile, writing to a temp file first and
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- then moving it into place. The temp file is stored in the same
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- directory as the final file to avoid cross-device renames.
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-
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- While this uses a temp file, the file will end up with the same
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- mode as it would when using writeFile, unless the writer action changes
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- it.
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-}
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viaTmp :: (MonadMask m, MonadIO m) => (FilePath -> v -> m ()) -> FilePath -> v -> m ()
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viaTmp a file content = bracketIO setup cleanup use
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where
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(dir, base) = splitFileName file
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template = relatedTemplate (base ++ ".tmp")
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setup = do
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createDirectoryIfMissing True dir
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openTempFile dir template
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cleanup (tmpfile, h) = do
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_ <- tryIO $ hClose h
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tryIO $ removeFile tmpfile
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use (tmpfile, h) = do
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-- Make mode the same as if the file were created usually,
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-- not as a temp file. (This may fail on some filesystems
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-- that don't support file modes well, so ignore
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-- exceptions.)
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_ <- liftIO $ tryIO $ setFileMode tmpfile =<< defaultFileMode
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liftIO $ hClose h
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a tmpfile content
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liftIO $ rename tmpfile file
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{- Runs an action with a tmp file located in the system's tmp directory
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- (or in "." if there is none) then removes the file. -}
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withTmpFile :: (MonadIO m, MonadMask m) => Template -> (FilePath -> Handle -> m a) -> m a
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withTmpFile template a = do
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tmpdir <- liftIO $ catchDefaultIO "." getTemporaryDirectory
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withTmpFileIn tmpdir template a
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{- Runs an action with a tmp file located in the specified directory,
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- then removes the file.
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-
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- Note that the tmp file will have a file mode that only allows the
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- current user to access it.
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-}
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withTmpFileIn :: (MonadIO m, MonadMask m) => FilePath -> Template -> (FilePath -> Handle -> m a) -> m a
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withTmpFileIn tmpdir template a = bracket create remove use
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where
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create = liftIO $ openTempFile tmpdir template
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remove (name, h) = liftIO $ do
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hClose h
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catchBoolIO (removeFile name >> return True)
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use (name, h) = a name h
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{- It's not safe to use a FilePath of an existing file as the template
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- for openTempFile, because if the FilePath is really long, the tmpfile
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- will be longer, and may exceed the maximum filename length.
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-
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- This generates a template that is never too long.
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- (Well, it allocates 20 characters for use in making a unique temp file,
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- anyway, which is enough for the current implementation and any
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- likely implementation.)
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-}
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relatedTemplate :: FilePath -> FilePath
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relatedTemplate f
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| len > 20 = truncateFilePath (len - 20) f
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| otherwise = f
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where
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len = length f
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