{- git-annex file content managing - - Copyright 2010-2021 Joey Hess - - Licensed under the GNU AGPL version 3 or higher. -} {-# LANGUAGE CPP #-} module Annex.Content ( inAnnex, inAnnex', inAnnexSafe, inAnnexCheck, objectFileExists, lockContentShared, lockContentForRemoval, ContentRemovalLock, RetrievalSecurityPolicy(..), getViaTmp, getViaTmpFromDisk, checkDiskSpaceToGet, checkSecureHashes, prepTmp, withTmp, checkDiskSpace, needMoreDiskSpace, moveAnnex, populatePointerFile, linkToAnnex, linkFromAnnex, linkFromAnnex', LinkAnnexResult(..), unlinkAnnex, checkedCopyFile, linkOrCopy, linkOrCopy', sendAnnex, prepSendAnnex, prepSendAnnex', removeAnnex, moveBad, KeyLocation(..), listKeys, saveState, downloadUrl, preseedTmp, dirKeys, withObjectLoc, staleKeysPrune, pruneTmpWorkDirBefore, isUnmodified, isUnmodifiedCheap, verifyKeyContentPostRetrieval, verifyKeyContent, VerifyConfig, VerifyConfigA(..), Verification(..), unVerified, withTmpWorkDir, ) where import System.IO.Unsafe (unsafeInterleaveIO) import qualified Data.Set as S import Annex.Common import Annex.Content.Presence import Annex.Content.LowLevel import Annex.Content.PointerFile import Annex.Verify import qualified Git import qualified Annex import qualified Annex.Queue import qualified Annex.Branch import qualified Annex.Url as Url import qualified Backend import qualified Database.Keys import Git.FilePath import Annex.Perms import Annex.Link import Annex.LockPool import Annex.UUID import Annex.InodeSentinal import Annex.ReplaceFile import Annex.AdjustedBranch (adjustedBranchRefresh) import Messages.Progress import Types.Remote (RetrievalSecurityPolicy(..), VerifyConfigA(..)) import Types.NumCopies import Types.Key import Types.Transfer import Logs.Transfer import Logs.Location import Utility.InodeCache import Utility.CopyFile import Utility.Metered import qualified Utility.RawFilePath as R import qualified System.FilePath.ByteString as P {- Prevents the content from being removed while the action is running. - Uses a shared lock. - - If locking fails, or the content is not present, throws an exception - rather than running the action. -} lockContentShared :: Key -> (VerifiedCopy -> Annex a) -> Annex a lockContentShared key a = lockContentUsing lock key notpresent $ ifM (inAnnex key) ( do u <- getUUID withVerifiedCopy LockedCopy u (return True) a , notpresent ) where notpresent = giveup $ "failed to lock content: not present" #ifndef mingw32_HOST_OS lock contentfile Nothing = tryLockShared Nothing contentfile lock _ (Just lockfile) = posixLocker tryLockShared lockfile #else lock = winLocker lockShared #endif {- Exclusively locks content, while performing an action that - might remove it. - - If locking fails, throws an exception rather than running the action. - - But, if locking fails because the the content is not present, runs the - fallback action instead. -} lockContentForRemoval :: Key -> Annex a -> (ContentRemovalLock -> Annex a) -> Annex a lockContentForRemoval key fallback a = lockContentUsing lock key fallback $ a (ContentRemovalLock key) where #ifndef mingw32_HOST_OS {- Since content files are stored with the write bit disabled, have - to fiddle with permissions to open for an exclusive lock. -} lock contentfile Nothing = bracket_ (thawContent contentfile) (freezeContent contentfile) (tryLockExclusive Nothing contentfile) lock _ (Just lockfile) = posixLocker tryLockExclusive lockfile #else lock = winLocker lockExclusive #endif {- Passed the object content file, and maybe a separate lock file to use, - when the content file itself should not be locked. -} type ContentLocker = RawFilePath -> Maybe LockFile -> Annex (Maybe LockHandle) #ifndef mingw32_HOST_OS posixLocker :: (Maybe FileMode -> LockFile -> Annex (Maybe LockHandle)) -> LockFile -> Annex (Maybe LockHandle) posixLocker takelock lockfile = do mode <- annexFileMode modifyContent lockfile $ takelock (Just mode) lockfile #else winLocker :: (LockFile -> IO (Maybe LockHandle)) -> ContentLocker winLocker takelock _ (Just lockfile) = do modifyContent lockfile $ void $ liftIO $ tryIO $ writeFile (fromRawFilePath lockfile) "" liftIO $ takelock lockfile -- never reached; windows always uses a separate lock file winLocker _ _ Nothing = return Nothing #endif {- The fallback action is run if the ContentLocker throws an IO exception - and the content is not present. It's not guaranteed to always run when - the content is not present, because the content file is not always - the file that is locked eg on Windows a different file is locked. -} lockContentUsing :: ContentLocker -> Key -> Annex a -> Annex a -> Annex a lockContentUsing locker key fallback a = do contentfile <- calcRepo (gitAnnexLocation key) lockfile <- contentLockFile key bracket (lock contentfile lockfile) (either (const noop) (unlock lockfile)) go where alreadylocked = giveup "content is locked" failedtolock e = giveup $ "failed to lock content: " ++ show e lock contentfile lockfile = tryIO $ maybe alreadylocked return =<< locker contentfile lockfile go (Right _) = a go (Left e) = ifM (inAnnex key) ( failedtolock e , fallback ) #ifndef mingw32_HOST_OS unlock mlockfile lck = do maybe noop cleanuplockfile mlockfile liftIO $ dropLock lck #else unlock mlockfile lck = do -- Can't delete a locked file on Windows liftIO $ dropLock lck maybe noop cleanuplockfile mlockfile #endif cleanuplockfile lockfile = modifyContent lockfile $ void $ liftIO $ tryIO $ removeWhenExistsWith R.removeLink lockfile {- Runs an action, passing it the temp file to get, - and if the action succeeds, verifies the file matches - the key and moves the file into the annex as a key's content. -} getViaTmp :: RetrievalSecurityPolicy -> VerifyConfig -> Key -> AssociatedFile -> (RawFilePath -> Annex (Bool, Verification)) -> Annex Bool getViaTmp rsp v key af action = checkDiskSpaceToGet key False $ getViaTmpFromDisk rsp v key af action {- Like getViaTmp, but does not check that there is enough disk space - for the incoming key. For use when the key content is already on disk - and not being copied into place. -} getViaTmpFromDisk :: RetrievalSecurityPolicy -> VerifyConfig -> Key -> AssociatedFile -> (RawFilePath -> Annex (Bool, Verification)) -> Annex Bool getViaTmpFromDisk rsp v key af action = checkallowed $ do tmpfile <- prepTmp key resuming <- liftIO $ R.doesPathExist tmpfile (ok, verification) <- action tmpfile -- When the temp file already had content, we don't know if -- that content is good or not, so only trust if it the action -- Verified it in passing. Otherwise, force verification even -- if the VerifyConfig normally disables it. let verification' = if resuming then case verification of Verified -> Verified _ -> MustVerify else verification if ok then ifM (verifyKeyContentPostRetrieval rsp v verification' key tmpfile) ( pruneTmpWorkDirBefore tmpfile (moveAnnex key af) , do warning "verification of content failed" -- The bad content is not retained, because -- a retry should not try to resume from it -- since it's apparently corrupted. -- Also, the bad content could be any data, -- including perhaps the content of another -- file than the one that was requested, -- and so it's best not to keep it on disk. pruneTmpWorkDirBefore tmpfile (liftIO . removeWhenExistsWith R.removeLink) return False ) -- On transfer failure, the tmp file is left behind, in case -- caller wants to resume its transfer else return False where -- Avoid running the action to get the content when the -- RetrievalSecurityPolicy would cause verification to always fail. checkallowed a = case rsp of RetrievalAllKeysSecure -> a RetrievalVerifiableKeysSecure -> ifM (isVerifiable key) ( a , ifM (annexAllowUnverifiedDownloads <$> Annex.getGitConfig) ( a , warnUnverifiableInsecure key >> return False ) ) {- Checks if there is enough free disk space to download a key - to its temp file. - - When the temp file already exists, count the space it is using as - free, since the download will overwrite it or resume. - - Wen there's enough free space, runs the download action. -} checkDiskSpaceToGet :: Key -> a -> Annex a -> Annex a checkDiskSpaceToGet key unabletoget getkey = do tmp <- fromRepo (gitAnnexTmpObjectLocation key) e <- liftIO $ doesFileExist (fromRawFilePath tmp) alreadythere <- liftIO $ if e then getFileSize tmp else return 0 ifM (checkDiskSpace Nothing key alreadythere True) ( do -- The tmp file may not have been left writable when e $ thawContent tmp getkey , return unabletoget ) prepTmp :: Key -> Annex RawFilePath prepTmp key = do tmp <- fromRepo $ gitAnnexTmpObjectLocation key createAnnexDirectory (parentDir tmp) return tmp {- Prepares a temp file for a key, runs an action on it, and cleans up - the temp file. If the action throws an exception, the temp file is - left behind, which allows for resuming. -} withTmp :: Key -> (RawFilePath -> Annex a) -> Annex a withTmp key action = do tmp <- prepTmp key res <- action tmp pruneTmpWorkDirBefore tmp (liftIO . removeWhenExistsWith R.removeLink) return res {- Moves a key's content into .git/annex/objects/ - - When a key has associated pointer files, the object is hard - linked (or copied) to the files, and the object file is left thawed. - - What if the key there already has content? This could happen for - various reasons; perhaps the same content is being annexed again. - Perhaps there has been a hash collision generating the keys. - - The current strategy is to assume that in this case it's safe to delete - one of the two copies of the content; and the one already in the annex - is left there, assuming it's the original, canonical copy. - - I considered being more paranoid, and checking that both files had - the same content. Decided against it because A) users explicitly choose - a backend based on its hashing properties and so if they're dealing - with colliding files it's their own fault and B) adding such a check - would not catch all cases of colliding keys. For example, perhaps - a remote has a key; if it's then added again with different content then - the overall system now has two different peices of content for that - key, and one of them will probably get deleted later. So, adding the - check here would only raise expectations that git-annex cannot truely - meet. - - May return false, when a particular variety of key is not being - accepted into the repository. Will display a warning message in this - case. May also throw exceptions in some cases. -} moveAnnex :: Key -> AssociatedFile -> RawFilePath -> Annex Bool moveAnnex key af src = ifM (checkSecureHashes' key) ( do withObjectLoc key storeobject return True , return False ) where storeobject dest = ifM (liftIO $ R.doesPathExist dest) ( alreadyhave , adjustedBranchRefresh af $ modifyContent dest $ do freezeContent src liftIO $ moveFile (fromRawFilePath src) (fromRawFilePath dest) g <- Annex.gitRepo fs <- map (`fromTopFilePath` g) <$> Database.Keys.getAssociatedFiles key unless (null fs) $ do destic <- withTSDelta $ liftIO . genInodeCache dest ics <- mapM (populatePointerFile (Restage True) key dest) fs Database.Keys.addInodeCaches key (catMaybes (destic:ics)) ) alreadyhave = liftIO $ R.removeLink src checkSecureHashes :: Key -> Annex (Maybe String) checkSecureHashes key = ifM (Backend.isCryptographicallySecure key) ( return Nothing , ifM (annexSecureHashesOnly <$> Annex.getGitConfig) ( return $ Just $ "annex.securehashesonly blocked adding " ++ decodeBS (formatKeyVariety (fromKey keyVariety key)) ++ " key" , return Nothing ) ) checkSecureHashes' :: Key -> Annex Bool checkSecureHashes' key = checkSecureHashes key >>= \case Nothing -> return True Just msg -> do warning $ msg ++ "to annex objects" return False data LinkAnnexResult = LinkAnnexOk | LinkAnnexFailed | LinkAnnexNoop deriving (Eq) {- Populates the annex object file by hard linking or copying a source - file to it. -} linkToAnnex :: Key -> RawFilePath -> Maybe InodeCache -> Annex LinkAnnexResult linkToAnnex key src srcic = ifM (checkSecureHashes' key) ( do dest <- calcRepo (gitAnnexLocation key) modifyContent dest $ linkAnnex To key src srcic dest Nothing , return LinkAnnexFailed ) {- Makes a destination file be a link or copy from the annex object. - - linkAnnex stats the file after copying it to add to the inode - cache. But dest may be a file in the working tree, which could - get modified immediately after being populated. To avoid such a - race, call linkAnnex on a temporary file and move it into place - afterwards. Note that a consequence of this is that, if the file - already exists, it will be overwritten. -} linkFromAnnex :: Key -> RawFilePath -> Maybe FileMode -> Annex LinkAnnexResult linkFromAnnex key dest destmode = replaceFile' (const noop) (fromRawFilePath dest) (== LinkAnnexOk) $ \tmp -> linkFromAnnex' key (toRawFilePath tmp) destmode {- This is only safe to use when dest is not a worktree file. -} linkFromAnnex' :: Key -> RawFilePath -> Maybe FileMode -> Annex LinkAnnexResult linkFromAnnex' key dest destmode = do src <- calcRepo (gitAnnexLocation key) srcic <- withTSDelta (liftIO . genInodeCache src) linkAnnex From key src srcic dest destmode data FromTo = From | To {- Hard links or copies from or to the annex object location. - Updates inode cache. - - Freezes or thaws the destination appropriately. - - When a hard link is made, the annex object necessarily has to be thawed - too. So, adding an object to the annex with a hard link can prevent - losing the content if the source file is deleted, but does not - guard against modifications. - - Nothing is done if the destination file already exists. -} linkAnnex :: FromTo -> Key -> RawFilePath -> Maybe InodeCache -> RawFilePath -> Maybe FileMode -> Annex LinkAnnexResult linkAnnex _ _ _ Nothing _ _ = return LinkAnnexFailed linkAnnex fromto key src (Just srcic) dest destmode = withTSDelta (liftIO . genInodeCache dest) >>= \case Just destic -> do cs <- Database.Keys.getInodeCaches key if null cs then Database.Keys.addInodeCaches key [srcic, destic] else Database.Keys.addInodeCaches key [srcic] return LinkAnnexNoop Nothing -> linkOrCopy key src dest destmode >>= \case Nothing -> failed Just r -> do case fromto of From -> thawContent dest To -> case r of Copied -> freezeContent dest Linked -> noop checksrcunchanged where failed = do Database.Keys.addInodeCaches key [srcic] return LinkAnnexFailed checksrcunchanged = withTSDelta (liftIO . genInodeCache src) >>= \case Just srcic' | compareStrong srcic srcic' -> do destic <- withTSDelta (liftIO . genInodeCache dest) Database.Keys.addInodeCaches key $ catMaybes [destic, Just srcic] return LinkAnnexOk _ -> do liftIO $ removeWhenExistsWith R.removeLink dest failed {- Removes the annex object file for a key. Lowlevel. -} unlinkAnnex :: Key -> Annex () unlinkAnnex key = do obj <- calcRepo (gitAnnexLocation key) modifyContent obj $ do secureErase obj liftIO $ removeWhenExistsWith R.removeLink obj {- Runs an action to transfer an object's content. - - In some cases, it's possible for the file to change as it's being sent. - If this happens, runs the rollback action and throws an exception. - The rollback action should remove the data that was transferred. -} sendAnnex :: Key -> Annex () -> (FilePath -> Annex a) -> Annex a sendAnnex key rollback sendobject = go =<< prepSendAnnex' key where go (Just (f, check)) = do r <- sendobject f check >>= \case Nothing -> return r Just err -> do rollback giveup err go Nothing = giveup "content not available to send" {- Returns a file that contains an object's content, - and a check to run after the transfer is complete. - - When a file is unlocked, it's possble for its content to - change as it's being sent. The check detects this case - and returns False. - - Note that the returned check action is, in some cases, run in the - Annex monad of the remote that is receiving the object, rather than - the sender. So it cannot rely on Annex state. -} prepSendAnnex :: Key -> Annex (Maybe (FilePath, Annex Bool)) prepSendAnnex key = withObjectLoc key $ \f -> do let retval c = return $ Just (fromRawFilePath f, sameInodeCache f c) cache <- Database.Keys.getInodeCaches key if null cache -- Since no inode cache is in the database, this -- object is not currently unlocked. But that could -- change while the transfer is in progress, so -- generate an inode cache for the starting -- content. then maybe (return Nothing) (retval . (:[])) =<< withTSDelta (liftIO . genInodeCache f) -- Verify that the object is not modified. Usually this -- only has to check the inode cache, but if the cache -- is somehow stale, it will fall back to verifying its -- content. else withTSDelta (liftIO . genInodeCache f) >>= \case Just fc -> ifM (isUnmodified' key f fc cache) ( retval (fc:cache) , return Nothing ) Nothing -> return Nothing prepSendAnnex' :: Key -> Annex (Maybe (FilePath, Annex (Maybe String))) prepSendAnnex' key = prepSendAnnex key >>= \case Just (f, checksuccess) -> let checksuccess' = ifM checksuccess ( return Nothing , return (Just "content changed while it was being sent") ) in return (Just (f, checksuccess')) Nothing -> return Nothing cleanObjectLoc :: Key -> Annex () -> Annex () cleanObjectLoc key cleaner = do file <- calcRepo (gitAnnexLocation key) void $ tryIO $ thawContentDir file cleaner liftIO $ removeparents file (3 :: Int) where removeparents _ 0 = noop removeparents file n = do let dir = parentDir file maybe noop (const $ removeparents dir (n-1)) <=< catchMaybeIO $ removeDirectory (fromRawFilePath dir) {- Removes a key's file from .git/annex/objects/ -} removeAnnex :: ContentRemovalLock -> Annex () removeAnnex (ContentRemovalLock key) = withObjectLoc key $ \file -> cleanObjectLoc key $ do secureErase file liftIO $ removeWhenExistsWith R.removeLink file g <- Annex.gitRepo mapM_ (\f -> void $ tryIO $ resetpointer $ fromTopFilePath f g) =<< Database.Keys.getAssociatedFiles key Database.Keys.removeInodeCaches key where -- Check associated pointer file for modifications, and reset if -- it's unmodified. resetpointer file = ifM (isUnmodified key file) ( adjustedBranchRefresh (AssociatedFile (Just file)) $ depopulatePointerFile key file -- Modified file, so leave it alone. -- If it was a hard link to the annex object, -- that object might have been frozen as part of the -- removal process, so thaw it. , void $ tryIO $ thawContent file ) {- Moves a key out of .git/annex/objects/ into .git/annex/bad, and - returns the file it was moved to. -} moveBad :: Key -> Annex FilePath moveBad key = do src <- calcRepo (gitAnnexLocation key) bad <- fromRepo gitAnnexBadDir let dest = bad P. P.takeFileName src let dest' = fromRawFilePath dest createAnnexDirectory (parentDir dest) cleanObjectLoc key $ liftIO $ moveFile (fromRawFilePath src) dest' logStatus key InfoMissing return dest' data KeyLocation = InAnnex | InAnywhere {- InAnnex only lists keys with content in .git/annex/objects. - InAnywhere lists all keys that have directories in - .git/annex/objects, whether or not the content is present. -} listKeys :: KeyLocation -> Annex [Key] listKeys keyloc = do dir <- fromRepo gitAnnexObjectDir {- In order to run Annex monad actions within unsafeInterleaveIO, - the current state is taken and reused. No changes made to this - state will be preserved. -} s <- Annex.getState id depth <- gitAnnexLocationDepth <$> Annex.getGitConfig liftIO $ walk s depth (fromRawFilePath dir) where walk s depth dir = do contents <- catchDefaultIO [] (dirContents dir) if depth < 2 then do contents' <- filterM (present s) contents let keys = mapMaybe (fileKey . P.takeFileName . toRawFilePath) contents' continue keys [] else do let deeper = walk s (depth - 1) continue [] (map deeper contents) continue keys [] = return keys continue keys (a:as) = do {- Force lazy traversal with unsafeInterleaveIO. -} morekeys <- unsafeInterleaveIO a continue (morekeys++keys) as inanywhere = case keyloc of InAnywhere -> True _ -> False present _ _ | inanywhere = pure True present _ d = presentInAnnex d presentInAnnex = doesFileExist . contentfile contentfile d = d takeFileName d {- Things to do to record changes to content when shutting down. - - It's acceptable to avoid committing changes to the branch, - especially if performing a short-lived action. -} saveState :: Bool -> Annex () saveState nocommit = doSideAction $ do Annex.Queue.flush Database.Keys.closeDb unless nocommit $ whenM (annexAlwaysCommit <$> Annex.getGitConfig) $ Annex.Branch.commit =<< Annex.Branch.commitMessage {- Downloads content from any of a list of urls, displaying a progress - meter. - - Only displays error message if all the urls fail to download. - When listfailedurls is set, lists each url and why it failed. - Otherwise, only displays one error message, from one of the urls - that failed. -} downloadUrl :: Bool -> Key -> MeterUpdate -> Maybe IncrementalVerifier -> [Url.URLString] -> FilePath -> Url.UrlOptions -> Annex Bool downloadUrl listfailedurls k p iv urls file uo = -- Poll the file to handle configurations where an external -- download command is used. meteredFile file (Just p) k (go urls []) where go (u:us) errs = Url.download' p iv u file uo >>= \case Right () -> return True Left err -> do -- If the incremental verifier was fed anything -- while the download that failed ran, it's unable -- to be used for the other urls. case iv of Just iv' -> liftIO $ positionIncremental iv' >>= \case Just n | n > 0 -> unableIncremental iv' _ -> noop Nothing -> noop go us ((u, err) : errs) go [] [] = return False go [] errs@((_, err):_) = do if listfailedurls then warning $ unlines $ flip map errs $ \(u, err') -> u ++ " " ++ err' else warning err return False {- Copies a key's content, when present, to a temp file. - This is used to speed up some rsyncs. -} preseedTmp :: Key -> FilePath -> Annex Bool preseedTmp key file = go =<< inAnnex key where go False = return False go True = do ok <- copy when ok $ thawContent (toRawFilePath file) return ok copy = ifM (liftIO $ doesFileExist file) ( return True , do s <- fromRawFilePath <$> (calcRepo $ gitAnnexLocation key) liftIO $ ifM (doesFileExist s) ( copyFileExternal CopyTimeStamps s file , return False ) ) {- Finds files directly inside a directory like gitAnnexBadDir - (not in subdirectories) and returns the corresponding keys. -} dirKeys :: (Git.Repo -> RawFilePath) -> Annex [Key] dirKeys dirspec = do dir <- fromRawFilePath <$> fromRepo dirspec ifM (liftIO $ doesDirectoryExist dir) ( do contents <- liftIO $ getDirectoryContents dir files <- liftIO $ filterM doesFileExist $ map (dir ) contents return $ mapMaybe (fileKey . P.takeFileName . toRawFilePath) files , return [] ) {- Looks in the specified directory for bad/tmp keys, and returns a list - of those that might still have value, or might be stale and removable. - - Also, stale keys that can be proven to have no value - (ie, their content is already present) are deleted. -} staleKeysPrune :: (Git.Repo -> RawFilePath) -> Bool -> Annex [Key] staleKeysPrune dirspec nottransferred = do contents <- dirKeys dirspec dups <- filterM inAnnex contents let stale = contents `exclude` dups dir <- fromRepo dirspec forM_ dups $ \k -> pruneTmpWorkDirBefore (dir P. keyFile k) (liftIO . R.removeLink) if nottransferred then do inprogress <- S.fromList . map (transferKey . fst) <$> getTransfers return $ filter (`S.notMember` inprogress) stale else return stale {- Prune the work dir associated with the specified content file, - before performing an action that deletes the file, or moves it away. - - This preserves the invariant that the workdir never exists without - the content file. -} pruneTmpWorkDirBefore :: RawFilePath -> (RawFilePath -> Annex a) -> Annex a pruneTmpWorkDirBefore f action = do let workdir = fromRawFilePath $ gitAnnexTmpWorkDir f liftIO $ whenM (doesDirectoryExist workdir) $ removeDirectoryRecursive workdir action f {- Runs an action, passing it a temporary work directory where - it can write files while receiving the content of a key. - - Preserves the invariant that the workdir never exists without the - content file, by creating an empty content file first. - - On exception, or when the action returns Nothing, - the temporary work directory is retained (unless - empty), so anything in it can be used on resume. -} withTmpWorkDir :: Key -> (RawFilePath -> Annex (Maybe a)) -> Annex (Maybe a) withTmpWorkDir key action = do -- Create the object file if it does not exist. This way, -- staleKeysPrune only has to look for object files, and can -- clean up gitAnnexTmpWorkDir for those it finds. obj <- prepTmp key let obj' = fromRawFilePath obj unlessM (liftIO $ doesFileExist obj') $ do liftIO $ writeFile obj' "" setAnnexFilePerm obj let tmpdir = gitAnnexTmpWorkDir obj createAnnexDirectory tmpdir res <- action tmpdir case res of Just _ -> liftIO $ removeDirectoryRecursive (fromRawFilePath tmpdir) Nothing -> liftIO $ void $ tryIO $ removeDirectory (fromRawFilePath tmpdir) return res {- Finds items in the first, smaller list, that are not - present in the second, larger list. - - Constructing a single set, of the list that tends to be - smaller, appears more efficient in both memory and CPU - than constructing and taking the S.difference of two sets. -} exclude :: Ord a => [a] -> [a] -> [a] exclude [] _ = [] -- optimisation exclude smaller larger = S.toList $ remove larger $ S.fromList smaller where remove a b = foldl (flip S.delete) b a