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+{- git-annex assistant tree watcher
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+{-# LANGUAGE CPP #-}
+
+module Assistant.Watcher where
+
+import Common.Annex
+import Assistant.ThreadedMonad
+import Assistant.DaemonStatus
+import Assistant.Committer
+import Utility.ThreadLock
+import qualified Annex.Queue
+import qualified Command.Add
+import qualified Git.Command
+import qualified Git.UpdateIndex
+import qualified Git.HashObject
+import qualified Git.LsFiles
+import qualified Backend
+import Annex.Content
+import Annex.CatFile
+import Git.Types
+
+import Control.Concurrent.STM
+import Data.Bits.Utils
+import qualified Data.ByteString.Lazy as L
+
+#if defined linux_HOST_OS
+import Utility.Inotify
+import System.INotify
+#endif
+
+type Handler = FilePath -> Maybe FileStatus -> DaemonStatusHandle -> Annex (Maybe Change)
+
+watchThread :: ThreadState -> DaemonStatusHandle -> ChangeChan -> IO ()
+#if defined linux_HOST_OS
+watchThread st dstatus changechan = withINotify $ \i -> do
+	runThreadState st $
+		showAction "scanning"
+	-- This does not return until the startup scan is done.
+	-- That can take some time for large trees.
+	watchDir i "." (ignored . takeFileName) hooks
+	runThreadState st $
+		modifyDaemonStatus dstatus $ \s -> s { scanComplete = True }
+	-- Notice any files that were deleted before inotify
+	-- was started.
+	runThreadState st $ do
+		inRepo $ Git.Command.run "add" [Param "--update"]
+		showAction "started"
+	waitForTermination
+	where
+		hook a = Just $ runHandler st dstatus changechan a
+		hooks = WatchHooks
+			{ addHook = hook onAdd
+			, delHook = hook onDel
+			, addSymlinkHook = hook onAddSymlink
+			, delDirHook = hook onDelDir
+			, errHook = hook onErr
+			}
+#else
+watchThread = error "so far only available on Linux"
+#endif
+
+ignored :: FilePath -> Bool
+ignored ".git" = True
+ignored ".gitignore" = True
+ignored ".gitattributes" = True
+ignored _ = False
+
+{- Runs an action handler, inside the Annex monad, and if there was a
+ - change, adds it to the ChangeChan.
+ -
+ - Exceptions are ignored, otherwise a whole watcher thread could be crashed.
+ -}
+runHandler :: ThreadState -> DaemonStatusHandle -> ChangeChan -> Handler -> FilePath -> Maybe FileStatus -> IO ()
+runHandler st dstatus changechan handler file filestatus = void $ do
+	r <- tryIO go
+	case r of
+		Left e -> print e
+		Right Nothing -> noop
+		Right (Just change) -> void $
+			runChangeChan $ writeTChan changechan change
+	where
+		go = runThreadState st $ handler file filestatus dstatus
+
+{- Adding a file is tricky; the file has to be replaced with a symlink
+ - but this is race prone, as the symlink could be changed immediately
+ - after creation. To avoid that race, git add is not used to stage the
+ - symlink.
+ -
+ - Inotify will notice the new symlink, so this Handler does not stage it
+ - or return a Change, leaving that to onAddSymlink.
+ -
+ - During initial directory scan, this will be run for any files that
+ - are already checked into git. We don't want to turn those into symlinks,
+ - so do a check. This is rather expensive, but only happens during
+ - startup.
+ -}
+onAdd :: Handler
+onAdd file _filestatus dstatus = do
+	ifM (scanComplete <$> getDaemonStatus dstatus)
+		( go
+		, ifM (null <$> inRepo (Git.LsFiles.notInRepo False [file]))
+			( noChange
+			, go
+			)
+		)
+	where
+		go = do
+			showStart "add" file
+			handle =<< Command.Add.ingest file
+			noChange
+		handle Nothing = showEndFail
+		handle (Just key) = do
+			Command.Add.link file key True
+			showEndOk
+
+{- A symlink might be an arbitrary symlink, which is just added.
+ - Or, if it is a git-annex symlink, ensure it points to the content
+ - before adding it.
+ -}
+onAddSymlink :: Handler
+onAddSymlink file filestatus dstatus = go =<< Backend.lookupFile file
+	where
+		go (Just (key, _)) = do
+			link <- calcGitLink file key
+			ifM ((==) link <$> liftIO (readSymbolicLink file))
+				( ensurestaged link =<< getDaemonStatus dstatus
+				, do
+					liftIO $ removeFile file
+					liftIO $ createSymbolicLink link file
+					addlink link
+				)
+		go Nothing = do -- other symlink
+			link <- liftIO (readSymbolicLink file)
+			ensurestaged link =<< getDaemonStatus dstatus
+
+		{- This is often called on symlinks that are already
+		 - staged correctly. A symlink may have been deleted
+		 - and being re-added, or added when the watcher was
+		 - not running. So they're normally restaged to make sure.
+		 -
+		 - As an optimisation, during the status scan, avoid
+		 - restaging everything. Only links that were created since
+		 - the last time the daemon was running are staged.
+		 - (If the daemon has never ran before, avoid staging
+		 - links too.)
+		 -}
+		ensurestaged link daemonstatus
+			| scanComplete daemonstatus = addlink link
+			| otherwise = case filestatus of
+				Just s
+					| safe (statusChangeTime s) -> noChange
+				_ -> addlink link
+			where
+				safe t = maybe True (> t) (lastRunning daemonstatus)
+
+		{- For speed, tries to reuse the existing blob for
+		 - the symlink target. -}
+		addlink link = do
+			v <- catObjectDetails $ Ref $ ':':file
+			case v of
+				Just (currlink, sha)
+					| s2w8 link == L.unpack currlink ->
+						stageSymlink file sha
+				_ -> do
+					sha <- inRepo $
+						Git.HashObject.hashObject BlobObject link
+					stageSymlink file sha
+			madeChange file "link"
+
+onDel :: Handler
+onDel file _ _dstatus = do
+	Annex.Queue.addUpdateIndex =<<
+		inRepo (Git.UpdateIndex.unstageFile file)
+	madeChange file "rm"
+
+{- A directory has been deleted, or moved, so tell git to remove anything
+ - that was inside it from its cache. Since it could reappear at any time,
+ - use --cached to only delete it from the index. 
+ -
+ - Note: This could use unstageFile, but would need to run another git
+ - command to get the recursive list of files in the directory, so rm is
+ - just as good. -}
+onDelDir :: Handler
+onDelDir dir _ _dstatus = do
+	Annex.Queue.addCommand "rm"
+		[Params "--quiet -r --cached --ignore-unmatch --"] [dir]
+	madeChange dir "rmdir"
+
+{- Called when there's an error with inotify. -}
+onErr :: Handler
+onErr msg _ _dstatus = do
+	warning msg
+	return Nothing
+
+{- Adds a symlink to the index, without ever accessing the actual symlink
+ - on disk. -}
+stageSymlink :: FilePath -> Sha -> Annex ()
+stageSymlink file sha =
+	Annex.Queue.addUpdateIndex =<<
+		inRepo (Git.UpdateIndex.stageSymlink file sha)