split transfer info and lock files

Since the lock file has to be kept open, this prevented the TransferWatcher
from noticing when it appeared, since inotify (and more importantly kqueue)
events happen when a new file is closed. Writing a separate info file fixes
that problem.

Logs/Transfer.hs

@@ -1,4 +1,4 @@
-{- git-annex transfer information files
+{- git-annex transfer information files and lock files
  -
  - Copyright 2012 Joey Hess <joey@kitenet.net>
  -
@@ -66,9 +66,9 @@ fieldTransfer direction key a = do
 	maybe a (\u -> transfer (Transfer direction (toUUID u) key) afile a)
 		=<< Fields.getField Fields.remoteUUID
 
-{- Runs a transfer action. Creates and locks the transfer information file
- - while the action is running. Will throw an error if the transfer is
- - already in progress.
+{- Runs a transfer action. Creates and locks the lock file while the
+ - action is running, and stores into in the transfer information
+ - file. Will throw an error if the transfer is already in progress.
  -}
 transfer :: Transfer -> Maybe FilePath -> Annex a -> Annex a
 transfer t file a = do
@@ -85,19 +85,18 @@ transfer t file a = do
 	bracketIO (prep tfile mode info) (cleanup tfile) a
 	where
 		prep tfile mode info = do
-			fd <- openFd tfile ReadWrite (Just mode)
+			fd <- openFd (transferLockFile tfile) ReadWrite (Just mode)
 				defaultFileFlags { trunc = True }
 			locked <- catchMaybeIO $
 				setLock fd (WriteLock, AbsoluteSeek, 0, 0)
 			when (locked == Nothing) $
 				error $ "transfer already in progress"
-			h <- fdToHandle fd
-			hPutStr h $ writeTransferInfo info
-			hFlush h
-			return h
-		cleanup tfile h = do
+			writeFile tfile $ writeTransferInfo info
+			return fd
+		cleanup tfile fd = do
 			removeFile tfile
-			hClose h
+			removeFile $ transferLockFile tfile
+			closeFd fd
 
 {- If a transfer is still running, returns its TransferInfo. -}
 checkTransfer :: Transfer -> Annex (Maybe TransferInfo)
@@ -105,22 +104,19 @@ checkTransfer t = do
 	mode <- annexFileMode
 	tfile <- fromRepo $ transferFile t
 	mfd <- liftIO $ catchMaybeIO $
-		openFd tfile ReadOnly (Just mode) defaultFileFlags
+		openFd (transferLockFile tfile) ReadOnly (Just mode) defaultFileFlags
 	case mfd of
 		Nothing -> return Nothing -- failed to open file; not running
 		Just fd -> do
 			locked <- liftIO $
 				getLock fd (WriteLock, AbsoluteSeek, 0, 0)
+			liftIO $ closeFd fd
 			case locked of
-				Nothing -> do
-					liftIO $ closeFd fd
-					return Nothing
-				Just (pid, _) -> liftIO $ do
-					h <- fdToHandle fd
-					info <- readTransferInfo pid
-						<$> hGetContentsStrict h
-					hClose h
-					return info
+				Nothing -> return Nothing
+				Just (pid, _) -> liftIO $
+					flip catchDefaultIO Nothing $
+						readTransferInfo pid 
+							<$> readFile tfile
 
 {- Gets all currently running transfers. -}
 getTransfers :: Annex [(Transfer, TransferInfo)]
@@ -141,6 +137,10 @@ transferFile (Transfer direction u key) r = gitAnnexTransferDir r
 	</> fromUUID u
 	</> keyFile key
 
+{- The transfer lock file corresponding to a given transfer info file. -}
+transferLockFile :: FilePath -> FilePath
+transferLockFile infofile = infofile ++ ".lck"
+
 {- Parses a transfer information filename to a Transfer. -}
 parseTransferFile :: FilePath -> Maybe Transfer
 parseTransferFile file =