improve git cat-file code

Now it reads the size specified, rather than using the sentinal hack to
determine EOF.

It still depends on error messages to handle files that are not present.

Branch.hs

@@ -17,7 +17,7 @@ module Branch (
 	name	
 ) where
 
-import Control.Monad (unless, liftM)
+import Control.Monad (when, unless, liftM)
 import Control.Monad.State (liftIO)
 import System.FilePath
 import System.Directory
@@ -26,6 +26,9 @@ import System.Cmd.Utils
 import Data.Maybe
 import Data.List
 import System.IO
+import System.IO.Unsafe
+import Foreign
+import Data.Char
 
 import Types.BranchState
 import qualified GitRepo as Git
@@ -239,32 +242,39 @@ catFile file = do
 			g <- Annex.gitRepo
 			let cmd = Git.gitCommandLine g
 				[Param "cat-file", Param "--batch"]
-			let gitcmd = join " " $ "git" : toCommand cmd
+			let gitcmd = join " " ("git" : toCommand cmd)
 			(_, from, to) <- liftIO $ hPipeBoth "sh"
-				-- want stderr on stdin for sentinal, and
+				-- want stderr on stdin to handle error messages
-				-- to ignore other error messages
+				["-c", "LANG=C exec " ++ gitcmd ++ " 2>&1"]
-				["-c", gitcmd ++ " 2>&1"]
 			setState state { catFileHandles = Just (from, to) }
 			ask (from, to)
-		ask (from, to) = do
+		ask (from, to) = liftIO $ do
-			_ <- liftIO $ do
+			let want = fullname ++ ":" ++ file
-				hPutStr to $
+			hPutStrLn to want
-					fullname ++ ":" ++ file ++ "\n" ++
+			hFlush to
-					sentinal ++ "\n"
+			header <- hGetLine from
-				hFlush to
+			if header == want ++ " missing"
-			return . unlines =<< readContent from []
+				then return ""
-		readContent from ls = do
+				else do
-			l <- liftIO $ hGetLine from
+					let [_sha, _type, size] = words header
-			if l == sentinal_line
+					let bytes = read size
-				-- first line is blob info,
+					fp <- mallocForeignPtrBytes (fromIntegral bytes)
-				-- or maybe an error message
+					len <- withForeignPtr fp $ \buf -> hGetBuf from buf (fromIntegral bytes)
-				then return $ drop 1 $ reverse ls
+					when (len /= bytes) $
-				else readContent from (l:ls)
+						error "short read from git cat-file"
-		-- To find the end of a catted file, ask for a sentinal
+					content <- lazySlurp fp 0 len
-		-- value that is always missing, and look for the error
+					c <- hGetChar from
-		-- message. Utterly nasty, probably will break one day.
+					when (c /= '\n') $
-		sentinal = ":"
+						error "missing newline from git cat-file"
-		sentinal_line = sentinal ++ " missing"
+					return content
+
+lazySlurp :: ForeignPtr Word8 -> Int -> Int -> IO String
+lazySlurp fp ix len
+	| ix == len = return []
+	| otherwise = do
+		c <- withForeignPtr fp $ \p -> peekElemOff p ix
+		cs <- unsafeInterleaveIO (lazySlurp fp (ix+1) len)
+		return $ chr (fromIntegral c) : cs
 
 {- Lists all files on the branch. There may be duplicates in the list. -}
 files :: Annex [FilePath]