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Git/Fsck.hs

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+{- git fsck interface
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Git.Fsck (
+	findBroken,
+	findMissing
+) where
+
+import Common
+import Git
+import Git.Command
+import Git.Sha
+import Git.CatFile
+
+import qualified Data.Set as S
+
+{- Runs fsck to find some of the broken objects in the repository.
+ - May not find all broken objects, if fsck fails on bad data in some of
+ - the broken objects it does find. If the fsck fails generally without
+ - finding any broken objects, returns Nothing.
+ -
+ - Strategy: Rather than parsing fsck's current specific output,
+ - look for anything in its output (both stdout and stderr) that appears
+ - to be a git sha. Not all such shas are of broken objects, so ask git
+ - to try to cat the object, and see if it fails.
+ -}
+findBroken :: Repo -> IO (Maybe (S.Set Sha))
+findBroken r = do
+	(output, fsckok) <- processTranscript "git" (toCommand $ fsckParams r) Nothing
+	let objs = parseFsckOutput output
+	badobjs <- findMissing objs r
+	if S.null badobjs && not fsckok
+		then return Nothing
+		else return $ Just badobjs
+
+{- Finds objects that are missing from the git repsitory, or are corrupt.
+ - Note that catting a corrupt object will cause cat-file to crash. -}
+findMissing :: [Sha] -> Repo -> IO (S.Set Sha)
+findMissing objs r = go objs [] =<< start
+  where
+	start = catFileStart' False r
+	go [] c h = do
+		catFileStop h
+		return $ S.fromList c
+	go (o:os) c h = do
+		v <- tryIO $ isNothing <$> catObjectDetails h o
+		case v of
+			Left _ -> do
+				void $ tryIO $ catFileStop h
+				go os (o:c) =<< start
+			Right True -> go os (o:c) h
+			Right False -> go os c h
+
+parseFsckOutput :: String -> [Sha]
+parseFsckOutput = catMaybes . map extractSha . concat . map words . lines
+
+fsckParams :: Repo -> [CommandParam]
+fsckParams = gitCommandLine
+	[ Param "fsck"
+	, Param "--no-dangling"
+	, Param "--no-reflogs"
+	]