1 files changed, 282 insertions, 0 deletions
diff --git a/src/Erebos/Storage/Internal.hs b/src/Erebos/Storage/Internal.hs
new file mode 100644
index 0000000..a61e705
--- /dev/null
+++ b/src/Erebos/Storage/Internal.hs
@@ -0,0 +1,282 @@
+{-# LANGUAGE CPP #-}
+
+module Erebos.Storage.Internal where
+
+import Codec.Compression.Zlib
+
+import Control.Arrow
+import Control.Concurrent
+import Control.DeepSeq
+import Control.Exception
+import Control.Monad
+import Control.Monad.Identity
+
+import Crypto.Hash
+
+import Data.Bits
+import Data.ByteArray (ByteArray, ByteArrayAccess, ScrubbedBytes)
+import qualified Data.ByteArray as BA
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Char8 as BC
+import qualified Data.ByteString.Lazy as BL
+import Data.Char
+import Data.Function
+import Data.Hashable
+import qualified Data.HashTable.IO as HT
+import Data.Kind
+import Data.List
+import Data.Map (Map)
+import qualified Data.Map as M
+import Data.UUID (UUID)
+
+import Foreign.Storable (peek)
+
+import System.Directory
+import System.FilePath
+import System.INotify (INotify)
+import System.IO
+import System.IO.Error
+import System.IO.Unsafe (unsafePerformIO)
+import System.Posix.Files
+import System.Posix.IO
+
+
+data Storage' c = Storage
+    { stBacking :: StorageBacking c
+    , stParent :: Maybe (Storage' Identity)
+    , stRefGeneration :: MVar (HT.BasicHashTable RefDigest Generation)
+    , stRefRoots :: MVar (HT.BasicHashTable RefDigest [RefDigest])
+    }
+
+instance Eq (Storage' c) where
+    (==) = (==) `on` (stBacking &&& stParent)
+
+instance Show (Storage' c) where
+    show st@(Storage { stBacking = StorageDir { dirPath = path }}) = "dir" ++ showParentStorage st ++ ":" ++ path
+    show st@(Storage { stBacking = StorageMemory {} }) = "mem" ++ showParentStorage st
+
+showParentStorage :: Storage' c -> String
+showParentStorage Storage { stParent = Nothing } = ""
+showParentStorage Storage { stParent = Just st } = "@" ++ show st
+
+data StorageBacking c
+         = StorageDir { dirPath :: FilePath
+                      , dirWatchers :: MVar ([(HeadTypeID, INotify)], WatchList c)
+                      }
+         | StorageMemory { memHeads :: MVar [((HeadTypeID, HeadID), Ref' c)]
+                         , memObjs :: MVar (Map RefDigest BL.ByteString)
+                         , memKeys :: MVar (Map RefDigest ScrubbedBytes)
+                         , memWatchers :: MVar (WatchList c)
+                         }
+    deriving (Eq)
+
+newtype WatchID = WatchID Int
+    deriving (Eq, Ord, Num)
+
+data WatchList c = WatchList
+    { wlNext :: WatchID
+    , wlList :: [WatchListItem c]
+    }
+
+data WatchListItem c = WatchListItem
+    { wlID :: WatchID
+    , wlHead :: (HeadTypeID, HeadID)
+    , wlFun :: Ref' c -> IO ()
+    }
+
+
+newtype RefDigest = RefDigest (Digest Blake2b_256)
+    deriving (Eq, Ord, NFData, ByteArrayAccess)
+
+instance Show RefDigest where
+    show = BC.unpack . showRefDigest
+
+data Ref' c = Ref (Storage' c) RefDigest
+
+instance Eq (Ref' c) where
+    Ref _ d1 == Ref _ d2  =  d1 == d2
+
+instance Show (Ref' c) where
+    show ref@(Ref st _) = show st ++ ":" ++ BC.unpack (showRef ref)
+
+instance ByteArrayAccess (Ref' c) where
+    length (Ref _ dgst) = BA.length dgst
+    withByteArray (Ref _ dgst) = BA.withByteArray dgst
+
+instance Hashable RefDigest where
+    hashWithSalt salt ref = salt `xor` unsafePerformIO (BA.withByteArray ref peek)
+
+instance Hashable (Ref' c) where
+    hashWithSalt salt ref = salt `xor` unsafePerformIO (BA.withByteArray ref peek)
+
+refStorage :: Ref' c -> Storage' c
+refStorage (Ref st _) = st
+
+refDigest :: Ref' c -> RefDigest
+refDigest (Ref _ dgst) = dgst
+
+showRef :: Ref' c -> ByteString
+showRef = showRefDigest . refDigest
+
+showRefDigestParts :: RefDigest -> (ByteString, ByteString)
+showRefDigestParts x = (BC.pack "blake2", showHex x)
+
+showRefDigest :: RefDigest -> ByteString
+showRefDigest = showRefDigestParts >>> \(alg, hex) -> alg <> BC.pack "#" <> hex
+
+readRefDigest :: ByteString -> Maybe RefDigest
+readRefDigest x = case BC.split '#' x of
+                       [alg, dgst] | BA.convert alg == BC.pack "blake2" ->
+                           refDigestFromByteString =<< readHex @ByteString dgst
+                       _ -> Nothing
+
+refDigestFromByteString :: ByteArrayAccess ba => ba -> Maybe RefDigest
+refDigestFromByteString = fmap RefDigest . digestFromByteString
+
+hashToRefDigest :: BL.ByteString -> RefDigest
+hashToRefDigest = RefDigest . hashFinalize . hashUpdates hashInit . BL.toChunks
+
+showHex :: ByteArrayAccess ba => ba -> ByteString
+showHex = B.concat . map showHexByte . BA.unpack
+    where showHexChar x | x < 10    = x + o '0'
+                        | otherwise = x + o 'a' - 10
+          showHexByte x = B.pack [ showHexChar (x `div` 16), showHexChar (x `mod` 16) ]
+          o = fromIntegral . ord
+
+readHex :: ByteArray ba => ByteString -> Maybe ba
+readHex = return . BA.concat <=< readHex'
+    where readHex' bs | B.null bs = Just []
+          readHex' bs = do (bx, bs') <- B.uncons bs
+                           (by, bs'') <- B.uncons bs'
+                           x <- hexDigit bx
+                           y <- hexDigit by
+                           (B.singleton (x * 16 + y) :) <$> readHex' bs''
+          hexDigit x | x >= o '0' && x <= o '9' = Just $ x - o '0'
+                     | x >= o 'a' && x <= o 'z' = Just $ x - o 'a' + 10
+                     | otherwise                = Nothing
+          o = fromIntegral . ord
+
+
+newtype Generation = Generation Int
+    deriving (Eq, Show)
+
+data Head' c a = Head HeadID (Stored' c a)
+    deriving (Eq, Show)
+
+newtype HeadID = HeadID UUID
+    deriving (Eq, Ord, Show)
+
+newtype HeadTypeID = HeadTypeID UUID
+    deriving (Eq, Ord)
+
+data Stored' c a = Stored (Ref' c) a
+    deriving (Show)
+
+instance Eq (Stored' c a) where
+    Stored r1 _ == Stored r2 _  =  refDigest r1 == refDigest r2
+
+instance Ord (Stored' c a) where
+    compare (Stored r1 _) (Stored r2 _) = compare (refDigest r1) (refDigest r2)
+
+storedStorage :: Stored' c a -> Storage' c
+storedStorage (Stored (Ref st _) _) = st
+
+
+type Complete = Identity
+type Partial = Either RefDigest
+
+class (Traversable compl, Monad compl) => StorageCompleteness compl where
+    type LoadResult compl a :: Type
+    returnLoadResult :: compl a -> LoadResult compl a
+    ioLoadBytes :: Ref' compl -> IO (compl BL.ByteString)
+
+instance StorageCompleteness Complete where
+    type LoadResult Complete a = a
+    returnLoadResult = runIdentity
+    ioLoadBytes ref@(Ref st dgst) = maybe (error $ "Ref not found in complete storage: "++show ref) Identity
+        <$> ioLoadBytesFromStorage st dgst
+
+instance StorageCompleteness Partial where
+    type LoadResult Partial a = Either RefDigest a
+    returnLoadResult = id
+    ioLoadBytes (Ref st dgst) = maybe (Left dgst) Right <$> ioLoadBytesFromStorage st dgst
+
+unsafeStoreRawBytes :: Storage' c -> BL.ByteString -> IO (Ref' c)
+unsafeStoreRawBytes st raw = do
+    let dgst = hashToRefDigest raw
+    case stBacking st of
+         StorageDir { dirPath = sdir } -> writeFileOnce (refPath sdir dgst) $ compress raw
+         StorageMemory { memObjs = tobjs } ->
+             dgst `deepseq` -- the TVar may be accessed when evaluating the data to be written
+                 modifyMVar_ tobjs (return . M.insert dgst raw)
+    return $ Ref st dgst
+
+ioLoadBytesFromStorage :: Storage' c -> RefDigest -> IO (Maybe BL.ByteString)
+ioLoadBytesFromStorage st dgst = loadCurrent st >>=
+    \case Just bytes -> return $ Just bytes
+          Nothing | Just parent <- stParent st -> ioLoadBytesFromStorage parent dgst
+                  | otherwise                  -> return Nothing
+    where loadCurrent Storage { stBacking = StorageDir { dirPath = spath } } = handleJust (guard . isDoesNotExistError) (const $ return Nothing) $
+              Just . decompress . BL.fromChunks . (:[]) <$> (B.readFile $ refPath spath dgst)
+          loadCurrent Storage { stBacking = StorageMemory { memObjs = tobjs } } = M.lookup dgst <$> readMVar tobjs
+
+refPath :: FilePath -> RefDigest -> FilePath
+refPath spath rdgst = intercalate "/" [spath, "objects", BC.unpack alg, pref, rest]
+    where (alg, dgst) = showRefDigestParts rdgst
+          (pref, rest) = splitAt 2 $ BC.unpack dgst
+
+
+openLockFile :: FilePath -> IO Handle
+openLockFile path = do
+    createDirectoryIfMissing True (takeDirectory path)
+    fd <- retry 10 $
+#if MIN_VERSION_unix(2,8,0)
+        openFd path WriteOnly defaultFileFlags
+            { creat = Just $ unionFileModes ownerReadMode ownerWriteMode
+            , exclusive = True
+            }
+#else
+        openFd path WriteOnly (Just $ unionFileModes ownerReadMode ownerWriteMode) (defaultFileFlags { exclusive = True })
+#endif
+    fdToHandle fd
+  where
+    retry :: Int -> IO a -> IO a
+    retry 0 act = act
+    retry n act = catchJust (\e -> if isAlreadyExistsError e then Just () else Nothing)
+                      act (\_ -> threadDelay (100 * 1000) >> retry (n - 1) act)
+
+writeFileOnce :: FilePath -> BL.ByteString -> IO ()
+writeFileOnce file content = bracket (openLockFile locked)
+    hClose $ \h -> do
+        fileExist file >>= \case
+            True  -> removeLink locked
+            False -> do BL.hPut h content
+                        hFlush h
+                        rename locked file
+    where locked = file ++ ".lock"
+
+writeFileChecked :: FilePath -> Maybe ByteString -> ByteString -> IO (Either (Maybe ByteString) ())
+writeFileChecked file prev content = bracket (openLockFile locked)
+    hClose $ \h -> do
+        (prev,) <$> fileExist file >>= \case
+            (Nothing, True) -> do
+                current <- B.readFile file
+                removeLink locked
+                return $ Left $ Just current
+            (Nothing, False) -> do B.hPut h content
+                                   hFlush h
+                                   rename locked file
+                                   return $ Right ()
+            (Just expected, True) -> do
+                current <- B.readFile file
+                if current == expected then do B.hPut h content
+                                               hFlush h
+                                               rename locked file
+                                               return $ return ()
+                                       else do removeLink locked
+                                               return $ Left $ Just current
+            (Just _, False) -> do
+                removeLink locked
+                return $ Left Nothing
+    where locked = file ++ ".lock"