200 lines
6 KiB
Haskell
200 lines
6 KiB
Haskell
{- git-tnnex hashing backends
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-
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- Copyright 2011-2013 Joey Hess <id@joeyh.name>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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module Backend.Hash (
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backends,
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testKeyBackend,
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) where
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import Common.Annex
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import qualified Annex
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import Types.Backend
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import Types.Key
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import Types.KeySource
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import Utility.Hash
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import Utility.ExternalSHA
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import qualified Build.SysConfig as SysConfig
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import qualified Data.ByteString.Lazy as L
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import Data.Char
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data Hash = SHAHash HashSize | SkeinHash HashSize | MD5Hash
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type HashSize = Int
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{- Order is slightly significant; want SHA256 first, and more general
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- sizes earlier. -}
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hashes :: [Hash]
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hashes = concat
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[ map SHAHash [256, 1, 512, 224, 384]
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, map SkeinHash [256, 512]
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, [MD5Hash]
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]
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{- The SHA256E backend is the default, so genBackendE comes first. -}
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backends :: [Backend]
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backends = map genBackendE hashes ++ map genBackend hashes
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genBackend :: Hash -> Backend
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genBackend hash = Backend
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{ name = hashName hash
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, getKey = keyValue hash
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, fsckKey = Just $ checkKeyChecksum hash
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, canUpgradeKey = Just needsUpgrade
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, fastMigrate = Just trivialMigrate
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, isStableKey = const True
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}
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genBackendE :: Hash -> Backend
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genBackendE hash = (genBackend hash)
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{ name = hashNameE hash
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, getKey = keyValueE hash
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}
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hashName :: Hash -> String
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hashName (SHAHash size) = "SHA" ++ show size
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hashName (SkeinHash size) = "SKEIN" ++ show size
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hashName MD5Hash = "MD5"
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hashNameE :: Hash -> String
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hashNameE hash = hashName hash ++ "E"
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{- A key is a hash of its contents. -}
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keyValue :: Hash -> KeySource -> Annex (Maybe Key)
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keyValue hash source = do
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let file = contentLocation source
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filesize <- liftIO $ getFileSize file
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s <- hashFile hash file filesize
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return $ Just $ stubKey
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{ keyName = s
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, keyBackendName = hashName hash
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, keySize = Just filesize
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}
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{- Extension preserving keys. -}
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keyValueE :: Hash -> KeySource -> Annex (Maybe Key)
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keyValueE hash source = keyValue hash source >>= maybe (return Nothing) addE
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where
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addE k = return $ Just $ k
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{ keyName = keyName k ++ selectExtension (keyFilename source)
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, keyBackendName = hashNameE hash
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}
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selectExtension :: FilePath -> String
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selectExtension f
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| null es = ""
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| otherwise = intercalate "." ("":es)
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where
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es = filter (not . null) $ reverse $
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take 2 $ takeWhile shortenough $
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reverse $ split "." $ filter validExtension $ takeExtensions f
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shortenough e = length e <= 4 -- long enough for "jpeg"
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{- A key's checksum is checked during fsck. -}
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checkKeyChecksum :: Hash -> Key -> FilePath -> Annex Bool
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checkKeyChecksum hash key file = do
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fast <- Annex.getState Annex.fast
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mstat <- liftIO $ catchMaybeIO $ getFileStatus file
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case (mstat, fast) of
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(Just stat, False) -> do
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filesize <- liftIO $ getFileSize' file stat
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showSideAction "checksum"
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check <$> hashFile hash file filesize
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_ -> return True
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where
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expected = keyHash key
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check s
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| s == expected = True
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{- A bug caused checksums to be prefixed with \ in some
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- cases; still accept these as legal now that the bug has been
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- fixed. -}
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| '\\' : s == expected = True
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| otherwise = False
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keyHash :: Key -> String
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keyHash key = dropExtensions (keyName key)
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validExtension :: Char -> Bool
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validExtension c
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| isAlphaNum c = True
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| c == '.' = True
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| otherwise = False
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{- Upgrade keys that have the \ prefix on their sha due to a bug, or
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- that contain non-alphanumeric characters in their extension. -}
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needsUpgrade :: Key -> Bool
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needsUpgrade key = "\\" `isPrefixOf` keyHash key ||
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any (not . validExtension) (takeExtensions $ keyName key)
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trivialMigrate :: Key -> Backend -> AssociatedFile -> Maybe Key
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trivialMigrate oldkey newbackend afile
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{- Fast migration from hashE to hash backend. -}
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| keyBackendName oldkey == name newbackend ++ "E" = Just $ oldkey
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{ keyName = keyHash oldkey
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, keyBackendName = name newbackend
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}
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{- Fast migration from hash to hashE backend. -}
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| keyBackendName oldkey ++"E" == name newbackend = case afile of
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Nothing -> Nothing
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Just file -> Just $ oldkey
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{ keyName = keyHash oldkey ++ selectExtension file
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, keyBackendName = name newbackend
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}
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| otherwise = Nothing
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hashFile :: Hash -> FilePath -> Integer -> Annex String
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hashFile hash file filesize = liftIO $ go hash
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where
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go (SHAHash hashsize) = case shaHasher hashsize filesize of
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Left sha -> sha <$> L.readFile file
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Right command ->
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either error return
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=<< externalSHA command hashsize file
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go (SkeinHash hashsize) = skeinHasher hashsize <$> L.readFile file
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go MD5Hash = md5Hasher <$> L.readFile file
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shaHasher :: HashSize -> Integer -> Either (L.ByteString -> String) String
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shaHasher hashsize filesize
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| hashsize == 1 = use SysConfig.sha1 sha1
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| hashsize == 256 = use SysConfig.sha256 sha256
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| hashsize == 224 = use SysConfig.sha224 sha224
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| hashsize == 384 = use SysConfig.sha384 sha384
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| hashsize == 512 = use SysConfig.sha512 sha512
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| otherwise = error $ "unsupported sha size " ++ show hashsize
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where
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use Nothing hasher = Left $ show . hasher
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use (Just c) hasher
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{- Use builtin, but slightly slower hashing for
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- smallish files. Cryptohash benchmarks 90 to 101%
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- faster than external hashers, depending on the hash
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- and system. So there is no point forking an external
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- process unless the file is large. -}
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| filesize < 1048576 = use Nothing hasher
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| otherwise = Right c
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skeinHasher :: HashSize -> (L.ByteString -> String)
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skeinHasher hashsize
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| hashsize == 256 = show . skein256
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| hashsize == 512 = show . skein512
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| otherwise = error $ "unsupported skein size " ++ show hashsize
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md5Hasher :: L.ByteString -> String
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md5Hasher = show . md5
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{- A varient of the SHA256E backend, for testing that needs special keys
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- that cannot collide with legitimate keys in the repository.
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-
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- This is accomplished by appending a special extension to the key,
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- that is not one that selectExtension would select (due to being too
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- long).
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-}
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testKeyBackend :: Backend
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testKeyBackend =
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let b = genBackendE (SHAHash 256)
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in b { getKey = (fmap addE) <$$> getKey b }
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where
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addE k = k { keyName = keyName k ++ longext }
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longext = ".this-is-a-test-key"
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