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|
{- git-annex file locations
-
- Copyright 2010-2015 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Annex.DirHashes (
Hasher,
HashLevels(..),
objectHashLevels,
branchHashLevels,
branchHashDir,
dirHashes,
hashDirMixed,
hashDirLower,
display_32bits_as_dir
) where
import Data.Bits
import Data.Word
import Data.Hash.MD5
import Data.Default
import Common
import Types.Key
import Types.GitConfig
import Types.Difference
type Hasher = Key -> FilePath
-- Number of hash levels to use. 2 is the default.
newtype HashLevels = HashLevels Int
instance Default HashLevels where
def = HashLevels 2
objectHashLevels :: GitConfig -> HashLevels
objectHashLevels = configHashLevels OneLevelObjectHash
branchHashLevels :: GitConfig -> HashLevels
branchHashLevels = configHashLevels OneLevelBranchHash
configHashLevels :: Difference -> GitConfig -> HashLevels
configHashLevels d config
| hasDifference d (annexDifferences config) = HashLevels 1
| otherwise = def
branchHashDir :: GitConfig -> Key -> String
branchHashDir = hashDirLower . branchHashLevels
{- Two different directory hashes may be used. The mixed case hash
- came first, and is fine, except for the problem of case-strict
- filesystems such as Linux VFAT (mounted with shortname=mixed),
- which do not allow using a directory "XX" when "xx" already exists.
- To support that, most repositories use the lower case hash for new data. -}
dirHashes :: [HashLevels -> Hasher]
dirHashes = [hashDirLower, hashDirMixed]
hashDirs :: HashLevels -> Int -> String -> FilePath
hashDirs (HashLevels 1) sz s = addTrailingPathSeparator $ take sz s
hashDirs _ sz s = addTrailingPathSeparator $ take sz s </> drop sz s
hashDirMixed :: HashLevels -> Hasher
hashDirMixed n k = hashDirs n 2 $ take 4 $ display_32bits_as_dir =<< [a,b,c,d]
where
ABCD (a,b,c,d) = md5 $ md5FilePath $ key2file $ nonChunkKey k
hashDirLower :: HashLevels -> Hasher
hashDirLower n k = hashDirs n 3 $ take 6 $ md5s $ md5FilePath $ key2file $ nonChunkKey k
{- modified version of display_32bits_as_hex from Data.Hash.MD5
- Copyright (C) 2001 Ian Lynagh
- License: Either BSD or GPL
-}
display_32bits_as_dir :: Word32 -> String
display_32bits_as_dir w = trim $ swap_pairs cs
where
-- Need 32 characters to use. To avoid inaverdently making
-- a real word, use letters that appear less frequently.
chars = ['0'..'9'] ++ "zqjxkmvwgpfZQJXKMVWGPF"
cs = map (\x -> getc $ (shiftR w (6*x)) .&. 31) [0..7]
getc n = chars !! fromIntegral n
swap_pairs (x1:x2:xs) = x2:x1:swap_pairs xs
swap_pairs _ = []
-- Last 2 will always be 00, so omit.
trim = take 6
|
