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|
{- git-annex key-value storage backends
-
- git-annex uses a key-value abstraction layer to allow files contents to be
- stored in different ways. In theory, any key-value storage system could be
- used to store the file contents, and git-annex would then retrieve them
- as needed and put them in `.git/annex/`.
-
- When a file is annexed, a key is generated from its content and/or metadata.
- This key can later be used to retrieve the file's content (its value). This
- key generation must be stable for a given file content, name, and size.
-
- Multiple pluggable backends are supported, and more than one can be used
- to store different files' contents in a given repository.
-
- Copyright 2010 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Backend (
list,
storeFileKey,
retrieveKeyFile,
removeKey,
hasKey,
fsckKey,
lookupFile,
chooseBackends,
keyBackend,
lookupBackendName
) where
import Control.Monad.State
import System.IO.Error (try)
import System.FilePath
import System.Posix.Files
import Locations
import qualified GitRepo as Git
import qualified Annex
import Types
import Key
import qualified BackendClass as B
import Messages
{- List of backends in the order to try them when storing a new key. -}
list :: Annex [Backend Annex]
list = do
l <- Annex.getState Annex.backends -- list is cached here
if not $ null l
then return l
else do
s <- getstandard
d <- Annex.getState Annex.defaultbackend
handle d s
where
parseBackendList l [] = l
parseBackendList bs s = map (lookupBackendName bs) $ words s
handle Nothing s = return s
handle (Just "") s = return s
handle (Just name) s = do
bs <- Annex.getState Annex.supportedBackends
let l' = (lookupBackendName bs name):s
Annex.changeState $ \state -> state { Annex.backends = l' }
return l'
getstandard = do
bs <- Annex.getState Annex.supportedBackends
g <- Annex.gitRepo
return $ parseBackendList bs $
Git.configGet g "annex.backends" ""
{- Looks up a backend in a list. May fail if unknown. -}
lookupBackendName :: [Backend Annex] -> String -> Backend Annex
lookupBackendName bs s =
case maybeLookupBackendName bs s of
Just b -> b
Nothing -> error $ "unknown backend " ++ s
maybeLookupBackendName :: [Backend Annex] -> String -> Maybe (Backend Annex)
maybeLookupBackendName bs s =
if 1 /= length matches
then Nothing
else Just $ head matches
where matches = filter (\b -> s == B.name b) bs
{- Attempts to store a file in one of the backends. -}
storeFileKey :: FilePath -> Maybe (Backend Annex) -> Annex (Maybe (Key, Backend Annex))
storeFileKey file trybackend = do
bs <- list
let bs' = case trybackend of
Nothing -> bs
Just backend -> backend:bs
storeFileKey' bs' file
storeFileKey' :: [Backend Annex] -> FilePath -> Annex (Maybe (Key, Backend Annex))
storeFileKey' [] _ = return Nothing
storeFileKey' (b:bs) file = do
result <- (B.getKey b) file
case result of
Nothing -> nextbackend
Just key -> do
stored <- (B.storeFileKey b) file key
if (not stored)
then nextbackend
else return $ Just (key, b)
where
nextbackend = storeFileKey' bs file
{- Attempts to retrieve an key from one of the backends, saving it to
- a specified location. -}
retrieveKeyFile :: Backend Annex -> Key -> FilePath -> Annex Bool
retrieveKeyFile backend key dest = (B.retrieveKeyFile backend) key dest
{- Removes a key from a backend. -}
removeKey :: Backend Annex -> Key -> Maybe Int -> Annex Bool
removeKey backend key numcopies = (B.removeKey backend) key numcopies
{- Checks if a key is present in its backend. -}
hasKey :: Key -> Annex Bool
hasKey key = do
backend <- keyBackend key
(B.hasKey backend) key
{- Checks a key's backend for problems. -}
fsckKey :: Backend Annex -> Key -> Maybe FilePath -> Maybe Int -> Annex Bool
fsckKey backend key file numcopies = (B.fsckKey backend) key file numcopies
{- Looks up the key and backend corresponding to an annexed file,
- by examining what the file symlinks to. -}
lookupFile :: FilePath -> Annex (Maybe (Key, Backend Annex))
lookupFile file = do
bs <- Annex.getState Annex.supportedBackends
tl <- liftIO $ try getsymlink
case tl of
Left _ -> return Nothing
Right l -> makekey bs l
where
getsymlink = do
l <- readSymbolicLink file
return $ takeFileName l
makekey bs l =
case fileKey l of
Just k -> makeret k l bs
Nothing -> return Nothing
makeret k l bs =
case maybeLookupBackendName bs bname of
Just backend -> return $ Just (k, backend)
Nothing -> do
when (isLinkToAnnex l) $
warning skip
return Nothing
where
bname = keyBackendName k
skip = "skipping " ++ file ++
" (unknown backend " ++ bname ++ ")"
{- Looks up the backends that should be used for each file in a list.
- That can be configured on a per-file basis in the gitattributes file.
-}
chooseBackends :: [FilePath] -> Annex [(FilePath, Maybe (Backend Annex))]
chooseBackends fs = do
g <- Annex.gitRepo
bs <- Annex.getState Annex.supportedBackends
pairs <- liftIO $ Git.checkAttr g "annex.backend" fs
return $ map (\(f,b) -> (f, maybeLookupBackendName bs b)) pairs
{- Returns the backend to use for a key. -}
keyBackend :: Key -> Annex (Backend Annex)
keyBackend key = do
bs <- Annex.getState Annex.supportedBackends
return $ lookupBackendName bs $ keyBackendName key
|
