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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.
- -}
module Backend (
list,
storeFileKey,
retrieveKeyFile,
removeKey,
hasKey,
lookupFile
) where
import Control.Monad.State
import Control.Exception
import System.Directory
import System.FilePath
import Data.String.Utils
import System.Posix.Files
import Locations
import qualified GitRepo as Git
import qualified Annex
import Utility
import Types
import qualified TypeInternals as Internals
{- List of backends in the order to try them when storing a new key. -}
list :: Annex [Backend]
list = do
l <- Annex.backends -- list is cached here
if (not $ null l)
then return l
else do
all <- Annex.supportedBackends
g <- Annex.gitRepo
let l = parseBackendList all $ Git.configGet g "annex.backends" ""
backendflag <- Annex.flagGet "backend"
let l' = if (not $ null backendflag)
then (lookupBackendName all backendflag):l
else l
Annex.backendsChange $ l'
return l'
where
parseBackendList all s =
if (null s)
then all
else map (lookupBackendName all) $ words s
{- Looks up a backend in a list -}
lookupBackendName :: [Backend] -> String -> Backend
lookupBackendName all s =
if ((length matches) /= 1)
then error $ "unknown backend " ++ s
else matches !! 0
where matches = filter (\b -> s == Internals.name b) all
{- Attempts to store a file in one of the backends. -}
storeFileKey :: FilePath -> Annex (Maybe (Key, Backend))
storeFileKey file = do
g <- Annex.gitRepo
let relfile = Git.relative g file
b <- list
storeFileKey' b file relfile
storeFileKey' [] _ _ = return Nothing
storeFileKey' (b:bs) file relfile = do
try <- (Internals.getKey b) relfile
case (try) of
Nothing -> nextbackend
Just key -> do
stored <- (Internals.storeFileKey b) file key
if (not stored)
then nextbackend
else do
return $ Just (key, b)
where
nextbackend = storeFileKey' bs file relfile
{- Attempts to retrieve an key from one of the backends, saving it to
- a specified location. -}
retrieveKeyFile :: Backend -> Key -> FilePath -> Annex Bool
retrieveKeyFile backend key dest = (Internals.retrieveKeyFile backend) key dest
{- Removes a key from a backend. -}
removeKey :: Backend -> Key -> Annex Bool
removeKey backend key = (Internals.removeKey backend) key
{- Checks if a backend has its key. -}
hasKey :: Key -> Annex Bool
hasKey key = do
all <- Annex.supportedBackends
(Internals.hasKey (lookupBackendName all $ backendName key)) key
{- Looks up the key and backend corresponding to an annexed file,
- by examining what the file symlinks to. -}
lookupFile :: FilePath -> Annex (Maybe (Key, Backend))
lookupFile file = do
all <- Annex.supportedBackends
result <- liftIO $ (try (lookup all)::IO (Either SomeException (Maybe (Key, Backend))))
case (result) of
Left err -> return Nothing
Right succ -> return succ
where
lookup all = do
l <- readSymbolicLink file
return $ Just $ pair all $ takeFileName l
pair all file = (k, b)
where
k = fileKey file
b = lookupBackendName all $ backendName k
|
