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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 (
storeFile,
dropFile,
retrieveFile,
lookupFile
) where
import Control.Exception
import System.Directory
import System.FilePath
import Data.String.Utils
import System.Posix.Files
import BackendList
import Locations
import GitRepo
import Utility
import Types
{- Attempts to store a file in one of the backends. -}
storeFile :: State -> FilePath -> IO (Maybe (Key, Backend))
storeFile state file = storeFile' (backends state) state file
storeFile' [] _ _ = return Nothing
storeFile' (b:bs) state file = do
try <- (getKey b) state (gitRelative (repo state) file)
case (try) of
Nothing -> nextbackend
Just key -> do
stored <- (storeFileKey b) state file key
if (not stored)
then nextbackend
else do
return $ Just (key, b)
where
nextbackend = storeFile' bs state file
{- Attempts to retrieve an key from one of the backends, saving it to
- a specified location. -}
retrieveFile :: State -> Backend -> Key -> FilePath -> IO Bool
retrieveFile state backend key dest = (retrieveKeyFile backend) state key dest
{- Drops a key from a backend. -}
dropFile :: State -> Backend -> Key -> IO Bool
dropFile state backend key = (removeKey backend) state key
{- Looks up the key and backend corresponding to an annexed file,
- by examining what the file symlinks to. -}
lookupFile :: FilePath -> IO (Maybe (Key, Backend))
lookupFile file = do
result <- try (lookup)::IO (Either SomeException (Maybe (Key, Backend)))
case (result) of
Left err -> return Nothing
Right succ -> return succ
where
lookup = do
l <- readSymbolicLink file
return $ Just (k l, b l)
k l = fileKey $ takeFileName $ l
b l = lookupBackendName $ takeFileName $ parentDir $ l
|
