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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 (
lookupBackend,
storeFile,
retrieveFile,
fileKey,
dropFile
) where
import System.Directory
import System.FilePath
import Data.String.Utils
import System.Posix.Files
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 file from one of the backends, saving it to
- a specified location. -}
retrieveFile :: State -> FilePath -> FilePath -> IO Bool
retrieveFile state file dest = do
result <- lookupBackend state file
case (result) of
Nothing -> return False
Just backend -> do
key <- fileKey file
(retrieveKeyFile backend) state key dest
{- Drops the key for a file from the backend that has it. -}
dropFile :: State -> FilePath -> IO (Maybe (Key, Backend))
dropFile state file = do
result <- lookupBackend state file
case (result) of
Nothing -> return Nothing
Just backend -> do
key <- fileKey file
(removeKey backend) state key
return $ Just (key, backend)
{- Looks up the backend used for an already annexed file. -}
lookupBackend :: State -> FilePath -> IO (Maybe Backend)
lookupBackend state file = lookupBackend' (backends state) state file
lookupBackend' [] _ _ = return Nothing
lookupBackend' (b:bs) state file = do
present <- checkBackend b state file
if present
then
return $ Just b
else
lookupBackend' bs state file
{- Checks if a file is available via a given backend. -}
checkBackend :: Backend -> State -> FilePath -> IO (Bool)
checkBackend backend state file =
doesFileExist $ annexLocation state backend file
{- Looks up the key corresponding to an annexed file,
- by examining what the file symlinks to. -}
fileKey :: FilePath -> IO Key
fileKey file = do
l <- readSymbolicLink (file)
return $ takeFileName $ l
|
