102 lines
3.4 KiB
Haskell
102 lines
3.4 KiB
Haskell
{- git-annex key/value storage backends
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-
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- git-annex uses a key/value abstraction layer to allow files contents to be
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- stored in different ways. In theory, any key/value storage system could be
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- used to store the file contents, and git-annex would then retrieve them
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- as needed and put them in `.git/annex/`.
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-
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- When a file is annexed, a key is generated from its content and/or metadata.
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- This key can later be used to retrieve the file's content (its value). This
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- key generation must be stable for a given file content, name, and size.
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-
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- The mapping from filename to its key is stored in the .git-annex directory,
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- in a file named `$filename.$backend`
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-
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- Multiple pluggable backends are supported, and more than one can be used
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- to store different files' contents in a given repository.
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- -}
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module Backend (
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Key,
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Backend, -- note only data type is exported, not destructors
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lookupBackend,
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storeFile,
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dropFile
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) where
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import System.Directory
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import Locations
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import GitRepo
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import Utility
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import Types
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{- Name of state file that holds the key for an annexed file,
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- using a given backend. -}
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backendFile :: Backend -> State -> FilePath -> String
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backendFile backend state file =
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gitStateDir (repo state) ++ (gitRelative (repo state) file) ++
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"." ++ (name backend)
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{- Attempts to store a file in one of the backends, and returns
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- its key. -}
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storeFile :: [Backend] -> State -> FilePath -> IO (Maybe Key)
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storeFile [] _ _ = return Nothing
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storeFile (b:bs) state file = do
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try <- (getKey b) state (gitRelative (repo state) file)
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case (try) of
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Nothing -> nextbackend
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Just key -> do
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stored <- (storeFileKey b) state file key
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if (not stored)
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then nextbackend
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else do
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bookkeeping key
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return $ Just key
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where
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nextbackend = storeFile bs state file
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backendfile = backendFile b state file
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bookkeeping key = do
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createDirectoryIfMissing True (parentDir backendfile)
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writeFile backendfile key
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{- Attempts to retrieve an file from one of the backends, saving it to
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- a specified location. -}
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retrieveFile :: [Backend] -> State -> FilePath -> FilePath -> IO Bool
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retrieveFile backends state file dest = do
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result <- lookupBackend backends state file
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case (result) of
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Nothing -> return False
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Just b -> do
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key <- lookupKey b state file
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(retrieveKeyFile b) key dest
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{- Drops the key for a file from the backend that has it. -}
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dropFile :: [Backend] -> State -> FilePath -> IO (Maybe Key)
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dropFile backends state file = do
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result <- lookupBackend backends state file
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case (result) of
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Nothing -> return Nothing
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Just b -> do
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key <- lookupKey b state file
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(removeKey b) key
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removeFile $ backendFile b state file
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return $ Just key
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{- Looks up the key a backend uses for an already annexed file. -}
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lookupKey :: Backend -> State -> FilePath -> IO Key
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lookupKey backend state file = readFile (backendFile backend state file)
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{- Looks up the backend used for an already annexed file. -}
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lookupBackend :: [Backend] -> State -> FilePath -> IO (Maybe Backend)
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lookupBackend [] _ _ = return Nothing
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lookupBackend (b:bs) state file = do
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present <- checkBackend b state file
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if present
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then
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return $ Just b
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else
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lookupBackend bs state file
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{- Checks if a file is available via a given backend. -}
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checkBackend :: Backend -> State -> FilePath -> IO (Bool)
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checkBackend backend state file = doesFileExist $ backendFile backend state file
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