blob: cb91325c61eb7c92e3443d479521d9ddfe01941b (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
{- 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.
-
- The mapping from filename to its key is stored in the .git-annex directory,
- in a file named `$filename.$backend`
-
- Multiple pluggable backends are supported, and more than one can be used
- to store different files' contents in a given repository.
- -}
module Backend where
import GitRepo
import System.Directory
data Backend = Backend {
name :: String, -- name of this backend
keyvalue :: FilePath -> Maybe String, -- maps from key to value
retrievekey :: IO String -> IO (Bool) -- retrieves value given key
}
{- Name of state file that holds the key for an annexed file,
- using a given backend. -}
backendFile :: Backend -> GitRepo -> FilePath -> String
backendFile backend repo file = gitStateDir repo ++
(gitRelative repo file) ++ "." ++ (name backend)
{- Looks up the backend used for an already annexed file. -}
lookupBackend :: [Backend] -> GitRepo -> FilePath -> IO (Maybe Backend)
lookupBackend [] repo file = return Nothing
lookupBackend (b:bs) repo file = do
present <- checkBackend b repo file
if present
then
return $ Just b
else
lookupBackend bs repo file
{- Checks if a file is available via a given backend. -}
checkBackend :: Backend -> GitRepo -> FilePath -> IO (Bool)
checkBackend backend repo file = doesFileExist $ backendFile backend repo file
{- Attempts to retrieve an annexed file from one of the backends. -}
retrieveFile :: [Backend] -> GitRepo -> FilePath -> IO (Bool)
retrieveFile backends repo file = do
result <- lookupBackend backends repo file
case (result) of
Nothing -> return False
Just b -> (retrievekey b) key
where key = readFile (backendFile b repo file)
|
