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|
{- git-annex location log
-
- git-annex keeps track of on which repository it last saw a file's content.
- This can be useful when using it for archiving with offline storage.
- When you indicate you --want a file, git-annex will tell you which
- repositories have the file's content.
-
- Location tracking information is stored in `.git-annex/$filename.log`.
- Repositories record their name and the date when they --get or --drop
- a file's content. (Git is configured to use a union merge for this file,
- so the lines may be in arbitrary order, but it will never conflict.)
-
- A line of the log will look like: "date reponame filename"
-
-}
module LocationLog where
import Data.DateTime
import System.IO
import System.Posix.IO
data LogLine = LogLine {
date :: DateTime,
repo :: String,
file :: String
} deriving (Eq)
-- a special value representing a log file line that could not be parsed
unparsable = (LogLine (fromSeconds 0) "" "")
instance Show LogLine where
show (LogLine date repo file) = unwords
[(show (toSeconds date)), repo, file]
instance Read LogLine where
-- this parser is robust in that even unparsable log lines are
-- read without an exception being thrown
readsPrec _ string = if (length w >= 3)
then [((LogLine time repo file), "")]
else [(unparsable, "")]
where
time = fromSeconds $ read $ w !! 0
repo = w !! 1
file = unwords $ rest w
w = words string
rest (_:_:l) = l
{- Reads a log file -}
readLog :: String -> IO [LogLine]
readLog file = do
h <- openLocked file ReadMode
s <- hGetContents h
-- hClose handle' -- TODO disabled due to lazy IO issue
-- filter out any unparsable lines
return $ filter ( /= unparsable ) $ map read $ lines s
{- Adds a LogLine to a log file -}
writeLog :: String -> LogLine -> IO ()
writeLog file line = do
h <- openLocked file AppendMode
hPutStrLn h $ show line
hClose h
{- Let's just say that Haskell makes reading/writing a file with
- file locking excessively difficult. -}
openLocked file mode = do
handle <- openFile file mode
lockfd <- handleToFd handle -- closes handle
waitToSetLock lockfd (lockType mode, AbsoluteSeek, 0, 0)
handle' <- fdToHandle lockfd
return handle'
where
lockType ReadMode = ReadLock
lockType _ = WriteLock
{- Generates a new log line with the current date. -}
logNow :: String -> String -> IO LogLine
logNow repo file = do
now <- getCurrentTime
return $ LogLine now repo file
|
