71 lines
2.1 KiB
Haskell
71 lines
2.1 KiB
Haskell
{- Calculating a SHA checksum with an external command.
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-
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- This is typically a bit faster than using Haskell libraries,
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- by around 1% to 10%. Worth it for really big files.
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-
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- Copyright 2011-2013 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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{-# OPTIONS_GHC -fno-warn-tabs #-}
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module Utility.ExternalSHA (externalSHA) where
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import Utility.SafeCommand
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import Utility.Process
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import Utility.FileSystemEncoding
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import Utility.Misc
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import Utility.Exception
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import Data.List
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import Data.Char
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import System.IO
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import Control.Applicative
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import Prelude
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externalSHA :: String -> Int -> FilePath -> IO (Either String String)
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externalSHA command shasize file = do
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ls <- lines <$> catchDefaultIO "" (readsha (toCommand [File file]))
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return $ sanitycheck =<< parse ls
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where
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{- sha commands output the filename, so need to set fileEncoding -}
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readsha args =
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withHandle StdoutHandle (createProcessChecked checkSuccessProcess) p $ \h -> do
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fileEncoding h
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output <- hGetContentsStrict h
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hClose h
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return output
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where
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p = (proc command args) { std_out = CreatePipe }
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{- The first word of the output is taken to be the sha. -}
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parse [] = bad
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parse (l:_)
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| null sha = bad
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-- sha is prefixed with \ when filename contains certian chars
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| "\\" `isPrefixOf` sha = Right $ drop 1 sha
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| otherwise = Right sha
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where
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sha = fst $ separate (== ' ') l
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bad = Left $ command ++ " parse error"
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{- Check that we've correctly parsing the output of the command,
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- by making sure the sha we read is of the expected length
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- and contains only the right characters. -}
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sanitycheck sha
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| length sha /= expectedSHALength shasize =
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Left $ "Failed to parse the output of " ++ command
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| any (`notElem` "0123456789abcdef") sha' =
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Left $ "Unexpected character in output of " ++ command ++ "\"" ++ sha ++ "\""
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| otherwise = Right sha'
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where
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sha' = map toLower sha
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expectedSHALength :: Int -> Int
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expectedSHALength 1 = 40
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expectedSHALength 256 = 64
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expectedSHALength 512 = 128
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expectedSHALength 224 = 56
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expectedSHALength 384 = 96
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expectedSHALength _ = 0
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