279991604d
This should make code that reads shas and refs from git faster. Does not compile yet, a lot needs to be done still.
74 lines
1.9 KiB
Haskell
74 lines
1.9 KiB
Haskell
{- git SHA stuff
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-
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- Copyright 2011,2020 Joey Hess <id@joeyh.name>
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-
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- Licensed under the GNU AGPL version 3 or higher.
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-}
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{-# LANGUAGE OverloadedStrings #-}
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module Git.Sha where
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import Common
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import Git.Types
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import qualified Data.ByteString as S
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import Data.Char
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{- Runs an action that causes a git subcommand to emit a Sha, and strips
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- any trailing newline, returning the sha. -}
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getSha :: String -> IO S.ByteString -> IO Sha
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getSha subcommand a = maybe bad return =<< extractSha <$> a
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where
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bad = error $ "failed to read sha from git " ++ subcommand
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{- Extracts the Sha from a ByteString.
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-
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- There can be a trailing newline after it, but nothing else.
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-}
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extractSha :: S.ByteString -> Maybe Sha
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extractSha s
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| len `elem` shaSizes = val s
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| len - 1 `elem` shaSizes && S.length s' == len - 1 = val s'
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| otherwise = Nothing
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where
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len = S.length s
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s' = firstLine' s
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val v
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| S.all validinsha v = Just $ Ref v
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| otherwise = Nothing
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validinsha w = or
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[ w >= 48 && w <= 57 -- 0-9
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, w >= 97 && w <= 102 -- a-f
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, w >= 65 && w <= 70 -- A-F
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]
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{- Sizes of git shas. -}
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shaSizes :: [Int]
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shaSizes =
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[ 40 -- sha1 (must come first)
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, 64 -- sha256
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]
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{- Git plumbing often uses a all 0 sha to represent things like a
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- deleted file. -}
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nullShas :: [Sha]
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nullShas = map (\n -> Ref (S.replicate n zero)) shaSizes
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where
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zero = fromIntegral (ord '0')
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{- Sha to provide to git plumbing when deleting a file.
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-
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- It's ok to provide a sha1; git versions that use sha256 will map the
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- sha1 to the sha256, or probably just treat all null sha1 specially
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- the same as all null sha256. -}
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deleteSha :: Sha
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deleteSha = Prelude.head nullShas
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{- Git's magic empty tree.
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-
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- It's ok to provide the sha1 of this to git to refer to an empty tree;
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- git versions that use sha256 will map the sha1 to the sha256.
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-}
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emptyTree :: Ref
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emptyTree = Ref "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
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