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{- git SHA stuff
-
- Copyright 2011,2020 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU AGPL version 3 or higher.
-}
{-# LANGUAGE OverloadedStrings #-}
module Git.Sha where
import Common
import Git.Types
import qualified Data.ByteString as S
import Data.Char
{- Runs an action that causes a git subcommand to emit a Sha, and strips
- any trailing newline, returning the sha. -}
getSha :: String -> IO S.ByteString -> IO Sha
getSha subcommand a = maybe bad return =<< extractSha <$> a
where
bad = giveup $ "failed to read sha from git " ++ subcommand
{- Extracts the Sha from a ByteString.
-
- There can be a trailing newline after it, but nothing else.
-}
extractSha :: S.ByteString -> Maybe Sha
extractSha s
| len `elem` shaSizes = val s
| len - 1 `elem` shaSizes && S.length s' == len - 1 = val s'
| otherwise = Nothing
where
len = S.length s
s' = firstLine' s
val v
| S.all validinsha v = Just $ Ref v
| otherwise = Nothing
validinsha w = or
[ w >= 48 && w <= 57 -- 0-9
, w >= 97 && w <= 102 -- a-f
, w >= 65 && w <= 70 -- A-F
]
{- Sizes of git shas. -}
shaSizes :: [Int]
shaSizes =
[ 40 -- sha1 (must come first)
, 64 -- sha256
]
{- Git plumbing often uses a all 0 sha to represent things like a
- deleted file. -}
nullShas :: [Sha]
nullShas = map (\n -> Ref (S.replicate n zero)) shaSizes
where
zero = fromIntegral (ord '0')
{- Sha to provide to git plumbing when deleting a file.
-
- It's ok to provide a sha1; git versions that use sha256 will map the
- sha1 to the sha256, or probably just treat all null sha1 specially
- the same as all null sha256. -}
deleteSha :: Sha
deleteSha = Prelude.head nullShas
{- Git's magic empty tree.
-
- It's ok to provide the sha1 of this to git to refer to an empty tree;
- git versions that use sha256 will map the sha1 to the sha256.
-}
emptyTree :: Ref
emptyTree = Ref "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
|
