Some optimisations to string splitting code.

Turns out that Data.List.Utils.split is slow and makes a lot of
allocations. Here's a much simpler single character splitter that behaves
the same (even in wacky corner cases) while running in half the time and
75% the allocations.

As well as being an optimisation, this helps move toward eliminating use of
missingh.

(Data.List.Split.splitOn is nearly as slow as Data.List.Utils.split and
allocates even more.)

I have not benchmarked the effect on git-annex, but would not be surprised
to see some parsing of eg, large streams from git commands run twice as
fast, and possibly in less memory.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.

Annex/Direct.hs

@@ -441,7 +441,7 @@ setDirect wantdirect = do
  - this way things that show HEAD (eg shell prompts) will
  - hopefully show just "master". -}
 directBranch :: Ref -> Ref
-directBranch orighead = case split "/" $ fromRef orighead of
+directBranch orighead = case splitc '/' $ fromRef orighead of
 	("refs":"heads":"annex":"direct":_) -> orighead
 	("refs":"heads":rest) ->
 		Ref $ "refs/heads/annex/direct/" ++ intercalate "/" rest
@@ -452,7 +452,7 @@ directBranch orighead = case split "/" $ fromRef orighead of
  - Any other ref is left unchanged.
  -}
 fromDirectBranch :: Ref -> Ref
-fromDirectBranch directhead = case split "/" $ fromRef directhead of
+fromDirectBranch directhead = case splitc '/' $ fromRef directhead of
 	("refs":"heads":"annex":"direct":rest) -> 
 		Ref $ "refs/heads/" ++ intercalate "/" rest
 	_ -> directhead

Annex/TaggedPush.hs

@@ -39,7 +39,7 @@ toTaggedBranch u info b = Git.Ref $ intercalate "/" $ catMaybes
 	]
 
 fromTaggedBranch :: Git.Branch -> Maybe (UUID, Maybe String)
-fromTaggedBranch b = case split "/" $ Git.fromRef b of
+fromTaggedBranch b = case splitc '/' $ Git.fromRef b of
 	("refs":"synced":u:info:_base) ->
 		Just (toUUID u, fromB64Maybe info)
 	("refs":"synced":u:_base) ->

Assistant/Ssh.hs

@@ -383,7 +383,7 @@ mangleSshHostName sshdata = intercalate "-"
 
 {- Extracts the real hostname from a mangled ssh hostname. -}
 unMangleSshHostName :: String -> String
-unMangleSshHostName h = case split "-" h of
+unMangleSshHostName h = case splitc '-' h of
 	("git":"annex":rest) -> unescape (intercalate "-" (beginning rest))
 	_ -> h
   where

Backend/Hash.hs

@@ -103,7 +103,7 @@ selectExtension f
 	es = filter (not . null) $ reverse $
 		take 2 $ map (filter validInExtension) $
 		takeWhile shortenough $
-		reverse $ split "." $ takeExtensions f
+		reverse $ splitc '.' $ takeExtensions f
 	shortenough e = length e <= 4 -- long enough for "jpeg"
 
 {- A key's checksum is checked during fsck. -}

Build/OSXMkLibs.hs

@@ -95,7 +95,7 @@ findLibPath l = go =<< getEnv "DYLD_LIBRARY_PATH"
   where
 	go Nothing = return l
 	go (Just p) = fromMaybe l
-		<$> firstM doesFileExist (map (</> f) (split ":" p))
+		<$> firstM doesFileExist (map (</> f) (splitc ':' p))
 	f = takeFileName l
 
 {- Expands any @rpath in the list of libraries.

CHANGELOG

@@ -8,6 +8,7 @@ git-annex (6.20170102) UNRELEASED; urgency=medium
   * vicfg: Include the numcopies configuation.
   * config: New command for storing configuration in the git-annex branch.
   * stack.yaml: Update to lts-7.18.
+  * Some optimisations to string splitting code.
 
  -- Joey Hess <id@joeyh.name>  Fri, 06 Jan 2017 15:22:06 -0400
 

Command/AddUrl.hs

@@ -387,7 +387,7 @@ url2file url pathdepth pathmax = case pathdepth of
 		]
 	frombits a = intercalate "/" $ a urlbits
 	urlbits = map (truncateFilePath pathmax . sanitizeFilePath) $
-		filter (not . null) $ split "/" fullurl
+		filter (not . null) $ splitc '/' fullurl
 
 urlString2file :: URLString -> Maybe Int -> Int -> FilePath
 urlString2file s pathdepth pathmax = case Url.parseURIRelaxed s of

Command/Map.hs

@@ -92,7 +92,7 @@ hostname r
 	| otherwise = "localhost"
 
 basehostname :: Git.Repo -> String
-basehostname r = fromMaybe "" $ headMaybe $ split "." $ hostname r
+basehostname r = fromMaybe "" $ headMaybe $ splitc '.' $ hostname r
 
 {- A name to display for a repo. Uses the name from uuid.log if available,
  - or the remote name if not. -}

Crypto.hs

@@ -231,8 +231,8 @@ instance LensGpgEncParams (RemoteConfig, RemoteGitConfig) where
  		{- When the remote is configured to use public-key encryption,
 		 - look up the recipient keys and add them to the option list. -}
 		case M.lookup "encryption" c of
-			Just "pubkey" -> Gpg.pkEncTo $ maybe [] (split ",") $ M.lookup "cipherkeys" c
+			Just "pubkey" -> Gpg.pkEncTo $ maybe [] (splitc ',') $ M.lookup "cipherkeys" c
-			Just "sharedpubkey" -> Gpg.pkEncTo $ maybe [] (split ",") $ M.lookup "pubkeys" c
+			Just "sharedpubkey" -> Gpg.pkEncTo $ maybe [] (splitc ',') $ M.lookup "pubkeys" c
 			_ -> []
 	getGpgDecParams (_c,gc) = map Param (remoteAnnexGnupgDecryptOptions gc)
 

Git/Command.hs

@@ -91,16 +91,16 @@ pipeWrite params repo = withHandle StdinHandle createProcessSuccess $
 pipeNullSplit :: [CommandParam] -> Repo -> IO ([String], IO Bool)
 pipeNullSplit params repo = do
 	(s, cleanup) <- pipeReadLazy params repo
-	return (filter (not . null) $ split sep s, cleanup)
+	return (filter (not . null) $ splitc sep s, cleanup)
   where
-	sep = "\0"
+	sep = '\0'
 
 pipeNullSplitStrict :: [CommandParam] -> Repo -> IO [String]
 pipeNullSplitStrict params repo = do
 	s <- pipeReadStrict params repo
-	return $ filter (not . null) $ split sep s
+	return $ filter (not . null) $ splitc sep s
   where
-	sep = "\0"
+	sep = '\0'
 
 pipeNullSplitZombie :: [CommandParam] -> Repo -> IO [String]
 pipeNullSplitZombie params repo = leaveZombie <$> pipeNullSplit params repo

Git/Config.hs

@@ -132,7 +132,7 @@ parse s
 	-- --list output will have an = in the first line
 	| all ('=' `elem`) (take 1 ls) = sep '=' ls
 	-- --null --list output separates keys from values with newlines
-	| otherwise = sep '\n' $ split "\0" s
+	| otherwise = sep '\n' $ splitc '\0' s
   where
 	ls = lines s
 	sep c = M.fromListWith (++) . map (\(k,v) -> (k, [v])) .

Git/Construct.hs

@@ -26,7 +26,7 @@ module Git.Construct (
 #ifndef mingw32_HOST_OS
 import System.Posix.User
 #endif
-import qualified Data.Map as M hiding (map, split)
+import qualified Data.Map as M
 import Network.URI
 
 import Common
@@ -143,7 +143,7 @@ remoteNamedFromKey :: String -> IO Repo -> IO Repo
 remoteNamedFromKey k = remoteNamed basename
   where
 	basename = intercalate "." $ 
-		reverse $ drop 1 $ reverse $ drop 1 $ split "." k
+		reverse $ drop 1 $ reverse $ drop 1 $ splitc '.' k
 
 {- Constructs a new Repo for one of a Repo's remotes using a given
  - location (ie, an url). -}

Git/Ref.hs

@@ -144,6 +144,6 @@ legal allowonelevel s = all (== False) illegal
 	ends v = v `isSuffixOf` s
 	begins v = v `isPrefixOf` s
 
-	pathbits = split "/" s
+	pathbits = splitc '/' s
 	illegalchars = " ~^:?*[\\" ++ controlchars
 	controlchars = chr 0o177 : [chr 0 .. chr (0o40-1)]

Limit.hs

@@ -161,7 +161,7 @@ addCopies :: String -> Annex ()
 addCopies = addLimit . limitCopies
 
 limitCopies :: MkLimit Annex
-limitCopies want = case split ":" want of
+limitCopies want = case splitc ':' want of
 	[v, n] -> case parsetrustspec v of
 		Just checker -> go n $ checktrust checker
 		Nothing -> go n $ checkgroup v

Logs/Transfer.hs

@@ -268,7 +268,7 @@ readTransferInfo mpid s = TransferInfo
 	filename
 		| end rest == "\n" = beginning rest
 		| otherwise = rest
-	bits = split " " firstline
+	bits = splitc ' ' firstline
 	numbits = length bits
 	time = if numbits > 0
 		then Just <$> parsePOSIXTime =<< headMaybe bits

Logs/UUID.hs

@@ -66,7 +66,7 @@ fixBadUUID = M.fromList . map fixup . M.toList
 	newertime (LogEntry (Date d) _) = d + minimumPOSIXTimeSlice
 	newertime (LogEntry Unknown _) = minimumPOSIXTimeSlice
 	minimumPOSIXTimeSlice = 0.000001
-	isuuid s = length s == 36 && length (split "-" s) == 5
+	isuuid s = length s == 36 && length (splitc '-' s) == 5
 
 {- Records the uuid in the log, if it's not already there. -}
 recordUUID :: UUID -> Annex ()

Remote.hs

@@ -140,7 +140,7 @@ byName' n = go . filter matching <$> remoteList
 byNameOrGroup :: RemoteName -> Annex [Remote]
 byNameOrGroup n = go =<< getConfigMaybe (ConfigKey ("remotes." ++ n))
   where
-	go (Just l) = catMaybes <$> mapM (byName . Just) (split " " l)
+	go (Just l) = catMaybes <$> mapM (byName . Just) (splitc ' ' l)
 	go Nothing = maybeToList <$> byName (Just n)
 
 {- Only matches remote name, not UUID -}

Remote/BitTorrent.hs

@@ -302,7 +302,7 @@ ariaProgress (Just sz) meter ps = do
 		=<< ariaParams ps
 
 parseAriaProgress :: Integer -> ProgressParser
-parseAriaProgress totalsize = go [] . reverse . split ['\r']
+parseAriaProgress totalsize = go [] . reverse . splitc '\r'
   where
 	go remainder [] = (Nothing, remainder)
 	go remainder (x:xs) = case readish (findpercent x) of

Remote/Bup.hs

@@ -254,7 +254,7 @@ bup2GitRemote r
 			else giveup "please specify an absolute path"
 	| otherwise = Git.Construct.fromUrl $ "ssh://" ++ host ++ slash dir
   where
-	bits = split ":" r
+	bits = splitc ':' r
 	host = Prelude.head bits
 	dir = intercalate ":" $ drop 1 bits
 	-- "host:~user/dir" is not supported specially by bup;

Remote/Helper/Encryptable.hs

@@ -165,7 +165,7 @@ extractCipher c = case (M.lookup "cipher" c,
 		Just $ SharedCipher (fromB64bs t)
 	_ -> Nothing
   where
-	readkeys = KeyIds . split ","
+	readkeys = KeyIds . splitc ','
 
 describeEncryption :: RemoteConfig -> String
 describeEncryption c = case extractCipher c of

Types/RefSpec.hs

@@ -25,7 +25,7 @@ allRefSpec :: RefSpec
 allRefSpec = [AddMatching $ compileGlob "*" CaseSensative]
 
 parseRefSpec :: String -> Either String RefSpec
-parseRefSpec v = case partitionEithers (map mk $ split ":" v) of
+parseRefSpec v = case partitionEithers (map mk $ splitc ':' v) of
 	([],refspec) -> Right refspec
 	(e:_,_) -> Left e
   where

Upgrade/V1.hs

@@ -148,7 +148,7 @@ readKey1 v
 		, keyMtime = t
 		}
   where
-	bits = split ":" v
+	bits = splitc ':' v
 	b = Prelude.head bits
 	n = intercalate ":" $ drop (if wormy then 3 else 1) bits
 	t = if wormy

Utility/DottedVersion.hs

@@ -25,7 +25,7 @@ instance Show DottedVersion where
 normalize :: String -> DottedVersion
 normalize v = DottedVersion v $ 
 	sum $ mult 1 $ reverse $ extend precision $ take precision $
-		map readi $ split "." v
+		map readi $ splitc '.' v
   where
 	extend n l = l ++ replicate (n - length l) 0
 	mult _ [] = []

Utility/Gpg.hs

@@ -162,7 +162,7 @@ findPubKeys :: GpgCmd -> String -> IO KeyIds
 findPubKeys cmd for = KeyIds . parse . lines <$> readStrict cmd params
   where
 	params = [Param "--with-colons", Param "--list-public-keys", Param for]
-	parse = mapMaybe (keyIdField . split ":")
+	parse = mapMaybe (keyIdField . splitc ':')
 	keyIdField ("pub":_:_:_:f:_) = Just f
 	keyIdField _ = Nothing
 
@@ -175,7 +175,7 @@ secretKeys cmd = catchDefaultIO M.empty makemap
   where
 	makemap = M.fromList . parse . lines <$> readStrict cmd params
 	params = [Param "--with-colons", Param "--list-secret-keys", Param "--fixed-list-mode"]
-	parse = extract [] Nothing . map (split ":")
+	parse = extract [] Nothing . map (splitc ':')
 	extract c (Just keyid) (("uid":_:_:_:_:_:_:_:_:userid:_):rest) =
 		extract ((keyid, decode_c userid):c) Nothing rest
 	extract c (Just keyid) rest@(("sec":_):_) =

Utility/Lsof.hs

@@ -107,7 +107,7 @@ parseFormatted s = bundle $ go [] $ lines s
 	parsemode ('u':_) = OpenReadWrite
 	parsemode _ = OpenUnknown
 
-	splitnull = split "\0"
+	splitnull = splitc '\0'
 
 	parsefail = error $ "failed to parse lsof output: " ++ show s
 

Utility/Misc.hs

@@ -45,6 +45,14 @@ separate c l = unbreak $ break c l
 		| null b = r
 		| otherwise = (a, tail b)
 
+{- Split on a single character. This is over twice as fast as using
+ - Data.List.Utils.split on a list of length 1, while producing
+ - identical results. -}
+splitc :: Char -> String -> [String]
+splitc c s = case break (== c) s of
+	(i, _c:rest) -> i : splitc c rest
+	(i, []) -> i : []
+
 {- Breaks out the first line. -}
 firstLine :: String -> String
 firstLine = takeWhile (/= '\n')

Utility/Quvi.hs

@@ -124,14 +124,14 @@ supported Quvi09 url = (firstlevel <&&> secondlevel)
 		Nothing -> return False
 		Just auth -> do
 			let domain = map toLower $ uriRegName auth
-			let basedomain = intercalate "." $ reverse $ take 2 $ reverse $ split "." domain
+			let basedomain = intercalate "." $ reverse $ take 2 $ reverse $ splitc '.' domain
 			any (\h -> domain `isSuffixOf` h || basedomain `isSuffixOf` h) 
 				. map (map toLower) <$> listdomains Quvi09
 	secondlevel = snd <$> processTranscript "quvi"
 		(toCommand [Param "dump", Param "-o", Param url]) Nothing
 
 listdomains :: QuviVersion -> IO [String]
-listdomains Quvi09 = concatMap (split ",") 
+listdomains Quvi09 = concatMap (splitc ',') 
 	. concatMap (drop 1 . words) 
 	. filter ("domains: " `isPrefixOf`) . lines
 	<$> readQuvi (toCommand [Param "info", Param "-p", Param "domains"])

Utility/Rsync.hs

@@ -24,7 +24,7 @@ rsyncShell command = [Param "-e", Param $ unwords $ map escape (toCommand comman
 	{- rsync requires some weird, non-shell like quoting in
 	- here. A doubled single quote inside the single quoted
 	- string is a single quote. -}
-	escape s = "'" ++  intercalate "''" (split "'" s) ++ "'"
+	escape s = "'" ++  intercalate "''" (splitc '\'' s) ++ "'"
 
 {- Runs rsync in server mode to send a file. -}
 rsyncServerSend :: [CommandParam] -> FilePath -> IO Bool
@@ -123,7 +123,7 @@ parseRsyncProgress = go [] . reverse . progresschunks
 	{- Find chunks that each start with delim.
 	 - The first chunk doesn't start with it
 	 - (it's empty when delim is at the start of the string). -}
-	progresschunks = drop 1 . split [delim]
+	progresschunks = drop 1 . splitc delim
 	findbytesstart s = dropWhile isSpace s
 
 	parsebytes :: String -> Maybe Integer

Utility/SafeCommand.hs

@@ -11,7 +11,7 @@ module Utility.SafeCommand where
 
 import System.Exit
 import Utility.Process
-import Data.String.Utils
+import Utility.Misc
 import System.FilePath
 import Data.Char
 import Data.List
@@ -86,7 +86,7 @@ shellEscape :: String -> String
 shellEscape f = "'" ++ escaped ++ "'"
   where
 	-- replace ' with '"'"'
-	escaped = intercalate "'\"'\"'" $ split "'" f
+	escaped = intercalate "'\"'\"'" $ splitc '\'' f
 
 -- | Unescapes a set of shellEscaped words or filenames.
 shellUnEscape :: String -> [String]