diff --git a/Annex/AdjustedBranch.hs b/Annex/AdjustedBranch.hs
index 1f1daecbc9..24f60b260d 100644
--- a/Annex/AdjustedBranch.hs
+++ b/Annex/AdjustedBranch.hs
@@ -5,7 +5,7 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE BangPatterns, OverloadedStrings #-}
 
 module Annex.AdjustedBranch (
 	Adjustment(..),
@@ -61,6 +61,7 @@ import qualified Database.Keys
 import Config
 
 import qualified Data.Map as M
+import qualified Data.ByteString as S
 
 -- How to perform various adjustments to a TreeItem.
 class AdjustTreeItem t where
@@ -128,7 +129,7 @@ newtype BasisBranch = BasisBranch Ref
 -- refs/basis/adjusted/master(unlocked).
 basisBranch :: AdjBranch -> BasisBranch
 basisBranch (AdjBranch adjbranch) = BasisBranch $
-	Ref ("refs/basis/" ++ fromRef (Git.Ref.base adjbranch))
+	Ref ("refs/basis/" <> fromRef' (Git.Ref.base adjbranch))
 
 getAdjustment :: Branch -> Maybe Adjustment
 getAdjustment = fmap fst . adjustedToOriginal
@@ -405,7 +406,8 @@ mergeToAdjustedBranch tomerge (origbranch, adj) mergeconfig canresolvemerge comm
 					<||> (resolveMerge (Just updatedorig) tomerge True <&&> commitResolvedMerge commitmode)
 				if merged
 					then do
-						!mergecommit <- liftIO $ extractSha <$> readFile (tmpgit </> "HEAD")
+						!mergecommit <- liftIO $ extractSha
+							<$> S.readFile (tmpgit </> "HEAD")
 						-- This is run after the commit lock is dropped.
 						return $ postmerge mergecommit
 					else return $ return False
diff --git a/Annex/AdjustedBranch/Name.hs b/Annex/AdjustedBranch/Name.hs
index 5987662b9a..d997e72309 100644
--- a/Annex/AdjustedBranch/Name.hs
+++ b/Annex/AdjustedBranch/Name.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Annex.AdjustedBranch.Name (
 	originalToAdjusted,
 	adjustedToOriginal,
@@ -18,14 +20,15 @@ import qualified Git.Ref
 import Utility.Misc
 
 import Control.Applicative
-import Data.List
+import Data.Char
+import qualified Data.ByteString as S
 
-adjustedBranchPrefix :: String
+adjustedBranchPrefix :: S.ByteString
 adjustedBranchPrefix = "refs/heads/adjusted/"
 
 class SerializeAdjustment t where
-	serializeAdjustment :: t -> String
-	deserializeAdjustment :: String -> Maybe t
+	serializeAdjustment :: t -> S.ByteString
+	deserializeAdjustment :: S.ByteString -> Maybe t
 
 instance SerializeAdjustment Adjustment where
 	serializeAdjustment (LinkAdjustment l) =
@@ -33,7 +36,7 @@ instance SerializeAdjustment Adjustment where
 	serializeAdjustment (PresenceAdjustment p Nothing) =
 		serializeAdjustment p
 	serializeAdjustment (PresenceAdjustment p (Just l)) = 
-		serializeAdjustment p ++ "-" ++ serializeAdjustment l
+		serializeAdjustment p <> "-" <> serializeAdjustment l
 	deserializeAdjustment s = 
 		(LinkAdjustment <$> deserializeAdjustment s)
 			<|>
@@ -41,7 +44,7 @@ instance SerializeAdjustment Adjustment where
 			<|>
 		(PresenceAdjustment <$> deserializeAdjustment s <*> pure Nothing)
 	  where
-		(s1, s2) = separate (== '-') s
+		(s1, s2) = separate' (== (fromIntegral (ord '-'))) s
 
 instance SerializeAdjustment LinkAdjustment where
 	serializeAdjustment UnlockAdjustment = "unlocked"
@@ -65,19 +68,21 @@ newtype AdjBranch = AdjBranch { adjBranch :: Branch }
 
 originalToAdjusted :: OrigBranch -> Adjustment -> AdjBranch
 originalToAdjusted orig adj = AdjBranch $ Ref $
-	adjustedBranchPrefix ++ base ++ '(' : serializeAdjustment adj ++ ")"
+	adjustedBranchPrefix <> base <> "(" <> serializeAdjustment adj <> ")"
   where
-	base = fromRef (Git.Ref.base orig)
+	base = fromRef' (Git.Ref.base orig)
 
 type OrigBranch = Branch
 
 adjustedToOriginal :: Branch -> Maybe (Adjustment, OrigBranch)
 adjustedToOriginal b
-	| adjustedBranchPrefix `isPrefixOf` bs = do
-		let (base, as) = separate (== '(') (drop prefixlen bs)
-		adj <- deserializeAdjustment (takeWhile (/= ')') as)
+	| adjustedBranchPrefix `S.isPrefixOf` bs = do
+		let (base, as) = separate' (== openparen) (S.drop prefixlen bs)
+		adj <- deserializeAdjustment (S.takeWhile (/= closeparen) as)
 		Just (adj, Git.Ref.branchRef (Ref base))
 	| otherwise = Nothing
   where
-	bs = fromRef b
-	prefixlen = length adjustedBranchPrefix
+	bs = fromRef' b
+	prefixlen = S.length adjustedBranchPrefix
+	openparen = fromIntegral (ord '(')
+	closeparen = fromIntegral (ord ')')
diff --git a/Annex/Branch.hs b/Annex/Branch.hs
index 91d0276daa..5870b6ad21 100644
--- a/Annex/Branch.hs
+++ b/Annex/Branch.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Annex.Branch (
 	fullname,
 	name,
@@ -29,7 +31,9 @@ module Annex.Branch (
 	withIndex,
 ) where
 
+import qualified Data.ByteString as B
 import qualified Data.ByteString.Lazy as L
+import qualified Data.ByteString.Char8 as B8
 import qualified Data.Set as S
 import qualified Data.Map as M
 import Data.Function
@@ -55,7 +59,7 @@ import qualified Git.LsTree
 import Git.LsTree (lsTreeParams)
 import qualified Git.HashObject
 import Annex.HashObject
-import Git.Types (Ref(..), fromRef, RefDate, TreeItemType(..))
+import Git.Types (Ref(..), fromRef, fromRef', RefDate, TreeItemType(..))
 import Git.FilePath
 import Annex.CatFile
 import Annex.Perms
@@ -77,11 +81,11 @@ name = Git.Ref "git-annex"
 
 {- Fully qualified name of the branch. -}
 fullname :: Git.Ref
-fullname = Git.Ref $ "refs/heads/" ++ fromRef name
+fullname = Git.Ref $ "refs/heads/" <> fromRef' name
 
 {- Branch's name in origin. -}
 originname :: Git.Ref
-originname = Git.Ref $ "origin/" ++ fromRef name
+originname = Git.Ref $ "origin/" <> fromRef' name
 
 {- Does origin/git-annex exist? -}
 hasOrigin :: Annex Bool
@@ -327,9 +331,9 @@ commitIndex' jl branchref message basemessage retrynum parents = do
   where
 	-- look for "parent ref" lines and return the refs
 	commitparents = map (Git.Ref . snd) . filter isparent .
-		map (toassoc . decodeBL) . L.split newline
+		map (toassoc . L.toStrict) . L.split newline
 	newline = fromIntegral (ord '\n')
-	toassoc = separate (== ' ')
+	toassoc = separate' (== (fromIntegral (ord ' ')))
 	isparent (k,_) = k == "parent"
 		
 	{- The race can be detected by checking the commit's
@@ -438,8 +442,8 @@ forceUpdateIndex jl branchref = do
 needUpdateIndex :: Git.Ref -> Annex Bool
 needUpdateIndex branchref = do
 	f <- fromRepo gitAnnexIndexStatus
-	committedref <- Git.Ref . firstLine <$>
-		liftIO (catchDefaultIO "" $ readFileStrict f)
+	committedref <- Git.Ref . firstLine' <$>
+		liftIO (catchDefaultIO mempty $ B.readFile f)
 	return (committedref /= branchref)
 
 {- Record that the branch's index has been updated to correspond to a
@@ -621,11 +625,12 @@ ignoreRefs rs = do
 		unlines $ map fromRef $ S.elems s
 
 getIgnoredRefs :: Annex (S.Set Git.Sha)
-getIgnoredRefs = S.fromList . mapMaybe Git.Sha.extractSha . lines <$> content
+getIgnoredRefs = 
+	S.fromList . mapMaybe Git.Sha.extractSha . B8.lines <$> content
   where
 	content = do
 		f <- fromRepo gitAnnexIgnoredRefs
-		liftIO $ catchDefaultIO "" $ readFile f
+		liftIO $ catchDefaultIO mempty $ B.readFile f
 
 addMergedRefs :: [(Git.Sha, Git.Branch)] -> Annex ()
 addMergedRefs [] = return ()
@@ -643,11 +648,11 @@ getMergedRefs = S.fromList . map fst <$> getMergedRefs'
 getMergedRefs' :: Annex [(Git.Sha, Git.Branch)]
 getMergedRefs' = do
 	f <- fromRepo gitAnnexMergedRefs
-	s <- liftIO $ catchDefaultIO "" $ readFile f
-	return $ map parse $ lines s
+	s <- liftIO $ catchDefaultIO mempty $ B.readFile f
+	return $ map parse $ B8.lines s
   where
 	parse l = 
-		let (s, b) = separate (== '\t') l
+		let (s, b) = separate' (== (fromIntegral (ord '\t'))) l
 		in (Ref s, Ref b)
 
 {- Grafts a treeish into the branch at the specified location,
diff --git a/Annex/ChangedRefs.hs b/Annex/ChangedRefs.hs
index 786a193e55..3fb9d1ef1b 100644
--- a/Annex/ChangedRefs.hs
+++ b/Annex/ChangedRefs.hs
@@ -1,6 +1,6 @@
 {- Waiting for changed git refs
  -
- - Copyright 2014-216 Joey Hess <id@joeyh.name>
+ - Copyright 2014-2016 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -24,13 +24,14 @@ import qualified Utility.SimpleProtocol as Proto
 import Control.Concurrent
 import Control.Concurrent.STM
 import Control.Concurrent.STM.TBMChan
+import qualified Data.ByteString as S
 
 newtype ChangedRefs = ChangedRefs [Git.Ref]
 	deriving (Show)
 
 instance Proto.Serializable ChangedRefs where
 	serialize (ChangedRefs l) = unwords $ map Git.fromRef l
-	deserialize = Just . ChangedRefs . map Git.Ref . words
+	deserialize = Just . ChangedRefs . map (Git.Ref . encodeBS) . words
 
 data ChangedRefsHandle = ChangedRefsHandle DirWatcherHandle (TBMChan Git.Sha)
 
@@ -97,7 +98,7 @@ notifyHook chan reffile _
 	| ".lock" `isSuffixOf` reffile = noop
 	| otherwise = void $ do
 		sha <- catchDefaultIO Nothing $
-			extractSha <$> readFile reffile
+			extractSha <$> S.readFile reffile
 		-- When the channel is full, there is probably no reader
 		-- running, or ref changes have been occuring very fast,
 		-- so it's ok to not write the change to it.
diff --git a/Annex/Export.hs b/Annex/Export.hs
index 16786476de..0d2ff65235 100644
--- a/Annex/Export.hs
+++ b/Annex/Export.hs
@@ -14,7 +14,6 @@ import Types.Key
 import qualified Git
 import qualified Types.Remote as Remote
 import Messages
-import Utility.FileSystemEncoding
 
 import Control.Applicative
 import Data.Maybe
@@ -34,7 +33,7 @@ exportKey sha = mk <$> catKey sha
   where
 	mk (Just k) = AnnexKey k
 	mk Nothing = GitKey $ mkKey $ \k -> k
-		{ keyName = encodeBS $ Git.fromRef sha
+		{ keyName = Git.fromRef' sha
 		, keyVariety = SHA1Key (HasExt False)
 		, keySize = Nothing
 		, keyMtime = Nothing
diff --git a/Annex/Import.hs b/Annex/Import.hs
index e346ff210e..9d21a27aff 100644
--- a/Annex/Import.hs
+++ b/Annex/Import.hs
@@ -122,7 +122,9 @@ buildImportCommit remote importtreeconfig importcommitconfig importable =
 			Nothing -> pure committedtree
 			Just dir -> 
 				let subtreeref = Ref $
-					fromRef committedtree ++ ":" ++ fromRawFilePath (getTopFilePath dir)
+					fromRef' committedtree 
+						<> ":"
+						<> getTopFilePath dir
 				in fromMaybe emptyTree
 					<$> inRepo (Git.Ref.tree subtreeref)
 		updateexportdb importedtree
diff --git a/Annex/TaggedPush.hs b/Annex/TaggedPush.hs
index b2368dba14..cde24cdb74 100644
--- a/Annex/TaggedPush.hs
+++ b/Annex/TaggedPush.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Annex.TaggedPush where
 
 import Annex.Common
@@ -16,6 +18,8 @@ import qualified Git.Command
 import qualified Git.Branch
 import Utility.Base64
 
+import qualified Data.ByteString as S
+
 {- Converts a git branch into a branch that is tagged with a UUID, typically
  - the UUID of the repo that will be pushing it, and possibly with other
  - information.
@@ -31,11 +35,11 @@ import Utility.Base64
  - refs, per git-check-ref-format.
  -}
 toTaggedBranch :: UUID -> Maybe String -> Git.Branch -> Git.Ref
-toTaggedBranch u info b = Git.Ref $ intercalate "/" $ catMaybes
+toTaggedBranch u info b = Git.Ref $ S.intercalate "/" $ catMaybes
 	[ Just "refs/synced"
 	, Just $ fromUUID u
-	, toB64 <$> info
-	, Just $ Git.fromRef $ Git.Ref.base b
+	, toB64' . encodeBS <$> info
+	, Just $ Git.fromRef' $ Git.Ref.base b
 	]
 
 fromTaggedBranch :: Git.Ref -> Maybe (UUID, Maybe String)
diff --git a/Assistant/Threads/Merger.hs b/Assistant/Threads/Merger.hs
index ac9435122a..49c3956f10 100644
--- a/Assistant/Threads/Merger.hs
+++ b/Assistant/Threads/Merger.hs
@@ -109,6 +109,6 @@ isAnnexBranch f = n `isSuffixOf` f
 	n = '/' : Git.fromRef Annex.Branch.name
 
 fileToBranch :: FilePath -> Git.Ref
-fileToBranch f = Git.Ref $ "refs" </> base
+fileToBranch f = Git.Ref $ encodeBS' $ "refs" </> base
   where
 	base = Prelude.last $ split "/refs/" f
diff --git a/Assistant/Threads/Watcher.hs b/Assistant/Threads/Watcher.hs
index 80523b5e55..0956f59ba5 100644
--- a/Assistant/Threads/Watcher.hs
+++ b/Assistant/Threads/Watcher.hs
@@ -330,7 +330,7 @@ addLink :: FilePath -> FilePath -> Maybe Key -> Assistant (Maybe Change)
 addLink file link mk = do
 	debug ["add symlink", file]
 	liftAnnex $ do
-		v <- catObjectDetails $ Ref $ ':':file
+		v <- catObjectDetails $ Ref $ encodeBS' $ ':':file
 		case v of
 			Just (currlink, sha, _type)
 				| s2w8 link == L.unpack currlink ->
diff --git a/Command/Export.hs b/Command/Export.hs
index f66c512d25..97c9014f51 100644
--- a/Command/Export.hs
+++ b/Command/Export.hs
@@ -37,6 +37,7 @@ import Utility.Tmp
 import Utility.Metered
 import Utility.Matcher
 
+import qualified Data.ByteString.Char8 as S8
 import qualified Data.ByteString.Lazy as L
 import qualified Data.Map as M
 import Control.Concurrent
@@ -112,7 +113,7 @@ getExportCommit r treeish
 		return (fmap (tb, ) commitsha)
 	| otherwise = return Nothing
   where
-	baseref = Ref $ takeWhile (/= ':') $ fromRef $ 
+	baseref = Ref $ S8.takeWhile (/= ':') $ fromRef' $ 
 		Git.Ref.removeBase refsheads treeish
 	refsheads = "refs/heads"
 
diff --git a/Command/FindRef.hs b/Command/FindRef.hs
index eb74928f4c..27dfcbe07a 100644
--- a/Command/FindRef.hs
+++ b/Command/FindRef.hs
@@ -22,6 +22,6 @@ seek o = Find.seek o'
   where
 	o' = o 
 		{ Find.keyOptions = Just $ WantBranchKeys $
-			map Git.Ref (Find.findThese o)
+			map (Git.Ref . encodeBS') (Find.findThese o)
 		, Find.findThese = []
 		}
diff --git a/Command/Import.hs b/Command/Import.hs
index 5447df5bff..5d1c87c320 100644
--- a/Command/Import.hs
+++ b/Command/Import.hs
@@ -66,7 +66,7 @@ optParser desc = do
 			[bs] -> 
 				let (branch, subdir) = separate (== ':') bs
 				in RemoteImportOptions r
-					(Ref branch)
+					(Ref (encodeBS' branch))
 					(if null subdir then Nothing else Just subdir)
 			_ -> giveup "expected BRANCH[:SUBDIR]"
 
diff --git a/Command/Info.hs b/Command/Info.hs
index 3448ee6ef2..7df42fa39a 100644
--- a/Command/Info.hs
+++ b/Command/Info.hs
@@ -181,7 +181,7 @@ dirInfo o dir = showCustom (unwords ["info", dir]) $ do
 
 treeishInfo :: InfoOptions -> String -> Annex ()
 treeishInfo o t = do
-	mi <- getTreeStatInfo o (Git.Ref t)
+	mi <- getTreeStatInfo o (Git.Ref (encodeBS' t))
 	case mi of
 		Nothing -> noInfo t
 		Just i -> showCustom (unwords ["info", t]) $ do
diff --git a/Command/Log.hs b/Command/Log.hs
index 5597bfbf47..b2a7ea7e12 100644
--- a/Command/Log.hs
+++ b/Command/Log.hs
@@ -264,7 +264,8 @@ parseGitRawLog config = parse epoch
 parseRawChangeLine :: String -> Maybe (Git.Ref, Git.Ref)
 parseRawChangeLine = go . words
   where
-	go (_:_:oldsha:newsha:_) = Just (Git.Ref oldsha, Git.Ref newsha)
+	go (_:_:oldsha:newsha:_) = 
+		Just (Git.Ref (encodeBS oldsha), Git.Ref (encodeBS newsha))
 	go _ = Nothing
 
 parseTimeStamp :: String -> POSIXTime
diff --git a/Command/Merge.hs b/Command/Merge.hs
index fe1119dc8a..ed075ad876 100644
--- a/Command/Merge.hs
+++ b/Command/Merge.hs
@@ -26,7 +26,7 @@ seek [] = do
 	commandAction mergeSyncedBranch
 seek bs = do
 	prepMerge
-	forM_ bs (commandAction . mergeBranch . Git.Ref)
+	forM_ bs (commandAction . mergeBranch . Git.Ref . encodeBS')
 
 mergeAnnexBranch :: CommandStart
 mergeAnnexBranch = starting "merge" (ActionItemOther (Just "git-annex")) $ do
diff --git a/Command/ResolveMerge.hs b/Command/ResolveMerge.hs
index e3d9829be8..10f5f98901 100644
--- a/Command/ResolveMerge.hs
+++ b/Command/ResolveMerge.hs
@@ -13,6 +13,8 @@ import Git.Sha
 import qualified Git.Branch
 import Annex.AutoMerge
 
+import qualified Data.ByteString as S
+
 cmd :: Command
 cmd = command "resolvemerge" SectionPlumbing
 	"resolve merge conflicts"
@@ -27,7 +29,7 @@ start = starting "resolvemerge" (ActionItemOther Nothing) $ do
 	d <- fromRawFilePath <$> fromRepo Git.localGitDir
 	let merge_head = d </> "MERGE_HEAD"
 	them <- fromMaybe (error nomergehead) . extractSha
-		<$> liftIO (readFile merge_head)
+		<$> liftIO (S.readFile merge_head)
 	ifM (resolveMerge (Just us) them False)
 		( do
 			void $ commitResolvedMerge Git.Branch.ManualCommit
diff --git a/Command/Sync.hs b/Command/Sync.hs
index 49ec61cb52..42afe518a9 100644
--- a/Command/Sync.hs
+++ b/Command/Sync.hs
@@ -72,6 +72,8 @@ import Utility.Process.Transcript
 
 import Control.Concurrent.MVar
 import qualified Data.Map as M
+import qualified Data.ByteString as S
+import Data.Char
 
 cmd :: Command
 cmd = withGlobalOptions [jobsOption] $
@@ -444,11 +446,11 @@ importRemote o mergeconfig remote currbranch
 	| otherwise = case remoteAnnexTrackingBranch (Remote.gitconfig remote) of
 		Nothing -> noop
 		Just tb -> do
-			let (b, s) = separate (== ':') (Git.fromRef tb)
+			let (b, p) = separate' (== (fromIntegral (ord ':'))) (Git.fromRef' tb)
 			let branch = Git.Ref b
-			let subdir = if null s
+			let subdir = if S.null p
 				then Nothing
-				else Just (asTopFilePath (toRawFilePath s))
+				else Just (asTopFilePath p)
 			Command.Import.seekRemote remote branch subdir
 			void $ mergeRemote remote currbranch mergeconfig o
   where
diff --git a/Command/Uninit.hs b/Command/Uninit.hs
index c64d4aa2dc..db7d25a7a8 100644
--- a/Command/Uninit.hs
+++ b/Command/Uninit.hs
@@ -35,7 +35,7 @@ check = do
 	whenM ((/=) <$> liftIO (absPath top) <*> liftIO (absPath currdir)) $
 		giveup "can only run uninit from the top of the git repository"
   where
-	current_branch = Git.Ref . Prelude.head . lines . decodeBS' <$> revhead
+	current_branch = Git.Ref . encodeBS' . Prelude.head . lines . decodeBS' <$> revhead
 	revhead = inRepo $ Git.Command.pipeReadStrict
 		[Param "rev-parse", Param "--abbrev-ref", Param "HEAD"]
 
diff --git a/Command/Unused.hs b/Command/Unused.hs
index b68452d5c8..4b2de82597 100644
--- a/Command/Unused.hs
+++ b/Command/Unused.hs
@@ -5,12 +5,10 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE BangPatterns, OverloadedStrings #-}
 
 module Command.Unused where
 
-import qualified Data.Map as M
-
 import Command
 import Logs.Unused
 import Annex.Content
@@ -37,6 +35,11 @@ import Annex.BloomFilter
 import qualified Database.Keys
 import Annex.InodeSentinal
 
+import qualified Data.Map as M
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
+import Data.Char
+
 cmd :: Command
 cmd = command "unused" SectionMaintenance "look for unused file content"
 	paramNothing (seek <$$> optParser)
@@ -221,8 +224,7 @@ withKeysReferenced' mdir initial a = do
 
 withKeysReferencedDiffGitRefs :: RefSpec -> (Key -> Annex ()) -> Annex ()
 withKeysReferencedDiffGitRefs refspec a = do
-	rs <- relevantrefs . decodeBS'
-		<$> inRepo (Git.Command.pipeReadStrict [Param "show-ref"])
+	rs <- relevantrefs <$> inRepo (Git.Command.pipeReadStrict [Param "show-ref"])
 	shaHead <- maybe (return Nothing) (inRepo . Git.Ref.sha)
 		=<< inRepo Git.Branch.currentUnsafe
 	let haveHead = any (\(shaRef, _) -> Just shaRef == shaHead) rs
@@ -233,12 +235,12 @@ withKeysReferencedDiffGitRefs refspec a = do
   where
 	relevantrefs = map (\(r, h) -> (Git.Ref r, Git.Ref h)) .
 		filter ourbranches .
-		map (separate (== ' ')) .
-		lines
+		map (separate' (== (fromIntegral (ord ' ')))) .
+		S8.lines
 	nubRefs = nubBy (\(x, _) (y, _) -> x == y)
-	ourbranchend = '/' : Git.fromRef Annex.Branch.name
-	ourbranches (_, b) = not (ourbranchend `isSuffixOf` b)
-		&& not ("refs/synced/" `isPrefixOf` b)
+	ourbranchend = S.cons (fromIntegral (ord '/')) (Git.fromRef' Annex.Branch.name)
+	ourbranches (_, b) = not (ourbranchend `S.isSuffixOf` b)
+		&& not ("refs/synced/" `S.isPrefixOf` b)
 		&& not (is_branchView (Git.Ref b))
 	getreflog rs = inRepo $ Git.RefLog.getMulti rs
 
diff --git a/Database/Keys.hs b/Database/Keys.hs
index b1650b286c..25954ba71a 100644
--- a/Database/Keys.hs
+++ b/Database/Keys.hs
@@ -6,6 +6,7 @@
  -}
 
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module Database.Keys (
 	DbHandle,
@@ -44,6 +45,7 @@ import Git.Types
 import Git.Index
 
 import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
 import qualified System.FilePath.ByteString as P
 
 {- Runs an action that reads from the database.
@@ -237,8 +239,8 @@ reconcileStaged qh = do
 		Nothing -> noop
   where
 	go cur indexcache = do
-		(l, cleanup) <- inRepo $ pipeNullSplit diff
-		changed <- procdiff (map decodeBL' l) False
+		(l, cleanup) <- inRepo $ pipeNullSplit' diff
+		changed <- procdiff l False
 		void $ liftIO cleanup
 		-- Flush database changes immediately
 		-- so other processes can see them.
@@ -278,15 +280,16 @@ reconcileStaged qh = do
 		, Param "--no-ext-diff"
 		]
 	
-	procdiff (info:file:rest) changed = case words info of
-		((':':_srcmode):dstmode:_srcsha:dstsha:_change:[])
-			-- Only want files, not symlinks
-			| dstmode /= decodeBS' (fmtTreeItemType TreeSymlink) -> do
-				maybe noop (reconcile (asTopFilePath (toRawFilePath file)))
-					=<< catKey (Ref dstsha)
-				procdiff rest True
-			| otherwise -> procdiff rest changed
-		_ -> return changed -- parse failed
+	procdiff (info:file:rest) changed
+		| ":" `S.isPrefixOf` info = case S8.words info of
+			(_colonsrcmode:dstmode:_srcsha:dstsha:_change:[])
+				-- Only want files, not symlinks
+				| dstmode /= fmtTreeItemType TreeSymlink -> do
+					maybe noop (reconcile (asTopFilePath file))
+						=<< catKey (Ref dstsha)
+					procdiff rest True
+				| otherwise -> procdiff rest changed
+			_ -> return changed -- parse failed
 	procdiff _ changed = return changed
 
 	-- Note that database writes done in here will not necessarily 
diff --git a/Database/Types.hs b/Database/Types.hs
index ac6aad2748..561972284a 100644
--- a/Database/Types.hs
+++ b/Database/Types.hs
@@ -28,6 +28,7 @@ import Foreign.C.Types
 import Key
 import Utility.InodeCache
 import Utility.FileSize
+import Utility.FileSystemEncoding
 import Git.Types
 import Types.UUID
 import Types.Import
@@ -94,10 +95,10 @@ newtype SSha = SSha String
 	deriving (Eq, Show)
 
 toSSha :: Sha -> SSha
-toSSha (Ref s) = SSha s
+toSSha (Ref s) = SSha (decodeBS' s)
 
 fromSSha :: SSha -> Ref
-fromSSha (SSha s) = Ref s
+fromSSha (SSha s) = Ref (encodeBS' s)
 
 instance PersistField SSha where
 	toPersistValue (SSha b) = toPersistValue b
diff --git a/Git.hs b/Git.hs
index 87a8d19720..d33345ed3f 100644
--- a/Git.hs
+++ b/Git.hs
@@ -14,6 +14,7 @@ module Git (
 	Repo(..),
 	Ref(..),
 	fromRef,
+	fromRef',
 	Branch,
 	Sha,
 	Tag,
diff --git a/Git/Branch.hs b/Git/Branch.hs
index 699fbf50e1..fcae905f64 100644
--- a/Git/Branch.hs
+++ b/Git/Branch.hs
@@ -18,6 +18,7 @@ import qualified Git.Config
 import qualified Git.Ref
 
 import qualified Data.ByteString as B
+import qualified Data.ByteString.Char8 as B8
 
 {- The currently checked out branch.
  -
@@ -39,25 +40,27 @@ current r = do
 
 {- The current branch, which may not really exist yet. -}
 currentUnsafe :: Repo -> IO (Maybe Branch)
-currentUnsafe r = parse . firstLine'
-	<$> pipeReadStrict [Param "symbolic-ref", Param "-q", Param $ fromRef Git.Ref.headRef] r
+currentUnsafe r = parse . firstLine' <$> pipeReadStrict
+	[ Param "symbolic-ref"
+	, Param "-q"
+	, Param $ fromRef Git.Ref.headRef
+	] r
   where
 	parse b
 		| B.null b = Nothing
-		| otherwise = Just $ Git.Ref $ decodeBS b
+		| otherwise = Just $ Git.Ref b
 
 {- Checks if the second branch has any commits not present on the first
  - branch. -}
 changed :: Branch -> Branch -> Repo -> IO Bool
 changed origbranch newbranch repo
 	| origbranch == newbranch = return False
-	| otherwise = not . null
+	| otherwise = not . B.null
 		<$> changed' origbranch newbranch [Param "-n1"] repo
   where
 
-changed' :: Branch -> Branch -> [CommandParam] -> Repo -> IO String
-changed' origbranch newbranch extraps repo =
-	decodeBS <$> pipeReadStrict ps repo
+changed' :: Branch -> Branch -> [CommandParam] -> Repo -> IO B.ByteString
+changed' origbranch newbranch extraps repo = pipeReadStrict ps repo
   where
 	ps =
 		[ Param "log"
@@ -68,7 +71,7 @@ changed' origbranch newbranch extraps repo =
 {- Lists commits that are in the second branch and not in the first branch. -}
 changedCommits :: Branch -> Branch -> [CommandParam] -> Repo -> IO [Sha]
 changedCommits origbranch newbranch extraps repo = 
-	catMaybes . map extractSha . lines
+	catMaybes . map extractSha . B8.lines
 		<$> changed' origbranch newbranch extraps repo
 	
 {- Check if it's possible to fast-forward from the old
@@ -163,8 +166,7 @@ commitCommand' runner commitmode ps = runner $
  -}
 commit :: CommitMode -> Bool -> String -> Branch -> [Ref] -> Repo -> IO (Maybe Sha)
 commit commitmode allowempty message branch parentrefs repo = do
-	tree <- getSha "write-tree" $
-		decodeBS' <$> pipeReadStrict [Param "write-tree"] repo
+	tree <- getSha "write-tree" $ pipeReadStrict [Param "write-tree"] repo
 	ifM (cancommit tree)
 		( do
 			sha <- commitTree commitmode message parentrefs tree repo
diff --git a/Git/CatFile.hs b/Git/CatFile.hs
index 980d289840..68850f075c 100644
--- a/Git/CatFile.hs
+++ b/Git/CatFile.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Git.CatFile (
 	CatFileHandle,
 	catFileStart,
@@ -22,7 +24,6 @@ module Git.CatFile (
 import System.IO
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
-import qualified Data.ByteString.Lazy.Char8 as L8
 import qualified Data.Map as M
 import Data.String
 import Data.Char
@@ -69,11 +70,11 @@ catFileStop h = do
 {- Reads a file from a specified branch. -}
 catFile :: CatFileHandle -> Branch -> RawFilePath -> IO L.ByteString
 catFile h branch file = catObject h $ Ref $
-	fromRef branch ++ ":" ++ fromRawFilePath (toInternalGitPath file)
+	fromRef' branch <> ":" <> toInternalGitPath file
 
 catFileDetails :: CatFileHandle -> Branch -> RawFilePath -> IO (Maybe (L.ByteString, Sha, ObjectType))
 catFileDetails h branch file = catObjectDetails h $ Ref $
-	fromRef branch ++ ":" ++ fromRawFilePath (toInternalGitPath file)
+	fromRef' branch <> ":" <> toInternalGitPath file
 
 {- Uses a running git cat-file read the content of an object.
  - Objects that do not exist will have "" returned. -}
@@ -148,7 +149,7 @@ parseResp object l
 	| " missing" `isSuffixOf` l -- less expensive than full check
 		&& l == fromRef object ++ " missing" = Just DNE
 	| otherwise = case words l of
-		[sha, objtype, size] -> case extractSha sha of
+		[sha, objtype, size] -> case extractSha (encodeBS sha) of
 			Just sha' -> case (readObjectType (encodeBS objtype), reads size) of
 				(Just t, [(bytes, "")]) -> 
 					Just $ ParsedResp sha' bytes t
@@ -218,39 +219,39 @@ catTree h treeref = go <$> catObjectDetails h treeref
 catCommit :: CatFileHandle -> Ref -> IO (Maybe Commit)
 catCommit h commitref = go <$> catObjectDetails h commitref
   where
-	go (Just (b, _, CommitObject)) = parseCommit b
+	go (Just (b, _, CommitObject)) = parseCommit (L.toStrict b)
 	go _ = Nothing
 
-parseCommit :: L.ByteString -> Maybe Commit
+parseCommit :: S.ByteString -> Maybe Commit
 parseCommit b = Commit
-	<$> (extractSha . L8.unpack =<< field "tree")
-	<*> Just (maybe [] (mapMaybe (extractSha . L8.unpack)) (fields "parent"))
+	<$> (extractSha =<< field "tree")
+	<*> Just (maybe [] (mapMaybe extractSha) (fields "parent"))
 	<*> (parsemetadata <$> field "author")
 	<*> (parsemetadata <$> field "committer")
-	<*> Just (L8.unpack $ L.intercalate (L.singleton nl) message)
+	<*> Just (decodeBS $ S.intercalate (S.singleton nl) message)
   where
 	field n = headMaybe =<< fields n
 	fields n = M.lookup (fromString n) fieldmap
 	fieldmap = M.fromListWith (++) ((map breakfield) header)
 	breakfield l =
-		let (k, sp_v) = L.break (== sp) l
-		in (k, [L.drop 1 sp_v])
-	(header, message) = separate L.null ls
-	ls = L.split nl b
+		let (k, sp_v) = S.break (== sp) l
+		in (k, [S.drop 1 sp_v])
+	(header, message) = separate S.null ls
+	ls = S.split nl b
 
 	-- author and committer lines have the form: "name <email> date"
 	-- The email is always present, even if empty "<>"
 	parsemetadata l = CommitMetaData
-		{ commitName = whenset $ L.init name_sp
+		{ commitName = whenset $ S.init name_sp
 		, commitEmail = whenset email
-		, commitDate = whenset $ L.drop 2 gt_sp_date
+		, commitDate = whenset $ S.drop 2 gt_sp_date
 		}
 	  where
-		(name_sp, rest) = L.break (== lt) l
-		(email, gt_sp_date) = L.break (== gt) (L.drop 1 rest)
+		(name_sp, rest) = S.break (== lt) l
+		(email, gt_sp_date) = S.break (== gt) (S.drop 1 rest)
 		whenset v
-			| L.null v = Nothing
-			| otherwise = Just (L8.unpack v)
+			| S.null v = Nothing
+			| otherwise = Just (decodeBS v)
 
 	nl = fromIntegral (ord '\n')
 	sp = fromIntegral (ord ' ')
diff --git a/Git/Command.hs b/Git/Command.hs
index eb20af2dc9..15157a08a5 100644
--- a/Git/Command.hs
+++ b/Git/Command.hs
@@ -81,11 +81,16 @@ pipeReadStrict' reader params repo = assertLocal repo $
 {- Runs a git command, feeding it an input, and returning its output,
  - which is expected to be fairly small, since it's all read into memory
  - strictly. -}
-pipeWriteRead :: [CommandParam] -> Maybe (Handle -> IO ()) -> Repo -> IO String
+pipeWriteRead :: [CommandParam] -> Maybe (Handle -> IO ()) -> Repo -> IO S.ByteString
 pipeWriteRead params writer repo = assertLocal repo $
 	writeReadProcessEnv "git" (toCommand $ gitCommandLine params repo) 
-		(gitEnv repo) writer (Just adjusthandle)
+		(gitEnv repo) writer'
   where
+	writer' = case writer of
+		Nothing -> Nothing
+		Just a -> Just $ \h -> do
+			adjusthandle h
+			a h
 	adjusthandle h = hSetNewlineMode h noNewlineTranslation
 
 {- Runs a git command, feeding it input on a handle with an action. -}
diff --git a/Git/Credential.hs b/Git/Credential.hs
index 9465d27963..2f926b0323 100644
--- a/Git/Credential.hs
+++ b/Git/Credential.hs
@@ -58,7 +58,7 @@ urlCredential = Credential . M.singleton "url"
 
 runCredential :: String -> Credential -> Repo -> IO Credential
 runCredential action input r =
-	parseCredential <$> pipeWriteRead 
+	parseCredential . decodeBS <$> pipeWriteRead 
 		[ Param "credential"
 		, Param action
 		]
diff --git a/Git/DiffTree.hs b/Git/DiffTree.hs
index bfd1a7a1bc..c566de3fd3 100644
--- a/Git/DiffTree.hs
+++ b/Git/DiffTree.hs
@@ -1,6 +1,6 @@
 {- git diff-tree interface
  -
- - Copyright 2012 Joey Hess <id@joeyh.name>
+ - Copyright 2012-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -17,7 +17,9 @@ module Git.DiffTree (
 	commitDiff,
 ) where
 
-import Numeric
+import qualified Data.ByteString.Lazy as L
+import qualified Data.Attoparsec.ByteString.Lazy as A
+import qualified Data.Attoparsec.ByteString.Char8 as A8
 
 import Common
 import Git
@@ -27,6 +29,7 @@ import Git.FilePath
 import Git.DiffTreeItem
 import qualified Git.Filename
 import qualified Git.Ref
+import Utility.Attoparsec
 
 {- Checks if the DiffTreeItem modifies a file with a given name
  - or under a directory by that name. -}
@@ -89,7 +92,7 @@ commitDiff ref = getdiff (Param "show")
 getdiff :: CommandParam -> [CommandParam] -> Repo -> IO ([DiffTreeItem], IO Bool)
 getdiff command params repo = do
 	(diff, cleanup) <- pipeNullSplit ps repo
-	return (parseDiffRaw (map decodeBL diff), cleanup)
+	return (parseDiffRaw diff, cleanup)
   where
 	ps = 
 		command :
@@ -100,26 +103,28 @@ getdiff command params repo = do
 		params
 
 {- Parses --raw output used by diff-tree and git-log. -}
-parseDiffRaw :: [String] -> [DiffTreeItem]
+parseDiffRaw :: [L.ByteString] -> [DiffTreeItem]
 parseDiffRaw l = go l
   where
 	go [] = []
-	go (info:f:rest) = mk info f : go rest
-	go (s:[]) = error $ "diff-tree parse error near \"" ++ s ++ "\""
+	go (info:f:rest) = case A.parse (parserDiffRaw (L.toStrict f)) info of
+		A.Done _ r -> r : go rest
+		A.Fail _ _ err -> error $ "diff-tree parse error: " ++ err
+	go (s:[]) = error $ "diff-tree parse error near \"" ++ decodeBL' s ++ "\""
 
-	mk info f = DiffTreeItem
-		{ srcmode = readmode srcm
-		, dstmode = readmode dstm
-		, srcsha = fromMaybe (error "bad srcsha") $ extractSha ssha
-		, dstsha = fromMaybe (error "bad dstsha") $ extractSha dsha
-		, status = s
-		, file = asTopFilePath $ fromInternalGitPath $ Git.Filename.decode $ toRawFilePath f
-		}
-	  where
-		readmode = fst . Prelude.head . readOct
-
-		-- info = :<srcmode> SP <dstmode> SP <srcsha> SP <dstsha> SP <status>
-		(srcm, past_srcm) = splitAt 7 $ drop 1 info
-		(dstm, past_dstm) = splitAt 7 past_srcm
-		(ssha, past_ssha) = separate (== ' ') past_dstm
-		(dsha, s) = separate (== ' ') past_ssha
+-- :<srcmode> SP <dstmode> SP <srcsha> SP <dstsha> SP <status>
+parserDiffRaw :: RawFilePath -> A.Parser DiffTreeItem
+parserDiffRaw f = DiffTreeItem
+	<$ A8.char ':'
+	<*> octal
+	<* A8.char ' '
+	<*> octal
+	<* A8.char ' '
+	<*> (maybe (fail "bad srcsha") return . extractSha =<< nextword)
+	<* A8.char ' '
+	<*> (maybe (fail "bad dstsha") return . extractSha =<< nextword)
+	<* A8.char ' '
+	<*> A.takeByteString
+	<*> pure (asTopFilePath $ fromInternalGitPath $ Git.Filename.decode f)
+  where
+	nextword = A8.takeTill (== ' ')
diff --git a/Git/DiffTreeItem.hs b/Git/DiffTreeItem.hs
index 4034e5ecfb..090ad3e008 100644
--- a/Git/DiffTreeItem.hs
+++ b/Git/DiffTreeItem.hs
@@ -10,6 +10,7 @@ module Git.DiffTreeItem (
 ) where
 
 import System.Posix.Types
+import qualified Data.ByteString as S
 
 import Git.FilePath
 import Git.Types
@@ -19,6 +20,6 @@ data DiffTreeItem = DiffTreeItem
 	, dstmode :: FileMode
 	, srcsha :: Sha -- null sha if file was added
 	, dstsha :: Sha -- null sha if file was deleted
-	, status :: String
+	, status :: S.ByteString
 	, file :: TopFilePath
 	} deriving Show
diff --git a/Git/FilePath.hs b/Git/FilePath.hs
index 66a015994e..d31b421a5a 100644
--- a/Git/FilePath.hs
+++ b/Git/FilePath.hs
@@ -50,7 +50,7 @@ data BranchFilePath = BranchFilePath Ref TopFilePath
 {- Git uses the branch:file form to refer to a BranchFilePath -}
 descBranchFilePath :: BranchFilePath -> S.ByteString
 descBranchFilePath (BranchFilePath b f) =
-	encodeBS' (fromRef b) <> ":" <> getTopFilePath f
+	fromRef' b <> ":" <> getTopFilePath f
 
 {- Path to a TopFilePath, within the provided git repo. -}
 fromTopFilePath :: TopFilePath -> Git.Repo -> RawFilePath
diff --git a/Git/Fsck.hs b/Git/Fsck.hs
index 6f33e11991..69a9e9f81e 100644
--- a/Git/Fsck.hs
+++ b/Git/Fsck.hs
@@ -139,7 +139,8 @@ isMissing s r = either (const True) (const False) <$> tryIO dump
 		] r
 
 findShas :: [String] -> [Sha]
-findShas = catMaybes . map extractSha . concat . map words . filter wanted
+findShas = catMaybes . map (extractSha . encodeBS') 
+	. concat . map words . filter wanted
   where
 	wanted l = not ("dangling " `isPrefixOf` l)
 
diff --git a/Git/HashObject.hs b/Git/HashObject.hs
index 3787c9cb57..bcad9a1109 100644
--- a/Git/HashObject.hs
+++ b/Git/HashObject.hs
@@ -18,6 +18,7 @@ import qualified Utility.CoProcess as CoProcess
 import Utility.Tmp
 
 import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
 import qualified Data.ByteString.Lazy as L
 import Data.ByteString.Builder
 
@@ -39,7 +40,7 @@ hashFile :: HashObjectHandle -> FilePath -> IO Sha
 hashFile h file = CoProcess.query h send receive
   where
 	send to = hPutStrLn to =<< absPath file
-	receive from = getSha "hash-object" $ hGetLine from
+	receive from = getSha "hash-object" $ S8.hGetLine from
 
 class HashableBlob t where
 	hashableBlobToHandle :: Handle -> t -> IO ()
diff --git a/Git/History.hs b/Git/History.hs
index 6706497317..1b7127229b 100644
--- a/Git/History.hs
+++ b/Git/History.hs
@@ -15,6 +15,9 @@ import Git.Command
 import Git.Sha
 
 import qualified Data.Set as S
+import qualified Data.ByteString.Lazy as L
+import qualified Data.ByteString.Char8 as B8
+import qualified Data.ByteString.Lazy.Char8 as L8
 
 data History t = History t (S.Set (History t))
 	deriving (Show, Eq, Ord)
@@ -53,8 +56,9 @@ getHistoryToDepth n commit r = do
 	!h <- fmap (truncateHistoryToDepth n) 
 		. build Nothing 
 		. map parsehistorycommit
-		. lines
-		<$> hGetContents inh
+		. map L.toStrict
+		. L8.lines
+		<$> L.hGetContents inh
 	hClose inh
 	void $ waitForProcess pid
 	return h
@@ -93,7 +97,7 @@ getHistoryToDepth n commit r = do
 		, Param "--format=%T %H %P"
 		]
 	
-	parsehistorycommit l = case map extractSha (splitc ' ' l) of
+	parsehistorycommit l = case map extractSha (B8.split ' ' l) of
 		(Just t:Just c:ps) -> Just $ 
 			( HistoryCommit
 				{ historyCommit = c
diff --git a/Git/LsFiles.hs b/Git/LsFiles.hs
index 31a74d4283..830b5f5bfe 100644
--- a/Git/LsFiles.hs
+++ b/Git/LsFiles.hs
@@ -36,9 +36,10 @@ import Utility.InodeCache
 import Utility.TimeStamp
 
 import Numeric
+import Data.Char
 import System.Posix.Types
 import qualified Data.Map as M
-import qualified Data.ByteString.Lazy as L
+import qualified Data.ByteString as S
 
 {- It's only safe to use git ls-files on the current repo, not on a remote.
  -
@@ -81,7 +82,7 @@ inRepo' ps l repo = guardSafeForLsFiles repo $ pipeNullSplit' params repo
 {- Files that are checked into the index or have been committed to a
  - branch. -}
 inRepoOrBranch :: Branch -> [RawFilePath] -> Repo -> IO ([RawFilePath], IO Bool)
-inRepoOrBranch (Ref b) = inRepo' [Param $ "--with-tree=" ++ b]
+inRepoOrBranch b = inRepo' [Param $ "--with-tree=" ++ fromRef b]
 
 {- Scans for files at the specified locations that are not checked into git. -}
 notInRepo :: Bool -> [RawFilePath] -> Repo -> IO ([RawFilePath], IO Bool)
@@ -189,21 +190,21 @@ stagedDetails = stagedDetails' []
  - contents. -}
 stagedDetails' :: [CommandParam] -> [RawFilePath] -> Repo -> IO ([StagedDetails], IO Bool)
 stagedDetails' ps l repo = guardSafeForLsFiles repo $ do
-	(ls, cleanup) <- pipeNullSplit params repo
+	(ls, cleanup) <- pipeNullSplit' params repo
 	return (map parseStagedDetails ls, cleanup)
   where
 	params = Param "ls-files" : Param "--stage" : Param "-z" : ps ++ 
 		Param "--" : map (File . fromRawFilePath) l
 
-parseStagedDetails :: L.ByteString -> StagedDetails
+parseStagedDetails :: S.ByteString -> StagedDetails
 parseStagedDetails s
-	| null file = (L.toStrict s, Nothing, Nothing)
-	| otherwise = (toRawFilePath file, extractSha sha, readmode mode)
+	| S.null file = (s, Nothing, Nothing)
+	| otherwise = (file, extractSha sha, readmode mode)
   where
-	(metadata, file) = separate (== '\t') (decodeBL' s)
-	(mode, metadata') = separate (== ' ') metadata
-	(sha, _) = separate (== ' ') metadata'
-	readmode = fst <$$> headMaybe . readOct
+	(metadata, file) = separate' (== fromIntegral (ord '\t')) s
+	(mode, metadata') = separate' (== fromIntegral (ord ' ')) metadata
+	(sha, _) = separate' (== fromIntegral (ord ' ')) metadata'
+	readmode = fst <$$> headMaybe . readOct . decodeBS'
 
 {- Returns a list of the files in the specified locations that are staged
  - for commit, and whose type has changed. -}
@@ -284,7 +285,7 @@ parseUnmerged s
 				then Nothing
 				else do
 					treeitemtype <- readTreeItemType (encodeBS rawtreeitemtype)
-					sha <- extractSha rawsha
+					sha <- extractSha (encodeBS' rawsha)
 					return $ InternalUnmerged (stage == 2) (toRawFilePath file)
 						(Just treeitemtype) (Just sha)
 		_ -> Nothing
diff --git a/Git/LsTree.hs b/Git/LsTree.hs
index 5175c39024..ead501f0dc 100644
--- a/Git/LsTree.hs
+++ b/Git/LsTree.hs
@@ -96,7 +96,7 @@ parserLsTree = TreeItem
 	<*> A8.takeTill (== ' ')
 	<* A8.char ' '
 	-- sha
-	<*> (Ref . decodeBS' <$> A8.takeTill (== '\t'))
+	<*> (Ref <$> A8.takeTill (== '\t'))
 	<* A8.char '\t'
 	-- file
 	<*> (asTopFilePath . Git.Filename.decode <$> A.takeByteString)
diff --git a/Git/Objects.hs b/Git/Objects.hs
index c9ede4da9a..6a240875e0 100644
--- a/Git/Objects.hs
+++ b/Git/Objects.hs
@@ -26,7 +26,7 @@ listPackFiles r = filter (".pack" `isSuffixOf`)
 
 listLooseObjectShas :: Repo -> IO [Sha]
 listLooseObjectShas r = catchDefaultIO [] $
-	mapMaybe (extractSha . concat . reverse . take 2 . reverse . splitDirectories)
+	mapMaybe (extractSha . encodeBS . concat . reverse . take 2 . reverse . splitDirectories)
 		<$> dirContentsRecursiveSkipping (== "pack") True (objectsDir r)
 
 looseObjectFile :: Repo -> Sha -> FilePath
diff --git a/Git/Ref.hs b/Git/Ref.hs
index 621e328f27..104a1db715 100644
--- a/Git/Ref.hs
+++ b/Git/Ref.hs
@@ -17,6 +17,7 @@ import Git.Types
 
 import Data.Char (chr, ord)
 import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
 
 headRef :: Ref
 headRef = Ref "HEAD"
@@ -25,7 +26,7 @@ headFile :: Repo -> FilePath
 headFile r = fromRawFilePath (localGitDir r) </> "HEAD"
 
 setHeadRef :: Ref -> Repo -> IO ()
-setHeadRef ref r = writeFile (headFile r) ("ref: " ++ fromRef ref)
+setHeadRef ref r = S.writeFile (headFile r) ("ref: " <> fromRef' ref)
 
 {- Converts a fully qualified git ref into a user-visible string. -}
 describe :: Ref -> String
@@ -41,10 +42,11 @@ base = removeBase "refs/heads/" . removeBase "refs/remotes/"
 {- Removes a directory such as "refs/heads/master" from a
  - fully qualified ref. Any ref not starting with it is left as-is. -}
 removeBase :: String -> Ref -> Ref
-removeBase dir (Ref r)
-	| prefix `isPrefixOf` r = Ref (drop (length prefix) r)
-	| otherwise = Ref r
+removeBase dir r
+	| prefix `isPrefixOf` rs = Ref $ encodeBS $ drop (length prefix) rs
+	| otherwise = r
   where
+	rs = fromRef r
 	prefix = case end dir of
 		['/'] -> dir
 		_ -> dir ++ "/"
@@ -53,7 +55,7 @@ removeBase dir (Ref r)
  - refs/heads/master, yields a version of that ref under the directory,
  - such as refs/remotes/origin/master. -}
 underBase :: String -> Ref -> Ref
-underBase dir r = Ref $ dir ++ "/" ++ fromRef (base r)
+underBase dir r = Ref $ encodeBS dir <> "/" <> fromRef' (base r)
 
 {- Convert a branch such as "master" into a fully qualified ref. -}
 branchRef :: Branch -> Ref
@@ -66,21 +68,25 @@ branchRef = underBase "refs/heads"
  - of a repo.
  -}
 fileRef :: RawFilePath -> Ref
-fileRef f = Ref $ ":./" ++ fromRawFilePath f
+fileRef f = Ref $ ":./" <> f
 
 {- Converts a Ref to refer to the content of the Ref on a given date. -}
 dateRef :: Ref -> RefDate -> Ref
-dateRef (Ref r) (RefDate d) = Ref $ r ++ "@" ++ d
+dateRef r (RefDate d) = Ref $ fromRef' r <> "@" <> encodeBS' d
 
 {- A Ref that can be used to refer to a file in the repository as it
  - appears in a given Ref. -}
 fileFromRef :: Ref -> RawFilePath -> Ref
-fileFromRef (Ref r) f = let (Ref fr) = fileRef f in Ref (r ++ fr)
+fileFromRef r f = let (Ref fr) = fileRef f in Ref (fromRef' r <> fr)
 
 {- Checks if a ref exists. -}
 exists :: Ref -> Repo -> IO Bool
 exists ref = runBool
-	[Param "show-ref", Param "--verify", Param "-q", Param $ fromRef ref]
+	[ Param "show-ref"
+	, Param "--verify"
+	, Param "-q"
+	, Param $ fromRef ref
+	]
 
 {- The file used to record a ref. (Git also stores some refs in a
  - packed-refs file.) -}
@@ -107,26 +113,26 @@ sha branch repo = process <$> showref repo
 		]
 	process s
 		| S.null s = Nothing
-		| otherwise = Just $ Ref $ decodeBS' $ firstLine' s
+		| otherwise = Just $ Ref $ firstLine' s
 
 headSha :: Repo -> IO (Maybe Sha)
 headSha = sha headRef
 
 {- List of (shas, branches) matching a given ref or refs. -}
 matching :: [Ref] -> Repo -> IO [(Sha, Branch)]
-matching refs repo =  matching' (map fromRef refs) repo
+matching = matching' []
 
 {- Includes HEAD in the output, if asked for it. -}
 matchingWithHEAD :: [Ref] -> Repo -> IO [(Sha, Branch)]
-matchingWithHEAD refs repo = matching' ("--head" : map fromRef refs) repo
+matchingWithHEAD = matching' [Param "--head"]
 
-{- List of (shas, branches) matching a given ref spec. -}
-matching' :: [String] -> Repo -> IO [(Sha, Branch)]
-matching' ps repo = map gen . lines . decodeBS' <$> 
-	pipeReadStrict (Param "show-ref" : map Param ps) repo
+matching' :: [CommandParam] -> [Ref] -> Repo -> IO [(Sha, Branch)]
+matching' ps rs repo = map gen . S8.lines <$> 
+	pipeReadStrict (Param "show-ref" : ps ++ rps) repo
   where
-	gen l = let (r, b) = separate (== ' ') l
+	gen l = let (r, b) = separate' (== fromIntegral (ord ' ')) l
 		in (Ref r, Ref b)
+	rps = map (Param . fromRef) rs
 
 {- List of (shas, branches) matching a given ref.
  - Duplicate shas are filtered out. -}
@@ -137,7 +143,7 @@ matchingUniq refs repo = nubBy uniqref <$> matching refs repo
 
 {- List of all refs. -}
 list :: Repo -> IO [(Sha, Ref)]
-list = matching' []
+list = matching' [] []
 
 {- Deletes a ref. This can delete refs that are not branches, 
  - which git branch --delete refuses to delete. -}
@@ -154,13 +160,17 @@ delete oldvalue ref = run
  - The ref may be something like a branch name, and it could contain
  - ":subdir" if a subtree is wanted. -}
 tree :: Ref -> Repo -> IO (Maybe Sha)
-tree (Ref ref) = extractSha . decodeBS <$$> pipeReadStrict
-	[ Param "rev-parse", Param "--verify", Param "--quiet", Param ref' ]
+tree (Ref ref) = extractSha <$$> pipeReadStrict
+	[ Param "rev-parse"
+	, Param "--verify"
+	, Param "--quiet"
+	, Param (decodeBS' ref')
+	]
   where
-	ref' = if ":" `isInfixOf` ref
+	ref' = if ":" `S.isInfixOf` ref
 		then ref
 		-- de-reference commit objects to the tree
-		else ref ++ ":"
+		else ref <> ":"
 
 {- Checks if a String is a legal git ref name.
  -
diff --git a/Git/RefLog.hs b/Git/RefLog.hs
index 7ba8713af7..b98833c391 100644
--- a/Git/RefLog.hs
+++ b/Git/RefLog.hs
@@ -12,6 +12,9 @@ import Git
 import Git.Command
 import Git.Sha
 
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
+
 {- Gets the reflog for a given branch. -}
 get :: Branch -> Repo -> IO [Sha]
 get b = getMulti [b]
@@ -21,7 +24,7 @@ getMulti :: [Branch] -> Repo -> IO [Sha]
 getMulti bs = get' (map (Param . fromRef) bs)
 
 get' :: [CommandParam] -> Repo -> IO [Sha]
-get' ps = mapMaybe extractSha . lines . decodeBS <$$> pipeReadStrict ps'
+get' ps = mapMaybe (extractSha . S.copy) . S8.lines <$$> pipeReadStrict ps'
   where
 	ps' = catMaybes
 		[ Just $ Param "log"
diff --git a/Git/Repair.hs b/Git/Repair.hs
index 10ea6a8ddc..f7a91ca0fe 100644
--- a/Git/Repair.hs
+++ b/Git/Repair.hs
@@ -232,7 +232,7 @@ getAllRefs r = getAllRefs' (fromRawFilePath (localGitDir r) </> "refs")
 getAllRefs' :: FilePath -> IO [Ref]
 getAllRefs' refdir = do
 	let topsegs = length (splitPath refdir) - 1
-	let toref = Ref . joinPath . drop topsegs . splitPath
+	let toref = Ref . encodeBS' . joinPath . drop topsegs . splitPath
 	map toref <$> dirContentsRecursive refdir
 
 explodePackedRefsFile :: Repo -> IO ()
@@ -257,8 +257,8 @@ packedRefsFile r = fromRawFilePath (localGitDir r) </> "packed-refs"
 parsePacked :: String -> Maybe (Sha, Ref)
 parsePacked l = case words l of
 	(sha:ref:[])
-		| isJust (extractSha sha) && Ref.legal True ref ->
-			Just (Ref sha, Ref ref)
+		| isJust (extractSha (encodeBS' sha)) && Ref.legal True ref ->
+			Just (Ref (encodeBS' sha), Ref (encodeBS' ref))
 	_ -> Nothing
 
 {- git-branch -d cannot be used to remove a branch that is directly
@@ -279,13 +279,13 @@ findUncorruptedCommit missing goodcommits branch r = do
 	if ok
 		then return (Just branch, goodcommits')
 		else do
-			(ls, cleanup) <- pipeNullSplit
+			(ls, cleanup) <- pipeNullSplit'
 				[ Param "log"
 				, Param "-z"
 				, Param "--format=%H"
 				, Param (fromRef branch)
 				] r
-			let branchshas = catMaybes $ map (extractSha . decodeBL) ls
+			let branchshas = catMaybes $ map extractSha ls
 			reflogshas <- RefLog.get branch r
 			-- XXX Could try a bit harder here, and look
 			-- for uncorrupted old commits in branches in the
@@ -328,8 +328,8 @@ verifyCommit missing goodcommits commit r
   where
 	parse l = case words l of
 		(commitsha:treesha:[]) -> (,)
-			<$> extractSha commitsha
-			<*> extractSha treesha
+			<$> extractSha (encodeBS' commitsha)
+			<*> extractSha (encodeBS' treesha)
 		_ -> Nothing
 	check [] = return True
 	check ((c, t):rest)
@@ -448,7 +448,8 @@ preRepair g = do
 		void $ tryIO $ allowWrite f
   where
 	headfile = fromRawFilePath (localGitDir g) </> "HEAD"
-	validhead s = "ref: refs/" `isPrefixOf` s || isJust (extractSha s)
+	validhead s = "ref: refs/" `isPrefixOf` s
+		|| isJust (extractSha (encodeBS' s))
 
 {- Put it all together. -}
 runRepair :: (Ref -> Bool) -> Bool -> Repo -> IO (Bool, [Branch])
diff --git a/Git/Sha.hs b/Git/Sha.hs
index 24fe546192..a66c34ee2c 100644
--- a/Git/Sha.hs
+++ b/Git/Sha.hs
@@ -5,31 +5,43 @@
  - 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 String -> IO Sha
+getSha :: String -> IO S.ByteString -> IO Sha
 getSha subcommand a = maybe bad return =<< extractSha <$> a
   where
 	bad = error $ "failed to read sha from git " ++ subcommand
 
-{- Extracts the Sha from a string. There can be a trailing newline after
- - it, but nothing else. -}
-extractSha :: String -> Maybe Sha
+{- 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 && length s' == len - 1 = val s'
+	| len - 1 `elem` shaSizes && S.length s' == len - 1 = val s'
 	| otherwise = Nothing
   where
-	len = length s
-	s' = firstLine s
+	len = S.length s
+	s' = firstLine' s
 	val v
-		| all (`elem` "1234567890ABCDEFabcdef") v = Just $ Ref 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]
@@ -41,7 +53,9 @@ shaSizes =
 {- Git plumbing often uses a all 0 sha to represent things like a
  - deleted file. -}
 nullShas :: [Sha]
-nullShas = map (\n -> Ref (replicate n '0')) shaSizes
+nullShas = map (\n -> Ref (S.replicate n zero)) shaSizes
+  where
+	zero = fromIntegral (ord '0')
 
 {- Sha to provide to git plumbing when deleting a file.
  -
diff --git a/Git/Tree.hs b/Git/Tree.hs
index 9627ae9690..491314fff5 100644
--- a/Git/Tree.hs
+++ b/Git/Tree.hs
@@ -38,6 +38,7 @@ import System.Posix.Types
 import Control.Monad.IO.Class
 import qualified Data.Set as S
 import qualified Data.Map as M
+import qualified Data.ByteString.Char8 as S8
 
 newtype Tree = Tree [TreeContent]
 	deriving (Show)
@@ -106,7 +107,7 @@ mkTree (MkTreeHandle cp) l = CoProcess.query cp send receive
 			NewSubTree _ _ -> error "recordSubTree internal error; unexpected NewSubTree"
 			TreeCommit f fm s -> mkTreeOutput fm CommitObject s f
 		hPutStr h "\NUL" -- signal end of tree to --batch
-	receive h = getSha "mktree" (hGetLine h)
+	receive h = getSha "mktree" (S8.hGetLine h)
 
 treeMode :: FileMode
 treeMode = 0o040000
diff --git a/Git/Types.hs b/Git/Types.hs
index 9c2754a7d3..6e4558d8fd 100644
--- a/Git/Types.hs
+++ b/Git/Types.hs
@@ -81,11 +81,14 @@ instance IsString ConfigValue where
 type RemoteName = String
 
 {- A git ref. Can be a sha1, or a branch or tag name. -}
-newtype Ref = Ref String
+newtype Ref = Ref S.ByteString
 	deriving (Eq, Ord, Read, Show)
 
 fromRef :: Ref -> String
-fromRef (Ref s) = s
+fromRef = decodeBS' . fromRef'
+
+fromRef' :: Ref -> S.ByteString
+fromRef' (Ref s) = s
 
 {- Aliases for Ref. -}
 type Branch = Ref
diff --git a/Git/UnionMerge.hs b/Git/UnionMerge.hs
index 2100f1dcf9..2cf103dd9d 100644
--- a/Git/UnionMerge.hs
+++ b/Git/UnionMerge.hs
@@ -10,8 +10,10 @@ module Git.UnionMerge (
 	mergeIndex
 ) where
 
+import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
 import qualified Data.ByteString.Lazy.Char8 as L8
+import qualified Data.ByteString.Char8 as S8
 import qualified Data.Set as S
 
 import Common
@@ -54,13 +56,13 @@ mergeIndex hashhandle ch repo bs = forM_ bs $ \b ->
 
 {- For merging two trees. -}
 mergeTrees :: Ref -> Ref -> HashObjectHandle -> CatFileHandle -> Repo -> Streamer
-mergeTrees (Ref x) (Ref y) hashhandle ch = doMerge hashhandle ch
-	("diff-tree":diffOpts ++ [x, y, "--"])
+mergeTrees x y hashhandle ch = doMerge hashhandle ch
+	("diff-tree":diffOpts ++ [fromRef x, fromRef y, "--"])
 
 {- For merging a single tree into the index. -}
 mergeTreeIndex :: Ref -> HashObjectHandle -> CatFileHandle -> Repo -> Streamer
-mergeTreeIndex (Ref r) hashhandle ch = doMerge hashhandle ch $
-	"diff-index" : diffOpts ++ ["--cached", r, "--"]
+mergeTreeIndex r hashhandle ch = doMerge hashhandle ch $
+	"diff-index" : diffOpts ++ ["--cached", fromRef r, "--"]
 
 diffOpts :: [String]
 diffOpts = ["--raw", "-z", "-r", "--no-renames", "-l0"]
@@ -69,19 +71,19 @@ diffOpts = ["--raw", "-z", "-r", "--no-renames", "-l0"]
  - using git to get a raw diff. -}
 doMerge :: HashObjectHandle -> CatFileHandle -> [String] -> Repo -> Streamer
 doMerge hashhandle ch differ repo streamer = do
-	(diff, cleanup) <- pipeNullSplit (map Param differ) repo
+	(diff, cleanup) <- pipeNullSplit' (map Param differ) repo
 	go diff
 	void $ cleanup
   where
 	go [] = noop
-	go (info:file:rest) = mergeFile (decodeBL' info) (L.toStrict file) hashhandle ch >>=
+	go (info:file:rest) = mergeFile info file hashhandle ch >>=
 		maybe (go rest) (\l -> streamer l >> go rest)
 	go (_:[]) = error $ "parse error " ++ show differ
 
 {- Given an info line from a git raw diff, and the filename, generates
  - a line suitable for update-index that union merges the two sides of the
  - diff. -}
-mergeFile :: String -> RawFilePath -> HashObjectHandle -> CatFileHandle -> IO (Maybe L.ByteString)
+mergeFile :: S.ByteString -> RawFilePath -> HashObjectHandle -> CatFileHandle -> IO (Maybe L.ByteString)
 mergeFile info file hashhandle h = case filter (`notElem` nullShas) [Ref asha, Ref bsha] of
 	[] -> return Nothing
 	(sha:[]) -> use sha
@@ -89,7 +91,7 @@ mergeFile info file hashhandle h = case filter (`notElem` nullShas) [Ref asha, R
 		=<< either return (hashBlob hashhandle . L8.unlines)
 		=<< calcMerge . zip shas <$> mapM getcontents shas
   where
-	[_colonmode, _bmode, asha, bsha, _status] = words info
+	[_colonmode, _bmode, asha, bsha, _status] = S8.words info
 	use sha = return $ Just $
 		updateIndexLine sha TreeFile $ asTopFilePath file
 	-- Get file and split into lines to union merge.
diff --git a/Git/UpdateIndex.hs b/Git/UpdateIndex.hs
index 68dc8b7097..f0331d5c1f 100644
--- a/Git/UpdateIndex.hs
+++ b/Git/UpdateIndex.hs
@@ -75,14 +75,14 @@ lsTree (Ref x) repo streamer = do
 	mapM_ streamer s
 	void $ cleanup
   where
-	params = map Param ["ls-tree", "-z", "-r", "--full-tree", x]
+	params = map Param ["ls-tree", "-z", "-r", "--full-tree", decodeBS' x]
 lsSubTree :: Ref -> FilePath -> Repo -> Streamer
 lsSubTree (Ref x) p repo streamer = do
 	(s, cleanup) <- pipeNullSplit params repo
 	mapM_ streamer s
 	void $ cleanup
   where
-	params = map Param ["ls-tree", "-z", "-r", "--full-tree", x, p]
+	params = map Param ["ls-tree", "-z", "-r", "--full-tree", decodeBS' x, p]
 
 {- Generates a line suitable to be fed into update-index, to add
  - a given file with a given sha. -}
@@ -90,7 +90,7 @@ updateIndexLine :: Sha -> TreeItemType -> TopFilePath -> L.ByteString
 updateIndexLine sha treeitemtype file = L.fromStrict $
 	fmtTreeItemType treeitemtype
 	<> " blob "
-	<> encodeBS (fromRef sha)
+	<> fromRef' sha
 	<> "\t"
 	<> indexPath file
 
@@ -108,7 +108,7 @@ unstageFile file repo = do
 unstageFile' :: TopFilePath -> Streamer
 unstageFile' p = pureStreamer $ L.fromStrict $
 	"0 "
-	<> encodeBS' (fromRef deleteSha)
+	<> fromRef' deleteSha
 	<> "\t"
 	<> indexPath p
 
diff --git a/Logs/Export.hs b/Logs/Export.hs
index aadd1b9c4a..586c789e86 100644
--- a/Logs/Export.hs
+++ b/Logs/Export.hs
@@ -158,12 +158,12 @@ buildExported exported = go (exportedTreeish exported : incompleteExportedTreeis
   where
 	go [] = mempty
 	go (r:rs) = rref r <> mconcat [ charUtf8 ' ' <> rref r' | r' <- rs ]
-	rref r = byteString (encodeBS' (Git.fromRef r))
+	rref = byteString . Git.fromRef'
 
 exportedParser :: A.Parser Exported
 exportedParser = Exported <$> refparser <*> many refparser
   where
-	refparser = (Git.Ref . decodeBS <$> A8.takeWhile1 (/= ' ') )
+	refparser = (Git.Ref <$> A8.takeWhile1 (/= ' ') )
 		<* ((const () <$> A8.char ' ') <|> A.endOfInput)
 
 logExportExcluded :: UUID -> ((Git.Tree.TreeItem -> IO ()) -> Annex a) -> Annex a
diff --git a/Logs/FsckResults.hs b/Logs/FsckResults.hs
index 73f6d4c6c0..1f188ed08f 100644
--- a/Logs/FsckResults.hs
+++ b/Logs/FsckResults.hs
@@ -43,7 +43,7 @@ readFsckResults u = do
 	deserialize ("truncated":ls) = deserialize' ls True
 	deserialize ls = deserialize' ls False
 	deserialize' ls t =
-		let s = S.fromList $ map Ref ls
+		let s = S.fromList $ map (Ref . encodeBS') ls
 		in if S.null s then FsckFailed else FsckFoundMissing s t
 
 clearFsckResults :: UUID -> Annex ()
diff --git a/Logs/View.hs b/Logs/View.hs
index b14d065166..ea28f29b55 100644
--- a/Logs/View.hs
+++ b/Logs/View.hs
@@ -9,6 +9,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Logs.View (
 	currentView,
 	setView,
@@ -31,6 +33,7 @@ import Logs.File
 import qualified Data.Text as T
 import qualified Data.Set as S
 import Data.Char
+import qualified Data.ByteString as B
 
 setView :: View -> Annex ()
 setView v = do
@@ -54,11 +57,11 @@ recentViews = do
 currentView :: Annex (Maybe View)
 currentView = go =<< inRepo Git.Branch.current
   where
-	go (Just b) | branchViewPrefix `isPrefixOf` fromRef b =
+	go (Just b) | branchViewPrefix `B.isPrefixOf` fromRef' b =
 		headMaybe . filter (\v -> branchView v == b) <$> recentViews
 	go _ = return Nothing
 
-branchViewPrefix :: String
+branchViewPrefix :: B.ByteString
 branchViewPrefix = "refs/heads/views"
 
 {- Generates a git branch name for a View.
@@ -68,10 +71,11 @@ branchViewPrefix = "refs/heads/views"
  -}
 branchView :: View -> Git.Branch
 branchView view
-	| null name = Git.Ref branchViewPrefix
-	| otherwise = Git.Ref $ branchViewPrefix ++ "/" ++ name
+	| B.null name = Git.Ref branchViewPrefix
+	| otherwise = Git.Ref $ branchViewPrefix <> "/" <> name
   where
-	name = intercalate ";" $ map branchcomp (viewComponents view)
+	name = encodeBS' $
+		intercalate ";" $ map branchcomp (viewComponents view)
 	branchcomp c
 		| viewVisible c = branchcomp' c
 		| otherwise = "(" ++ branchcomp' c ++ ")"
@@ -92,7 +96,7 @@ branchView view
 is_branchView :: Git.Branch -> Bool
 is_branchView (Ref b)
 	| b == branchViewPrefix = True
-	| otherwise = (branchViewPrefix ++ "/") `isPrefixOf` b
+	| otherwise = (branchViewPrefix <> "/") `B.isPrefixOf` b
 
 prop_branchView_legal :: View -> Bool
 prop_branchView_legal = Git.Ref.legal False . fromRef . branchView
diff --git a/Test.hs b/Test.hs
index 29f891dc4e..04d36424e9 100644
--- a/Test.hs
+++ b/Test.hs
@@ -1664,7 +1664,7 @@ test_add_subdirs = intmpclonerepo $ do
 	unlessM (hasUnlockedFiles <$> getTestMode) $ do
 		git_annex "sync" [] @? "sync failed"
 		l <- annexeval $ Utility.FileSystemEncoding.decodeBL
-			<$> Annex.CatFile.catObject (Git.Types.Ref "HEAD:dir/foo")
+			<$> Annex.CatFile.catObject (Git.Types.Ref (encodeBS "HEAD:dir/foo"))
 		"../.git/annex/" `isPrefixOf` l @? ("symlink from subdir to .git/annex is wrong: " ++ l)
 
 	createDirectory "dir2"
diff --git a/Types/GitConfig.hs b/Types/GitConfig.hs
index 91c8701811..35e9ad91c7 100644
--- a/Types/GitConfig.hs
+++ b/Types/GitConfig.hs
@@ -343,7 +343,7 @@ extractRemoteGitConfig r remotename = do
 		, remoteAnnexReadOnly = getbool "readonly" False
 		, remoteAnnexCheckUUID = getbool "checkuuid" True
 		, remoteAnnexVerify = getbool "verify" True
-		, remoteAnnexTrackingBranch = Git.Ref <$>
+		, remoteAnnexTrackingBranch = Git.Ref . encodeBS <$>
 			( notempty (getmaybe "tracking-branch")
 			<|> notempty (getmaybe "export-tracking") -- old name
 			)
diff --git a/Types/RefSpec.hs b/Types/RefSpec.hs
index 8479a69a6b..0f3dded9d9 100644
--- a/Types/RefSpec.hs
+++ b/Types/RefSpec.hs
@@ -32,7 +32,7 @@ parseRefSpec v = case partitionEithers (map mk $ splitc ':' v) of
 	mk ('+':s)
 		| any (`elem` s) "*?" =
 			Right $ AddMatching $ compileGlob s CaseSensative
-		| otherwise = Right $ AddRef $ Ref s
+		| otherwise = Right $ AddRef $ Ref $ encodeBS s
 	mk ('-':s) = Right $ RemoveMatching $ compileGlob s CaseSensative
 	mk "reflog" = Right AddRefLog
 	mk s = Left $ "bad refspec item \"" ++ s ++ "\" (expected + or - prefix)"
diff --git a/Types/View.hs b/Types/View.hs
index 1185afd982..5b3f9d906d 100644
--- a/Types/View.hs
+++ b/Types/View.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Types.View where
 
 import Annex.Common
diff --git a/Upgrade/V2.hs b/Upgrade/V2.hs
index 4a70a05d1a..24d92e4ffc 100644
--- a/Upgrade/V2.hs
+++ b/Upgrade/V2.hs
@@ -92,7 +92,8 @@ logFiles dir = return . filter (".log" `isSuffixOf`)
 
 push :: Annex ()
 push = do
-	origin_master <- inRepo $ Git.Ref.exists $ Git.Ref "origin/master"
+	origin_master <- inRepo $ Git.Ref.exists $ 
+		Git.Ref $ encodeBS' "origin/master"
 	origin_gitannex <- Annex.Branch.hasOrigin
 	case (origin_master, origin_gitannex) of
 		(_, True) -> do
diff --git a/Upgrade/V5/Direct.hs b/Upgrade/V5/Direct.hs
index 1fcf8c4eeb..9af32e79ce 100644
--- a/Upgrade/V5/Direct.hs
+++ b/Upgrade/V5/Direct.hs
@@ -59,7 +59,7 @@ setIndirect = do
 fromDirectBranch :: Ref -> Ref
 fromDirectBranch directhead = case splitc '/' $ fromRef directhead of
 	("refs":"heads":"annex":"direct":rest) -> 
-		Ref $ "refs/heads/" ++ intercalate "/" rest
+		Ref $ encodeBS' $ "refs/heads/" ++ intercalate "/" rest
 	_ -> directhead
 
 switchHEADBack :: Annex ()
diff --git a/Utility/Misc.hs b/Utility/Misc.hs
index 2f1766ec23..01ae178d85 100644
--- a/Utility/Misc.hs
+++ b/Utility/Misc.hs
@@ -11,6 +11,7 @@ module Utility.Misc (
 	hGetContentsStrict,
 	readFileStrict,
 	separate,
+	separate',
 	firstLine,
 	firstLine',
 	segment,
@@ -54,6 +55,13 @@ separate c l = unbreak $ break c l
 		| null b = r
 		| otherwise = (a, tail b)
 
+separate' :: (Word8 -> Bool) -> S.ByteString -> (S.ByteString, S.ByteString)
+separate' c l = unbreak $ S.break c l
+  where
+	unbreak r@(a, b)
+		| S.null b = r
+		| otherwise = (a, S.tail b)
+
 {- Breaks out the first line. -}
 firstLine :: String -> String
 firstLine = takeWhile (/= '\n')
diff --git a/Utility/Process.hs b/Utility/Process.hs
index af3a5f4f62..e7142b9ecb 100644
--- a/Utility/Process.hs
+++ b/Utility/Process.hs
@@ -1,7 +1,7 @@
 {- System.Process enhancements, including additional ways of running
  - processes, and logging.
  -
- - Copyright 2012-2015 Joey Hess <id@joeyh.name>
+ - Copyright 2012-2020 Joey Hess <id@joeyh.name>
  -
  - License: BSD-2-clause
  -}
@@ -53,6 +53,7 @@ import System.Log.Logger
 import Control.Concurrent
 import qualified Control.Exception as E
 import Control.Monad
+import qualified Data.ByteString as S
 
 type CreateProcessRunner = forall a. CreateProcess -> ((Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> IO a) -> IO a
 
@@ -85,25 +86,20 @@ writeReadProcessEnv
 	-> [String]
 	-> Maybe [(String, String)]
 	-> (Maybe (Handle -> IO ()))
-	-> (Maybe (Handle -> IO ()))
-	-> IO String
-writeReadProcessEnv cmd args environ writestdin adjusthandle = do
+	-> IO S.ByteString
+writeReadProcessEnv cmd args environ writestdin = do
 	(Just inh, Just outh, _, pid) <- createProcess p
 
-	maybe (return ()) (\a -> a inh) adjusthandle
-	maybe (return ()) (\a -> a outh) adjusthandle
-
 	-- fork off a thread to start consuming the output
-	output  <- hGetContents outh
 	outMVar <- newEmptyMVar
-	_ <- forkIO $ E.evaluate (length output) >> putMVar outMVar ()
+	_ <- forkIO $ putMVar outMVar =<< S.hGetContents outh
 
 	-- now write and flush any input
 	maybe (return ()) (\a -> a inh >> hFlush inh) writestdin
 	hClose inh -- done with stdin
 
 	-- wait on the output
-	takeMVar outMVar
+	output <- takeMVar outMVar
 	hClose outh
 
 	-- wait on the process
diff --git a/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn b/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
index 6434c4de3d..8b9f79c2da 100644
--- a/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
+++ b/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
@@ -3,3 +3,9 @@ to contain a ByteString, rather than a String, would eliminate a
 fromRawFilePath that uses about 1% of runtime.
 
 [[!tag confirmed]]
+
+> Well, I did the conversion. Running that command does not seem to have 
+> sped up by any appreciable amount. But, I did notice several places where
+> using ByteString is certainly more efficient. It may just be that it
+> doesn't matter if git-annex is IO bound etc. Still, glad I did it.
+> [[done]] --[[Joey]]