pushed checkPresent exception handling out of Remote implementations

I tend to prefer moving toward explicit exception handling, not away from
it, but in this case, I think there are good reasons to let checkPresent
throw exceptions:

1. They can all be caught in one place (Remote.hasKey), and we know
   every possible exception is caught there now, which we didn't before.
2. It simplified the code of the Remotes. I think it makes sense for
   Remotes to be able to be implemented without needing to worry about
   catching exceptions inside them. (Mostly.)
3. Types.StoreRetrieve.Preparer can only work on things that return a
   Bool, which all the other relevant remote methods already did.
   I do not see a good way to generalize that type; my previous attempts
   failed miserably.

20 files changed, 138 insertions, 150 deletions

diff --git a/Remote/Bup.hs b/Remote/Bup.hs
index 6a04ad5f7..2e68f30ef 100644
--- a/Remote/Bup.hs
+++ b/Remote/Bup.hs
@@ -58,8 +58,8 @@ gen r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = retrieveCheap buprepo
 		, removeKey = remove buprepo
-		, hasKey = checkPresent r bupr'
-		, hasKeyCheap = bupLocal buprepo
+		, checkPresent = checkKey r bupr'
+		, checkPresentCheap = bupLocal buprepo
 		, whereisKey = Nothing
 		, remoteFsck = Nothing
 		, repairRepo = Nothing
@@ -163,14 +163,13 @@ remove buprepo k = do
  - in a bup repository. One way it to check if the git repository has
  - a branch matching the name (as created by bup split -n).
  -}
-checkPresent :: Git.Repo -> Git.Repo -> Key -> Annex (Either String Bool)
-checkPresent r bupr k
+checkKey :: Git.Repo -> Git.Repo -> Key -> Annex Bool
+checkKey r bupr k
 	| Git.repoIsUrl bupr = do
 		showChecking r
-		ok <- onBupRemote bupr boolSystem "git" params
-		return $ Right ok
-	| otherwise = liftIO $ catchMsgIO $
-		boolSystem "git" $ Git.Command.gitCommandLine params bupr
+		onBupRemote bupr boolSystem "git" params
+	| otherwise = liftIO $ boolSystem "git" $
+		Git.Command.gitCommandLine params bupr
   where
 	params = 
 		[ Params "show-ref --quiet --verify"
diff --git a/Remote/Ddar.hs b/Remote/Ddar.hs
index b4c7ac1e6..1227b5275 100644
--- a/Remote/Ddar.hs
+++ b/Remote/Ddar.hs
@@ -54,8 +54,8 @@ gen r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = retrieveCheap
 		, removeKey = remove ddarrepo
-		, hasKey = checkPresent ddarrepo
-		, hasKeyCheap = ddarLocal ddarrepo
+		, checkPresent = checkKey ddarrepo
+		, checkPresentCheap = ddarLocal ddarrepo
 		, whereisKey = Nothing
 		, remoteFsck = Nothing
 		, repairRepo = Nothing
@@ -181,13 +181,14 @@ inDdarManifest ddarrepo k = do
   where
 	k' = key2file k
 
-checkPresent :: DdarRepo -> Key -> Annex (Either String Bool)
-checkPresent ddarrepo key = do
+checkKey :: DdarRepo -> Key -> Annex Bool
+checkKey ddarrepo key = do
 	directoryExists <- ddarDirectoryExists ddarrepo
 	case directoryExists of
-		Left e -> return $ Left e
-		Right True -> inDdarManifest ddarrepo key
-		Right False -> return $ Right False
+		Left e -> error e
+		Right True -> either error return
+			=<< inDdarManifest ddarrepo key
+		Right False -> return False
 
 ddarLocal :: DdarRepo -> Bool
 ddarLocal = notElem ':'
diff --git a/Remote/Directory.hs b/Remote/Directory.hs
index 9b3c15695..0a2532aa5 100644
--- a/Remote/Directory.hs
+++ b/Remote/Directory.hs
@@ -52,8 +52,8 @@ gen r u c gc = do
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = retrieveCheap dir chunkconfig,
 			removeKey = remove dir,
-			hasKey = checkPresent dir chunkconfig,
-			hasKeyCheap = True,
+			checkPresent = checkKey dir chunkconfig,
+			checkPresentCheap = True,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -189,13 +189,10 @@ removeDirGeneric topdir dir = do
 		then return ok
 		else doesDirectoryExist topdir <&&> (not <$> doesDirectoryExist dir)
 
-checkPresent :: FilePath -> ChunkConfig -> Key -> Annex (Either String Bool)
-checkPresent d (LegacyChunks _) k = Legacy.checkPresent d locations k
-checkPresent d _ k = liftIO $ do
-	v <- catchMsgIO $ anyM doesFileExist (locations d k)
-	case v of
-		Right False -> ifM (doesDirectoryExist d)
-			( return v
-			, return $ Left $ "directory " ++ d ++ " is not accessible"
-			)
-		_ -> return v
+checkKey :: FilePath -> ChunkConfig -> Key -> Annex Bool
+checkKey d (LegacyChunks _) k = Legacy.checkKey d locations k
+checkKey d _ k = liftIO $
+	ifM (anyM doesFileExist (locations d k))
+		( return True
+		, error $ "directory " ++ d ++ " is not accessible"
+		)
diff --git a/Remote/Directory/LegacyChunked.hs b/Remote/Directory/LegacyChunked.hs
index 1be885db2..b2248c5f6 100644
--- a/Remote/Directory/LegacyChunked.hs
+++ b/Remote/Directory/LegacyChunked.hs
@@ -103,8 +103,7 @@ retrieve locations d basek a = do
 		liftIO $ nukeFile tmp
 		sink b
 
-checkPresent :: FilePath -> (FilePath -> Key -> [FilePath]) -> Key -> Annex (Either String Bool)
-checkPresent d locations k = liftIO $ catchMsgIO $
-	withStoredFiles d locations k $
-		-- withStoredFiles checked that it exists
-		const $ return True
+checkKey :: FilePath -> (FilePath -> Key -> [FilePath]) -> Key -> Annex Bool
+checkKey d locations k = liftIO $ withStoredFiles d locations k $
+	-- withStoredFiles checked that it exists
+	const $ return True
diff --git a/Remote/External.hs b/Remote/External.hs
index c00093402..ffae94ec9 100644
--- a/Remote/External.hs
+++ b/Remote/External.hs
@@ -53,8 +53,8 @@ gen r u c gc = do
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = \_ _ -> return False,
 			removeKey = remove external,
-			hasKey = checkPresent external,
-			hasKeyCheap = False,
+			checkPresent = checkKey external,
+			checkPresentCheap = False,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -121,8 +121,8 @@ remove external k = safely $
 					return False
 			_ -> Nothing
 
-checkPresent :: External -> Key -> Annex (Either String Bool)
-checkPresent external k = either (Left . show) id <$> tryAnnex go
+checkKey :: External -> Key -> Annex Bool
+checkKey external k = either error id <$> go
   where
 	go = handleRequest external (CHECKPRESENT k) Nothing $ \resp ->
 		case resp of
diff --git a/Remote/GCrypt.hs b/Remote/GCrypt.hs
index d969e02f8..f971ff754 100644
--- a/Remote/GCrypt.hs
+++ b/Remote/GCrypt.hs
@@ -46,7 +46,6 @@ import Utility.Tmp
 import Logs.Remote
 import Logs.Transfer
 import Utility.Gpg
-import Utility.FileMode
 
 remote :: RemoteType
 remote = RemoteType {
@@ -109,8 +108,8 @@ gen' r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = \_ _ -> return False
 		, removeKey = remove this rsyncopts
-		, hasKey = checkPresent this rsyncopts
-		, hasKeyCheap = repoCheap r
+		, checkPresent = checkKey this rsyncopts
+		, checkPresentCheap = repoCheap r
 		, whereisKey = Nothing
 		, remoteFsck = Nothing
 		, repairRepo = Nothing
@@ -342,16 +341,15 @@ remove r rsyncopts k
 	removersync = Remote.Rsync.remove rsyncopts k
 	removeshell = Ssh.dropKey (repo r) k
 
-checkPresent :: Remote -> Remote.Rsync.RsyncOpts -> Key -> Annex (Either String Bool)
-checkPresent r rsyncopts k
+checkKey :: Remote -> Remote.Rsync.RsyncOpts -> Key -> Annex Bool
+checkKey r rsyncopts k
 	| not $ Git.repoIsUrl (repo r) =
 		guardUsable (repo r) (cantCheck $ repo r) $
-			liftIO $ catchDefaultIO (cantCheck $ repo r) $
-				Right <$> doesFileExist (gCryptLocation r k)
+			liftIO $ doesFileExist (gCryptLocation r k)
 	| Git.repoIsSsh (repo r) = shellOrRsync r checkshell checkrsync
 	| otherwise = unsupportedUrl
   where
-  	checkrsync = Remote.Rsync.checkPresent (repo r) rsyncopts k
+  	checkrsync = Remote.Rsync.checkKey (repo r) rsyncopts k
 	checkshell = Ssh.inAnnex (repo r) k
 
 {- Annexed objects are hashed using lower-case directories for max
diff --git a/Remote/Git.hs b/Remote/Git.hs
index c35f9f32a..da5ca4c4a 100644
--- a/Remote/Git.hs
+++ b/Remote/Git.hs
@@ -141,8 +141,8 @@ gen r u c gc
 			, retrieveKeyFile = copyFromRemote new
 			, retrieveKeyFileCheap = copyFromRemoteCheap new
 			, removeKey = dropKey new
-			, hasKey = inAnnex new
-			, hasKeyCheap = repoCheap r
+			, checkPresent = inAnnex new
+			, checkPresentCheap = repoCheap r
 			, whereisKey = Nothing
 			, remoteFsck = if Git.repoIsUrl r
 				then Nothing
@@ -284,11 +284,8 @@ tryGitConfigRead r
 			void $ tryAnnex $ ensureInitialized
 			Annex.getState Annex.repo
 
-{- Checks if a given remote has the content for a key inAnnex.
- - If the remote cannot be accessed, or if it cannot determine
- - whether it has the content, returns a Left error message.
- -}
-inAnnex :: Remote -> Key -> Annex (Either String Bool)
+{- Checks if a given remote has the content for a key in its annex. -}
+inAnnex :: Remote -> Key -> Annex Bool
 inAnnex rmt key
 	| Git.repoIsHttp r = checkhttp
 	| Git.repoIsUrl r = checkremote
@@ -298,17 +295,13 @@ inAnnex rmt key
 	checkhttp = do
 		showChecking r
 		ifM (Url.withUrlOptions $ \uo -> anyM (\u -> Url.checkBoth u (keySize key) uo) (keyUrls rmt key))
-			( return $ Right True
-			, return $ Left "not found"
+			( return True
+			, error "not found"
 			)
 	checkremote = Ssh.inAnnex r key
-	checklocal = guardUsable r (cantCheck r) $ dispatch <$> check
-	  where
-		check = either (Left . show) Right 
-			<$> tryAnnex (onLocal rmt $ Annex.Content.inAnnexSafe key)
-		dispatch (Left e) = Left e
-		dispatch (Right (Just b)) = Right b
-		dispatch (Right Nothing) = cantCheck r
+	checklocal = guardUsable r (cantCheck r) $
+		fromMaybe (cantCheck r)
+			<$> onLocal rmt (Annex.Content.inAnnexSafe key)
 
 keyUrls :: Remote -> Key -> [String]
 keyUrls r key = map tourl locs'
diff --git a/Remote/Glacier.hs b/Remote/Glacier.hs
index c5bfefa64..2ade37011 100644
--- a/Remote/Glacier.hs
+++ b/Remote/Glacier.hs
@@ -52,8 +52,8 @@ gen r u c gc = new <$> remoteCost gc veryExpensiveRemoteCost
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = retrieveCheap this,
 			removeKey = remove this,
-			hasKey = checkPresent this,
-			hasKeyCheap = False,
+			checkPresent = checkKey this,
+			checkPresentCheap = False,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -164,25 +164,21 @@ remove r k = glacierAction r
 	, Param $ archive r k
 	]
 
-checkPresent :: Remote -> Key -> Annex (Either String Bool)
-checkPresent r k = do
+checkKey :: Remote -> Key -> Annex Bool
+checkKey r k = do
 	showAction $ "checking " ++ name r
 	go =<< glacierEnv (config r) (uuid r)
   where
-	go Nothing = return $ Left "cannot check glacier"
+	go Nothing = error "cannot check glacier"
 	go (Just e) = do
 		{- glacier checkpresent outputs the archive name to stdout if
 		 - it's present. -}
-		v <- liftIO $ catchMsgIO $ 
-			readProcessEnv "glacier" (toCommand params) (Just e)
-		case v of
-			Right s -> do
-				let probablypresent = key2file k `elem` lines s
-				if probablypresent
-					then ifM (Annex.getFlag "trustglacier")
-						( return $ Right True, untrusted )
-					else return $ Right False
-			Left err -> return $ Left err
+		s <- liftIO $ readProcessEnv "glacier" (toCommand params) (Just e)
+		let probablypresent = key2file k `elem` lines s
+		if probablypresent
+			then ifM (Annex.getFlag "trustglacier")
+				( return True, error untrusted )
+			else return False
 
 	params = glacierParams (config r)
 		[ Param "archive"
@@ -192,7 +188,7 @@ checkPresent r k = do
 		, Param $ archive r k
 		]
 
-	untrusted = return $ Left $ unlines
+	untrusted = unlines
 			[ "Glacier's inventory says it has a copy."
 			, "However, the inventory could be out of date, if it was recently removed."
 			, "(Use --trust-glacier if you're sure it's still in Glacier.)"
diff --git a/Remote/Helper/Chunked.hs b/Remote/Helper/Chunked.hs
index 7ad790cb1..953c533b6 100644
--- a/Remote/Helper/Chunked.hs
+++ b/Remote/Helper/Chunked.hs
@@ -12,7 +12,7 @@ module Remote.Helper.Chunked (
 	storeChunks,
 	removeChunks,
 	retrieveChunks,
-	hasKeyChunks,
+	checkPresentChunks,
 ) where
 
 import Common.Annex
@@ -94,8 +94,8 @@ storeChunks
 	-> Key
 	-> FilePath
 	-> MeterUpdate
-	-> (Key -> ContentSource -> MeterUpdate -> Annex Bool)
-	-> (Key -> Annex (Either String Bool))
+	-> Storer
+	-> CheckPresent
 	-> Annex Bool
 storeChunks u chunkconfig k f p storer checker = 
 	case chunkconfig of
@@ -158,7 +158,7 @@ storeChunks u chunkconfig k f p storer checker =
 seekResume
 	:: Handle
 	-> ChunkKeyStream
-	-> (Key -> Annex (Either String Bool))
+	-> CheckPresent
 	-> Annex (ChunkKeyStream, BytesProcessed)
 seekResume h chunkkeys checker = do
 	sz <- liftIO (hFileSize h)
@@ -172,7 +172,7 @@ seekResume h chunkkeys checker = do
 			liftIO $ hSeek h AbsoluteSeek sz
 			return (cks, toBytesProcessed sz)
 		| otherwise = do
-			v <- checker k
+			v <- tryNonAsyncAnnex (checker k)
 			case v of
 				Right True ->
 					check pos' cks' sz
@@ -331,43 +331,48 @@ setupResume ls currsize = map dropunneeded ls
 {- Checks if a key is present in a remote. This requires any one
  - of the lists of options returned by chunkKeys to all check out
  - as being present using the checker action.
+ -
+ - Throws an exception if the remote is not accessible.
  -}
-hasKeyChunks
-	:: (Key -> Annex (Either String Bool))
+checkPresentChunks
+	:: CheckPresent
 	-> UUID
 	-> ChunkConfig
 	-> EncKey
 	-> Key
-	-> Annex (Either String Bool)
-hasKeyChunks checker u chunkconfig encryptor basek
-	| noChunks chunkconfig =
+	-> Annex Bool
+checkPresentChunks checker u chunkconfig encryptor basek
+	| noChunks chunkconfig = do
 		-- Optimisation: Try the unchunked key first, to avoid
 		-- looking in the git-annex branch for chunk counts
 		-- that are likely not there.
-		ifM ((Right True ==) <$> checker (encryptor basek))
-			( return (Right True)
-			, checklists Nothing =<< chunkKeysOnly u basek
-			)
+		v <- check basek
+		case v of
+			Right True -> return True
+			_ -> checklists Nothing =<< chunkKeysOnly u basek
 	| otherwise = checklists Nothing =<< chunkKeys u chunkconfig basek
   where
-	checklists Nothing [] = return (Right False)
-	checklists (Just deferrederror) [] = return (Left deferrederror)
+	checklists Nothing [] = return False
+	checklists (Just deferrederror) [] = error deferrederror
 	checklists d (l:ls)
 		| not (null l) = do
 			v <- checkchunks l
 			case v of
 				Left e -> checklists (Just e) ls
-				Right True -> return (Right True)
+				Right True -> return True
 				Right False -> checklists Nothing ls
 		| otherwise = checklists d ls
 	
 	checkchunks :: [Key] -> Annex (Either String Bool)
 	checkchunks [] = return (Right True)
 	checkchunks (k:ks) = do
-		v <- checker (encryptor k)
-		if v == Right True
-			then checkchunks ks
-			else return v
+		v <- check k
+		case v of
+			Right True -> checkchunks ks
+			Right False -> return $ Right False
+			Left e -> return $ Left $ show e
+
+	check = tryNonAsyncAnnex . checker . encryptor
 
 {- A key can be stored in a remote unchunked, or as a list of chunked keys.
  - This can be the case whether or not the remote is currently configured
diff --git a/Remote/Helper/Encryptable.hs b/Remote/Helper/Encryptable.hs
index 65a3ba284..c364a69e7 100644
--- a/Remote/Helper/Encryptable.hs
+++ b/Remote/Helper/Encryptable.hs
@@ -91,9 +91,9 @@ encryptableRemote c storeKeyEncrypted retrieveKeyFileEncrypted r = r
 	, removeKey = \k -> cip k >>= maybe
 		(removeKey r k)
 		(\(_, enckey) -> removeKey r enckey)
-	, hasKey = \k -> cip k >>= maybe
-		(hasKey r k)
-		(\(_, enckey) -> hasKey r enckey)
+	, checkPresent = \k -> cip k >>= maybe
+		(checkPresent r k)
+		(\(_, enckey) -> checkPresent r enckey)
 	, cost = maybe
 		(cost r)
 		(const $ cost r + encryptedRemoteCostAdj)
diff --git a/Remote/Helper/Hooks.hs b/Remote/Helper/Hooks.hs
index c3ff970c6..907400bd1 100644
--- a/Remote/Helper/Hooks.hs
+++ b/Remote/Helper/Hooks.hs
@@ -39,7 +39,7 @@ addHooks' r starthook stophook = r'
 		, retrieveKeyFile = \k f d p -> wrapper $ retrieveKeyFile r k f d p
 		, retrieveKeyFileCheap = \k f -> wrapper $ retrieveKeyFileCheap r k f
 		, removeKey = wrapper . removeKey r
-		, hasKey = wrapper . hasKey r
+		, checkPresent = wrapper . checkPresent r
 		}
 	  where
 		wrapper = runHooks r' starthook stophook
diff --git a/Remote/Helper/Messages.hs b/Remote/Helper/Messages.hs
index c4b1966dc..3088a9ab2 100644
--- a/Remote/Helper/Messages.hs
+++ b/Remote/Helper/Messages.hs
@@ -13,5 +13,5 @@ import qualified Git
 showChecking :: Git.Repo -> Annex ()
 showChecking r = showAction $ "checking " ++ Git.repoDescribe r
 
-cantCheck :: Git.Repo -> Either String Bool
-cantCheck r = Left $ "unable to check " ++ Git.repoDescribe r
+cantCheck :: Git.Repo -> a
+cantCheck r = error $ "unable to check " ++ Git.repoDescribe r
diff --git a/Remote/Helper/Special.hs b/Remote/Helper/Special.hs
index 2bcb7d530..3c19f25eb 100644
--- a/Remote/Helper/Special.hs
+++ b/Remote/Helper/Special.hs
@@ -148,7 +148,7 @@ specialRemote' cfg c preparestorer prepareretriever baser = encr
 			(retrieveKeyFileCheap baser k d)
 			(\_ -> return False)
 		, removeKey = \k -> cip >>= removeKeyGen k
-		, hasKey = \k -> cip >>= hasKeyGen k
+		, checkPresent = \k -> cip >>= checkPresentGen k
 		, cost = maybe
 			(cost baser)
 			(const $ cost baser + encryptedRemoteCostAdj)
@@ -167,7 +167,7 @@ specialRemote' cfg c preparestorer prepareretriever baser = encr
 			displayprogress p k $ \p' ->
 				storeChunks (uuid baser) chunkconfig k src p'
 					(storechunk enc storer)
-					(hasKey baser)
+					(checkPresent baser)
 		go Nothing = return False
 		rollback = void $ removeKey encr k
 
@@ -193,10 +193,10 @@ specialRemote' cfg c preparestorer prepareretriever baser = encr
 		enck = maybe id snd enc
 		remover = removeKey baser
 
-	hasKeyGen k enc = hasKeyChunks checker (uuid baser) chunkconfig enck k
+	checkPresentGen k enc = checkPresentChunks checker (uuid baser) chunkconfig enck k
 	  where
 		enck = maybe id snd enc
-		checker = hasKey baser
+		checker = checkPresent baser
 
 	chunkconfig = chunkConfig cfg
 
diff --git a/Remote/Helper/Ssh.hs b/Remote/Helper/Ssh.hs
index 05a98865f..42d77ea59 100644
--- a/Remote/Helper/Ssh.hs
+++ b/Remote/Helper/Ssh.hs
@@ -81,14 +81,14 @@ onRemote r (with, errorval) command params fields = do
 		Nothing -> return errorval
 
 {- Checks if a remote contains a key. -}
-inAnnex :: Git.Repo -> Key -> Annex (Either String Bool)
+inAnnex :: Git.Repo -> Key -> Annex Bool
 inAnnex r k = do
 	showChecking r
 	onRemote r (check, cantCheck r) "inannex" [Param $ key2file k] []
   where
 	check c p = dispatch <$> safeSystem c p
-	dispatch ExitSuccess = Right True
-	dispatch (ExitFailure 1) = Right False
+	dispatch ExitSuccess = True
+	dispatch (ExitFailure 1) = False
 	dispatch _ = cantCheck r
 
 {- Removes a key from a remote. -}
diff --git a/Remote/Hook.hs b/Remote/Hook.hs
index efbd9f8ba..037f71ced 100644
--- a/Remote/Hook.hs
+++ b/Remote/Hook.hs
@@ -45,8 +45,8 @@ gen r u c gc = do
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = retrieveCheap hooktype,
 			removeKey = remove hooktype,
-			hasKey = checkPresent r hooktype,
-			hasKeyCheap = False,
+			checkPresent = checkKey r hooktype,
+			checkPresentCheap = False,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -128,11 +128,11 @@ retrieveCheap _ _ _ = return False
 remove :: HookName -> Key -> Annex Bool
 remove h k = runHook h "remove" k Nothing $ return True
 
-checkPresent :: Git.Repo -> HookName -> Key -> Annex (Either String Bool)
-checkPresent r h k = do
+checkKey :: Git.Repo -> HookName -> Key -> Annex Bool
+checkKey r h k = do
 	showAction $ "checking " ++ Git.repoDescribe r
 	v <- lookupHook h action
-	liftIO $ catchMsgIO $ check v
+	liftIO $ check v
   where
   	action = "checkpresent"
 	findkey s = key2file k `elem` lines s
diff --git a/Remote/Rsync.hs b/Remote/Rsync.hs
index 421c451bd..91070fe84 100644
--- a/Remote/Rsync.hs
+++ b/Remote/Rsync.hs
@@ -12,7 +12,7 @@ module Remote.Rsync (
 	store,
 	retrieve,
 	remove,
-	checkPresent,
+	checkKey,
 	withRsyncScratchDir,
 	genRsyncOpts,
 	RsyncOpts
@@ -66,8 +66,8 @@ gen r u c gc = do
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap o
 			, removeKey = remove o
-			, hasKey = checkPresent r o
-			, hasKeyCheap = False
+			, checkPresent = checkKey r o
+			, checkPresentCheap = False
 			, whereisKey = Nothing
 			, remoteFsck = Nothing
 			, repairRepo = Nothing
@@ -214,14 +214,12 @@ remove o k = do
 		, dir </> keyFile k </> "***"
 		]
 
-checkPresent :: Git.Repo -> RsyncOpts -> Key -> Annex (Either String Bool)
-checkPresent r o k = do
+checkKey :: Git.Repo -> RsyncOpts -> Key -> Annex Bool
+checkKey r o k = do
 	showAction $ "checking " ++ Git.repoDescribe r
 	-- note: Does not currently differentiate between rsync failing
 	-- to connect, and the file not being present.
-	Right <$> check
-  where
-	check = untilTrue (rsyncUrls o k) $ \u -> 
+	untilTrue (rsyncUrls o k) $ \u -> 
 		liftIO $ catchBoolIO $ do
 			withQuietOutput createProcessSuccess $
 				proc "rsync" $ toCommand $
diff --git a/Remote/S3.hs b/Remote/S3.hs
index 8603757eb..4c1f1ecfd 100644
--- a/Remote/S3.hs
+++ b/Remote/S3.hs
@@ -57,8 +57,8 @@ gen r u c gc = new <$> remoteCost gc expensiveRemoteCost
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = retrieveCheap this,
 			removeKey = remove this c,
-			hasKey = checkPresent this,
-			hasKeyCheap = False,
+			checkPresent = checkKey this,
+			checkPresentCheap = False,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -167,16 +167,16 @@ remove' :: Remote -> Key -> Annex Bool
 remove' r k = s3Action r False $ \(conn, bucket) ->
 	s3Bool =<< liftIO (deleteObject conn $ bucketKey r bucket k)
 
-checkPresent :: Remote -> Key -> Annex (Either String Bool)
-checkPresent r k = s3Action r noconn $ \(conn, bucket) -> do
+checkKey :: Remote -> Key -> Annex Bool
+checkKey r k = s3Action r noconn $ \(conn, bucket) -> do
 	showAction $ "checking " ++ name r
 	res <- liftIO $ getObjectInfo conn $ bucketKey r bucket k
 	case res of
-		Right _ -> return $ Right True
-		Left (AWSError _ _) -> return $ Right False
-		Left e -> return $ Left (s3Error e)
+		Right _ -> return True
+		Left (AWSError _ _) -> return False
+		Left e -> s3Error e
   where
-	noconn = Left $ error "S3 not configured"
+	noconn = error "S3 not configured"
 			
 s3Warning :: ReqError -> Annex Bool
 s3Warning e = do
diff --git a/Remote/Tahoe.hs b/Remote/Tahoe.hs
index d265d7ac1..6e52c0981 100644
--- a/Remote/Tahoe.hs
+++ b/Remote/Tahoe.hs
@@ -72,8 +72,8 @@ gen r u c gc = do
 		retrieveKeyFile = retrieve u hdl,
 		retrieveKeyFileCheap = \_ _ -> return False,
 		removeKey = remove,
-		hasKey = checkPresent u hdl,
-		hasKeyCheap = False,
+		checkPresent = checkKey u hdl,
+		checkPresentCheap = False,
 		whereisKey = Nothing,
 		remoteFsck = Nothing,
 		repairRepo = Nothing,
@@ -123,14 +123,16 @@ remove _k = do
 	warning "content cannot be removed from tahoe remote"
 	return False
 
-checkPresent :: UUID -> TahoeHandle -> Key -> Annex (Either String Bool)
-checkPresent u hdl k = go =<< getCapability u k
+checkKey :: UUID -> TahoeHandle -> Key -> Annex Bool
+checkKey u hdl k = go =<< getCapability u k
   where
-	go Nothing = return (Right False)
-	go (Just cap) = liftIO $ parseCheck <$> readTahoe hdl "check"
-		[ Param "--raw"
-		, Param cap
-		]
+	go Nothing = return False
+	go (Just cap) = liftIO $ do
+		v <- parseCheck <$> readTahoe hdl "check"
+			[ Param "--raw"
+			, Param cap
+			]
+		either error return v
 
 defaultTahoeConfigDir :: UUID -> IO TahoeConfigDir
 defaultTahoeConfigDir u = do
diff --git a/Remote/Web.hs b/Remote/Web.hs
index ddd1fc1cc..7bdd8d185 100644
--- a/Remote/Web.hs
+++ b/Remote/Web.hs
@@ -50,8 +50,8 @@ gen r _ c gc =
 		retrieveKeyFile = downloadKey,
 		retrieveKeyFileCheap = downloadKeyCheap,
 		removeKey = dropKey,
-		hasKey = checkKey,
-		hasKeyCheap = False,
+		checkPresent = checkKey,
+		checkPresentCheap = False,
 		whereisKey = Just getUrls,
 		remoteFsck = Nothing,
 		repairRepo = Nothing,
@@ -98,12 +98,12 @@ dropKey k = do
 	mapM_ (setUrlMissing k) =<< getUrls k
 	return True
 
-checkKey :: Key -> Annex (Either String Bool)
+checkKey :: Key -> Annex Bool
 checkKey key = do
 	us <- getUrls key
 	if null us
-		then return $ Right False
-		else return =<< checkKey' key us
+		then return False
+		else either error return =<< checkKey' key us
 checkKey' :: Key -> [URLString] -> Annex (Either String Bool)
 checkKey' key us = firsthit us (Right False) $ \u -> do
 	let (u', downloader) = getDownloader u
diff --git a/Remote/WebDAV.hs b/Remote/WebDAV.hs
index 0bdd38360..f0bcac10e 100644
--- a/Remote/WebDAV.hs
+++ b/Remote/WebDAV.hs
@@ -63,8 +63,8 @@ gen r u c gc = new <$> remoteCost gc expensiveRemoteCost
 			retrieveKeyFile = retrieve this,
 			retrieveKeyFileCheap = retrieveCheap this,
 			removeKey = remove this,
-			hasKey = checkPresent this,
-			hasKeyCheap = False,
+			checkPresent = checkKey this,
+			checkPresentCheap = False,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
 			repairRepo = Nothing,
@@ -170,10 +170,10 @@ remove r k = davAction r False $ \(baseurl, user, pass) -> liftIO $ do
 	let url = davLocation baseurl k
 	isJust . eitherToMaybe <$> tryNonAsync (deleteDAV url user pass)
 
-checkPresent :: Remote -> Key -> Annex (Either String Bool)
-checkPresent r k = davAction r noconn go
+checkKey :: Remote -> Key -> Annex Bool
+checkKey r k = davAction r noconn (either error id <$$> go)
   where
-	noconn = Left $ error $ name r ++ " not configured"
+	noconn = error $ name r ++ " not configured"
 
 	go (baseurl, user, pass) = do
 		showAction $ "checking " ++ name r