add removeKey action to Remote

Not implemented for any remotes yet; probably the git remote is the only
one that will ever implement it.

Command/Drop.hs

@@ -91,7 +91,7 @@ startRemote afile numcopies key remote = do
 -- Note that lockContentExclusive is called before checking if the key is
 -- present on enough remotes to allow removal. This avoids a scenario where two
 -- or more remotes are trying to remove a key at the same time, and each
--- see the key is present on the other.
+-- sees the key is present on the other.
 performLocal :: Key -> AssociatedFile -> NumCopies -> Maybe Remote -> CommandPerform
 performLocal key afile numcopies knownpresentremote = lockContentExclusive key $ \contentlock -> do
 	(remotes, trusteduuids) <- Remote.keyPossibilitiesTrusted key

Remote/BitTorrent.hs

@@ -58,6 +58,7 @@ gen r _ c gc =
 		, retrieveKeyFile = downloadKey
 		, retrieveKeyFileCheap = downloadKeyCheap
 		, removeKey = dropKey
+		, lockContent = Nothing
 		, checkPresent = checkKey
 		, checkPresentCheap = False
 		, whereisKey = Nothing

Remote/Bup.hs

@@ -58,6 +58,7 @@ gen r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = retrieveCheap buprepo
 		, removeKey = removeKeyDummy
+		, lockContent = Nothing
 		, checkPresent = checkPresentDummy
 		, checkPresentCheap = bupLocal buprepo
 		, whereisKey = Nothing

Remote/Ddar.hs

@@ -57,6 +57,7 @@ gen r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = retrieveCheap
 		, removeKey = removeKeyDummy
+		, lockContent = Nothing
 		, checkPresent = checkPresentDummy
 		, checkPresentCheap = ddarLocal ddarrepo
 		, whereisKey = Nothing

Remote/Directory.hs

@@ -55,6 +55,7 @@ gen r u c gc = do
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap dir chunkconfig
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = True
 			, whereisKey = Nothing

Remote/External.hs

@@ -81,6 +81,7 @@ gen r u c gc
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = \_ _ _ -> return False
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = towhereis

Remote/GCrypt.hs

@@ -111,6 +111,7 @@ gen' r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = \_ _ _ -> return False
 		, removeKey = removeKeyDummy
+		, lockContent = Nothing
 		, checkPresent = checkPresentDummy
 		, checkPresentCheap = repoCheap r
 		, whereisKey = Nothing

Remote/Git.hs

@@ -142,6 +142,7 @@ gen r u c gc
 			, retrieveKeyFile = copyFromRemote new
 			, retrieveKeyFileCheap = copyFromRemoteCheap new
 			, removeKey = dropKey new
+			, lockContent = Nothing
 			, checkPresent = inAnnex new
 			, checkPresentCheap = repoCheap r
 			, whereisKey = Nothing

Remote/Glacier.hs

@@ -55,6 +55,7 @@ gen r u c gc = new <$> remoteCost gc veryExpensiveRemoteCost
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap this
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = Nothing

Remote/Hook.hs

@@ -49,6 +49,7 @@ gen r u c gc = do
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap hooktype
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = Nothing

Remote/Rsync.hs

@@ -70,6 +70,7 @@ gen r u c gc = do
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap o
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = Nothing

Remote/S3.hs

@@ -81,6 +81,7 @@ gen r u c gc = do
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = Just (getWebUrls info)

Remote/Tahoe.hs

@@ -72,6 +72,7 @@ gen r u c gc = do
 		, retrieveKeyFile = retrieve u hdl
 		, retrieveKeyFileCheap = \_ _ _ -> return False
 		, removeKey = remove
+		, lockContent = Nothing
 		, checkPresent = checkKey u hdl
 		, checkPresentCheap = False
 		, whereisKey = Nothing

Remote/Web.hs

@@ -52,6 +52,7 @@ gen r _ c gc =
 		, retrieveKeyFile = downloadKey
 		, retrieveKeyFileCheap = downloadKeyCheap
 		, removeKey = dropKey
+		, lockContent = Nothing
 		, checkPresent = checkKey
 		, checkPresentCheap = False
 		, whereisKey = Nothing

Remote/WebDAV.hs

@@ -60,6 +60,7 @@ gen r u c gc = new <$> remoteCost gc expensiveRemoteCost
 			, retrieveKeyFile = retreiveKeyFileDummy
 			, retrieveKeyFileCheap = retrieveCheap
 			, removeKey = removeKeyDummy
+			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = False
 			, whereisKey = Nothing

Types/Remote.hs

@@ -7,6 +7,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE RankNTypes #-}
+
 module Types.Remote
 	( RemoteConfigKey
 	, RemoteConfig
@@ -72,8 +74,12 @@ data RemoteA a = Remote {
 	-- Retrieves a key's contents to a tmp file, if it can be done cheaply.
 	-- It's ok to create a symlink or hardlink.
 	retrieveKeyFileCheap :: Key -> AssociatedFile -> FilePath -> a Bool,
-	-- removes a key's contents (succeeds if the contents are not present)
+	-- Removes a key's contents (succeeds if the contents are not present)
 	removeKey :: Key -> a Bool,
+	-- Uses locking to prevent removal of a key's contents,
+	-- and runs the passed action while it's locked.
+	-- This is optional; remotes do not have to support locking.
+	lockContent :: forall r. Maybe (Key -> a r -> a r),
 	-- Checks if a key is present in the remote.
 	-- Throws an exception if the remote cannot be accessed.
 	checkPresent :: Key -> a Bool,