migrate: WORM keys containing spaces will be migrated to not contain spaces anymore

To work around the problem that the external special remote protocol does
not support keys containing spaces.

This commit was sponsored by Denis Dzyubenko on Patreon.

Backend/WORM.hs

@@ -22,8 +22,8 @@ backend = Backend
 	{ backendVariety = WORMKey
 	, getKey = keyValue
 	, verifyKeyContent = Nothing
-	, canUpgradeKey = Nothing
-	, fastMigrate = Nothing
+	, canUpgradeKey = Just needsUpgrade
+	, fastMigrate = Just removeSpaces
 	, isStableKey = const True
 	}
 
@@ -42,3 +42,17 @@ keyValue source = do
 		, keySize = Just sz
 		, keyMtime = Just $ modificationTime stat
 		}
+
+{- Old WORM keys could contain spaces, and can be upgraded to remove them. -}
+needsUpgrade :: Key -> Bool
+needsUpgrade key = ' ' `elem` keyName key
+
+removeSpaces :: Key -> Backend -> AssociatedFile -> Maybe Key
+removeSpaces oldkey newbackend _
+	| migratable = Just $ oldkey
+		{ keyName = reSanitizeKeyName (keyName oldkey) }
+	| otherwise = Nothing
+  where
+	migratable = oldvariety == newvariety
+	oldvariety = keyVariety oldkey
+	newvariety = backendVariety newbackend