add key stability checking interface

Needed for resuming from chunks.

Url keys are considered not stable. I considered treating url keys with a
known size as stable, but just don't feel that is enough information.

3 files changed, 5 insertions, 0 deletions

diff --git a/Backend/Hash.hs b/Backend/Hash.hs
index 3ff496271..91267ed67 100644
--- a/Backend/Hash.hs
+++ b/Backend/Hash.hs
@@ -45,6 +45,7 @@ genBackend hash = Just Backend
 	, fsckKey = Just $ checkKeyChecksum hash
 	, canUpgradeKey = Just needsUpgrade
 	, fastMigrate = Just trivialMigrate
+	, isStableKey = const True
 	}
 
 genBackendE :: Hash -> Maybe Backend
diff --git a/Backend/URL.hs b/Backend/URL.hs
index 4233c56bc..2c2988ac0 100644
--- a/Backend/URL.hs
+++ b/Backend/URL.hs
@@ -25,6 +25,9 @@ backend = Backend
 	, fsckKey = Nothing
 	, canUpgradeKey = Nothing
 	, fastMigrate = Nothing
+	-- The content of an url can change at any time, so URL keys are
+	-- not stable.
+	, isStableKey = const False
 	}
 
 {- Every unique url has a corresponding key. -}
diff --git a/Backend/WORM.hs b/Backend/WORM.hs
index fdeea6f89..c972602ad 100644
--- a/Backend/WORM.hs
+++ b/Backend/WORM.hs
@@ -23,6 +23,7 @@ backend = Backend
 	, fsckKey = Nothing
 	, canUpgradeKey = Nothing
 	, fastMigrate = Nothing
+	, isStableKey = const True
 	}
 
 {- The key includes the file size, modification time, and the