run Preparer to get Remover and CheckPresent actions

This will allow special remotes to eg, open a http connection and reuse it,
while checking if chunks are present, or removing chunks.

S3 and WebDAV both need this to support chunks with reasonable speed.

Note that a special remote might want to cache a http connection across
multiple requests. A simple case of this is that CheckPresent is typically
called before Store or Remove. A remote using this interface can certianly
use a Preparer that eg, uses a MVar to cache a http connection.

However, it's up to the remote to then deal with things like stale or
stalled http connections when eg, doing a series of downloads from a remote
and other places. There could be long delays between calls to a remote,
which could lead to eg, http connection stalls; the machine might even
move to a new network, etc.

It might be nice to improve this interface later to allow
the simple case without needing to handle the full complex case.
One way to do it would be to have a `Transaction SpecialRemote cache`,
where SpecialRemote contains methods for Storer, Retriever, Remover, and
CheckPresent, that all expect to be passed a `cache`.

1 files changed, 6 insertions, 4 deletions

diff --git a/Remote/Directory.hs b/Remote/Directory.hs
index 0a2532aa5..d9419757f 100644
--- a/Remote/Directory.hs
+++ b/Remote/Directory.hs
@@ -44,6 +44,8 @@ gen r u c gc = do
 	return $ Just $ specialRemote c
 		(prepareStore dir chunkconfig)
 		(retrieve dir chunkconfig)
+		(simplyPrepare $ remove dir)
+		(simplyPrepare $ checkKey dir chunkconfig)
 		Remote {
 			uuid = u,
 			cost = cst,
@@ -51,8 +53,8 @@ gen r u c gc = do
 			storeKey = storeKeyDummy,
 			retrieveKeyFile = retreiveKeyFileDummy,
 			retrieveKeyFileCheap = retrieveCheap dir chunkconfig,
-			removeKey = remove dir,
-			checkPresent = checkKey dir chunkconfig,
+			removeKey = removeKeyDummy,
+			checkPresent = checkPresentDummy,
 			checkPresentCheap = True,
 			whereisKey = Nothing,
 			remoteFsck = Nothing,
@@ -161,7 +163,7 @@ retrieveCheap d NoChunks k f = liftIO $ catchBoolIO $ do
 retrieveCheap _ _ _ _ = return False
 #endif
 
-remove :: FilePath -> Key -> Annex Bool
+remove :: FilePath -> Remover
 remove d k = liftIO $ removeDirGeneric d (storeDir d k)
 
 {- Removes the directory, which must be located under the topdir.
@@ -189,7 +191,7 @@ removeDirGeneric topdir dir = do
 		then return ok
 		else doesDirectoryExist topdir <&&> (not <$> doesDirectoryExist dir)
 
-checkKey :: FilePath -> ChunkConfig -> Key -> Annex Bool
+checkKey :: FilePath -> ChunkConfig -> CheckPresent
 checkKey d (LegacyChunks _) k = Legacy.checkKey d locations k
 checkKey d _ k = liftIO $
 	ifM (anyM doesFileExist (locations d k))