better byteRetriever

Make the byteRetriever be passed the callback that consumes the bytestring.

This way, there's no worries about the lazy bytestring not all being read
when the resource that's creating it is closed.

Which in turn lets bup, ddar, and S3 each switch from using an unncessary
fileRetriver to a byteRetriever. So, more efficient on chunks and encrypted
files.

The only remaining fileRetrievers are hook and external, which really do
retrieve to files.

Remote/Bup.hs

@@ -8,6 +8,7 @@
 module Remote.Bup (remote) where
 
 import qualified Data.Map as M
+import qualified Data.ByteString.Lazy as L
 import Data.ByteString.Lazy.UTF8 (fromString)
 
 import Common.Annex
@@ -127,12 +128,12 @@ store r buprepo = byteStorer $ \k b p -> do
 		return True
 
 retrieve :: BupRepo -> Retriever
-retrieve buprepo = fileRetriever $ \d k _p ->
-	liftIO $ withFile d WriteMode $ \h -> do
-		let params = bupParams "join" buprepo [Param $ bupRef k]
-		let p = proc "bup" (toCommand params)
-		(_, _, _, pid) <- createProcess $ p { std_out = UseHandle h }
-		forceSuccessProcess p pid
+retrieve buprepo = byteRetriever $ \k sink -> do
+	let params = bupParams "join" buprepo [Param $ bupRef k]
+	let p = proc "bup" (toCommand params)
+	(_, Just h, _, pid) <- liftIO $ createProcess $ p { std_out = CreatePipe }
+	liftIO (hClose h >> forceSuccessProcess p pid)
+		`after` (sink =<< liftIO (L.hGetContents h))
 
 retrieveCheap :: BupRepo -> Key -> FilePath -> Annex Bool
 retrieveCheap _ _ _ = return False