other 80% of avoding verification when hard linking to objects in shared repo

In c6632ee5c8, it actually only handled
uploading objects to a shared repository. To avoid verification when
downloading objects from a shared repository, was a lot harder.

On the plus side, if the process of downloading a file from a remote
is able to verify its content on the side, the remote can indicate this
now, and avoid the extra post-download verification.

As of yet, I don't have any remotes (except Git) using this ability.
Some more work would be needed to support it in special remotes.

It would make sense for tahoe to implicitly verify things downloaded from it;
as long as you trust your tahoe server (which typically runs locally),
there's cryptographic integrity. OTOH, despite bup being based on shas,
a bup repo under an attacker's control could have the git ref used for an
object changed, and so a bup repo shouldn't implicitly verify. Indeed,
tahoe seems unique in being trustworthy enough to implicitly verify.

Command/AddUrl.hs

@@ -154,7 +154,7 @@ downloadRemoteFile r relaxed uri file sz = do
 			-- so that the remote knows what url it
 			-- should use to download it.
 			setTempUrl urlkey loguri
-			let downloader = Remote.retrieveKeyFile r urlkey (Just file)
+			let downloader = \dest p -> fst <$> Remote.retrieveKeyFile r urlkey (Just file) dest p
 			ret <- downloadWith downloader urlkey (Remote.uuid r) loguri file
 			removeTempUrl urlkey
 			return ret

Command/Fsck.hs

@@ -161,7 +161,7 @@ performRemote key file backend numcopies remote =
 			( return (Just True)
 			, ifM (Annex.getState Annex.fast)
 				( return Nothing
-				, Just <$>
+				, Just . fst <$>
 					Remote.retrieveKeyFile remote key Nothing tmp dummymeter
 				)
 			)

Command/ReKey.hs

@@ -52,7 +52,7 @@ perform file oldkey newkey = do
 {- Make a hard link to the old key content (when supported),
  - to avoid wasting disk space. -}
 linkKey :: Key -> Key -> Annex Bool
-linkKey oldkey newkey = getViaTmp' DefaultVerify newkey $ \tmp -> do
+linkKey oldkey newkey = getViaTmp' DefaultVerify newkey $ \tmp -> unVerified $ do
 	src <- calcRepo $ gitAnnexLocation oldkey
 	liftIO $ ifM (doesFileExist tmp)
 		( return True

Command/RecvKey.hs

@@ -40,7 +40,7 @@ start key = fieldTransfer Download key $ \_p -> do
 		, return False
 		)
   where
-	go tmp = do
+	go tmp = unVerified $ do
 		opts <- filterRsyncSafeOptions . maybe [] words
 			<$> getField "RsyncOptions"
 		liftIO $ rsyncServerReceive (map Param opts) tmp

Command/Reinject.hs

@@ -43,7 +43,7 @@ perform src _dest key = ifM move
 	-- so moveFile is used rather than simply calling
 	-- moveToObjectDir; disk space is also checked this way,
 	-- and the file's content is verified to match the key.
-	move = getViaTmp DefaultVerify key $ \tmp ->
+	move = getViaTmp DefaultVerify key $ \tmp -> unVerified $
 		liftIO $ catchBoolIO $ do
 			moveFile src tmp
 			return True

Command/SetKey.hs

@@ -35,7 +35,7 @@ perform file key = do
 	-- the file might be on a different filesystem, so moveFile is used
 	-- rather than simply calling moveAnnex; disk space is also
 	-- checked this way.
-	ok <- getViaTmp DefaultVerify key $ \dest ->
+	ok <- getViaTmp DefaultVerify key $ \dest -> unVerified $
 		if dest /= file
 			then liftIO $ catchBoolIO $ do
 				moveFile file dest

Command/TestRemote.hs

@@ -176,7 +176,7 @@ testUnavailable st r k =
 		getViaTmp (RemoteVerify r) k $ \dest ->
 			Remote.retrieveKeyFile r k Nothing dest nullMeterUpdate
 	, check (== Right False) "retrieveKeyFileCheap" $
-		getViaTmp (RemoteVerify r) k $ \dest ->
+		getViaTmp (RemoteVerify r) k $ \dest -> unVerified $
 			Remote.retrieveKeyFileCheap r k Nothing dest
 	]
   where