incremental checksum for local remotes

This benchmarks only slightly faster than the old git-annex. Eg, for a 1
gb file, 14.56s vs 15.57s. (On a ram disk; there would certianly be
more of an effect if the file was written to disk and didn't stay in
cache.)

Commenting out the updateIncremental calls make the same run in 6.31s.
May be that overhead in the implementation, other than the actual
checksumming, is slowing it down. Eg, MVar access.

(I also tried using 10x larger chunks, which did not change the speed.)

CHANGELOG

@@ -24,8 +24,8 @@ git-annex (8.20210128) UNRELEASED; urgency=medium
   * Include libkqueue.h file needed to build the assistant on BSDs.
   * Tahoe: Avoid verifying hash after download, since tahoe does sufficient
     verification itself.
-  * Checksum as content is received from a remote git-annex repository
+  * Checksum as content is received from a remote git-annex repository,
-    over ssh/p2p protocols, rather than doing it in a second pass.
+    rather than doing it in a second pass.
   * Bugfix: fsck --from a ssh remote did not actually check that the
     content on the remote is not corrupted.
 

Remote/Git.hs

@@ -62,7 +62,10 @@ import Annex.Path
 import Creds
 import Types.NumCopies
 import Types.ProposedAccepted
+import Types.Backend
+import Backend
 import Annex.Action
+import Annex.Verify
 import Messages.Progress
 
 #ifndef mingw32_HOST_OS
@@ -542,11 +545,12 @@ copyFromRemote'' repo forcersync r st@(State connpool _ _ _ _) key file dest met
 		-- run copy from perspective of remote
 		onLocalFast st $ Annex.Content.prepSendAnnex key >>= \case
 			Just (object, checksuccess) -> do
+				let verify = Annex.Content.RemoteVerify r
 				copier <- mkCopier hardlink st
 				(ok, v) <- runTransfer (Transfer Download u (fromKey id key))
 					file Nothing stdRetry $ \p ->
 						metered (Just (combineMeterUpdate p meterupdate)) key $ \_ p' -> 
-							copier object dest key p' checksuccess
+							copier object dest key p' checksuccess verify
 				if ok
 					then return v
 					else giveup "failed to retrieve content from remote"
@@ -685,12 +689,12 @@ copyToRemote' repo r st@(State connpool duc _ _ _) key file meterupdate
 		res <- onLocalFast st $ ifM (Annex.Content.inAnnex key)
 			( return True
 			, runTransfer (Transfer Download u (fromKey id key)) file Nothing stdRetry $ \p -> do
-				copier <- mkCopier hardlink st
 				let verify = Annex.Content.RemoteVerify r
+				copier <- mkCopier hardlink st
 				let rsp = RetrievalAllKeysSecure
 				res <- logStatusAfter key $ Annex.Content.getViaTmp rsp verify key file $ \dest ->
 					metered (Just (combineMeterUpdate meterupdate p)) key $ \_ p' -> 
-						copier object (fromRawFilePath dest) key p' (liftIO checksuccessio)
+						copier object (fromRawFilePath dest) key p' (liftIO checksuccessio) verify
 				Annex.Content.saveState True
 				return res
 			)
@@ -825,7 +829,7 @@ wantHardLink = (annexHardLink <$> Annex.getGitConfig)
 -- from is implicitly trusted, so no expensive verification needs to be
 -- done. Also returns Verified if the key's content is verified while
 -- copying it.
-type Copier = FilePath -> FilePath -> Key -> MeterUpdate -> Annex Bool -> Annex (Bool, Verification)
+type Copier = FilePath -> FilePath -> Key -> MeterUpdate -> Annex Bool -> VerifyConfig -> Annex (Bool, Verification)
 
 mkCopier :: Bool -> State -> Annex Copier
 mkCopier remotewanthardlink st = do
@@ -833,13 +837,13 @@ mkCopier remotewanthardlink st = do
 	localwanthardlink <- wantHardLink
 	let linker = \src dest -> createLink src dest >> return True
 	if remotewanthardlink || localwanthardlink
-		then return $ \src dest k p check ->
+		then return $ \src dest k p check verifyconfig ->
 			ifM (liftIO (catchBoolIO (linker src dest)))
 				( ifM check
 					( return (True, Verified)
 					, return (False, UnVerified)
 					)
-				, copier src dest k p check
+				, copier src dest k p check verifyconfig
 				)
 		else return copier
 
@@ -922,9 +926,9 @@ newCopyCoWTried = CopyCoWTried <$> newEmptyMVar
  -}
 fileCopier :: State -> Copier
 #ifdef mingw32_HOST_OS
-fileCopier _st src dest k meterupdate check = docopy
+fileCopier _st src dest k meterupdate check verifyconfig = docopy
 #else
-fileCopier st src dest k meterupdate check =
+fileCopier st src dest k meterupdate check verifyconfig =
 	-- If multiple threads reach this at the same time, they
 	-- will both try CoW, which is acceptable.
 	ifM (liftIO $ isEmptyMVar copycowtried)
@@ -953,14 +957,16 @@ fileCopier st src dest k meterupdate check =
 	dest' = toRawFilePath dest
 
 	docopy = do
+		iv <- startVerifyKeyContentIncrementally verifyconfig k
+
 		-- The file might have had the write bit removed,
 		-- so make sure we can write to it.
 		void $ liftIO $ tryIO $ allowWrite dest'
 
 		liftIO $ withBinaryFile dest ReadWriteMode $ \hdest ->
 			withBinaryFile src ReadMode $ \hsrc -> do
-				sofar <- compareexisting hdest hsrc zeroBytesProcessed
+				sofar <- compareexisting iv hdest hsrc zeroBytesProcessed
-				docopy' hdest hsrc sofar
+				docopy' iv hdest hsrc sofar
 
 		-- Copy src mode and mtime.
 		mode <- liftIO $ fileMode <$> getFileStatus src
@@ -969,24 +975,30 @@ fileCopier st src dest k meterupdate check =
 		liftIO $ touch dest' mtime False
 
 		ifM check
-			( return (True, UnVerified)
+			( case iv of
+				Just x -> ifM (liftIO $ finalizeIncremental x)
+					( return (True, Verified)
+					, return (False, UnVerified)
+					)
+				Nothing -> return (True, UnVerified)
 			, return (False, UnVerified)
 			)
 	
-	docopy' hdest hsrc sofar = do
+	docopy' iv hdest hsrc sofar = do
 		s <- S.hGet hsrc defaultChunkSize
 		if s == S.empty
 			then return ()
 			else do
 				let sofar' = addBytesProcessed sofar (S.length s)
 				S.hPut hdest s
+				maybe noop (flip updateIncremental s) iv
 				meterupdate sofar'
-				docopy' hdest hsrc sofar'
+				docopy' iv hdest hsrc sofar'
 
 	-- Leaves hdest and hsrc seeked to wherever the two diverge,
 	-- so typically hdest will be seeked to end, and hsrc to the same
 	-- position.
-	compareexisting hdest hsrc sofar = do
+	compareexisting iv hdest hsrc sofar = do
 		s <- S.hGet hdest defaultChunkSize
 		if s == S.empty
 			then return sofar
@@ -994,9 +1006,10 @@ fileCopier st src dest k meterupdate check =
 				s' <- getnoshort (S.length s) hsrc
 				if s == s'
 					then do
+						maybe noop (flip updateIncremental s) iv
 						let sofar' = addBytesProcessed sofar (S.length s)
 						meterupdate sofar'
-						compareexisting hdest hsrc sofar'
+						compareexisting iv hdest hsrc sofar'
 					else do
 						seekbefore hdest s
 						seekbefore hsrc s'

doc/todo/OPT__58_____34__bundle__34___get_+_check___40__of_checksum__41___in_a_single_operation/comment_10_695d1269ab20c66630ddfa2d8cbabbef._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 10"""
+ date="2021-02-10T19:48:58Z"
+ content="""
+Incremental hashing implemented for local git remotes.
+
+Next step should be a special remote, such as directory,
+that uses byteRetriever. Chunking and encryption will complicate them..
+"""]]

doc/todo/OPT__58_____34__bundle__34___get_+_check___40__of_checksum__41___in_a_single_operation/comment_9_4f4f4a42adafe52207ed32a5d20e94be._comment

@@ -20,6 +20,6 @@ checksum.
 
 Urk: Using rsync currently protects against
 [[bugs/URL_key_potential_data_loss]], so the replacement would also need to
-deal with that. Probably by refusing to resume a partial transfer of an
+deal with that. Eg, by comparing the temp file content with the start of
-affected key. (Or it could just fall back to rsync for such keys.)
+the object when resuming.
 """]]