fix slowloris timeout in hashing resume of download of large file

Hash the data that is already present in the file before connecting to
the http server.

Annex/Verify.hs

@@ -234,16 +234,12 @@ resumeVerifyFromOffset
 	-> IO MeterUpdate
 resumeVerifyFromOffset o incrementalverifier meterupdate h
 	| o /= 0 = do
-		p' <- case incrementalverifier of
-			Just iv -> do
-				go iv o
-				return offsetmeterupdate
-			_ -> return offsetmeterupdate
+		maybe noop (`go` o) incrementalverifier
 		-- Make sure the handle is seeked to the offset.
 		-- (Reading the file probably left it there
 		-- when that was done, but let's be sure.)
 		hSeek h AbsoluteSeek o
-		return p'
+		return offsetmeterupdate
 	| otherwise = return meterupdate
   where
 	offsetmeterupdate = offsetMeterUpdate meterupdate (toBytesProcessed o)

P2P/Http/Client.hs

@@ -144,33 +144,32 @@ runP2PHttpClient rmt fallback () = fallback
 #endif
 
 #ifdef WITH_SERVANT
+-- Downloads and writes to the Handle. If the file already exists, provide
+-- its starting size, and it will resume from that point. Note that the
+-- IncrementalVerifier needs to have already been fed the existing content
+-- of the file.
 clientGet
 	:: MeterUpdate
 	-> Maybe IncrementalVerifier
 	-> Key
 	-> AssociatedFile
-	-> RawFilePath
+	-> Handle
+	-> Maybe FileSize
 	-> ClientAction Validity
-clientGet meterupdate iv k af dest clientenv (ProtocolVersion ver) su cu bypass auth = liftIO $ do
-	startsz <- tryWhenExists $ getFileSize dest
+clientGet meterupdate iv k af h startsz clientenv (ProtocolVersion ver) su cu bypass auth = liftIO $ do
 	let offset = fmap (Offset . fromIntegral) startsz
 	withClientM (cli (B64Key k) cu bypass baf offset auth) clientenv $ \case
 		Left err -> return (Left err)
-		Right respheaders ->
-			withBinaryFile (fromRawFilePath dest) ReadWriteMode $ \h -> do
-				meterupdate' <- case startsz of
-					Just startsz' ->
-						resumeVerifyFromOffset startsz' iv meterupdate h 
-					_ -> return meterupdate
-				b <- S.unSourceT (getResponse respheaders) gather
-				BytesProcessed len <- meteredWrite'
-					meterupdate'
-					(writeVerifyChunk iv h) b
-				let DataLength dl = case lookupResponseHeader @DataLengthHeader' respheaders of
-					Header hdr -> hdr
-					_ -> error "missing data length header"
-				return $ Right $ 
-					if dl == len then Valid else Invalid
+		Right respheaders -> do
+			b <- S.unSourceT (getResponse respheaders) gather
+			BytesProcessed len <- meteredWrite'
+				meterupdate
+				(writeVerifyChunk iv h) b
+			let DataLength dl = case lookupResponseHeader @DataLengthHeader' respheaders of
+				Header hdr -> hdr
+				_ -> error "missing data length header"
+			return $ Right $ 
+				if dl == len then Valid else Invalid
   where
 	cli =case ver of
 		3 -> v3 su V3

Remote/Git.hs

@@ -539,11 +539,7 @@ copyFromRemote r st key file dest meterupdate vc = do
 
 copyFromRemote'' :: Git.Repo -> Remote -> State -> Key -> AssociatedFile -> FilePath -> MeterUpdate -> VerifyConfig -> Annex Verification
 copyFromRemote'' repo r st@(State connpool _ _ _ _) key af dest meterupdate vc
-	| isP2PHttp r = verifyKeyContentIncrementally vc key $ \iv ->
-		metered (Just meterupdate) key bwlimit $ \_ p ->
-		p2pHttpClient r giveup (clientGet p iv key af (encodeBS dest)) >>= \case
-			Valid -> return ()
-			Invalid -> giveup "Transfer failed"
+	| isP2PHttp r = p2phttp
 	| Git.repoIsHttp repo = verifyKeyContentIncrementally vc key $ \iv -> do
 		gc <- Annex.getGitConfig
 		ok <- Url.withUrlOptionsPromptingCreds $
@@ -577,6 +573,19 @@ copyFromRemote'' repo r st@(State connpool _ _ _ _) key af dest meterupdate vc
   where
 	bwlimit = remoteAnnexBwLimitDownload (gitconfig r)
 		<|> remoteAnnexBwLimit (gitconfig r)
+		
+	p2phttp = verifyKeyContentIncrementally vc key $ \iv -> do
+		startsz <- liftIO $ tryWhenExists $
+			getFileSize (toRawFilePath dest)
+		bracketIO (openBinaryFile dest ReadWriteMode) (hClose) $ \h -> do
+			metered (Just meterupdate) key bwlimit $ \_ p -> do
+				p' <- case startsz of
+					Just startsz' -> liftIO $ do
+						resumeVerifyFromOffset startsz' iv p h 
+					_ -> return p
+				p2pHttpClient r giveup (clientGet p' iv key af h startsz) >>= \case
+					Valid -> return ()
+					Invalid -> giveup "Transfer failed"
 
 copyFromRemoteCheap :: State -> Git.Repo -> Maybe (Key -> AssociatedFile -> FilePath -> Annex ())
 #ifndef mingw32_HOST_OS

doc/todo/git-annex_proxies.mdwn

@@ -28,13 +28,6 @@ Planned schedule of work:
 
 ## work notes
 
-* Test resume of download of large file when large amount of file is
-  already downloaded and verification takes a long time. Will the http
-  connection be dropped due to inactivity? May need to do verification in a
-  separate thread that feeds in the existing file followed by the newly
-  downloaded data. Eg, a version of tailVerify that operates on a handle
-  open for read+write.
-
 * Rest of Remote.Git needs implementing.
 
 * git-annex p2phttp serving .well-known for ACME.