fix memory leak

Unfortunately, I don't fully understand why it was leaking using the old
method of a lazy bytestring. I just know that it was leaking, despite
neither hGetUntilMetered nor byteStringPopper seeming to leak by
themselves.

The new method avoids the lazy bytestring, and simply reads chunks from the
handle and streams them out to the http socket.

Remote/Helper/Http.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE BangPatterns #-}
+
 module Remote.Helper.Http where
 
 import Common.Annex
@@ -31,17 +33,38 @@ httpStorer a = fileStorer $ \k f m -> a k =<< liftIO (httpBodyStorer f m)
 httpBodyStorer :: FilePath -> MeterUpdate -> IO RequestBody
 httpBodyStorer src m = do
 	size <- fromIntegral . fileSize <$> getFileStatus src :: IO Integer
-	let streamer sink = withMeteredFile src m $ \b -> mkPopper b sink
+	let streamer sink = withMeteredFile src m $ \b -> byteStringPopper b sink
 	return $ RequestBodyStream (fromInteger size) streamer
 
-mkPopper :: L.ByteString -> NeedsPopper () -> IO ()
-mkPopper b sink = do
+byteStringPopper :: L.ByteString -> NeedsPopper () -> IO ()
+byteStringPopper b sink = do
 	mvar <- newMVar $ L.toChunks b
-	let getnextchunk = modifyMVar mvar $ pure . pop
+	let getnextchunk = modifyMVar mvar $ \v ->
+		case v of
+			[] -> return ([], S.empty)
+			(c:cs) -> return (cs, c)
+	sink getnextchunk
+
+{- Makes a Popper that streams a given number of chunks of a given
+ - size from the handle, updating the meter as the chunks are read. -}
+handlePopper :: Integer -> Int -> MeterUpdate -> Handle -> NeedsPopper () -> IO ()
+handlePopper numchunks chunksize meterupdate h sink = do
+	mvar <- newMVar zeroBytesProcessed
+	let getnextchunk = do
+		sent <- takeMVar mvar
+		if sent >= target
+			then do
+				putMVar mvar sent
+				return S.empty
+			else do
+				b <- S.hGet h chunksize
+				let !sent' = addBytesProcessed sent chunksize
+				putMVar mvar sent'
+                                meterupdate sent'
+				return b
 	sink getnextchunk
   where
-	pop [] = ([], S.empty)
-	pop (c:cs) = (cs, c)
+	target = toBytesProcessed (numchunks * fromIntegral chunksize)
 
 -- Reads the http body and stores it to the specified file, updating the
 -- meter as it goes.

Remote/S3.hs

@@ -198,10 +198,11 @@ store r h = fileStorer $ \k f p -> do
 						let sz = if fsz - pos < partsz'
 							then fsz - pos
 							else partsz'
-						b <- liftIO $ hGetUntilMetered fh (< partsz') meter
-						let body = RequestBodyStream (fromIntegral sz) (mkPopper b)
-						S3.UploadPartResponse _ etag <- sendS3Handle h $
-							 S3.uploadPart (bucket info) object partnum uploadid body
+						let numchunks = ceiling (fromIntegral sz / defaultChunkSize)
+						let popper = handlePopper numchunks defaultChunkSize p fh
+						let req = S3.uploadPart (bucket info) object partnum uploadid $
+							 RequestBodyStream (fromIntegral sz) popper
+						S3.UploadPartResponse _ etag <- sendS3Handle h req
 						sendparts (offsetMeterUpdate meter (toBytesProcessed sz)) (etag:etags) (partnum + 1)
 			sendparts p [] 1