refactor(journal): use bulk copy in getByteString

Thanks Daniel

src/journal/src/Journal.hs

@@ -44,6 +44,7 @@ defaultOptions = Options 1024 (64 * 1024)
 
 allocateJournal :: FilePath -> Options -> IO ()
 allocateJournal = undefined
+  -- System.Posix.Fcntl.fileAllocate
 
 startJournal' :: FilePath -> Options -> IO Journal'
 startJournal' fp (Options _ termLength) = do

src/journal/src/Journal/Internal.hs

@@ -113,6 +113,7 @@ tryClaim jour len = do
     return (backPressureStatus position len)
 
 calculatePositionLimit = undefined
+backPressureStatus = undefined
 
 newPosition :: Metadata -> Maybe TermOffset -> IO (Maybe Int64)
 newPosition meta mResultingOffset =
@@ -139,8 +140,6 @@ newPosition meta mResultingOffset =
       rotateTerm meta
       return Nothing -- ADMIN_ACTION
 
-backPressureStatus = undefined
-
 fRAME_ALIGNMENT :: Int
 fRAME_ALIGNMENT = 32
 
@@ -223,7 +222,6 @@ commit = undefined
 
 abort = undefined
 
-
 ------------------------------------------------------------------------
 
 claim :: Journal -> Int -> IO Int

src/journal/src/Journal/Internal/ByteBuffer.hs

@@ -283,9 +283,14 @@ putLazyByteString bb lbs = do
       s' -> (# s', () #)
 
 getByteString :: ByteBuffer -> Int -> IO BS.ByteString
-getByteString bb len = do
-  bytes <- replicateM len (getByte bb)
-  return (BS.packBytes bytes)
+getByteString bb len@(I# len#) = do
+  boundCheck bb (len - 1)
+  Position (I# offset#) <- readPosition bb
+  bs <- BS.create len $ \(Ptr addr#) -> IO $ \s ->
+    case copyMutableByteArrayToAddr# (bbData bb) offset# addr# len# s of
+      s' -> (# s', () #)
+  incrPosition bb len
+  return bs
 
 getLazyByteString :: ByteBuffer -> Int -> IO LBS.ByteString
 getLazyByteString bb len = do