Conduit to yield first lines from file without leaking space or file handles?

I’ve looked into this for longer than I should have, but I think the problem is that you need to make take aware of the ResourceT for this to work. Here’s a hack I came up with:

takeRes :: MonadResource m => Int -> ConduitT a a m ()
takeRes 0 = liftResourceT $ do
  is <- getInternalState
  closeInternalState is
  liftIO $ writeIORef is $ ReleaseMap maxBound (minBound + 1) mempty
takeRes n = await >>= \case
  Nothing -> mempty
  Just x -> yield x *> takeRes (n - 1)

Full code (click for more details)

With that, it does output what you expect:

1
close
1
2
close
1
2
3
close
1
2
3
close