Memory leak

[shlok]

It seems this library (random-bytestring-0.1.3.2) leaks memory. One can run the program

module Main where
import Data.ByteString.Random.MWC (random)
main :: IO ()
main = random 10000 >> main

and watch memory blowing up.

Here are two ideas for fixes to Data.ByteString.Random.Internal:

1. Replace bracketOnError with bracket and copy the ByteString at the end:

bracket (mallocBytes len8) free $ \ptr@(Ptr !addr) → do
    {-# SCC "go" #-} go ptr
    {-# SCC "pack" #-} unsafePackAddressLen len8 addr >>= return . copy

2. Somehow replace unsafePackAddressLen with unsafePackMallocCStringLen. This sounds better (no copying), but I didn’t manage to get the types to match.

Update. For 2, here is a suggestion:

bracketOnError (mallocBytes len8) free $ \ptr@(Ptr !addr) → do
    {-# SCC "go" #-} go ptr
    {-# SCC "pack" #-} unsafePackMallocCStringLen (castPtr ptr :: Ptr CChar, len8)