ChunkChan.hs

chunkChan :: Int -> Int -> TChan a -> IO [a]
chunkChan numItems timeoutSeconds chan = do
  maybeRead <- timeout (timeoutSeconds * 60 * 1000) . atomically $ replicateM numItems (readTChan chan)
  case maybeRead of
    Just as -> return as
    Nothing -> do
      as <- emptyChannel chan
      if null as
        then chunkChan numItems timeoutSeconds chan
        else return as

emptyChannel :: TChan a -> IO [a]
emptyChannel = undefined

A version that does not explode STM transactions:

chunkChan :: Int -> Int -> TChan a -> IO [a]
chunkChan numItems timeoutSeconds chan = do
  a <- atomically $ readTChan chan
  computeRef <- newIORef [a]

  let takeOne = atomically (readTChan chan)
      appendOne = takeOne >>= modifyIORef' computeRef . (:)
      appendN = replicateM_ (numItems - 1) appendOne

  _ <- timeout (timeoutSeconds * 1000000) appendN
  reverse <$> readIORef computeRef