Intermediate flow WAI with safety pipes

I am using channels and WAI for audio streaming. The problem is that I need to look at some data in a safe-pipe and then select the response headers based on the information fetched and then continue to stream that pipe as the response body. Here's what I have now and what works well:

respond $ Wai.responseStream status200 headers $ \write flush -> do
    runSafeT $ runEffect $ do
        (mph, chunks) <- lift $ Mpeg.headerFromPipe pipe
        for chunks $ \chunk -> liftIO $ do
            write $ BB.byteString chunk
            flush     

      

        
        
        
      

    

respond

is the standard Application funarg, and Mpeg.headerFromPipe

this is my perspective computation:

respond :: Response -> IO ResponseReceived

Mpeg.headerFromPipe :: Monad m 
    => Producer ByteString m r
    -> m (Mpeg.Header, Producer ByteString m r)

pipe :: Producer ByteString (SafeT IO) ()

Wai.responseStream :: Status -> ResponseHeaders -> StreamingBody -> Response

type StreamingBody = (Builder -> IO ()) -> IO () -> IO ()

      

        
        
        
      

    

So the question is: is there a way to move respond

between headerFromPipe

and for

to use mph

to select the headings to give responseStream

. I cannot split headerFromPipe

and for

into two different SafeT -goods, because then the first one runSafeT

will complete the pipe and the pipe chunks

(which is the result several times next

, checking the data, putting the stuff back and chains with the remainder) will fail.