Haskell broken pipe error when working with streams-CodePudding

I'm trying to build a player using streams. The main idea is to have a thread running a player that reads from bytes that come from another thread that downloads youtube audio concurrently. The code works for a while and the content is streamed correctly, but after a few seconds I always got this error: Exception: fd:13: hPutBuf: resource vanished (Broken pipe).

I guess I'm missing something, because even when using the connect function the result is the same. Here's the code (simplified):

import Control.Concurrent
import System.IO.Streams 
import Data.ByteString

main = do
  (sink,_,_,_) <- runInteractiveCommand "mplayer -novideo - cache 5096 -"
  mainSink <- lockingOutputStream sink  -- main audio stream, goes straight to player

  (_,source,_,_) <- runInteractiveCommand "yt-dlp \"https://www.youtube.com/watch?v=uFtfDK39ZhI\" -f bv ba -o -"
  loop mainSink source


loop :: OutputStream ByteString -> InputStream ByteString -> IO ()
loop sink src = do
  sourceBytes <- peek src
  case sourceBytes of
    Nothing -> do loop sink src
    Just _  -> do
      audioBytes <- read src 
      write audioBytes sink
      loop sink src

CodePudding user response：

The problem appears to be that mplayer is generating its usual verbose terminal output on stdout and stderr, while yt-dlp is similarly generating output on stderr. Since you toss these handles away and never drain them, eventually the pipe buffers fill, and the processes get stuck. I can't say precisely why one or both of the processes dies instead of just hanging, but that's what's happening. Here's a simple example that redirects the unneeded output to /dev/null and appears to work:

import System.IO.Streams

main = do
  (sink,_,_,_) <- runInteractiveCommand "mplayer -cache 5096 - 2>/dev/null >&2"
  (_,source,_,_) <- runInteractiveCommand "yt-dlp \"https://www.youtube.com/watch?v=uFtfDK39ZhI\" -f bv ba -o - 2>/dev/null"
  connect source sink