Problems with handling update window in tokio_yamux crate

[mcrakhman]

Hi all!

I tried to use your library for my simple project related to sending files.

I have the code looking like stream.write_all(...).await. The problem is that when the self.send_window == 0 the writer waits until it is waken up by handle_window_update. The window update is actually being received by the session and successfully sent to frame_receiver channel. But because nobody is reading this (i.e. nobody is actually polling the stream), the window can't be updated and the write is stuck forever.

I looked in other solution related to Yamux in Rust (https://github.com/libp2p/rust-yamux), and it seems they actually solve this problem by updating windows on the "session" side not on the stream side (see below), so you don't need to poll the stream, the "session" side manages the window frames (so I assume my code would work as it is, I will try to do it to confirm).

https://github.com/libp2p/rust-yamux/blob/81913c4d85544a8a0453b7fa17021d0ef7aba7e2/yamux/src/connection.rs#L726C9-L739C10

if let Some(s) = self.streams.get_mut(&stream_id) {
    let mut shared = s.lock();
    shared.increase_send_window_by(frame.header().credit());
    if is_finish {
        shared.update_state(self.id, stream_id, State::RecvClosed);
  
        if let Some(w) = shared.reader.take() {
            w.wake()
        }
    }
    if let Some(w) = shared.writer.take() {
        w.wake()
    }
}

Please correct me if I'm missing something, thanks!

[driftluo]

I checked the code. In the current implementation, if the stream is not read, the windowupdate message will not be able to update the window size, which will indeed cause a freeze. It seems that the window update must be handled by the session end to avoid such problems. （the go impl also handle window update on session side https://github.com/hashicorp/yamux/blob/master/session.go#L609-L617 ）

Thanks for your report, I will fix this problem (I haven't tested the case of only writing but not reading)