code: private void sendInitialConnectionWindow() throws Http2Exception {
      if (ctx.channel().isActive() && initialConnectionWindow > 0) {
        Http2Stream connectionStream = connection().connectionStream();
        int currentSize = connection().local().flowController().windowSize(connectionStream);
        int delta = initialConnectionWindow - currentSize;
        decoder().flowController().incrementWindowSize(connectionStream, delta);
        initialConnectionWindow = -1;
        ctx.flush();
      }
    }
docs: Sends initial connection window to the remote endpoint if necessary.