code: func (s *Stream) incrSendWindow(hdr header, flags uint16) error {
  	if err := s.processFlags(flags); err != nil {
  		return err
  	}
  
  	// Increase window, unblock a sender
  	atomic.AddUint32(&s.sendWindow, hdr.Length())
  	asyncNotify(s.sendNotifyCh)
  	return nil
  }
docs: // incrSendWindow updates the size of our send window