docs: def filter_leading_non_json_lines(buf):
      '''
      used to avoid random output from SSH at the top of JSON output, like messages from
      tcagetattr, or where dropbear spews MOTD on every single command (which is nuts).
  
      need to filter anything which starts not with '{', '[', ', '=' or is an empty line.
      filter only leading lines since multiline JSON is valid.
      '''
  
      filtered_lines = StringIO.StringIO()
      stop_filtering = False
      for line in buf.splitlines():
          if stop_filtering or "=" in line or line.startswith('{') or line.startswith('['):
              stop_filtering = True
              filtered_lines.write(line + '\n')
      return filtered_lines.getvalue()