code: private int getStreamId(HttpHeaders httpHeaders) throws Exception {
          return httpHeaders.getInt(HttpConversionUtil.ExtensionHeaderNames.STREAM_ID.text(),
                                    connection().local().incrementAndGetNextStreamId());
      }
docs: Get the next stream id either from the {@link HttpHeaders} object or HTTP/2 codec
  
  @param httpHeaders The HTTP/1.x headers object to look for the stream id
  @return The stream id to use with this {@link HttpHeaders} object
  @throws Exception If the {@code httpHeaders} object specifies an invalid stream id