code: function ReadableStreamDefaultControllerClose(controller) {
    const stream = controller._controlledReadableStream;
  
    assert(controller._closeRequested === false);
    assert(stream._state === 'readable');
  
    controller._closeRequested = true;
  
    if (controller._queue.length === 0) {
      ReadableStreamClose(stream);
    }
  }
docs: A client of ReadableStreamDefaultController may use these functions directly to bypass state check.