HarmonyOS鸿蒙Next中使用RCP下载文件，如何控制调用writeSync时传入的ArrayBuffer的长度以实现下载限速功能

HarmonyOS鸿蒙Next中使用RCP下载文件，如何控制调用writeSync时传入的ArrayBuffer的长度以实现下载限速功能

export function getContentLength(url: string): Promise<number> {
  const session = rcp.createSession(sessionConfiguration);
  return session.head(url).then(res => {
    const contentLength = res.headers['content-length'];
    return contentLength ? Number(contentLength) : 0;
  }).finally(() => {
    session.close();
  });
}

export async function start(url: string, filePath: string,onProgress: (nowFileSize: number, contentLength: number, progressValue: number) => void) {
  //head请求获取文件大小
  let contentLength = await getContentLength(url)
  const file = fileIo.openSync(filePath, fileIo.OpenMode.WRITE_ONLY | fileIo.OpenMode.CREATE);
  let nowFileSize = await fileIo.statSync(file.fd).size;
  onProgress(nowFileSize, contentLength, Number((nowFileSize / contentLength * 100).toFixed(2)));
  
  const writeSync = (arrayBuffer: ArrayBuffer) => {
    fileIo.writeSync(file.fd, arrayBuffer, { offset: nowFileSize }) //写入文件
    nowFileSize = fileIo.statSync(file.fd).size; //写入完成,修改当前文件大小
    const progressValue = Number((nowFileSize / contentLength * 100).toFixed(2)); //并将结果保留两位小数
    onProgress(nowFileSize, contentLength, progressValue); //通知下载进度
  }

  const session = rcp.createSession(sessionConfiguration);
  const request = new rcp.Request(url, `GET`);
  request.transferRange = { from: nowFileSize };//请求体了Range参数,从当前位置开始下载
  request.destination = {
    kind: 'stream',
    stream: { writeSync }
  };
  session.fetch(request).then((response) => {
  },()=>{
    console.log(`aaa`,'Download 下载失败响应异常.');
  }).finally(() => {
    session.close();
    fileIo.close(file)
  });
}

使用RCP下载文件,要实现下载限速功能,如何控制调用writeSync时传入的ArrayBuffer的长度. 华为有提供相关的API吗?