HarmonyOS 文件资源动态下载能否实现

可以写入到应用沙箱目录下：

https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/app-sandbox-directory-V5

写入方式（以读取resource中的rawfile下文件为例）：

getContext(this).resourceManager.getRawFd("test.txt", async (error, value) => {
  if (error != null) {
    console.error(`callback getRawFd failed error code: ${error.code}, message: ${error.message}.`);
  } else {
    let fd = value.fd;
    // let offset = value.offset;
    // let length = value.length;

    let filesDir = getContext(this).filesDir;
    // 打开文件流
    let inputStream = fs.fdopenStreamSync(fd, "r+");
    // let inputStream = fs.createStreamSync(filesDir + '/test.txt', 'r+');
    let outputStream = fs.createStreamSync(filesDir + '/test.txt', "w+");
    // 以流的形式读取源文件内容并写入目的文件
    let bufSize = 4096;
    let readSize = 0;
    let buf = new ArrayBuffer(bufSize);

    class Option {
      public offset: number = 0;
      public length: number = bufSize;
    }

    let option = new Option();
    option.offset = value.offset;
    if (bufSize > value.length) {
      option.length = value.length;
    }
    let readLen = await inputStream.read(buf, option);
    readSize += readLen;
    while (readLen > 0) {
      await outputStream.write(buf);
      option.offset = readSize + value.offset;
      option.length = value.length - readSize >= bufSize ? bufSize : value.length - readSize;
      readLen = await inputStream.read(buf, option);
      readSize += readLen;
    }
    // 关闭文件流
    inputStream.closeSync();
    outputStream.closeSync();
  }

这段代码是将文件以流的形式从rawfile下转存到应用沙箱的file目录下（el2）