HarmonyOS 文件上传RemoteCommunicationKit+FROM表单+POST

相册路径不能直接用于传输，可以通过将相册图片复制到应用沙箱路径下，然后再用沙箱路径下的文件进行传输。从相册复制文件到沙箱目录，可参考如下代码：

function SavePhotoToFileDir() {
  try {
    let photoSelectOptions = new picker.PhotoSelectOptions();
    photoSelectOptions.MIMEType = picker.PhotoViewMIMETypes.IMAGE_TYPE;
    photoSelectOptions.maxSelectNumber = 1;
    let photoPicker = new picker.PhotoViewPicker();
    let uris: Array<string> = [];
    photoPicker.select(photoSelectOptions).then((photoSelectResult: picker.PhotoSelectResult) => {
      uris = photoSelectResult.photoUris;
      let fileArray = uris[0].split("/");
      let fileName = fileArray[fileArray.length - 1];
      let file = fs.openSync(uris[0], fs.OpenMode.READ_ONLY);
      let cacheDir = mContext.filesDir;
      let dstPath = cacheDir + '/' + fileName;
      let file2 = fs.openSync(dstPath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
      fs.copyFileSync(file.fd, file2.fd);
      fs.closeSync(file);
      console.info('PhotoViewPicker.select successfully, photoSelectResult uri: ' + JSON.stringify(photoSelectResult));
    }).catch((err: BusinessError) => {
      console.error('PhotoViewPicker.select failed with err: ' + JSON.stringify(err));
    });
  } catch (error) {
    let err: BusinessError = error as BusinessError;
    console.error('PhotoViewPicker failed with err: ' + JSON.stringify(err));
  }
}