AWS S3 API 的默认 getObject() 函数有一个 5GB 的大小限制，如果需要下载更大的文件，则需要使用 Multipart Downloads。以下是一个示例代码，可以实现文件的分块下载：

const AWS = require('aws-sdk');
const s3 = new AWS.S3();

const bucketName = 'your-bucket-name';
const objectKey = 'your-object-key';
const downloadFilePath = 'download-path';
const multipartThreshold = 1024 * 1024 * 5; // 5 MB
const multipartSize = 1024 * 1024 * 5; // 5 MB

const params = {
  Bucket: bucketName,
  Key: objectKey,
};

s3.headObject(params, function(err, metadata) {
  if (err) {
    console.error(err);
    return;
  }

  const fileSize = metadata.ContentLength;
  console.log(`File size is ${fileSize}`);

  if (fileSize > multipartThreshold) {
    const parts = Math.ceil(fileSize / multipartSize);
    console.log(`File will be downloaded in ${parts} parts`);

    const downloadParams = {
      ...params,
      SSECustomerAlgorithm: 'AES256',
      SSECustomerKey: 'your-customer-key',
      SSECustomerKeyMD5: 'your-customer-key-md5',
      PartSize: multipartSize,
      QueueSize: 4,
      Key: objectKey,
      Bucket: bucketName,
    };

    const downloader = s3.download(downloadParams);
    downloader.on('error', function(err) {
      console.error(`Download failed: ${err}`);
      return;
    });

    downloader.on('end', function() {
      console.log('Download completed');
    });

    downloader.pipe(fs.createWriteStream(downloadFilePath));
  } else {
    const downloadParams = {
      ...params,
      SSECustomerAlgorithm: 'AES256',
      SSECustomerKey: 'your-customer-key',
      SSECustomerKeyMD5: 'your-customer-key-md5',
    };

    const file = fs.createWriteStream(downloadFilePath);
    const downloader = s3.getObject(downloadParams).createReadStream();

    downloader.on('error', function(err) {
      console.error(`Download failed: ${err}`);
      return;
    });

    downloader.on('end