Stream S3 Object Data with AWS SDK v3

I have recently worked on upgrading a small utility library I have developed from the AWS JavaScript SDK v2 to v3: @goldstack/utils-s3. This library simply provides a method to download a file from S3 to the local file system via the download method:

export const download = async (params: {
  key: string;
  filePath: string;
  s3: S3Client;
  bucketName: string;
}): Promise<boolean> => {
}

I encountered an error after upgrading from the legacy S3 client to the new, recommend S3Client. The latter is suggest to be used due to better support for tree shaking.

The error I encountered was  .createReadStream() method was no longer available on the Body property returned in the response from the S3 client.

I previously created this stream to then pipe the data of the object into a local object.

To get this working in the new v3 SDK library was a bit tricky. Essentially, the default S3Client provided is designed to support both browser and Node-based environment. Since browser-based environments will not support NodeJs file streams, thus any methods related to that are missing in the API.

The work around for this is the following:

First, add the @smithy/types package to your project.

npm install @smithy/types

Then add the following import to your source file.

import { NodeJsClient } from '@smithy/types';

Now after we have constructed the command, we cast the S3Client to NodeJsClient<S3Client>:

      const s3Client = new S3Client();
      
      const cmd = new GetObjectCommand({
        Bucket: params.bucketName,
        Key: params.key,
      });

      const res = await (s3Client as NodeJsClient<S3Client>).send(cmd);

In result, the the type for res.Body will be SdkStream<IncomingMessage> which offers all the methods we need for NodeJs streams, such as pipe:

      res.Body?.pipe(file);