I'm trying to serve videos and images from a private S3 bucket. I can download the files from the bucket and when I download them directly via the web interface they work fine, but when I use the SDK to server them using express I get a corrupted file. Currently, I use this code to fetch the file from S3:

export async function getObjectAsString(key: string): Promise<S3File> {

    const accessKeyId = process.env.AWS_KEY_ID as string;
    const secretAccessKey = process.env.AWS_SECRET_KEY as string;
    const bucketName = process.env.AWS_BUCKET_NAME as string;

    const client = new S3Client({
        region: 'eu-west-1',
        credentials: {
            accessKeyId: accessKeyId,
            secretAccessKey: secretAccessKey,
        },
    });
    const response = await client.send(
        new GetObjectCommand({
            Bucket: bucketName,
            Key: key,
        }),
    );

    // The code like below should really be provided as nice interfaces by the SDK itself.
    return new Promise((resolve, reject) => {
        if (!response.Body) {
            reject('No Body on response.');
        } else {
            const chunks: Uint8Array[] = [];
            const bodyStream = response.Body! as Readable;
            bodyStream.once("error", (error) => reject(error));
            bodyStream.on('data', (chunk) => chunks.push(Buffer.from(chunk)));
            bodyStream.on('end', () =>
                resolve({
                    file: Buffer.concat(chunks).toString('utf-8'),
                    type: response.ContentType!,
                    length: response.ContentLength!,
                }),
            );
        }
    });
}

It's a slightly modified version of this: https://github.com/aws/aws-sdk-js-v3/issues/1877#issuecomment-1129709683

Then I use the result of that function in this express endpoint:

router.get('/media/:id', async (req, res) => {
    const file = await getObjectAsString(req.params.id);
    if (!file) {
        return res.status(404).send({error: 'File not found'});
    }
    writeFileSync('./img.jpeg', file.file); // I use this to debug, this will later be removed

    res.setHeader('Content-Type', 'image/jpeg').send(file.file);
});

As you can see I also tried just writing the output to a file, but that file also got corrupted, so my guess is that I'm not fetching the file correctly. Also, the S3File type looks like this:

type S3File = {
    file: string,
    type: string
    length: number
}