nativescript image upload to s3 encoding issue - amazon-s3

Question

I'm having issues uploading an image from Nativescript to AWS, and I'm pretty sure it's a configuration issue.
select an image
const context = imagepicker.create({
mode: 'single' // use "multiple" for multiple selection
});
await context.authorize();
const selection: Array<ImageAsset> = await context.present();
const imageAsset = selection[0];
const source: ImageSource = await new ImageSource().fromAsset(imageAsset);
const fileLocation = imageAsset.android ? imageAsset.android : imageAsset.ios;
const fileType = mime.extension(mime.lookup(fileLocation));
const image = source.toBase64String(fileType);
console.log(image);
image at this point is: iVBORw0KGgoAAAANSUhEUgAAB4AAAASwCAIAAACVUsChAAAAA3NCSVQI...
image location at this point is: /storage/emulated/0/DCIM/Screenshots/Screenshot_20181106-150854.png
const fileLocation = imageAsset.android ? imageAsset.android : imageAsset.ios;
const signedUrl = await this.getSignedUrl(fileLocation);
Backend Code to get signedURL
const getSignedUrlPromise = (operation, params) => {
return new Promise((resolve, reject) => {
s3.getSignedUrl(operation, params, (err, url) => {
err ? reject(err) : resolve(url);
});
});
}
const params = {
Bucket: BUCKET_NAME,
Key: `abc123/456/3/${fileName}`,
ContentType: contentType,
ContentEncoding: 'base64'
}
const url = await getSignedUrlPromise('putObject', params).catch(err => {
console.log('error', JSON.stringify(err))
return {
statusCode: 400,
body: JSON.stringify(err)
}
});
console.log('success', url);
return {
statusCode: 200,
body: JSON.stringify({ url: url })
}
signedUrl at this point is:
https://myproject.s3.amazonaws.com/abc123/456/3/Screenshot_20181106-150854.png?AWSAccessKeyId=xxxxxxxxxxxxxx&Content-Encoding=base64&Content-Type=image%2Fpng&Expires=1555517358&Signature=yyyyyyyy&x-amz-security-token=long_token
Then, using the signedURL, i upload the image:
const mimeType = mime.lookup(fileLocation);
this.http.put(signedUrl, image, {
headers: {
'Content-Type': mimeType,
'Content-Encoding': 'base64'
}
}).subscribe((resp) => {
console.log('resp2', resp);
});
}
When I open the file, this is what I see
and the meta-data on the S3 object looks correct
When I download the file and open it in NP++, I see the base64 value.
iVBORw0KGgoAAAANSUhEUgAAB4AAAASwCAIAAACVUsChAAAAA3NCSVQI...
I also cannot open the downloaded image
ATTEMPT 2
I saw where some people were using buffers, so I changed my image code to
const image = Buffer.from(source.toBase64String(fileType).replace(/^data:image\/\w+;base64,/, ''), 'base64');
which the image is still broken, and when I download and open the file using NP++ I see
{"type":"Buffer","data":[137,80,78,71,13,10,26,10,0,0,0,13,73,72,68,82,0,0,7,128,0,0,4,176,8,2,0,0,0