使用预签名 URL 上传后，AWS S3 上的文件在文件中包含额外信息

Question

I am trying to upload file directly to S3 bucket using presigned url.

Below is the server end code written in node.js, and it creates signed url successfully.

const s3 = new AWS.S3({
    accessKeyId: config.accessKeyId,
    secretAccessKey:  config.secretAccessKey,
    region: config.awsConfig.region
});
const signedUrlExpireSeconds = 60 * 60;
let mimeType = "video/mp4";

const filename =Date.now();

const Key = `${filename}.mp4`;

const params = {
    Bucket: config.awsConfig.aws_upload_bucket, 
    Key: Key,
    Expires: signedUrlExpireSeconds,
    ACL: 'public-read',
    ContentType: mimeType
    };

s3.getSignedUrl('putObject', params, function (err, url) {
    if (err) {
        console.log('Error getting presigned url from AWS S3');
        res.json({ success: false, message: 'Pre-Signed URL error', urls: fileurls });
    }
    else {
        console.log('Presigned URL: ', url);
        res.json({ success: true, message: 'AWS SDK S3 Pre-signed urls generated successfully.', url: url, Key:Key, ContentType: mimeType  });
    }
});

Below is the code written at React end.

const DropzoneArea = props => {
    const [files, setFiles] = useState([]);
    let awsFile = '';

    const onUploadHandler = files => {
        if (files.length === 0) {
            console.log('Debug : [components DropzoneArea onUploadHandler] files => ', files);
            return;
        }
        awsFile = files[0]
        // calling the API to get presigned url.
        getPreSignedURL(files[0].type,S3preSignedURLCallback)        
    };

    const S3preSignedURLCallback = videoData => {
        const xhr = new XMLHttpRequest();
        xhr.open('PUT', videoData.url);
        xhr.setRequestHeader('Content-Type', videoData.ContentType);
        var res = new FormData();
        res.append('file', awsFile);
        xhr.send(res);
    };
}

using above code the File upload to s3 successfully but the video couldn't play. So I compared files on S3 with the actual file the I uploaded. I found that few extra request data also written in S3 file.

A minor mistake I am doing here, can't locate the bug. Please help.

Answer 1

Don't use formData , just send the file directly.

const S3preSignedURLCallback = videoData => {
        const xhr = new XMLHttpRequest();
        xhr.open('PUT', videoData.url);
        xhr.setRequestHeader('Content-Type', videoData.ContentType);
        // Send the binary data.
        // Since a File is a Blob, you can send it directly.
        xmlHttpRequest.send(awsFile);
};

The difference you see, is because AWS is saving the raw request, without parsing it, and you can see that the right image is a multipart/form-data request.