[Fixed]-AWS S3 presigned URL with metadata

I was using createPresignedPost and for me I got this working by adding the metadata I wanted to the Fields param like so :-

const params = {
    Expires: 60,
    Bucket: process.env.fileStorageName,
    Conditions: [['content-length-range', 1, 1000000000]], // 1GB
    Fields: {
        'Content-Type': 'application/pdf',
        key: strippedName,
        'x-amz-meta-pdf-type': pdfType,
        'x-amz-meta-pdf-id': pdfId,
    },
};

As long as you pass the data you want, in the file’s metadata, to the lambda that you’re using to create the preSignedPost response then the above will work. Hopefully will help someone else…

I found the metadata object needs to be key/value pairs, with the value as a string (example is Nodejs lambda):

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

exports.handler = async (event) => {
    const { key, type, metadata } = JSON.parse(event.body);

    // example
    /*metadata: {
      foo: 'bar',
      x: '123',
      y: '22.4213213'
    }*/

    return await s3.getSignedUrlPromise('putObject', {
        Bucket: 'the-product-uploads',
        Key: key,
        Expires: 300,
        ContentType: type,
        Metadata: metadata
    });
};

Then in your request headers you need to add each k/v explicitly:

await fetch(signedUrl, {
      method: "PUT",
      headers: {
        "Content-Type": fileData.type,
        "x-amz-meta-foo": "bar",
        "x-amz-meta-x": x.toString(),
        "x-amz-meta-y": y.toString()
      },
      body: fileBuffer
    });

In boto, you should provide the Metadata parameter passing the dict of your key, value metadata. You don’t need to name the key as x-amz-meta as apparently boto is doing it for you now.

Also, I didn’t have to pass the metadata again when uploading to the pre-signed URL:

params = {'Bucket': bucket_name, 
          'Key': object_key, 
          'Metadata': {'test-key': value}
         }

response = s3_client.generate_presigned_url('put_object',
                                             Params=params,
                                             ExpiresIn=3600)

I’m using a similar code in a lambda function behind an API