Return excel file from AWS Lambda function

Question

I'm trying to return an excel file through Lambda. It succeeded, but the content is only the base64 encoded string of the file.

Here's the code:

const xl = require("excel4node")

module.exports.handler = async () => {
    var wb = new xl.Workbook()
    var ws = wb.addWorksheet('Sheet 1')
    const cols = [ "col1", "col2" ]
    cols.forEach((c,i) => { ws.cell(1, i+1).string(c) })
    const buffer = await wb.writeToBuffer()
    return {
        statusCode: 200,
        headers: {
            'Access-Control-Allow-Origin': "*",
            'Access-Control-Allow-Methods': "*",
            'Content-type' : "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
            'Content-Disposition': `attachment; filename="test.xlsx"`,
        },
        isBase64Encoded: true,
        body: buffer.toString('base64')
    }
}

and this is what's generated

I'm using Serverless framework, and I've set contentHandling config to CONVERT_TO_BINARY.

Many thanks,

Answer 1

solved! after rereading @jarmod's answer above, turns out I had not set the API binary media type to '*/*'

added apiGateWay.binaryMediaTypes in serverless config file and it worked