Use original file name in AWS s3 uploader

I have implemented a s3 uploader per these instructions https://aws.amazon.com/blogs/compute/uploading-to-amazon-s3-directly-from-a-web-or-mobile-application/

This is the Lambda function code

AWS.config.update({ region: process.env.AWS_REGION })
const s3 = new AWS.S3()
const URL_EXPIRATION_SECONDS = 300

// Main Lambda entry point
exports.handler = async (event) => {
  return await getUploadURL(event)
}

const getUploadURL = async function(event) {
  const randomID = parseInt(Math.random() * 10000000)
  const Key = `${randomID}.jpg`

  // Get signed URL from S3
  const s3Params = {
    Bucket: process.env.UploadBucket,
    Key,
    Expires: URL_EXPIRATION_SECONDS,

Currently the filename (key) is generated using a random ID.

I would like to change that to use the original filename of the uploaded file.

I tried a couple approaches such as using the the fs.readfile() to get the filename but have not had any luck.

There is a webpage with a form that works in conjunction with the Lambda to upload the file to s3.

How do I get the filename?

If you want to save the file with the original filename, you have to pass that filename as part of the key you use to request the signed url. You don't show how you're getting the file to upload, but if it is part of a web site, you get this from the client.

On the client side you have the user identify the file to upload and pass that to your code that calls getUploadURL(). Maybe in your code it is part of event? Then you send the signed URL back to the client and then the client can send the file to the signed URL.

Therefore to upload a file, your client has to send two requests to your server -- one to get the URL and one to upload the file.

You do mention that you're using fs.readFile() If you're able to get the file with this call, then you already have the file name. All you have to do is pass the same name to getUploadURL() as an additional parameter or as part of event. You may have to parse the filename first or within getUploadURL() if it includes a path to someplace other than your current working directory.

The code above looks like it may be a Lambda that's getting called with some event. If that event is a trigger of some sort that you can include a file name, then you can look pull it from that variable. For example:

const getUploadURL = async function(event) {
  const randomID = parseInt(Math.random() * 10000000)
  const Key = `${event.fileNameFromTrigger}`

  // Get signed URL from S3
  const s3Params = {
    Bucket: process.env.UploadBucket,
    Key,
    Expires: URL_EXPIRATION_SECONDS.

    ...

}

If the file name includes the extension, then you don't need to append that as you were with the random name.