Q:

Amazon S3 Change file download name

I have files stored on S3 with a GUID as the key name.
I am using a pre signed URL to download as per S3 REST API
I store the original file name in my own Database.  When a user clicks to download a file from my web application I want to return their original file name, but currently all they get is a GUID. How can I achieve this?
My web app is in salesforce so I do not have much control to do response.redirects all download the file to the web server then rename it due to governor limitations.
Is there some HTML redirect, meta refresh, Javascript I can use?  Is there some way to change the download file name for S3 (the only thing I can think of is coping the object to a new name, downloading it, then deleting it).
I want to avoid creating a bucket per user as we will have a lot of users and still no guarantee each file with in each bucket will have a unique name
Any other solutions?

A:

I guess your cross posted this questions to Amazon S3 forum, but for the sake of others I'd like to post the answer here:
If there is only ever one "user filename" for each S3 object, then you can set the Content-Disposition header on your s3 file to set the downloading filename:
Content-Disposition: attachment; filename=foo.bar
For the sake of fairness I'd like to mention that it was not me to provide the right answer on Amazon forum and all credits should go to  Colin Rhodes ;-)

A:

While the accepted answer is correct I find it very abstract and hard to utilize.
Here is a piece of node.js code that solves the problem stated. I advise to execute it as the AWS Lambda to generate pre-signed Url.
var AWS = require('aws-sdk');
var s3 = new AWS.S3({
    signatureVersion: 'v4'
});
const s3Url = process.env.BUCKET;

module.exports.main = (event, context, callback) => {
var s3key = event.s3key
var originalFilename = event.originalFilename

var url = s3.getSignedUrl('getObject', {
        Bucket: s3Url,
        Key: s3key,
        Expires: 600,
        ResponseContentDisposition: 'attachment; filename ="' + originalFilename + '"'
    });

[... rest of Lambda stuff...]

}

Please, take note of ResponseContentDisposition attribute of params object passed into s3.getSignedUrl function.
More information under getObject function doc at http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#getObject-property

A:

In early January 2011 S3 added request header overrides. This functionality allows you to 'dynamically' alter the Content-Disposition header for individual requests.
See the S3 documentation on getting objects for more details.

