AWS Revert File Version Rework

new.js

import { promisify } from 'util';
const readFilePromise = promisify(fs.readFile);

AwsFinder.prototype.revertFileVersion = async function(data, cb) {
    log('aws', ['Reverting version:', data.id]);

    // Get the current file buffer for diff comparison
    try {
        let originalBuffer = await readFilePromise(data.remote);
    } catch (e) {
        let originalBuffer = '';
    }

    var params = {
        localFile: data.remote,
        s3Params: {
            Bucket: 'userlitelink',
            Key: idToKey(data.id)
        }
    };

    var downloader = client.downloadFile(params);
    downloader.on('error', function(err) {
        log('error_trace', { message: 'unable to download:', err });
        cb({ success: false });
    });

    downloader.on('end', () => {
        await readFilePromise(data.remote, function(err, buffer) {
            if (err) throw err;

            // Create a new version with the updated file
            this.upload({
                user: connection.user,
                path: data.remote,
                size: buffer.length,
                comment: 'Revert to version ' + data.version,
                diffs: JSON.stringify(
                    diffs.getHTMLDiffs(originalBuffer, buffer)
                )
            });

            cb({ success: true, buffer });
        });
    });
    
};

original.js

AwsFinder.prototype.revertFileVersion = function(data, cb) {
    log('aws', ['Reverting version:', data.id]);

    // Get the current file buffer for diff comparison
    fs.readFile(data.remote, function(err, originalBuffer) {
        if (err) originalBuffer = '';

        var params = {
            localFile: data.remote,
            s3Params: {
                Bucket: 'userlitelink',
                Key: idToKey(data.id)
            }
        };

        var downloader = client.downloadFile(params);
        downloader.on('error', function(err) {
            log('error_trace', { message: 'unable to download:', err });
            cb({ success: false });
        });

        downloader.on('end', () => {
            console.log('Reading file...', data.remote);
            fs.readFile(data.remote, function(err, buffer) {
                if (err) throw err;

                // Create a new version with the updated file
                this.upload({
                    user: connection.user,
                    path: data.remote,
                    size: buffer.length,
                    comment: 'Revert to version ' + data.version,
                    diffs: JSON.stringify(
                        diffs.getHTMLDiffs(originalBuffer, buffer)
                    )
                });

                cb({ success: true, buffer });
            });
        });
    });
};

This is an example of using the async and await keywords to flatten nested callbacks.