express-return-buffer.js

import stream from 'stream';

app.get('/', function (req, res) {
    const buffer = Buffer.from('p8AuXbAKFihL9N1H4aYi7w==', 'base64');
    const bufferStream = new stream.PassThrough();
    bufferStream.end(buffer);
    bufferStream.pipe(res);
});