Express.js - how to download base64 string as PDF file? - node.js

Question

I have pdf file encoded as base64 string. How to download this string to the browser as file in .pdf format?
What I have already tried:
res.set('Content-Disposition', 'attachment; filename="filename.pdf"');
res.set('Content-Type', 'application/pdf');
res.write(fileBase64String, 'base64');

Answer 1

I ended up to decode the pdf first and then send it to the browser as binary as follows:
(For simplicity I use node-http here but the functions are available in express as well)
const http = require('http');
http
.createServer(function(req, res) {
getEncodedPDF(function(encodedPDF) {
res.writeHead(200, {
'Content-Type': 'application/pdf',
'Content-Disposition': 'attachment; filename="filename.pdf"'
});
const download = Buffer.from(encodedPDF.toString('utf-8'), 'base64');
res.end(download);
});
})
.listen(1337);
What drove me nuts here was the testing with Postman:
I was using the Send Button instead of the Send and Download Button to submit the request:
Using the Send button for this request causes that the pdf file becomes corrupted after saving.

Answer 2

Just a reference for Express. This answer is based on ofhouse's answer.
This solution is downloading a png file. I was missing the "Content-Disposition" part, which makes the browser not display the png, but download it. png is a Buffer-object.
app.get("/image", (req, res) => {
getPng()
.then((png) => {
res.writeHead(200, {
"Content-Type": png.ContentType,
"Content-Length": png.ContentLength,
"Content-Disposition": 'attachment; filename="image.png"',
});
res.end(png.Body);
})
.catch(() => {
res.send("Couldn't load the image.");
});
});