Handling errors in express pipelines - node.js

Question

I have a small web service that basically receives a PUT and saves the payload to a file. It can happen that the file write fails due to permission issues. I would like that to be communicated back to the client.
To make it easier to read I have boiled the program down to a minimum. The req.pipe chain is way longer in the real program. (with many more possibilities for errors)
const fs = require('fs');
const express = require('express');
const app = express();
app.put('/write/:id', (req, res, next) => {
const filename = 'data/' + req.params.id;
console.log("write: " + filename);
req
.pipe(fs.createWriteStream(filename))
.on('error', next)
req.on('end', () => {
res.send('saved\n' );
console.log("sent response");
})
});
app.listen(8081, '0.0.0.0');
Trouble is that no matter what I do it will always respond "saved" to the client. I had kinda hoped the next call would have got me out of there.
What is the elegant way to make differentiated responses on errors occurring server side?

Answer 1

several hours later it seems I nailed it:
const fs = require('fs');
const express = require('express');
const app = express();
app.put('/write/:id', (req, res, next) => {
const filename = 'data/' + req.params.id;
console.log("write: " + filename);
req
.pipe(fs.createWriteStream(filename))
.on('error', (e) => {
console.log("error ", e);
res.status(400).send("failed");
})
.on('close', () => {
res.send("saved\n");
})
});
app.listen(8081, '0.0.0.0');
Notice how I'm listening for close within the pipeline and not end on the request it self.