How to push to Node stream after error in 10+?

Question

I picked up some old stream code recently (written when 8.x was LTS) and attempted to update it to 12.x. This led to an interesting break in the way I dealt with ENOENT file errors.

Here's a simplification:

const { createServer } = require('http')
const { createReadStream } = require('fs')

const PORT = 3000

const server = createServer((req, res) => {
  res.writeHead(200, {
    'Content-Type': 'application/json'
  })

  const stream = createReadStream(`not-here.json`, {encoding: 'utf8'})

  stream.on('error', err => {
    stream.push(JSON.stringify({data: [1,2,3,4,5]}))
    stream.push(null)
  })

  stream.pipe(res)
})

server.listen(PORT)
server.on('listening', () => {
  console.log(`Server running at http://localhost:${PORT}/`)
})

In Node 8, the above code works fine. I'm able to intercept the error, write something to the stream and let it close normally.

In Node 10+ (tested 10, 12, and 13) the stream is already destroyed when my error callback is called. I can't push new things on the stream and handle the error gracefully for the client side.

Was this an intentional change and can I still handle this error in a nice way for the clint side?

Answer 1

One possibility. Open the file yourself and only create the stream with that already successfully opened file. That will allow you to handle ENOENT (or any other errors upon opening the file) before you get into the messy stream error handling mechanics. The stream architecture seems most aligned with aborting upon error, not recovering with some alternate behavior.

const { createServer } = require('http');
const fs = require('fs');

const PORT = 3000;

const server = createServer((req, res) => {
    res.writeHead(200, {'Content-Type': 'application/json'});

    fs.open('not-here.json', {encoding: 'utf8'}, (err, fd) => {
        if (err) {
            // send alternative response here
            res.end(JSON.stringify({data: [1,2,3,4,5]}));
        } else {
            const stream = fs.createReadStream(null, {fd, encoding: 'utf8'});
            stream.pipe(res);
        }
    });
});

server.listen(PORT);
server.on('listening', () => {
    console.log(`Server running at http://localhost:${PORT}/`)
});

---

You could also try experimenting with the autoDestroy or autoClose options on your stream to see if any of those flags will allow the stream to still be open for you to push data into it, even if the file created an error opening or reading. The doc on those flags is not very complete so some combination of programming experiements and studying the code would be required to see if they could be manipulated to still add data to the stream after your stream got an error.