stream: Readable iterator unhandled error when piping

[marcosc90]

• Version: 12.4
• Platform: Ubuntu 18.04

When using asyncIterator on a piped stream, the error is not handled correctly.

const fs = require('fs');
const { PassThrough } = require('stream');

async function print() {

	const read = fs.createReadStream('file');
	const iterator = read.pipe(new PassThrough())

	for await (const k of iterator) {
		console.log(k);
	}
}

print()
  .then(() => console.log('done')) // never called
  .catch(console.log); // never called

In the above example, the .catch is not catching the error, and the script crashes.

I know, that I should catch the error of each stream, but if I do:

read.on('error', console.log);

The print function never resolves nor rejects. The only solution I've found is to emit the error to the piped stream.

async function print() {

	const read = fs.createReadStream('file');
	const stream = new PassThrough();
	
	read.on('error', (err) => stream.emit('error', err));

	const iterator = read.pipe(stream);

	for await (const k of iterator) {
		console.log(k);
	}
}

When you have multiple pipes, this can get very ugly. I don't know if this is the intended behaviour, but makes it hard & ugly to work with async iterators.

[Fishrock123]

I don't know for sure, but does stream.pipeline() solve this?

[marcosc90]

No, it doesn't unfortunately, because the error is passed to the .pipeline callback, so the for await does not throw, and the print function resolves without iterating anything, instead of throwing.

async function print() {

	const read = fs.createReadStream('file');
	const stream = new PassThrough();

	const iterator = pipeline(read, stream, (err) => {
           // I get the error here
           // print will resolve, without iterating.
        });

	for await (const k of iterator) {
		console.log(k);
	}
}