stream: 'prefinish' timing and 'finish' after 'close'

[ronag]

• 'finish' can be emitted after 'close' if destroy() is called inside a'prefinish' handler.
• 'prefinish' has different timing (sync vs async) depending on whether Writable implements _final which can cause problems such as above to occur or not occur. (stream: simplify Transform stream implementation #32763)

I assume 'prefinish' is mostly used internally so it's probably not a huge issue.

[ronag]

One of these will fail while the other won't:

{
  const write = new Writable({
    write(chunk, enc, cb) { cb(); },
    final(cb) { cb(); }
  });

  write.on('close', common.mustCall(() => {
    write.on('finish', common.mustNotCall());
  }));
  write.on('prefinish', common.mustCall(() => {
    write.destroy();
  }));
  write.end();
}

{
  const write = new Writable({
    write(chunk, enc, cb) { cb(); }
  });

  write.on('close', common.mustCall(() => {
    write.on('finish', common.mustNotCall()); // fails
  }));
  write.on('prefinish', common.mustCall(() => {
    write.destroy();
  }));
  write.end();
}

[targos]

what's the status on this?

[ronag]

I think this is fixed.