Close listener leak in fs/promises `createReadStream`

[davidje13]

Version

v24.18.0

Platform

Darwin *.local 24.6.0 Darwin Kernel Version 24.6.0: Tue Apr 21 20:19:12 PDT 2026; root:xnu-11417.140.69.710.16~1/RELEASE_ARM64_T6041 arm64

Subsystem

fs/promises

What steps will reproduce the bug?

Here is a silly example which prints the first 11 bytes of a file by reading them separately from disk:

import { buffer } from 'node:stream/consumers';
import { open } from 'node:fs/promises';

const f = await open('my-file.txt');
for (let i = 0; i < 11; i++) {
  const byte = await buffer(f.createReadStream({ start: i, end: i, autoClose: false }));
  console.log(`byte ${i} is ${byte[0]}. Close listeners = ${f.listeners('close').length}`);
}

Running it (pointing at any file containing at least 11 bytes) will demonstrate the issue (output below)

How often does it reproduce? Is there a required condition?

Every call to createReadStream adds a close listener to the file handle, and I have not found a way to remove this listener. If called at least 11 times, it will trigger Node.js' built-in event leak detection warning. The threshold can be increased to avoid this warning, but the leak remains.

What is the expected behavior? Why is that the expected behavior?

Once a stream is consumed, the close event listener it attaches to the FileHandle should be removed, even when autoClose is false, so that applications can read arbitrarily many ranges from a file.

What do you see instead?

byte 0 is 0. Close listeners = 1
byte 1 is 0. Close listeners = 2
byte 2 is 0. Close listeners = 3
byte 3 is 0. Close listeners = 4
byte 4 is 0. Close listeners = 5
byte 5 is 0. Close listeners = 6
byte 6 is 0. Close listeners = 7
byte 7 is 0. Close listeners = 8
byte 8 is 0. Close listeners = 9
byte 9 is 0. Close listeners = 10
(node:70360) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 close listeners added to [FileHandle]. MaxListeners is 10. Use emitter.setMaxListeners() to increase limit
    at genericNodeError (node:internal/errors:985:15)
    at wrappedFn (node:internal/errors:539:14)
    at _addListener (node:events:590:17)
    at FileHandle.addListener (node:events:608:10)
    at importFd (node:internal/fs/streams:156:16)
    at new ReadStream (node:internal/fs/streams:189:30)
    at FileHandle.createReadStream (node:internal/fs/promises:363:12)
    at file:///[...]/test.mts:6:15
    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
byte 10 is 0. Close listeners = 11

Additional information

This can be worked around in user-space with a hacky approach:

function createSafeReadStream(handle, options) {
  const before = handle.listeners('close').length;
  const stream = handle.createReadStream(options);
  const after = handle.listeners('close');
  if (after.length > before) {
    const listener = after[after.length - 1];
    const teardown = () => {
      handle.off('close', listener);
      stream.off('end', teardown);
      stream.off('error', teardown);
    };
    stream.once('end', teardown);
    stream.once('error', teardown);
  }
  return stream;
}

// ...

for (let i = 0; i < 11; i++) {
  const byte = await buffer(createSafeReadStream(f, { start: i, end: i, autoClose: false }));
  console.log(`byte ${i} is ${byte[0]}. Close listeners = ${f.listeners('close').length}`);
}

[Paraspandey-debugs]

The workaround is great!

I was thinking, should there be stream.once('close', teardown) in

if (after.length > before) {
  const listener = after[after.length - 1];
  const teardown = () => {
  // teardown code
  };
  //-->here<---
  stream.once('end', teardown);
  stream.once('error', teardown);
}
return stream;

since if stream is destroyed early and listener stays attached, it may cause leak.

[MikeMcC399]

Re-opening, since #64227 was deemed to be broken (see #64227 (comment)).

#65387 reverts the fix, and includes #65387 (comment):

Proper fix is to use eos/finished instead of 'close' listener