Cursor 'close' event emitted twice

[iovanom]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When the cursor is used with pause/resume the event 'close' is emitted twice.

If the current behavior is a bug, please provide the steps to reproduce.

cursor = TestModel.find({}).cursor();
cursor.on('data', (obj) => {
  cursor.pause();
  // simulate the async actions using obj
  setTimeout(() => cursor.resume(), 50);
});
cursor.on('close', () => console.log('close'));

The code below will get two 'close' in the console;

What is the expected behavior?

The expected behavior is to receive only one 'close' event.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
node - 14.18.0
mongoose - 5.13.11
MongoDB - 4.4.9

[iovanom]

I've found this PR https://github.com/Automattic/mongoose/pull/8834/files
I think, instead to user this solution with setTimeout should be used the _this.destroy() because the solution from PR fixed the issue only if the 'close' from autoDestroy was called first, instead if our _this.emit('close') was called first then the autoDestroy will emit 'close' one more time. With _this.destroy() this will be fixed.

[IslandRhythms]

close only fires once for me

const mongoose = require('mongoose');

const testSchema = new mongoose.Schema({
    name: String
});

const Test = mongoose.model('Test', testSchema);



async function run() {
    await mongoose.connect('mongodb://localhost:27017/', {useNewUrlParser: true,
    useUnifiedTopology: true,});
    await mongoose.connection.dropDatabase();
    const cursor =  await Test.find({}).cursor();

    cursor.on('data', (obj) => {
      cursor.pause();
      // simulate the async actions using obj
      setTimeout(() => cursor.resume(), 50);
    });
    cursor.on('close', () => console.log('close'));
  
}


run();

[iovanom]

close only fires once for me

const mongoose = require('mongoose');

const testSchema = new mongoose.Schema({
    name: String
});

const Test = mongoose.model('Test', testSchema);



async function run() {
    await mongoose.connect('mongodb://localhost:27017/', {useNewUrlParser: true,
    useUnifiedTopology: true,});
    await mongoose.connection.dropDatabase();
    const cursor =  await Test.find({}).cursor();

    cursor.on('data', (obj) => {
      cursor.pause();
      // simulate the async actions using obj
      setTimeout(() => cursor.resume(), 50);
    });
    cursor.on('close', () => console.log('close'));
  
}


run();

you don't have any document in collection, the pause/resume is not called if no documents. Have a look on my tests that I have added.

[IslandRhythms]

const mongoose = require('mongoose');

const testSchema = new mongoose.Schema({
    name: String
});

const Test = mongoose.model('Test', testSchema);



async function run() {
    await mongoose.connect('mongodb://localhost:27017/', {useNewUrlParser: true,
    useUnifiedTopology: true,});
    await mongoose.connection.dropDatabase();
    await Test.create({name: 'Test'});
    await Test.create({name: 'Other Test'})
    const cursor =  await Test.find({}).cursor();

    cursor.on('data', (obj) => {
      cursor.pause();
      // simulate the async actions using obj
      setTimeout(() => cursor.resume(), 50);
    });
    cursor.on('close', () => console.log('close'));
  
}


run();

[iovanom]

@vkarpov15 I've created a PR for version 5.x
#10897