ENOBUFS error on Mongodb Nodejs

Question

My database connectorMongo for nodejs, after a while running triggers the ENOBUFS error, knocking down all the tcp connections from the computer.. other apps claim tcp exhaustion.. however I could not solve the problem, it seems after each query the application leaves the connection open.. To diagnose regarding the error source was made the "crash" of mongodb service and was reestablished the connections immediately.

below is the data

connection string

const mongoUrl = 'mongodb://localhost:27017/?readPreference=primary&appname=meuAplicativo&ssl=false&authSource=database01&keepAlive=false&poolSize=5&agent=false';

open connection to server

MongoClient.connect(mongoUrl, { "useUnifiedTopology": true, /*directConnection :true,*/ keepAlive: false, maxPoolSize:20},   async function(err, client) {
                        if(err) throw err
    
                        // entra na base de dados      
                        const database = client.db(mongoDBName);  
                        findAndModifyTags(__postBody['data'], database, 0, res, null);
                    });

Query

//seleciona coleção de dados
tagCollection = database.collection('values');

//procura e atualiza registro
tagCollection.updateOne(query, update,{returnNewDocument: false, upsert: true, new: true}, (error) => 
{
    if(!error) {
        console.log(`Successfully updated document`)
        //console.log(`Successfully updated document: ${JSON.stringify(doc)}.`)
    } else {
        console.log("No document matches the provided query.")
        console.log(error)
    }
    
    //resposta positiva    
    res.write("{'status': 'ok'}");
    res.end();
});  

Details of the Error

debug ->  2021-3-19 9:45:56 AM notnull
debug ->  2021-3-19 9:45:56 AM notnull
debug ->  2021-3-19 9:45:56 AM has data
(node:28792) UnhandledPromiseRejectionWarning: MongoServerSelectionError: connect ENOBUFS 127.0.0.1:27017 - Local (undefined:undefined)
    at Timeout.waitQueueMember.timer.setTimeout [as _onTimeout] (E:\Projetos\Telemetria Raspberry Zero\node_modules\mongodb\lib\core\sdam\topology.js:438:30)
    at ontimeout (timers.js:436:11)
    at tryOnTimeout (timers.js:300:5)
    at listOnTimeout (timers.js:263:5)
    at Timer.processTimers (timers.js:223:10)
(node:28792) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 357)

as can be seen, I have already made the pool reduction and some more procedures, but I still continue with the error

Answer 1

In this solution we make the connection with the mongo only at the time of npm start (an alias for node bin/www). Check into my package.json the section scritps.

After creating the connection we only use to make queries to the bank.

For a better understanding of the solution I use the architecture model defined by express-generator, para saber mais.

The directory structure:

.
├── app.js
├── bin
│   └── www
├── db
│   └── index.js
├── package.json
└── server
    |── routes
    |   └── tag.route.js
    ├── services
    |   └── tag.service.js
    └── index.js

In the archive db/index.js I make use of the lib mongodb, and export two functions connect() and get(). The function get will obtain the instance of our database, following the same idea of padrão de projeto Singleton.

db/index.js

const MongoClient = require('mongodb').MongoClient;
const url = `mongodb://${process.env.MONGOHOST}:${process.env.MONGOPORT}`
let dbinstance;

// Use connect method to connect to the server
connect = (callback) => {
    MongoClient.connect(url, { useUnifiedTopology: true }, (err, client) => {
        dbinstance = client.db(process.env.MONGONAME);
        callback (err);
    })
}

get = () => {
    return dbinstance;
}

module.exports = {
    connect,
    get
}

bin/www

#!/usr/bin/env node
const app = require('../app');
const dbinstance = require('../db/index')
dbinstance.connect(() => {
    app.listen(process.env.PORT);
    console.log(`Listening at http://localhost:${process.env.PORT}`);
});

In our service we only import our lib from the database(bd/index.js) and when consulting the bank use the method get() as can be seen from the following:

server/services/tag.service.js

const db = require('../../db/index');
const ObjectId = require('mongodb').ObjectID;

exports.updateTagbyId = (req, res) => {
    const options = {returnNewDocument: false, upsert: true, new: true}
    db.get().collection('tag').findOneAndUpdate({_id: ObjectId(req.params.id)}, {$set: {"name": req.body.name }}, options).then((result) => {
        if (result.value === null) {
            res.status(404).json({ msg: 'Não encontrado' })
            return
        }
        res.status(200).json({ status: 'ok' });
    }).catch((err) => {
        console.log(err)
        res.status(500).json({ msg: 'pff, houve um erro' })
    })
}

In this implementation I am using the res.json but it is possible to continue using the res.write the way you do in your code.

In this way we call the function connect() only in the bin/www in our service layer we are only using the connection through the method get().

package json.

//...
"scripts": {
    "dev": "nodemon ./bin/www",
    "start": "node ./bin/www"
},
"keywords": [
    "express",
    "mongodb"
],
//...

In my implementation I took the liberty of refactoring some parts, for example it is possible to see in your code that even if there is an error the return is 200. So in this my code there is the treatment for this case, in its code it uses the callback model to consult the mongodb, in my I use the promise/then/catch.

Some more recommendations that are not part of the code but that are needed:

1. When I do the insertion in the database I include only the attributes that are part of my model. This will avoid adding unnecessary records and save a few cents of storage.
2. Adding a record is only done after sanitizing and validating the data. This will prevent malicious entries and remote code execution.