Node.js AsyncLocalStorage store is lost on callbacks (works with promises)

Pablo_Caselas_Pedrei · January 19, 2021, 8:06pm

Hi,
I think there’s something wrong with the callback API of node.js mongodb driver.
I’m trying to use node’s asyncLocalStorage API and found out that I get undefined store when using callbacks and get the store correctly when using promises

Here’s a sample app:

github.com

kas84/MongoDBCallbacksAsyncLocalStorage/blob/master/app.js

const express = require('express')
const { AsyncLocalStorage } = require('async_hooks')
const asyncLocalStorage = new AsyncLocalStorage()
const MongoClient = require('mongodb').MongoClient

var url = 'mongodb://localhost:27017/'
//MongoClient.connect(url, function (err, db) {
MongoClient.connect(url,{useUnifiedTopology:true}, function (err, db) {
  if (err) throw err
  console.log('connected to db!')

  const requestIdMiddleware = (req, res, next) => {
    asyncLocalStorage.run(new Map(), () => {
      asyncLocalStorage.getStore().set('requestId', Math.random())
      next()
    })
  }

  const app = express()

This file has been truncated. show original

[0.21756164732220062] request received
[0.21756164732220062] request received setTimeout
[undefined] request callback received
[0.21756164732220062] request promise received

When used with {useUnifiedTopology:true} , instead of undefined, you get the store, but on subsequent requests, you still get the first store

[0.7697388970645624] request received
[0.7697388970645624] request received setTimeout
[0.7697388970645624] request callback received
[0.7697388970645624] request promise received


[0.6329185718150439] request received
[0.6329185718150439] request received setTimeout
[0.7697388970645624] request callback received
[0.6329185718150439] request promise received


[0.2698320081709449] request received
[0.2698320081709449] request received setTimeout
[0.2698320081709449] request promise received
[0.7697388970645624] request callback received