Fire and forget worker inside controller - node.js

Question

I need to create a simple solution to receive input from an user, query our database and return the result in any way, but the queries can take as long as half an hour to run (and our cloud is configured to timeout after 2 minutes, I'm not allowed to change that).
I made the following solution that works locally, and want to include code to send the query's result via email to the user (in a fire and forget manner), but am unsure as how to do that while returning HTTP 200 to the user.
index.js:
const express = require('express')
const bodyParser = require('body-parser')
const db = require('./queries')
const app = express()
const port = 3000
app.use(bodyParser.json())
app.use(
bodyParser.urlencoded({
extended: true,
})
)
app.get('/', (request, response) => {
response.json({ info: 'Node.js, Express, and Postgres API' })
})
app.post('/report', db.getReport)
app.get('/test', db.getTest)
app.listen(port, () => {
console.log(`App running on port ${port}.`)
})
queries.js:
const Pool = require('pg').Pool
const pool = new Pool({
user: 'xxx',
host: 'xx.xxx.xx.xxx',
database: 'xxxxxxxx',
password: 'xxxxxxxx',
port: xxxx,
})
const getReport = (request, response) => {
const { business_group_id, initial_date, final_date } = request.body
pool.query(` SELECT GIANT QUERY`, [business_group_id, initial_date, final_date], (error, results) => {
if (error) {
throw error
}
response.status(200).json(results.rows)
})
// I want to change that to something like:
// FireNForgetWorker(params)
// response.status(200)
}
module.exports = {
getReport
}

Answer 1

Through the use of callbacks, and based on the design of express, you can send a response and continue to perform actions in that same function. You can, therefore, restructure it to look something like this:
const Pool = require('pg').Pool
const pool = new Pool({
user: 'xxx',
host: 'xx.xxx.xx.xxx',
database: 'xxxxxxxx',
password: 'xxxxxxxx',
port: xxxx,
})
const getReport = (request, response) => {
const { business_group_id, initial_date, final_date } = request.body
pool.query(` SELECT GIANT QUERY`, [business_group_id, initial_date, final_date], (error, results) => {
if (error) {
// TODO: Do something to handle error, or send an email that the query was unsucessfull
throw error
}
// Send the email here.
})
response.status(200).json({message: 'Process Began'});
}
module.exports = {
getReport
}
=============================================================================
Another approach could be to implement a queuing system that would push these requests to a queue, and have another process listening and sending the emails. That would be a bit more complicated though.