Using Cloud Functions to store data form an external API on Firestore database

Question

I have a Vue.js app running on Firebase and as a database I use Firestore. The app has to import data (clientes) form another app (app2), but app2 only exports by sending an XML code through POST to an address. To receive the POST from app2, my app utilizes Firebase Cloud Functions.

const xml2js = require("xml2js");
const functions = require("firebase-functions");
const cors = require("cors");
const express = require("express");
const app = express(); 
const admin = require("firebase-admin");

const db = admin.initializeApp().firestore();

function parseXml(xml) {
    return new Promise((resolve, reject) => {
        xml2js.parseString(xml, { explicitArray: false }, (err, result) => {
            if (err) {
                reject(err);
            } else {
                resolve(result);
            }
        });
    });
}

app.use(cors({ origen: true }));
    app.post("/", async (request, response) => {
    let xml = request.body.XMLRecords.toString();
    const clientes = db.collection("clientes");
    xml = xml.replace(/&(?!(?:apos|quot|[gl]t|amp);|#)/g, "&").trim();
    xml = " " + xml;

    console.log("Prep XML:");
    console.log(xml);

    let parsXml = await parseXml(xml);
    console.log("parsXML");
    console.log(parsXml);

    Array.from(parsXml.Records.Clientes.Cliente).forEach(async cli => {
        if (cli !== null) {
            delete cli.$;
            const docRef = clientes.doc(cli.CliCodigo);
            console.log("cli " + cli.CliCodigo);
            console.log(cli);
            const writeResult = await docRef.set(cli);
            console.log("Cliente " + cli.CliCodigo + " salvo");
        }
    });

    response.send("Received.");
});

exports.apiClientes = functions.https.onRequest((request, response) => {
    if (!request.path) {
        request.url = `/${request.url}`; // prepend '/' to keep query params if any
    }
    return app(request, response);
});

The app does receive the request and is able to process it, but when I try to comunicate with the Firestore database the function stops sending the console.log()staments and won't save the data to the database. What am I doing wrong?

Answer 1

This is most probably because within your Array.from(parsXml.Records.Clientes.Cliente).forEach() loop you are executing several asynchronous set() operations but you are returning the response (response.send("Received.");) before those asynchronous operations are done.

By doing response.send("Received."); you are indicating to the instance running your Cloud Function that it can terminate it, but in most cases the asynchronous writes to Firestore are not completed.

You need to correctly handle the Promises returned by the set() method calls, as follows (untested):

//....
const promises = [];

Array.from(parsXml.Records.Clientes.Cliente).forEach(cli => {
    if (cli !== null) {
        delete cli.$;   
        const docRef = clientes.doc(cli.CliCodigo);

        promises.push(docRef.set(cli));
    }
});

await Promise.all(promises);
response.send("Received.");
//....

So, we use Promise.all() to execute in parallel all the set() method calls. Promise.all() method returns a single Promise that fulfills when all of the promises passed to as an iterable (i.e. the promises array) have been fulfilled. Therefore you are sure that all the asynchronous work is done when you send back the response, indicating to the Cloud Function platform that it can safely terminate your Cloud Function.