dialogflow fullfilment and firebase response time - node.js

Question

I am trying to build a simple chatbot with DialogFlow.
My aim is to give information from user question, like : where can I slackline above water in croatia ? I have two parameters (croatia, waterline) and a list of slackline places.
So I need a data base to retrieve information from parameters. DialogFlow allows fulfillment with Firebase. I build a database with places (name, country, type of slack) and enable webhook call for my intent.
I use Inline Editor and index.js
const parameters = request.body.queryResult.parameters;
var country = parameters.country.toString();
function show(snap) {
console.log('snap');
agent.add(JSON.stringify(snap.val(),null,2));
}
function slkplc(agent) {
var testRef;
firebase.database().ref('slackplace').once('value',show);
}
// Run the proper function handler based on the matched Dialogflow intent name
let intentMap = new Map();
intentMap.set('slack place', slkplc);
agent.handleRequest(intentMap);
But I do not get the expected result while trying it on DialogFlow or Google Assistant. The function show is asynchronously called but too late and the response is not available for DialogFlow :
I see three way to deal with this problem :
use blocking call to database : another database ?
treat asynchronous message with DialogFlow ???
response to user that an error occured.
The third that I choose, but it is always on error.
After trying several things to wait data from database response, the only thing I managed is to freeze the response, therefore the timeout of DialogFlow - 5s -and Firebase - 60s - were reached.
A workaround
Another way to do it is to separate database acquisition and request/response from DialogFlow. The data of database is collected outside of the dialogflowFirebaseFulfillment
var data;
var inidata = firebase.database().ref().on('value',function(snap) {
console.log('snap');
data = snap.val();
});
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
const agent = new WebhookClient({ request, response });
...
function slkplc(agent) {
agent.add(JSON.stringify(data,null,2));
}
// Run the proper function handler based on the matched Dialogflow intent name
let intentMap = new Map();
intentMap.set('slack place', slkplc);
agent.handleRequest(intentMap);
}
Now I can do what I want with data, and I am able to find the place where I can practice waterline in croatia. But there is always something weird, the data of the database is duplicated ...

Answer 1

The "right" solution is option 2 that you suggest: since you're doing an asynchronous call, you need to handle this correctly when working with the dialogflow-fulfillment library.
Basically, if your handler makes an asynchronous call, it needs to be asynchronous as well. To indicate to the handleRequest() method that your handler is async, you need to return a Promise object.
Firebase's once() method returns a Promise if you don't pass it a callback function. You can take advantage of this, return that Promise, and also handle what you want it to do as part of a .then() clause. It might look something like this:
function slkplc(agent) {
var testRef;
return firebase.database().ref('slackplace').once('value')
.then( snap => {
var val = snap.val();
return agent.add( JSON.stringify( val, null, 2 ) );
});
}
The important part isn't just that you use a Promise, but also that you return that Promise.