Firebase Cloud Function executing twice when triggered over HTTP

Question

I'm trying to integrate Firebase Cloud Functions into my Ionic 3 App. The goal is to create a cloud function that will create a user using the admin SDK.

However, when triggering this function over HTTP it will execute twice only when passing data to it, if I just call the function with no data it executes once as intended.

Cloud Function Code:

const functions = require('firebase-functions');

exports.createUser = functions.https.onRequest((request, response) => {
  response.set('Access-Control-Allow-Origin', '*');
  response.set('Access-Control-Allow-Headers', 'Content-Type');
  console.log(request.body);
  response.status(200).send('Hello from Firebase!');
});

HTTP Request:

axios.post(functionURL, {
  data: 'some data'
})
.then(res => {
  console.log(res.data);
})
.catch(err => console.log(err));

The HTTP request above works as intended and I see "Hello from Firebase! " only once in the console, however when I look at the functions logs it's showing it's being executed twice.

I'm very new to Firebase Cloud Functions so any input or suggestions would be greatly appreciated!

Answer 1

Solved

Solution found here: Cloud Functions for Firebase triggering function on CORS preflight request

As I was sending the data as application/json it was triggering a CORS preflight request, which is exactly what was causing the function to execute twice when passing data.

To bypass this, I simply sent the data as a application/x-www-form-urlencoded string like this:

const dataStr = JSON.stringify(objectToPass);

axios({
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded'
  },
  data: `data=${dataStr}`
})

And then parse the body back into an object in the function like this:

const data = JSON.parse(request.body.data);