Firebase Cloud Functions https.onCall finished with status code: 204

Question

Firebase Function

const functions = require('firebase-functions');
const admin = require('firebase-admin');
const cors = require('cors')({ origin: true });

exports.addMessage = functions.https.onCall((data, context) => {
  return { text: "Test" };
});

Issue

The problem is when i call this function from the app i first get finished with status code: 204 and after that finished with status code: 200

204

How can i prevent this?

Answer 1

This is normal, and you shouldn't do anything to prevent it. The first request that results in 204 is what happens when CORS performs a preflight request. The 200 is the final serviced request.

You can read more about that here:

Two calls on Post request: with http 204 and 200