Return promise from Firebase Cloud Function - node.js

Question

I have callable function in my Cloud Functions:
export const getUserByEmail = functions.https.onCall((data, context) => {
const email = data.email
return admin.auth().getUserByEmail(email)
})
And I call it in my Angular application:
public getUserByEmail(email: string) {
return this.cloudFunctions.httpsCallable('getUserByEmail')(email)
}
...
this.getUserByEmail(email)
How should I change my function to be able to use it like this:
this.getUserByEmail(email)
.then(data => console.log(data))
.catch(error => console.log(error))
And return 500 from cloud function on error?

Answer 1

As explained in the documentation, if you want your client (front-end) to receive errors sent from the Callable Cloud Function, you need to "return errors from a callable by throwing (or returning a Promise rejected with) an instance of functions.https.HttpsError".
So, in your Cloud Function you need to throw an HttpsError, as shown below. In this example we treat the case of a user-not-found error thrown by the Admin SDK and, in turn we throw an HttpsError with a not-found code.
See other possibilities for the HttpsError codes in the doc (table "Parameter"), and here for the Admin Authentication API errors codes.
export const getUserByEmail = functions.https.onCall((data, context) => {
const email = data.email
return admin.auth().getUserByEmail(email)
.catch(error => { //Catching the error thrown by the Admin SDK
if (error.code === 'auth/user-not-found') {
throw new functions.https.HttpsError( //throwing the HttpsError
'not-found',
'User with email (' + email + ') was not found!'
);
} else if (error.code === 'auth/...') {
//Possibly manage other Admin Authentication API errors codes
} else {
//...
}
})
})
And then, in your front-end, you do as follows (again, based on the doc, see the specific section):
this.getUserByEmail(email)
.then(data => console.log(data))
.catch(error => {
var code = error.code;
var message = error.message;
console.log(code + '/' + message);
})

Answer 2

If you have something else to do (that might cause error) before returning the user data in the https callable function, you can do like this:
export const getUserByEmail = functions.https.onCall((data, context) => {
const email = data.email
// Return your own promise.
return new Promise((resolve, reject) => {
try {
// Do other stuff there might cause error.
} catch (error) {
// Reject if error.
// But you might need to throw the HttpsError again if the client
// can only get INTERNAL as error message.
return reject(error);
};
return admin.auth().getUserByEmail(email)
.then((data) => {
// Remember to resolve the promise, or else you may get an unexpected
// error, such as timeout or even an irrelevant CORS error.
resolve(data);
}
.catch((error) => {
// Follow #Renaud's idea in his answer.
});
});
});