Receiving returned data from firebase callable functions

Question

I'm playing with Callable HTTPS-functions in iOS. I've created and deployed the following function:

export const generateLoginToken = functions.https.onCall((data, context) => {

    const uid = data.user_id
    if (!(typeof uid === 'string') || uid.length === 0) {
        throw new functions.https.HttpsError('invalid-argument', 'The function must be called with one argument "user_id" ');
    }

    admin.auth().createCustomToken(uid)
    .then((token) => {
        console.log("Did create custom token:", token)
        return { text: "some_data" };
    }).catch((error) => {
        console.log("Error creating custom token:", error)
        throw new functions.https.HttpsError('internal', 'createCustomToken(uid) has failed for some reason')
    })
})

Then I call the function from my iOS-app like this:

let callParameters = ["user_id": userId]
    self?.functions.httpsCallable("generateLoginToken").call(callParameters) { [weak self] (result, error) in
    if let localError = self?.makeCallableFunctionError(error) {
        single(SingleEvent.error(localError))
    } else {
        print("Result", result)
        print("data", result?.data)
        if let text = (result?.data as? [String: Any])?["text"] as? String {
            single(SingleEvent.success(text))
        } else {
            let error = NSError.init(domain: "CallableFunctionError", code: 3, userInfo: ["info": "didn't find custom access token in the returned result"])
            single(SingleEvent.error(error))
        }
    }
}

I can see on the logs that the function is invoked on the server with the right parameters, but I can't seem to the get data that is being returned from the function back into the app. It seems that the result.data value is nilfor some reason, even though I return {text: "some_data"} from the cloud function. How come?

Also, what do you get if you call your Function via a browser? — Renaud Tarnec
– Renaud Tarnec, Commented Apr 24, 2018 at 15:13
You could be doing something wrong in your function code. Without seeing it, there's no way to tell. — Doug Stevenson
– Doug Stevenson, Commented Apr 24, 2018 at 20:38
Sorry.. I've added the cloud function :) It's an onCall function, I don't know how I would call it via a browser. When I try to paste the URL directly into an browser or do curl from the terminal, I get {"error":{"status":"INVALID_ARGUMENT","message":"Bad Request"}}. — Wiingaard
– Wiingaard, Commented Apr 24, 2018 at 21:00

Wiingaard · Accepted Answer · 2018-04-25 10:00:25Z

5

Yikes! The issue was that I forgot to return the actual promise from the cloud function. This function is working:

export const generateLoginToken = functions.https.onCall((data, context) => {

    const uid = data.user_id
    if (!(typeof uid === 'string') || uid.length === 0) {
        throw new functions.https.HttpsError('invalid-argument', 'The function must be called with one argument "user_id" ');
    }

    return admin.auth().createCustomToken(uid)
    .then((token) => {
        console.log("Did create custom token:", token)
        return { text: "some_data" };
    }).catch((error) => {
        console.log("Error creating custom token:", error)
        throw new functions.https.HttpsError('internal', 'createCustomToken(uid) has failed for some reason')
    })
})

answered Apr 25, 2018 at 10:00

Wiingaard

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3 Comments

Serdnad Over a year ago

Thanks for making me double check. For future reference: returning inside of a regular callback does NOT work. Must use promises.

ahagbani Over a year ago

Is there any additional steps other than adding this function to index.js? I copied it then deployed it "firebase deploy" through terminal but I get this error "Parsing error: 'import' and 'export' may appear only with 'sourceType: module' "

Wiingaard Over a year ago

Hmm.. Yes, there are a few other steps. You need to initialize the admin SDK with your service account key. You should probably find a tutorial for how to make the "createCustomToken" work. Here's how I do: justpaste.it/57hqz . And then I deploy with "firebase deploy --only functions". Also follow this link, it's should cover the basics: firebase.google.com/docs/functions/get-started

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