task.result?.data returning null in HTTP Cloud Function call - firebase

Question

I'm calling a Cloud Function from my app with the following code:
private fun search(g: String, l: GeoPoint): Task<String> {
val data = hashMapOf(
"uid" to user.uid,
"first_name" to user.first_name,
"age" to user.age,
"gender" to user.gender,
"bio" to user.bio,
"img1" to user.img1,
"img2" to user.img2,
"latitude" to l.latitude.toString(),
"longitude" to l.longitude.toString(),
"g" to g,
"fcmToken" to fcmToken,
"pronoun" to if (user.gender == "male") "him" else "her"
)
log("data: $data") // successfully logs all values as non-null
return functions
.getHttpsCallable("searchNearby")
.call(data)
.continueWith { task ->
log("result: ${task.result?.data}")
// This continuation runs on either success or failure, but if the task
// has failed then result will throw an Exception which will be
// propagated down.
val result = task.result?.data as String
result
}
.addOnSuccessListener { result ->
log("search(): success $result")
}
.addOnFailureListener { exception ->
log("search(): exception $exception") // exception kotlin.TypeCastException: null cannot be cast to non-null type kotlin.String
log("search(): localMsg ${exception.localizedMessage}") // localMsg null cannot be cast to non-null type kotlin.String
log("search(): cause ${exception.cause}") // cause null
log("search(): msg ${exception.message}") // msg null cannot be cast to non-null type kotlin.String
}
}
Why is task.result?.data returning null if every item in data is non-null?
EDIT
.addOnFailureListener() now returns another weird error: HashMap cannot be cast to java.lang.String.
Here is my cloud function:
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const db = admin.firestore();
const geofirestore = require('geofirestore');
const { GeoCollectionReference, GeoFirestore, GeoQuery, GeoQuerySnapshot } = require('geofirestore');
const user = {};
exports.searchNearby = functions.https.onCall((data, context) => {
return admin.firestore().collection('blocks').add({
user1name: "1142",
user1bio: data.bio,
user1img1: data.img1,
user1img2: data.img2,
user1fcmToken: data.fcmToken,
user1pronoun: data.pronoun
}).then(result => {
console.log("Successfully created document");
return { result: "Successfully created document" };
}).catch(error => {
console.log("Error creating document " + error);
return { errorCreatingDocument: error };
});
});
The document is successfully created, and { result: "Successfully created document" } successfully gets sent back to the client, but it's still firing an exception java.util.HashMap cannot be cast to java.lang.String. Any idea what the problem is? It's also especially hard to debug because it doesn't tell you what like in my Cloud Functions the error is.

Answer 1

You are returning a JavaScript object to the client from the callable function:
return { result: "Successfully created document" };
The object contains a single property named result. Since your function returns an object, your client needs to assume the result from the callable is a Map. The Map will have a single entry with key also named result. This should be pretty easy to verify if you just log the value of result here:
val result = task.result?.data
Instead of casting this to a String, cast it to Map<String, *>, and fetch the entry named result out of it:
val data = task.result?.data as Map<String, *>
val result = data["result"]
Or, you can change your function to return a string instead of a JavaScript object:
return "Successfully created document";