Flutter - Firebase callable functions with region not working

Question

we currently facing the problem in our flutter app, that httpsCallable functions which are defined with a region, in our case "europe-west1", is throwing an exception:

[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: [firebase_functions/internal] Response is not valid JSON object.

#0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:607:7)
#1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:167:18)
<asynchronous suspension>
#2      MethodChannelHttpsCallable.call (package:cloud_functions_platform_interface/src/method_channel/method_channel_https_callable.dart:23:24)
<asynchronous suspension>
#3      HttpsCallable.call (package:cloud_functions/src/https_callable.dart:35:37)
<asynchronous suspension>

#0      MethodChannelHttpsCallable.call (package:cloud_functions_platform_interface/src/method_channel/method_channel_https_callable.dart:39:7)
<asynchronous suspension>
#1      HttpsCallable.call (package:cloud_functions/src/https_callable.dart:35:37)
<asynchronous suspension>

As far, as we tested, it makes no difference, if we define the region in flutter accordingly to docs:

final result = await FirebaseFunctions.instanceFor(region: 'europe-west1').httpsCallable('myCallableFunction').call();

Or directly in the cloud function:

exports.myCallableFunction = functions.region("europe-west1").https.onCall((data, context) => {
   // ... return result
});

If we remove the region on both lines above, the callable function is working and returning the expected result.

Is there something, what I miss or is there currently an issue in flutter itself?

Solution

After some testing and the comment from Peter Koltai, the solution is defining the region in both, flutter and cloud functions:

flutter:

final result = await FirebaseFunctions.instanceFor(region: 'europe-west1').httpsCallable('myCallableFunction').call();

cloud functions:

exports.myCallableFunction = functions.region("europe-west1").https.onCall((data, context) => {
   // ... return result
});

Of course, this makes sense, because as the caller, I want to call the callable functions out of the "europe-west1" region. This gives, if required, the flexibility to call different functions for different regions.

Comments

[Peter Koltai]

You need both, in Cloud Functions and in Flutter. Have you re-deployed your functions after this change?

[Peter Koltai]

This works for me for the Node.js part: const functions = require("firebase-functions").region('europe-west3'); and then: exports.something = functions.https.onCall.... Dart side I have the same as yours.

[xbalaj]

Go and check what is the response of the endpoint result, print it. Then you will probably know.