Handling multiple FCM services

If you have added other push notifications plugins/dependencies in your project, in short, if your project contains multiple messaging services then this article is for you.

Countly push notifications work perfectly fine on their own but if the host project contains other messaging services then there could be a chance that Countly push will not work properly.

To support multiple messaging services you need to create a wrapper messaging service and register it as a messaging service in your AndroidManifest.xml 

<service android:name=".WrapperMessagingService">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

Inside WrapperMessagingService you need to forward the message to other messaging services.

package com.countly.demo;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

import com.google.firebase.messaging.FirebaseMessagingService;
import com.google.firebase.messaging.RemoteMessage;

import io.invertase.firebase.messaging.ReactNativeFirebaseMessagingService;
import ly.count.android.sdk.react.CountlyMessagingService;


public class WrapperMessagingService extends FirebaseMessagingService {


    private List<FirebaseMessagingService> messagingServices = new ArrayList<>(2);

    public WrapperMessagingService() {
        messagingServices.add(new CountlyMessagingService());
        messagingServices.add(new ReactNativeFirebaseMessagingService());
    }

    private void addService(FirebaseMessagingService firebaseMessagingService) {
        injectContext(firebaseMessagingService);
        messagingServices.add(firebaseMessagingService);
    }

    @Override
    public void onNewToken(String s) {
        delegate(service -> {
            injectContext(service);
            service.onNewToken(s);
        });
    }

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        delegate(service -> {
            injectContext(service);
            service.onMessageReceived(remoteMessage);
        });
    }

    private void delegate(GCAction1<FirebaseMessagingService> action) {
        for (FirebaseMessagingService service : messagingServices) {
            action.run(service);
        }
    }

    private void injectContext(FirebaseMessagingService service) {
        // tested on emulator with Android Q (Dev Preview 1)
        // Accessing hidden field Landroid/content/ContextWrapper;->mBase:Landroid/content/Context; (greylist, reflection)
        //
        // https://developer.android.com/distribute/best-practices/develop/restrictions-non-sdk-interfaces
        // https://android.googlesource.com/platform/frameworks/base/+/pie-release/config/hiddenapi-light-greylist.txt
        setField(service, "mBase", this);
    }

    private boolean setField(Object targetObject, String fieldName, Object fieldValue) {
        Field field;
        try {
            field = targetObject.getClass().getDeclaredField(fieldName);
        } catch (NoSuchFieldException e) {
            field = null;
        }
        Class superClass = targetObject.getClass().getSuperclass();
        while (field == null && superClass != null) {
            try {
                field = superClass.getDeclaredField(fieldName);
            } catch (NoSuchFieldException e) {
                superClass = superClass.getSuperclass();
            }
        }
        if (field == null) {
            return false;
        }
        field.setAccessible(true);
        try {
            field.set(targetObject, fieldValue);
            return true;
        } catch (IllegalAccessException e) {
            return false;
        }
    }

    interface GCAction1<T> {
        void run(T t);
    }
}