[expo-background-fetch] App has stopped when is killed and background task try to execute

🐛 Bug Report

Summary of Issue

I’m having the AppName has stopped alert when use expo-background-fetch AND I have Proguard enabled. The issue is similar but not is the same that was reported. All works great if Proguard is disabled, but when I enable Proguard the app crash in background.

This happen in Bare workflow, I’m not tested in Managed workflow. Only Android.

Related Issues

Another related issues to background-location, but I have this with expo-background-fetch and only when Proguard is enabled.

• https://github.com/expo/expo/issues/9570
• https://github.com/expo/expo/issues/9288
• https://github.com/expo/expo/issues/8483

Logcat

2020-09-30 07:53:43.632 5371-5371/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: xxx, PID: 5371
    java.lang.RuntimeException: java.lang.NullPointerException: Attempt to invoke interface method 'void l.b.a.b.a(android.content.Context, l.b.a.b$b, java.lang.Runnable, l.b.b.l.e)' on a null object reference
        at android.app.job.JobServiceEngine$JobHandler.handleMessage(JobServiceEngine.java:112)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void l.b.a.b.a(android.content.Context, l.b.a.b$b, java.lang.Runnable, l.b.b.l.e)' on a null object reference
        at expo.modules.taskManager.h.a(Unknown Source:125)
        at expo.modules.taskManager.c.a(Unknown Source:2)
        at expo.modules.backgroundfetch.BackgroundFetchTaskConsumer.didExecuteJob(Unknown Source:8)
        at expo.modules.taskManager.h.b(Unknown Source:64)
        at expo.modules.taskManager.TaskJobService.onStartJob(Unknown Source:9)
        at android.app.job.JobService$1.onStartJob(JobService.java:71)
        at android.app.job.JobServiceEngine$JobHandler.handleMessage(JobServiceEngine.java:108)

Environment - output of expo diagnostics & the platform(s) you’re targeting

  Expo CLI 3.27.12 environment info:
    System:
      OS: macOS 10.15.5
      Shell: 5.7.1 - /bin/zsh
    Binaries:
      Node: 14.4.0 - /usr/local/bin/node
      Yarn: 1.19.1 - /usr/local/bin/yarn
      npm: 6.14.5 - /usr/local/bin/npm
      Watchman: 4.9.0 - /usr/local/bin/watchman
    Managers:
      CocoaPods: 1.9.3 - /usr/local/bin/pod
    SDKs:
      iOS SDK:
        Platforms: iOS 14.0, DriverKit 19.0, macOS 10.15, tvOS 14.0, watchOS 7.0
      Android SDK:
        Android NDK: 21.3.6528147
    IDEs:
      Android Studio: 4.0 AI-193.6911.18.40.6514223
      Xcode: 12.0/12A7209 - /usr/bin/xcodebuild
    npmPackages:
      expo: ~39.0.3 => 39.0.3
      react: 16.13.1 => 16.13.1
      react-native: ~0.63.3 => 0.63.3
    npmGlobalPackages:
      expo-cli: 3.27.12
    Expo Workflow: bare

expo-background-fetch: 8.5.0
expo-task-manager: 8.5.0

Reproducible Demo

Steps to Reproduce

1. Create a Bare project
2. Install expo-background-fetch
3. Create a task to run in background
4. Open Android Studio and enable Proguard (def enableProguardInReleaseBuilds = true)
5. Create a release sdk
6. Install in your device, open the app and kill the app.
7. Wait a few minutes to see the AppName has stopped

Expected Behavior vs Actual Behavior

Expected Behavior: background tasks works great Actual Behavior: Error AppName has stopped

I tested with the following proguard rule but doesn’t work.

-keep class expo.modules.taskManager { *; }

[RodolfoGS]

Hi @byCedric, I created a reproducible demo: https://github.com/RodolfoGS/expo-background-fetch-isseu10475

How to reproduce.

1. Create a release APK from demo
2. Install APK on your device
3. KILL THE APP (too many important) and wait for 1 minute
4. You’ll see the TestBackgroundFetch has stopped alert

---

How I created this demo:

1. expo init TestBackgroundFetch
2. Select Bare workflow -> minimal
3. cd TestBackgroundFetch
4. expo install expo-background-fetch
5. expo install expo-task-manager
6. Add following code to App.js:

import * as TaskManager from 'expo-task-manager';
import * as BackgroundFetch from 'expo-background-fetch';

TaskManager.defineTask('demo-task', async () => {
  console.log('demo-task is running');
  return BackgroundFetch.Result.NewData;
});

BackgroundFetch.registerTaskAsync('demo-task', {
  minimumInterval: 60, // 1 min
  stopOnTerminate: false,
  startOnBoot: true,
})
  .then(() => alert('BackgroundFetch.registerTaskAsync success'))
  .catch(error => alert(`Error registerTaskAsync: ${error.message}`));

1. Enable proguard editing android/app/build.gradle: def enableProguardInReleaseBuilds = true
2. Add the following rule to proguard-rules.pro file to fix another bug that are described below

-keep class expo.modules.backgroundfetch.** { *; }

1. Create release apk (Android Studio: Build -> Generate Signed Bundle / APK…)
2. Install in your device
3. Open the app
4. KILL THE APP (too many important)
5. Wait 1 minute and you will see the TestBackgroundFetch has stopped alert

---

Additional to this, I found another bug when you run BackgroundFetch.registerTaskAsync.

Initializing task consumer 'e.a.a.c' failed. Inherited error: <init> [class android.content.Context, interface i.b.c.f.f]"

I fixed this bug adding this rule to proguard rules file https://github.com/RodolfoGS/expo-background-fetch-isseu10475/blob/master/android/app/proguard-rules.pro#L12

-keep class expo.modules.backgroundfetch.** { *; }

---

Tested on Android Nexus 6P - Android 8.1.0

[lukmccall]

@byCedric, I don’t think that my PR fixed this bug. However, we now can add DoNotStrip annotation to BackgrondFetchTaskConsumer… and this should fix the problem with BackgroundFetch.registerTaskAsync.

Unfortunately, it won’t fix the problem with the AppName has stopped alert.

Frankly speaking, I really don’t understand why the BackgrondFetchTaskConsumer is dropped here 🤷🏼‍♂️ I’m not familiar with the task manager code.