[jnigen] Initial JNI support (#11)

Author: mahesh-hegde

.github/workflows/test-package.yml

@@ -72,27 +72,58 @@ jobs:
         uses: coverallsapp/[email protected]
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
+          flag-name: jni_gen_tests
+          parallel: true
           path-to-lcov: ./jni_gen/coverage/lcov.info
 
-  build_jni_example_linux:
+  ## TODO: More minimal test on windows after fixing dev dependency.
+  ## i.e do not rerun analyze and format steps, and do not require flutter.
+  ## IssueRef: https://github.com/dart-lang/jni_gen/issues/15
+
+  test_jni:
     runs-on: ubuntu-latest
     defaults:
       run:
-        working-directory: pkgs/jni/example
+        working-directory: pkgs/jni
     steps:
       - uses: actions/checkout@v3
+      ## Requires flutter to analyze example.
+      ## Using dart alone doesn't work.
       - uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
+      - uses: actions/setup-java@v2
+        with:
+          distribution: 'zulu'
+          java-version: '11'
       - run: |
           sudo apt-get update -y
           sudo apt-get install -y ninja-build libgtk-3-dev
-      - run: flutter config --enable-linux-desktop
+      - run: dart pub get
+      - run: dart run bin/setup.dart
       - run: flutter pub get
-      - run: flutter build linux
+      - name: Check formatting
+        run: flutter format --output=none --set-exit-if-changed .
+      - name: Run lints
+        run: flutter analyze --fatal-infos
+      - name: Get dependencies
+        run: dart pub get
+      - name: Run tests
+        run: dart test
+      - name: Install coverage
+        run: dart pub global activate coverage
+      - name: Collect coverage
+        run: dart pub global run coverage:test_with_coverage
+      - name: Upload coverage
+        uses: coverallsapp/[email protected]
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          flag-name: jni_tests
+          parallel: true
+          path-to-lcov: ./jni/coverage/lcov.info
 
-  build_jni_example_windows:
-    runs-on: windows-latest
+  build_jni_example_linux:
+    runs-on: ubuntu-latest
     defaults:
       run:
         working-directory: pkgs/jni/example
@@ -101,12 +132,24 @@ jobs:
       - uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
-      - run: flutter config --enable-windows-desktop
+      - uses: actions/setup-java@v2
+        with:
+          distribution: 'zulu'
+          java-version: '11'
+      - run: |
+          sudo apt-get update -y
+          sudo apt-get install -y ninja-build libgtk-3-dev
+      - run: dart pub get
+        working-directory: pkgs/jni
+      - run: dart run bin/setup.dart
+        working-directory: pkgs/jni
+      - run: flutter config --enable-linux-desktop
       - run: flutter pub get
-      - run: flutter build windows
+      - run: flutter test
+      - run: flutter build linux
 
-  build_jni_example_macos:
-    runs-on: macos-latest
+  build_jni_example_windows:
+    runs-on: windows-latest
     defaults:
       run:
         working-directory: pkgs/jni/example
@@ -115,10 +158,13 @@ jobs:
       - uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
-          architecture: x64
-      - run: flutter config --enable-macos-desktop
+      - uses: actions/setup-java@v2
+        with:
+          distribution: 'zulu'
+          java-version: '11'
+      - run: flutter config --enable-windows-desktop
       - run: flutter pub get
-      - run: flutter build macos
+      - run: flutter build windows
 
   build_jni_example_android:
     runs-on: ubuntu-latest
@@ -138,3 +184,13 @@ jobs:
       - run: flutter build apk
       - run: flutter build appbundle
 
+  coveralls_finish:
+    needs: [test_jni_gen, test_jni]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Coveralls finished
+        uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.github_token }}
+          parallel-finished: true
+

pkgs/jni/README.md

@@ -1,92 +1,37 @@
-# jni
+# jni (experimental module)
 
-A new Flutter FFI plugin project.
+This is a utility library to access JNI from Dart / Flutter code, intended as a supplement for `jnigen` code generator, as well as provide the common base components (such as managing the JVM instance) to the code generated by `jni_gen`.
 
-## Getting Started
+This library contains:
 
-This project is a starting point for a Flutter 
-[FFI plugin](https://docs.flutter.dev/development/platform-integration/c-interop),
-a specialized package that includes native code directly invoked with Dart FFI.
+* functions to access the JNIEnv and JavaVM variables from JNI, and wrapper functions to those provided by JNI. (`Jni.getEnv`, `Jni.getJavaVM`).
 
-## Project stucture
+* Functions to spawn a JVM on desktop platforms (`Jni.spawn`).
 
-This template uses the following structure:
+* Some utility functions to make it easier to work with JNI in Dart; eg: To convert a java string object to Dart string (mostly as extension methods on `Pointer<JniEnv>`).
 
-* `src`: Contains the native source code, and a CmakeFile.txt file for building
-  that source code into a dynamic library.
+* Some Android-specific helpers (get application context and current activity references).
 
-* `lib`: Contains the Dart code that defines the API of the plugin, and which
-  calls into the native code using `dart:ffi`.
+* Some helper classes and functions to simplify one-off uses (`JniObject` and `JniClass` intended for calling functions by specifying the name and arguments. It will reduce some boilerplate when you're debugging. Note: this API is slightly incomplete).
 
-* platform folders (`android`, `ios`, `windows`, etc.): Contains the build files
-  for building and bundling the native code library with the platform application.
+This is intended for one-off / debugging uses of JNI, as well as providing a base library for code generated by jni_gen. 
 
-## Buidling and bundling native code
+__To interface a complete java library, look forward for `jni_gen`.__
 
-The `pubspec.yaml` specifies FFI plugins as follows:
+## Platform support
+The focus of this project is Flutter Android, since Flutter Android apps already have a JVM, and JNI enables interop with existing Java code and Android Platform APIs. This project also (partially) supports Linux desktop by spawning a JVM through JNI.
 
-```yaml
-  plugin:
-    platforms:
-      some_platform:
-        ffiPlugin: true
-```
+## Version note
+This library is at an early stage of development and we do not provide backwards compatibility of the API at this point.
 
-This configuration invokes the native build for the various target platforms
-and bundles the binaries in Flutter applications using these FFI plugins.
+## Documentation
+The test/ directory contains files with comments explaining the basics of this module, and the example/ directory contains a flutter example which also touches some Android-specifics.
 
-This can be combined with dartPluginClass, such as when FFI is used for the
-implementation of one platform in a federated plugin:
+Using this library assumes some familiarity with JNI - it's threading model and object references, among other things.
 
-```yaml
-  plugin:
-    implements: some_other_plugin
-    platforms:
-      some_platform:
-        dartPluginClass: SomeClass
-        ffiPlugin: true
-```
+## jni_gen
 
-A plugin can have both FFI and method channels:
+This library is a part of `jni_gen` - a 2022 GSoC project.
 
-```yaml
-  plugin:
-    platforms:
-      some_platform:
-        pluginClass: SomeName
-        ffiPlugin: true
-```
-
-The native build systems that are invoked by FFI (and method channel) plugins are:
-
-* For Android: Gradle, which invokes the Android NDK for native builds.
-  * See the documentation in android/build.gradle.
-* For iOS and MacOS: Xcode, via CocoaPods.
-  * See the documentation in ios/jni.podspec.
-  * See the documentation in macos/jni.podspec.
-* For Linux and Windows: CMake.
-  * See the documentation in linux/CMakeLists.txt.
-  * See the documentation in windows/CMakeLists.txt.
-
-## Binding to native code
-
-To use the native code, bindings in Dart are needed.
-To avoid writing these by hand, they are generated from the header file
-(`src/jni.h`) by `package:ffigen`.
-Regenerate the bindings by running `flutter pub run ffigen --config ffigen.yaml`.
-
-## Invoking native code
-
-Very short-running native functions can be directly invoked from any isolate.
-For example, see `sum` in `lib/jni.dart`.
-
-Longer-running functions should be invoked on a helper isolate to avoid
-dropping frames in Flutter applications.
-For example, see `sumAsync` in `lib/jni.dart`.
-
-## Flutter help
-
-For help getting started with Flutter, view our
-[online documentation](https://flutter.dev/docs), which offers tutorials,
-samples, guidance on mobile development, and a full API reference.
+The broader aim of jni_gen is making Java APIs accessible from dart in an idiomatic way.
 

pkgs/jni/analysis_options.yaml

@@ -1,4 +1,13 @@
 include: package:flutter_lints/flutter.yaml
 
+analyzer:
+  exclude: [build/**]
+  language:
+    strict-raw-types: true
+
+linter:
+  rules:
+    - prefer_final_locals
+    - prefer_const_declarations
 # Additional information about this file can be found at
 # https://dart.dev/guides/language/analysis-options

pkgs/jni/android/src/main/java/dev/dart/jni/JniPlugin.java

@@ -0,0 +1,61 @@
+package dev.dart.jni;
+
+import androidx.annotation.Keep;
+import androidx.annotation.NonNull;
+import android.util.Log;
+import android.app.Activity;
+import io.flutter.plugin.common.PluginRegistry.Registrar;
+import io.flutter.embedding.engine.plugins.FlutterPlugin;
+import io.flutter.embedding.engine.plugins.activity.ActivityAware;
+import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
+
+import android.content.Context;
+
+@Keep
+public class JniPlugin implements FlutterPlugin, ActivityAware {
+  
+  @Override
+  public void
+  onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
+	  setup(binding.getApplicationContext());
+  }
+
+  public static void registerWith(Registrar registrar) {
+    JniPlugin plugin = new JniPlugin();
+	plugin.setup(registrar.activeContext());
+  }
+
+  private void setup(Context context) {
+	initializeJni(context, getClass().getClassLoader());
+  }
+
+  @Override
+  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {}
+
+  // Activity handling methods
+  @Override
+  public void onAttachedToActivity(@NonNull ActivityPluginBinding binding) {
+	Activity activity = binding.getActivity();
+	setJniActivity(activity, activity.getApplicationContext());
+  }
+
+  @Override
+  public void onDetachedFromActivityForConfigChanges() {}
+
+  @Override
+  public void onReattachedToActivityForConfigChanges(@NonNull ActivityPluginBinding binding) {
+	Activity activity = binding.getActivity();
+	setJniActivity(activity, activity.getApplicationContext());
+  }
+
+  @Override
+  public void onDetachedFromActivity() {}
+
+  native void initializeJni(Context context, ClassLoader classLoader);
+  native void setJniActivity(Activity activity, Context context);
+
+  static {
+	System.loadLibrary("dartjni");
+  }
+}
+