Expose asset lookup from plugin binding. (#42019)

shell/platform/android/BUILD.gn

@@ -422,6 +422,7 @@ action("robolectric_tests") {
     "test/io/flutter/embedding/engine/FlutterEngineCacheTest.java",
     "test/io/flutter/embedding/engine/FlutterEngineTest.java",
     "test/io/flutter/embedding/engine/FlutterJNITest.java",
+    "test/io/flutter/embedding/engine/PluginComponentTest.java",
     "test/io/flutter/embedding/engine/RenderingComponentTest.java",
     "test/io/flutter/embedding/engine/dart/DartExecutorTest.java",
     "test/io/flutter/embedding/engine/plugins/shim/ShimPluginRegistryTest.java",

shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java

@@ -207,7 +207,8 @@ public FlutterEngine(
 
     this.pluginRegistry = new FlutterEnginePluginRegistry(
       context.getApplicationContext(),
-      this
+      this,
+      flutterLoader
     );
 
     if (automaticallyRegisterPlugins) {

shell/platform/android/io/flutter/embedding/engine/FlutterEnginePluginRegistry.java

@@ -21,6 +21,7 @@
 import java.util.Set;
 
 import io.flutter.Log;
+import io.flutter.embedding.engine.loader.FlutterLoader;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.PluginRegistry;
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
@@ -90,15 +91,17 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
 
   FlutterEnginePluginRegistry(
       @NonNull Context appContext,
-      @NonNull FlutterEngine flutterEngine
+      @NonNull FlutterEngine flutterEngine,
+      @NonNull FlutterLoader flutterLoader
   ) {
     this.flutterEngine = flutterEngine;
     pluginBinding = new FlutterPlugin.FlutterPluginBinding(
         appContext,
         flutterEngine,
         flutterEngine.getDartExecutor(),
         flutterEngine.getRenderer(),
-        flutterEngine.getPlatformViewsController().getRegistry()
+        flutterEngine.getPlatformViewsController().getRegistry(),
+        new DefaultFlutterAssets(flutterLoader)
     );
   }
 
@@ -532,6 +535,30 @@ public void detachFromContentProvider() {
   }
   //----- End ContentProviderControlSurface -----
 
+  private static class DefaultFlutterAssets implements FlutterPlugin.FlutterAssets {
+    final FlutterLoader flutterLoader;
+
+    private DefaultFlutterAssets(@NonNull FlutterLoader flutterLoader) {
+      this.flutterLoader = flutterLoader;
+    }
+
+    public String getAssetFilePathByName(@NonNull String assetFileName) {
+      return flutterLoader.getLookupKeyForAsset(assetFileName);
+    }
+
+    public String getAssetFilePathByName(@NonNull String assetFileName, @NonNull String packageName) {
+      return flutterLoader.getLookupKeyForAsset(assetFileName, packageName);
+    }
+
+    public String getAssetFilePathBySubpath(@NonNull String assetSubpath) {
+      return flutterLoader.getLookupKeyForAsset(assetSubpath);
+    }
+
+    public String getAssetFilePathBySubpath(@NonNull String assetSubpath, @NonNull String packageName) {
+      return flutterLoader.getLookupKeyForAsset(assetSubpath, packageName);
+    }
+  }
+
   private static class FlutterEngineActivityPluginBinding implements ActivityPluginBinding {
     @NonNull
     private final Activity activity;

shell/platform/android/io/flutter/embedding/engine/plugins/FlutterPlugin.java

@@ -9,6 +9,7 @@
 import android.support.annotation.NonNull;
 
 import io.flutter.embedding.engine.FlutterEngine;
+import io.flutter.embedding.engine.loader.FlutterLoader;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.platform.PlatformViewRegistry;
 import io.flutter.view.TextureRegistry;
@@ -101,19 +102,22 @@ class FlutterPluginBinding {
         private final BinaryMessenger binaryMessenger;
         private final TextureRegistry textureRegistry;
         private final PlatformViewRegistry platformViewRegistry;
+        private final FlutterAssets flutterAssets;
 
         public FlutterPluginBinding(
             @NonNull Context applicationContext,
             @NonNull FlutterEngine flutterEngine,
             @NonNull BinaryMessenger binaryMessenger,
             @NonNull TextureRegistry textureRegistry,
-            @NonNull PlatformViewRegistry platformViewRegistry
+            @NonNull PlatformViewRegistry platformViewRegistry,
+            @NonNull FlutterAssets flutterAssets
         ) {
             this.applicationContext = applicationContext;
             this.flutterEngine = flutterEngine;
             this.binaryMessenger = binaryMessenger;
             this.textureRegistry = textureRegistry;
             this.platformViewRegistry = platformViewRegistry;
+            this.flutterAssets = flutterAssets;
         }
 
         @NonNull
@@ -146,5 +150,47 @@ public TextureRegistry getTextureRegistry() {
         public PlatformViewRegistry getPlatformViewRegistry() {
           return platformViewRegistry;
         }
+
+        @NonNull
+        public FlutterAssets getFlutterAssets() {
+          return flutterAssets;
+        }
     }
+
+  /**
+   * Provides Flutter plugins with access to Flutter asset information.
+   */
+  interface FlutterAssets {
+      /**
+       * Returns the relative file path to the Flutter asset with the given name, including the file's
+       * extension, e.g., {@code "myImage.jpg"}.
+       *
+       * <p>The returned file path is relative to the Android app's standard assets directory.
+       * Therefore, the returned path is appropriate to pass to Android's {@code AssetManager},
+       * but the path is not appropriate to load as an absolute path.
+       */
+      String getAssetFilePathByName(@NonNull String assetFileName);
+
+      /**
+       * Same as {@link #getAssetFilePathByName(String)} but with added support for an explicit
+       * Android {@code packageName}.
+       */
+      String getAssetFilePathByName(@NonNull String assetFileName, @NonNull String packageName);
+
+      /**
+       * Returns the relative file path to the Flutter asset with the given subpath, including the file's
+       * extension, e.g., {@code "/dir1/dir2/myImage.jpg"}.
+       *
+       * <p>The returned file path is relative to the Android app's standard assets directory.
+       * Therefore, the returned path is appropriate to pass to Android's {@code AssetManager},
+       * but the path is not appropriate to load as an absolute path.
+       */
+      String getAssetFilePathBySubpath(@NonNull String assetSubpath);
+
+      /**
+       * Same as {@link #getAssetFilePathBySubpath(String)} but with added support for an explicit
+       * Android {@code packageName}.
+       */
+      String getAssetFilePathBySubpath(@NonNull String assetSubpath, @NonNull String packageName);
+  }
 }

shell/platform/android/test/io/flutter/FlutterTestSuite.java

@@ -23,6 +23,7 @@
 import io.flutter.plugin.platform.SingleViewPresentationTest;
 import io.flutter.util.PreconditionsTest;
 import test.io.flutter.embedding.engine.FlutterEngineTest;
+import test.io.flutter.embedding.engine.PluginComponentTest;
 import test.io.flutter.embedding.engine.dart.DartExecutorTest;
 
 @RunWith(Suite.class)
@@ -38,6 +39,7 @@
     FlutterRendererTest.class,
     FlutterViewTest.class,
     PlatformChannelTest.class,
+    PluginComponentTest.class,
     PreconditionsTest.class,
     RenderingComponentTest.class,
     StandardMessageCodecTest.class,

shell/platform/android/test/io/flutter/embedding/engine/PluginComponentTest.java

@@ -0,0 +1,123 @@
+package test.io.flutter.embedding.engine;
+
+import android.support.annotation.NonNull;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+import org.robolectric.annotation.Config;
+
+import io.flutter.embedding.engine.FlutterEngine;
+import io.flutter.embedding.engine.FlutterJNI;
+import io.flutter.embedding.engine.loader.FlutterLoader;
+import io.flutter.embedding.engine.plugins.FlutterPlugin;
+
+import static junit.framework.TestCase.assertEquals;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+@Config(manifest=Config.NONE)
+@RunWith(RobolectricTestRunner.class)
+public class PluginComponentTest {
+  @Test
+  public void pluginsCanAccessFlutterAssetPaths() {
+    // Setup test.
+    FlutterJNI flutterJNI = mock(FlutterJNI.class);
+    when(flutterJNI.isAttached()).thenReturn(true);
+
+    // FlutterLoader is the object to which the PluginRegistry defers for obtaining
+    // the path to a Flutter asset. Ideally in this component test we would use a
+    // real FlutterLoader and directly verify the relationship between FlutterAssets
+    // and FlutterLoader. However, a real FlutterLoader cannot be used in a JVM test
+    // because it would attempt to load native libraries. Therefore, we create a fake
+    // FlutterLoader, but then we defer the corresponding asset lookup methods to the
+    // real FlutterLoader singleton. This test ends up verifying that when FlutterAssets
+    // is queried for an asset path, it returns the real expected path based on real
+    // FlutterLoader behavior.
+    FlutterLoader flutterLoader = mock(FlutterLoader.class);
+    when(flutterLoader.getLookupKeyForAsset(any(String.class))).thenAnswer(new Answer<String>() {
+      @Override
+      public String answer(InvocationOnMock invocation) throws Throwable {
+        // Defer to a real FlutterLoader to return the asset path.
+        String fileNameOrSubpath = (String) invocation.getArguments()[0];
+        return FlutterLoader.getInstance().getLookupKeyForAsset(fileNameOrSubpath);
+      }
+    });
+    when(flutterLoader.getLookupKeyForAsset(any(String.class), any(String.class))).thenAnswer(new Answer<String>() {
+      @Override
+      public String answer(InvocationOnMock invocation) throws Throwable {
+        // Defer to a real FlutterLoader to return the asset path.
+        String fileNameOrSubpath = (String) invocation.getArguments()[0];
+        String packageName = (String) invocation.getArguments()[1];
+        return FlutterLoader.getInstance().getLookupKeyForAsset(fileNameOrSubpath, packageName);
+      }
+    });
+
+    // Execute behavior under test.
+    FlutterEngine flutterEngine = new FlutterEngine(
+        RuntimeEnvironment.application,
+        flutterLoader,
+        flutterJNI
+    );
+
+    // As soon as our plugin is registered it will look up asset paths and store them
+    // for our verification.
+    PluginThatAccessesAssets plugin = new PluginThatAccessesAssets();
+    flutterEngine.getPlugins().add(plugin);
+
+    // Verify results.
+    assertEquals("flutter_assets/fake_asset.jpg", plugin.getAssetPathBasedOnName());
+    assertEquals("flutter_assets/packages/fakepackage/fake_asset.jpg", plugin.getAssetPathBasedOnNameAndPackage());
+    assertEquals("flutter_assets/some/path/fake_asset.jpg", plugin.getAssetPathBasedOnSubpath());
+    assertEquals("flutter_assets/packages/fakepackage/some/path/fake_asset.jpg", plugin.getAssetPathBasedOnSubpathAndPackage());
+  }
+
+  private static class PluginThatAccessesAssets implements FlutterPlugin {
+    private String assetPathBasedOnName;
+    private String assetPathBasedOnNameAndPackage;
+    private String assetPathBasedOnSubpath;
+    private String assetPathBasedOnSubpathAndPackage;
+
+    public String getAssetPathBasedOnName() {
+      return assetPathBasedOnName;
+    }
+
+    public String getAssetPathBasedOnNameAndPackage() {
+      return assetPathBasedOnNameAndPackage;
+    }
+
+    public String getAssetPathBasedOnSubpath() {
+      return assetPathBasedOnSubpath;
+    }
+
+    public String getAssetPathBasedOnSubpathAndPackage() {
+      return assetPathBasedOnSubpathAndPackage;
+    }
+
+    @Override
+    public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
+      assetPathBasedOnName = binding
+          .getFlutterAssets()
+          .getAssetFilePathByName("fake_asset.jpg");
+
+      assetPathBasedOnNameAndPackage = binding
+          .getFlutterAssets()
+          .getAssetFilePathByName("fake_asset.jpg", "fakepackage");
+
+      assetPathBasedOnSubpath = binding
+          .getFlutterAssets()
+          .getAssetFilePathByName("some/path/fake_asset.jpg");
+
+      assetPathBasedOnSubpathAndPackage = binding
+          .getFlutterAssets()
+          .getAssetFilePathByName("some/path/fake_asset.jpg", "fakepackage");
+    }
+
+    @Override
+    public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {}
+  }
+}