[jnigen] Implement multiple interfaces

pkgs/jni/example/lib/main.dart

@@ -7,9 +7,17 @@
 import 'dart:ffi';
 import 'dart:io';
 
+import 'package:ffi/ffi.dart';
 import 'package:flutter/material.dart';
 import 'package:jni/jni.dart';
 
+extension on String {
+  /// Returns a Utf-8 encoded `Pointer<Char>` with contents same as this string.
+  Pointer<Char> toNativeChars(Allocator allocator) {
+    return toNativeUtf8(allocator: allocator).cast<Char>();
+  }
+}
+
 // An example of calling JNI methods using low level primitives.
 // GlobalJniEnv is a thin abstraction over JNIEnv in JNI C API.
 //
@@ -18,7 +26,7 @@ import 'package:jni/jni.dart';
 String toJavaStringUsingEnv(int n) => using((arena) {
       final env = Jni.env;
       final cls = env.FindClass("java/lang/String".toNativeChars(arena));
-      final mId = env.GetStaticMethodID(cls, "valueOf".toNativeChars(),
+      final mId = env.GetStaticMethodID(cls, "valueOf".toNativeChars(arena),
           "(I)Ljava/lang/String;".toNativeChars(arena));
       final i = arena<JValue>();
       i.ref.i = n;

pkgs/jni/java/src/main/java/com/github/dart_lang/jni/PortProxy.java → pkgs/jni/java/src/main/java/com/github/dart_lang/jni/PortProxyBuilder.java

@@ -5,22 +5,32 @@
 package com.github.dart_lang.jni;
 
 import java.lang.reflect.*;
+import java.util.ArrayList;
+import java.util.HashMap;
 
-public class PortProxy implements InvocationHandler {
+public class PortProxyBuilder implements InvocationHandler {
   private static final PortCleaner cleaner = new PortCleaner();
 
   static {
     System.loadLibrary("dartjni");
   }
 
-  private final long port;
+  private static final class DartImplementation {
+    final long port;
+    final long pointer;
+
+    DartImplementation(long port, long pointer) {
+      this.port = port;
+      this.pointer = pointer;
+    }
+  }
+
+  private boolean built = false;
   private final long isolateId;
-  private final long functionPtr;
+  private final HashMap<String, DartImplementation> implementations = new HashMap<>();
 
-  private PortProxy(long port, long isolateId, long functionPtr) {
-    this.port = port;
+  public PortProxyBuilder(long isolateId) {
     this.isolateId = isolateId;
-    this.functionPtr = functionPtr;
   }
 
   private static String getDescriptor(Method method) {
@@ -62,15 +72,28 @@ private static void appendType(StringBuilder descriptor, Class<?> type) {
     }
   }
 
-  public static Object newInstance(String binaryName, long port, long isolateId, long functionPtr)
-      throws ClassNotFoundException {
-    Class<?> clazz = Class.forName(binaryName);
+  public void addImplementation(String binaryName, long port, long functionPointer) {
+    implementations.put(binaryName, new DartImplementation(port, functionPointer));
+  }
+
+  public Object build() throws ClassNotFoundException {
+    if (implementations.isEmpty()) {
+      throw new IllegalStateException("No interface implementation added");
+    }
+    if (built) {
+      throw new IllegalStateException("This proxy has already been built");
+    }
+    built = true;
+    ArrayList<Class<?>> classes = new ArrayList<>();
+    for (String binaryName : implementations.keySet()) {
+      classes.add(Class.forName(binaryName));
+    }
     Object obj =
         Proxy.newProxyInstance(
-            clazz.getClassLoader(),
-            new Class[] {clazz},
-            new PortProxy(port, isolateId, functionPtr));
-    cleaner.register(obj, port);
+            classes.get(0).getClassLoader(), classes.toArray(new Class<?>[0]), this);
+    for (DartImplementation implementation : implementations.values()) {
+      cleaner.register(obj, implementation.port);
+    }
     return obj;
   }
 
@@ -89,7 +112,15 @@ private static native Object[] _invoke(
 
   @Override
   public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
-    Object[] result = _invoke(port, isolateId, functionPtr, proxy, getDescriptor(method), args);
+    DartImplementation implementation = implementations.get(method.getDeclaringClass().getName());
+    Object[] result =
+        _invoke(
+            implementation.port,
+            isolateId,
+            implementation.pointer,
+            proxy,
+            getDescriptor(method),
+            args);
     _cleanUp((Long) result[0]);
     if (result[1] instanceof DartException) {
       Throwable cause = ((DartException) result[1]).cause;

pkgs/jni/lib/jni.dart

@@ -65,7 +65,8 @@ export 'dart:ffi' show nullptr;
 export 'package:ffi/ffi.dart' show Arena, using;
 
 export 'src/errors.dart';
-export 'src/jni.dart' hide ProtectedJniExtensions;
+export 'src/jimplementer.dart';
+export 'src/jni.dart' hide ProtectedJniExtensions, StringMethodsForJni;
 export 'src/jobject.dart';
 export 'src/jreference.dart' hide ProtectedJReference;
 export 'src/jvalues.dart';

pkgs/jni/lib/src/accessors.dart

@@ -59,7 +59,8 @@ extension JniResultMethods on JniResult {
   }
 
   JReference get reference {
-    return JGlobalReference(objectPointer);
+    final pointer = objectPointer;
+    return pointer == nullptr ? jNullReference : JGlobalReference(pointer);
   }
 
   T object<T extends JObject>(JObjType<T> type) {

pkgs/jni/lib/src/jimplementer.dart

@@ -0,0 +1,118 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:ffi';
+import 'dart:isolate';
+
+import 'package:ffi/ffi.dart';
+import 'package:meta/meta.dart';
+
+import '../_internal.dart';
+import 'jobject.dart';
+import 'lang/jstring.dart';
+import 'third_party/generated_bindings.dart';
+import 'types.dart';
+
+/// A builder that builds proxy objects that implement one or more interfaces.
+///
+/// Example:
+/// ```dart
+/// final implementer = JImplemeneter();
+/// Foo.implementIn(implementer, fooImpl);
+/// Bar.implementIn(implementer, barImpl);
+/// final foobar = implementer.build(Foo.type); // Or `Bar.type`.
+/// ```
+class JImplementer extends JObject {
+  JImplementer.fromReference(super.reference) : super.fromReference();
+
+  static final _class =
+      JClass.forName(r'com/github/dart_lang/jni/PortProxyBuilder');
+
+  static final _newId = _class.constructorId(r'(J)V');
+
+  static final _new = ProtectedJniExtensions.lookup<
+          NativeFunction<
+              JniResult Function(Pointer<Void>, JMethodIDPtr,
+                  VarArgs<(Int64,)>)>>('globalEnv_NewObject')
+      .asFunction<JniResult Function(Pointer<Void>, JMethodIDPtr, int)>();
+
+  factory JImplementer() {
+    ProtectedJniExtensions.ensureInitialized();
+    return JImplementer.fromReference(_new(
+            _class.reference.pointer,
+            _newId as JMethodIDPtr,
+            ProtectedJniExtensions.getCurrentIsolateId())
+        .reference);
+  }
+
+  static final _addImplementationId = _class.instanceMethodId(
+    r'addImplementation',
+    r'(Ljava/lang/String;JJ)V',
+  );
+
+  static final _addImplementation = ProtectedJniExtensions.lookup<
+              NativeFunction<
+                  JThrowablePtr Function(Pointer<Void>, JMethodIDPtr,
+                      VarArgs<(Pointer<Void>, Int64, Int64)>)>>(
+          'globalEnv_CallVoidMethod')
+      .asFunction<
+          JThrowablePtr Function(
+              Pointer<Void>, JMethodIDPtr, Pointer<Void>, int, int)>();
+
+  /// Should not be used directly.
+  ///
+  /// Use `implementIn` from the generated interface instead.
+  @internal
+  void add(
+    String binaryName,
+    RawReceivePort port,
+    Pointer<NativeFunction<JObjectPtr Function(Int64, JObjectPtr, JObjectPtr)>>
+        pointer,
+  ) {
+    using((arena) {
+      _addImplementation(
+              reference.pointer,
+              _addImplementationId as JMethodIDPtr,
+              (binaryName.toJString()..releasedBy(arena)).reference.pointer,
+              port.sendPort.nativePort,
+              pointer.address)
+          .check();
+    });
+  }
+
+  static final _buildId = _class.instanceMethodId(
+    r'build',
+    r'()Ljava/lang/Object;',
+  );
+
+  static final _build = ProtectedJniExtensions.lookup<
+          NativeFunction<
+              JniResult Function(
+                Pointer<Void>,
+                JMethodIDPtr,
+              )>>('globalEnv_CallObjectMethod')
+      .asFunction<
+          JniResult Function(
+            Pointer<Void>,
+            JMethodIDPtr,
+          )>();
+
+  /// Builds an proxy object with the specified [type] that implements all the
+  /// added interfaces with the given implementations.
+  ///
+  /// Releases this implementer.
+  T implement<T extends JObject>(JObjType<T> type) {
+    return type.fromReference(implementReference());
+  }
+
+  /// Used in the JNIgen generated code.
+  ///
+  /// It is unnecessary to construct the type object when the code is generated.
+  @internal
+  JReference implementReference() {
+    final ref = _build(reference.pointer, _buildId as JMethodIDPtr).reference;
+    release();
+    return ref;
+  }
+}