[jnigen] Check for free in reference getter (#361)

Author: HosseinYousefi

pkgs/jni/example/pubspec.lock

@@ -519,5 +519,5 @@ packages:
     source: hosted
     version: "3.1.2"
 sdks:
-  dart: ">=3.1.0 <4.0.0"
+  dart: ">=3.1.0-262.3.beta <4.0.0"
   flutter: ">=2.11.0"

pkgs/jni/example/pubspec.yaml

@@ -18,7 +18,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.0+1
 
 environment:
-  sdk: '>=3.1.0 <4.0.0'
+  sdk: '>=3.1.0-262.3.beta <4.0.0'
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions

pkgs/jni/lib/src/jexceptions.dart

@@ -9,37 +9,38 @@ import 'package:jni/src/third_party/generated_bindings.dart';
 abstract class JException implements Exception {}
 
 class UseAfterFreeException implements JException {
-  dynamic object;
-  Pointer<Void> ptr;
-  UseAfterFreeException(this.object, this.ptr);
+  final Pointer<Void> ptr;
+  UseAfterFreeException(this.ptr);
 
   @override
   String toString() {
-    return "use after free on $ptr through $object";
+    return 'Use after free on $ptr.';
   }
 }
 
-class NullJStringException implements JException {
+class JNullException implements JException {
+  const JNullException();
+
   @override
-  String toString() => 'toDartString called on null JString reference';
+  String toString() => 'The reference was null.';
 }
 
 class InvalidJStringException implements JException {
-  Pointer<Void> reference;
+  final Pointer<Void> reference;
   InvalidJStringException(this.reference);
+
   @override
   String toString() => 'Not a valid Java String: '
-      '0x${reference.address.toRadixString(16)}';
+      '0x${reference.address.toRadixString(16)}.';
 }
 
 class DoubleFreeException implements JException {
-  dynamic object;
-  Pointer<Void> ptr;
-  DoubleFreeException(this.object, this.ptr);
+  final Pointer<Void> ptr;
+  DoubleFreeException(this.ptr);
 
   @override
   String toString() {
-    return "double free on $ptr through $object";
+    return 'Double free on $ptr.';
   }
 }
 
@@ -113,9 +114,10 @@ class HelperNotFoundException implements JException {
   final String path;
 
   @override
-  String toString() => "Lookup for helper library $path failed.\n"
-      "Please ensure that `dartjni` shared library is built.\n"
-      "Provided jni:setup script can be used to build the shared library."
-      "If the library is already built, ensure that the JVM libraries can be "
-      "loaded from Dart.";
+  String toString() => '''
+Lookup for helper library $path failed.
+Please ensure that `dartjni` shared library is built.
+Provided jni:setup script can be used to build the shared library.
+If the library is already built, ensure that the JVM libraries can be 
+loaded from Dart.''';
 }

pkgs/jni/lib/src/jni.dart

@@ -337,7 +337,7 @@ extension AdditionalEnvMethods on GlobalJniEnv {
   /// DeleteLocalRef.
   String toDartString(JStringPtr jstringPtr, {bool deleteOriginal = false}) {
     if (jstringPtr == nullptr) {
-      throw NullJStringException();
+      throw const JNullException();
     }
     final chars = GetStringUTFChars(jstringPtr, nullptr);
     if (chars == nullptr) {

pkgs/jni/lib/src/jobject.dart

@@ -189,7 +189,6 @@ class JObject extends JReference {
   ///
   /// This may be a subclass of compile-time class.
   JClass getClass() {
-    ensureNotDeleted();
     final classRef = Jni.env.GetObjectClass(reference);
     if (classRef == nullptr) {
       Jni.accessors.throwException(Jni.env.ExceptionOccurred());
@@ -199,28 +198,24 @@ class JObject extends JReference {
 
   /// Get [JFieldIDPtr] of instance field identified by [fieldName] & [signature].
   JFieldIDPtr getFieldID(String fieldName, String signature) {
-    ensureNotDeleted();
     return _getID(
         Jni.accessors.getFieldID, _class.reference, fieldName, signature);
   }
 
   /// Get [JFieldIDPtr] of static field identified by [fieldName] & [signature].
   JFieldIDPtr getStaticFieldID(String fieldName, String signature) {
-    ensureNotDeleted();
     return _getID<jfieldID_>(
         Jni.accessors.getStaticFieldID, _class.reference, fieldName, signature);
   }
 
   /// Get [JMethodIDPtr] of instance method [methodName] with [signature].
   JMethodIDPtr getMethodID(String methodName, String signature) {
-    ensureNotDeleted();
     return _getID<jmethodID_>(
         Jni.accessors.getMethodID, _class.reference, methodName, signature);
   }
 
   /// Get [JMethodIDPtr] of static method [methodName] with [signature].
   JMethodIDPtr getStaticMethodID(String methodName, String signature) {
-    ensureNotDeleted();
     return _getID<jmethodID_>(Jni.accessors.getStaticMethodID, _class.reference,
         methodName, signature);
   }
@@ -235,7 +230,6 @@ class JObject extends JReference {
   /// If [T] is String or [JObject], required conversions are performed and
   /// final value is returned.
   T getField<T>(JFieldIDPtr fieldID, [int? callType]) {
-    ensureNotDeleted();
     if (callType == JniCallType.voidType) {
       throw ArgumentError("void is not a valid field type.");
     }
@@ -258,7 +252,6 @@ class JObject extends JReference {
     if (callType == JniCallType.voidType) {
       throw ArgumentError("void is not a valid field type.");
     }
-    ensureNotDeleted();
     return _getField<T>(callType,
         (ct) => Jni.accessors.getStaticField(_class.reference, fieldID, ct));
   }
@@ -278,7 +271,6 @@ class JObject extends JReference {
   ///
   /// See [getField] for an explanation about [callType] and return type [T].
   T callMethod<T>(JMethodIDPtr methodID, List<dynamic> args, [int? callType]) {
-    ensureNotDeleted();
     return _callMethod<T>(callType, args,
         (ct, jvs) => Jni.accessors.callMethod(reference, methodID, ct, jvs));
   }
@@ -296,7 +288,6 @@ class JObject extends JReference {
   /// more details about [args] and [callType].
   T callStaticMethod<T>(JMethodIDPtr methodID, List<dynamic> args,
       [int? callType]) {
-    ensureNotDeleted();
     return _callMethod<T>(
         callType,
         args,
@@ -317,8 +308,9 @@ class JObject extends JReference {
   T castTo<T extends JObject>(JObjType<T> type, {bool deleteOriginal = false}) {
     if (deleteOriginal) {
       _jClass?.delete();
+      final ret = type.fromRef(reference);
       setAsDeleted();
-      return type.fromRef(reference);
+      return ret;
     }
     final newRef = Jni.env.NewGlobalRef(reference);
     return type.fromRef(newRef);
@@ -360,28 +352,24 @@ class JClass extends JReference {
 
   /// Get [JFieldIDPtr] of static field [fieldName] with [signature].
   JFieldIDPtr getStaticFieldID(String fieldName, String signature) {
-    ensureNotDeleted();
     return _getID<jfieldID_>(
         Jni.accessors.getStaticFieldID, reference, fieldName, signature);
   }
 
   /// Get [JMethodIDPtr] of static method [methodName] with [signature].
   JMethodIDPtr getStaticMethodID(String methodName, String signature) {
-    ensureNotDeleted();
     return _getID<jmethodID_>(
         Jni.accessors.getStaticMethodID, reference, methodName, signature);
   }
 
   /// Get [JFieldIDPtr] of field [fieldName] with [signature].
   JFieldIDPtr getFieldID(String fieldName, String signature) {
-    ensureNotDeleted();
     return _getID<jfieldID_>(
         Jni.accessors.getFieldID, reference, fieldName, signature);
   }
 
   /// Get [JMethodIDPtr] of method [methodName] with [signature].
   JMethodIDPtr getMethodID(String methodName, String signature) {
-    ensureNotDeleted();
     return _getID<jmethodID_>(
         Jni.accessors.getMethodID, reference, methodName, signature);
   }
@@ -396,7 +384,6 @@ class JClass extends JReference {
     if (callType == JniCallType.voidType) {
       throw ArgumentError("void is not a valid field type.");
     }
-    ensureNotDeleted();
     return _getField<T>(
         callType, (ct) => Jni.accessors.getStaticField(reference, fieldID, ct));
   }
@@ -415,7 +402,6 @@ class JClass extends JReference {
   /// about [args] and [callType].
   T callStaticMethod<T>(JMethodIDPtr methodID, List<dynamic> args,
       [int? callType]) {
-    ensureNotDeleted();
     return _callMethod<T>(
         callType,
         args,
@@ -434,7 +420,6 @@ class JClass extends JReference {
 
   /// Create a new instance of this class with [ctor] and [args].
   JObject newInstance(JMethodIDPtr ctor, List<dynamic> args) => using((arena) {
-        ensureNotDeleted();
         final jArgs = JValueArgs(args, arena);
         final res =
             Jni.accessors.newObject(reference, ctor, jArgs.values).object;

pkgs/jni/lib/src/jreference.dart

@@ -11,28 +11,37 @@ import 'jexceptions.dart';
 import 'jni.dart';
 
 extension ProtectedJReference on JReference {
-  void ensureNotDeleted() {
-    if (_deleted) throw UseAfterFreeException(this, reference);
-  }
-
   void setAsDeleted() {
     if (_deleted) {
-      throw DoubleFreeException(this, reference);
+      throw DoubleFreeException(_reference);
     }
     _deleted = true;
     JReference._finalizer.detach(this);
   }
+
+  void ensureNotNull() {
+    if (isNull) {
+      throw const JNullException();
+    }
+  }
+
+  /// Similar to [reference].
+  ///
+  /// Detaches the finalizer so the underlying pointer will not be deleted.
+  JObjectPtr toPointer() {
+    setAsDeleted();
+    return _reference;
+  }
 }
 
 /// A class which holds one or more JNI references, and has a `delete` operation
 /// which disposes the reference(s).
 abstract class JReference implements Finalizable {
-  //TODO(PR): Is it safe to cast void *f (void *) to void f (void *)?
   static final _finalizer =
       NativeFinalizer(Jni.env.ptr.ref.DeleteGlobalRef.cast());
 
-  JReference.fromRef(this.reference) {
-    _finalizer.attach(this, reference, detach: this);
+  JReference.fromRef(this._reference) {
+    _finalizer.attach(this, _reference, detach: this);
   }
 
   bool _deleted = false;
@@ -43,15 +52,26 @@ abstract class JReference implements Finalizable {
   /// Returns whether this object is deleted.
   bool get isDeleted => _deleted;
 
-  /// Deletes the underlying JNI reference. Further uses will throw
-  /// [UseAfterFreeException].
+  /// Deletes the underlying JNI reference.
+  ///
+  /// Further uses will throw [UseAfterFreeException].
   void delete() {
     setAsDeleted();
-    Jni.env.DeleteGlobalRef(reference);
+    Jni.env.DeleteGlobalRef(_reference);
   }
 
   /// The underlying JNI global object reference.
-  final JObjectPtr reference;
+  ///
+  /// Throws [UseAfterFreeException] if the object is previously deleted.
+  ///
+  /// Be careful when storing this reference in a variable, since the underlying
+  /// object might get deleted.
+  JObjectPtr get reference {
+    if (_deleted) throw UseAfterFreeException(_reference);
+    return _reference;
+  }
+
+  final JObjectPtr _reference;
 
   /// Registers this object to be deleted at the end of [arena]'s lifetime.
   void deletedIn(Arena arena) => arena.onReleaseAll(delete);
@@ -61,7 +81,6 @@ extension JReferenceUseExtension<T extends JReference> on T {
   /// Applies [callback] on [this] object and then delete the underlying JNI
   /// reference, returning the result of [callback].
   R use<R>(R Function(T) callback) {
-    ensureNotDeleted();
     try {
       final result = callback(this);
       delete();

pkgs/jni/lib/src/lang/jboolean.dart

@@ -4,6 +4,7 @@
 
 import '../accessors.dart';
 import '../jobject.dart';
+import '../jreference.dart';
 import '../jni.dart';
 import '../third_party/generated_bindings.dart';
 import '../types.dart';
@@ -56,6 +57,7 @@ class JBoolean extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"booleanValue", r"()Z");
 
   bool booleanValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _booleanValueId, JniCallType.booleanType, []).boolean;
     if (deleteOriginal) {

pkgs/jni/lib/src/lang/jcharacter.dart

@@ -1,6 +1,7 @@
 import '../accessors.dart';
 import '../jni.dart';
 import '../jobject.dart';
+import '../jreference.dart';
 import '../jvalues.dart';
 import '../third_party/generated_bindings.dart';
 import '../types.dart';
@@ -54,6 +55,7 @@ class JCharacter extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"charValue", r"()C");
 
   int charValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _charValueId, JniCallType.charType, []).char;
     if (deleteOriginal) {

pkgs/jni/lib/src/lang/jnumber.dart

@@ -5,6 +5,7 @@
 import '../accessors.dart';
 import '../jni.dart';
 import '../jobject.dart';
+import '../jreference.dart';
 import '../third_party/generated_bindings.dart';
 import '../types.dart';
 import 'jboolean.dart';
@@ -64,6 +65,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"intValue", r"()I");
 
   int intValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _intValueId, JniCallType.intType, []).integer;
     if (deleteOriginal) {
@@ -76,6 +78,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"longValue", r"()J");
 
   int longValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _longValueId, JniCallType.longType, []).long;
     if (deleteOriginal) {
@@ -88,6 +91,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"floatValue", r"()F");
 
   double floatValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _floatValueId, JniCallType.floatType, []).float;
     if (deleteOriginal) {
@@ -100,6 +104,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"doubleValue", r"()D");
 
   double doubleValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _doubleValueId, JniCallType.doubleType, []).doubleFloat;
     if (deleteOriginal) {
@@ -112,6 +117,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"byteValue", r"()B");
 
   int byteValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _byteValueId, JniCallType.byteType, []).byte;
     if (deleteOriginal) {
@@ -124,6 +130,7 @@ class JNumber extends JObject {
       Jni.accessors.getMethodIDOf(_class.reference, r"shortValue", r"()S");
 
   int shortValue({bool deleteOriginal = false}) {
+    ensureNotNull();
     final ret = Jni.accessors.callMethodWithArgs(
         reference, _shortValueId, JniCallType.shortType, []).short;
     if (deleteOriginal) {