android/jni/Refs.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_jni_Refs_h__
#define mozilla_jni_Refs_h__

#include <jni.h>

#include <utility>

#include "mozilla/fallible.h"
#include "mozilla/jni/Utils.h"
#include "mozilla/jni/TypeAdapter.h"
#include "nsError.h"  // for nsresult
#include "nsString.h"
#include "nsTArray.h"

namespace mozilla {
namespace jni {

// Wrapped object reference (e.g. jobject, jclass, etc...)
template <class Cls, typename JNIType>
class Ref;
// Represents a calling context for JNI methods.
template <class Cls, typename JNIType>
class Context;
// Wrapped local reference that inherits from Ref.
template <class Cls>
class LocalRef;
// Wrapped global reference that inherits from Ref.
template <class Cls>
class GlobalRef;
// Wrapped weak reference that inherits from Ref.
template <class Cls>
class WeakRef;
// Wrapped dangling reference that's owned by someone else.
template <class Cls>
class DependentRef;

// Class to hold the native types of a method's arguments.
// For example, if a method has signature (ILjava/lang/String;)V,
// its arguments class would be jni::Args<int32_t, jni::String::Param>
template <typename...>
struct Args {};

class Object;

// Base class for Ref and its specializations.
template <class Cls, typename Type>
class Ref {
  template <class C, typename T>
  friend class Ref;

  using Self = Ref<Cls, Type>;
  using bool_type = void (Self::*)() const;
  void non_null_reference() const {}

  // A Cls-derivative that allows copying
  // (e.g. when acting as a return value).
  struct CopyableCtx : public Context<Cls, Type> {
    CopyableCtx(JNIEnv* env, Type instance)
        : Context<Cls, Type>(env, instance) {}

    CopyableCtx(const CopyableCtx& cls)
        : Context<Cls, Type>(cls.Env(), cls.Get()) {}
  };

  // Private copy constructor so that there's no danger of assigning a
  // temporary LocalRef/GlobalRef to a Ref, and potentially use the Ref
  // after the source had been freed.
  Ref(const Ref&) = default;

 protected:
  static JNIEnv* FindEnv() {
    return Cls::callingThread == CallingThread::GECKO ? GetGeckoThreadEnv()
                                                      : GetEnvForThread();
  }

  Type mInstance;

  // Protected jobject constructor because outside code should be using
  // Ref::From. Using Ref::From makes it very easy to see which code is using
  // raw JNI types for future refactoring.
  explicit Ref(Type instance) : mInstance(instance) {}

 public:
  using JNIType = Type;

  class AutoLock {
    friend class Ref<Cls, Type>;

    JNIEnv* const mEnv;
    Type mInstance;

    explicit AutoLock(Type aInstance)
        : mEnv(FindEnv()), mInstance(mEnv->NewLocalRef(aInstance)) {
      mEnv->MonitorEnter(mInstance);
      MOZ_CATCH_JNI_EXCEPTION(mEnv);
    }

   public:
    AutoLock(AutoLock&& aOther)
        : mEnv(aOther.mEnv), mInstance(aOther.mInstance) {
      aOther.mInstance = nullptr;
    }

    ~AutoLock() { Unlock(); }

    void Unlock() {
      if (mInstance) {
        mEnv->MonitorExit(mInstance);
        mEnv->DeleteLocalRef(mInstance);
        MOZ_CATCH_JNI_EXCEPTION(mEnv);
        mInstance = nullptr;
      }
    }
  };

  // Construct a Ref form a raw JNI reference.
  static Ref<Cls, Type> From(JNIType obj) { return Ref<Cls, Type>(obj); }

  // Construct a Ref form a generic object reference.
  static Ref<Cls, Type> From(const Ref<Object, jobject>& obj) {
    return Ref<Cls, Type>(JNIType(obj.Get()));
  }

  MOZ_IMPLICIT Ref(decltype(nullptr)) : mInstance(nullptr) {}

  // Get the raw JNI reference.
  JNIType Get() const { return mInstance; }

  template <class T>
  bool IsInstanceOf() const {
    return FindEnv()->IsInstanceOf(mInstance, typename T::Context().ClassRef());
  }

  template <class T>
  typename T::Ref Cast() const {
#ifdef MOZ_CHECK_JNI
    MOZ_RELEASE_ASSERT(FindEnv()->IsAssignableFrom(
        Context<Cls, Type>().ClassRef(), typename T::Context().ClassRef()));
#endif
    return T::Ref::From(*this);
  }

  AutoLock Lock() const { return AutoLock(mInstance); }

  bool operator==(const Ref& other) const {
    // Treat two references of the same object as being the same.
    return mInstance == other.mInstance ||
           JNI_FALSE != FindEnv()->IsSameObject(mInstance, other.mInstance);
  }

  bool operator!=(const Ref& other) const { return !operator==(other); }

  bool operator==(decltype(nullptr)) const { return !mInstance; }

  bool operator!=(decltype(nullptr)) const { return !!mInstance; }

  CopyableCtx operator->() const { return CopyableCtx(FindEnv(), mInstance); }

  CopyableCtx operator*() const { return operator->(); }

  // Any ref can be cast to an object ref.
  operator Ref<Object, jobject>() const {
    return Ref<Object, jobject>(mInstance);
  }

  // Null checking (e.g. !!ref) using the safe-bool idiom.
  operator bool_type() const {
    return mInstance ? &Self::non_null_reference : nullptr;
  }

  // We don't allow implicit conversion to jobject because that can lead
  // to easy mistakes such as assigning a temporary LocalRef to a jobject,
  // and using the jobject after the LocalRef has been freed.

  // We don't allow explicit conversion, to make outside code use Ref::Get.
  // Using Ref::Get makes it very easy to see which code is using raw JNI
  // types to make future refactoring easier.

  // operator JNIType() const = delete;
};

// Represents a calling context for JNI methods.
template <class Cls, typename Type>
class Context : public Ref<Cls, Type> {
  using Ref = jni::Ref<Cls, Type>;

  static jclass sClassRef;  // global reference

 protected:
  JNIEnv* const mEnv;

 public:
  Context() : Ref(nullptr), mEnv(Ref::FindEnv()) {}

  Context(JNIEnv* env, Type instance) : Ref(instance), mEnv(env) {}

  jclass ClassRef() const {
    if (!sClassRef) {
      const jclass cls = GetClassRef(mEnv, Cls::name);
      sClassRef = jclass(mEnv->NewGlobalRef(cls));
      mEnv->DeleteLocalRef(cls);
    }
    return sClassRef;
  }

  JNIEnv* Env() const { return mEnv; }

  template <class T>
  bool IsInstanceOf() const {
    return mEnv->IsInstanceOf(Ref::mInstance,
                              typename T::Context(mEnv, nullptr).ClassRef());
  }

  bool operator==(const Ref& other) const {
    // Treat two references of the same object as being the same.
    return Ref::mInstance == other.Get() ||
           JNI_FALSE != mEnv->IsSameObject(Ref::mInstance, other.Get());
  }

  bool operator!=(const Ref& other) const { return !operator==(other); }

  bool operator==(decltype(nullptr)) const { return !Ref::mInstance; }

  bool operator!=(decltype(nullptr)) const { return !!Ref::mInstance; }

  Cls operator->() const {
    MOZ_ASSERT(Ref::mInstance, "Null jobject");
    return Cls(*this);
  }

  const Context<Cls, Type>& operator*() const { return *this; }
};

template <class C, typename T>
jclass Context<C, T>::sClassRef;

template <class Cls, typename Type = jobject>
class ObjectBase {
 protected:
  const jni::Context<Cls, Type>& mCtx;

  jclass ClassRef() const { return mCtx.ClassRef(); }
  JNIEnv* Env() const { return mCtx.Env(); }
  Type Instance() const { return mCtx.Get(); }

 public:
  using Ref = jni::Ref<Cls, Type>;
  using Context = jni::Context<Cls, Type>;
  using LocalRef = jni::LocalRef<Cls>;
  using GlobalRef = jni::GlobalRef<Cls>;
  using WeakRef = jni::WeakRef<Cls>;
  using Param = const Ref&;

  static const CallingThread callingThread = CallingThread::ANY;
  static const char name[];

  explicit ObjectBase(const Context& ctx) : mCtx(ctx) {}

  Cls* operator->() { return static_cast<Cls*>(this); }
};

// Binding for a plain jobject.
class Object : public ObjectBase<Object, jobject> {
 public:
  explicit Object(const Context& ctx) : ObjectBase<Object, jobject>(ctx) {}
};

// Binding for a built-in object reference other than jobject.
template <typename T>
class TypedObject : public ObjectBase<TypedObject<T>, T> {
 public:
  explicit TypedObject(const Context<TypedObject<T>, T>& ctx)
      : ObjectBase<TypedObject<T>, T>(ctx) {}
};

// Binding for a boxed primitive object.
template <typename T>
class BoxedObject : public ObjectBase<BoxedObject<T>, jobject> {
 public:
  explicit BoxedObject(const Context<BoxedObject<T>, jobject>& ctx)
      : ObjectBase<BoxedObject<T>, jobject>(ctx) {}
};

template <>
const char ObjectBase<Object, jobject>::name[];
template <>
const char ObjectBase<TypedObject<jstring>, jstring>::name[];
template <>
const char ObjectBase<TypedObject<jclass>, jclass>::name[];
template <>
const char ObjectBase<TypedObject<jthrowable>, jthrowable>::name[];
template <>
const char ObjectBase<BoxedObject<jboolean>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jbyte>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jchar>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jshort>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jint>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jlong>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jfloat>, jobject>::name[];
template <>
const char ObjectBase<BoxedObject<jdouble>, jobject>::name[];
template <>
const char ObjectBase<TypedObject<jbooleanArray>, jbooleanArray>::name[];
template <>
const char ObjectBase<TypedObject<jbyteArray>, jbyteArray>::name[];
template <>
const char ObjectBase<TypedObject<jcharArray>, jcharArray>::name[];
template <>
const char ObjectBase<TypedObject<jshortArray>, jshortArray>::name[];
template <>
const char ObjectBase<TypedObject<jintArray>, jintArray>::name[];
template <>
const char ObjectBase<TypedObject<jlongArray>, jlongArray>::name[];
template <>
const char ObjectBase<TypedObject<jfloatArray>, jfloatArray>::name[];
template <>
const char ObjectBase<TypedObject<jdoubleArray>, jdoubleArray>::name[];
template <>
const char ObjectBase<TypedObject<jobjectArray>, jobjectArray>::name[];

// Define bindings for built-in types.
using String = TypedObject<jstring>;
using Class = TypedObject<jclass>;
using Throwable = TypedObject<jthrowable>;

using Boolean = BoxedObject<jboolean>;
using Byte = BoxedObject<jbyte>;
using Character = BoxedObject<jchar>;
using Short = BoxedObject<jshort>;
using Integer = BoxedObject<jint>;
using Long = BoxedObject<jlong>;
using Float = BoxedObject<jfloat>;
using Double = BoxedObject<jdouble>;

using BooleanArray = TypedObject<jbooleanArray>;
using ByteArray = TypedObject<jbyteArray>;
using CharArray = TypedObject<jcharArray>;
using ShortArray = TypedObject<jshortArray>;
using IntArray = TypedObject<jintArray>;
using LongArray = TypedObject<jlongArray>;
using FloatArray = TypedObject<jfloatArray>;
using DoubleArray = TypedObject<jdoubleArray>;
using ObjectArray = TypedObject<jobjectArray>;

namespace detail {

// See explanation in LocalRef.
template <class Cls>
struct GenericObject {
  using Type = Object;
};
template <>
struct GenericObject<Object> {
  struct Type {
    using Ref = jni::Ref<Type, jobject>;
    using Context = jni::Context<Type, jobject>;
  };
};
template <class Cls>
struct GenericLocalRef {
  template <class C>
  struct Type : jni::Object {};
};
template <>
struct GenericLocalRef<Object> {
  template <class C>
  using Type = jni::LocalRef<C>;
};

}  // namespace detail

template <class Cls>
class LocalRef : public Cls::Context {
  template <class C>
  friend class LocalRef;

  using Ctx = typename Cls::Context;
  using Ref = typename Cls::Ref;
  using JNIType = typename Ref::JNIType;

  // In order to be able to convert LocalRef<Object> to LocalRef<Cls>, we
  // need constructors and copy assignment operators that take in a
  // LocalRef<Object> argument. However, if Cls *is* Object, we would have
  // duplicated constructors and operators with LocalRef<Object> arguments. To
  // avoid this conflict, we use GenericObject, which is defined as Object for
  // LocalRef<non-Object> and defined as a dummy class for LocalRef<Object>.
  using GenericObject = typename detail::GenericObject<Cls>::Type;

  // Similarly, GenericLocalRef is useed to convert LocalRef<Cls> to,
  // LocalRef<Object>. It's defined as LocalRef<C> for Cls == Object,
  // and defined as a dummy template class for Cls != Object.
  template <class C>
  using GenericLocalRef =
      typename detail::GenericLocalRef<Cls>::template Type<C>;

  static JNIType NewLocalRef(JNIEnv* env, JNIType obj) {
    return JNIType(obj ? env->NewLocalRef(obj) : nullptr);
  }

  LocalRef(JNIEnv* env, JNIType instance) : Ctx(env, instance) {}

  LocalRef& swap(LocalRef& other) {
    auto instance = other.mInstance;
    other.mInstance = Ctx::mInstance;
    Ctx::mInstance = instance;
    return *this;
  }

 public:
  // Construct a LocalRef from a raw JNI local reference. Unlike Ref::From,
  // LocalRef::Adopt returns a LocalRef that will delete the local reference
  // when going out of scope.
  static LocalRef Adopt(JNIType instance) {
    return LocalRef(Ref::FindEnv(), instance);
  }

  static LocalRef Adopt(JNIEnv* env, JNIType instance) {
    return LocalRef(env, instance);
  }

  // Copy constructor.
  LocalRef(const LocalRef<Cls>& ref)
      : Ctx(ref.mEnv, NewLocalRef(ref.mEnv, ref.mInstance)) {}

  // Move constructor.
  LocalRef(LocalRef<Cls>&& ref) : Ctx(ref.mEnv, ref.mInstance) {
    ref.mInstance = nullptr;
  }

  explicit LocalRef(JNIEnv* env = Ref::FindEnv()) : Ctx(env, nullptr) {}

  // Construct a LocalRef from any Ref,
  // which means creating a new local reference.
  MOZ_IMPLICIT LocalRef(const Ref& ref) : Ctx(Ref::FindEnv(), nullptr) {
    Ctx::mInstance = NewLocalRef(Ctx::mEnv, ref.Get());
  }

  LocalRef(JNIEnv* env, const Ref& ref)
      : Ctx(env, NewLocalRef(env, ref.Get())) {}

  // Move a LocalRef<Object> into a LocalRef<Cls> without
  // creating/deleting local references.
  MOZ_IMPLICIT LocalRef(LocalRef<GenericObject>&& ref)
      : Ctx(ref.mEnv, JNIType(ref.mInstance)) {
    ref.mInstance = nullptr;
  }

  template <class C>
  MOZ_IMPLICIT LocalRef(GenericLocalRef<C>&& ref)
      : Ctx(ref.mEnv, ref.mInstance) {
    ref.mInstance = nullptr;
  }

  // Implicitly converts nullptr to LocalRef.
  MOZ_IMPLICIT LocalRef(decltype(nullptr)) : Ctx(Ref::FindEnv(), nullptr) {}

  ~LocalRef() {
    if (Ctx::mInstance) {
      Ctx::mEnv->DeleteLocalRef(Ctx::mInstance);
      Ctx::mInstance = nullptr;
    }
  }

  // Get the raw JNI reference that can be used as a return value.
  // Returns the same JNI type (jobject, jstring, etc.) as the underlying Ref.
  typename Ref::JNIType Forget() {
    const auto obj = Ctx::Get();
    Ctx::mInstance = nullptr;
    return obj;
  }

  LocalRef<Cls>& operator=(LocalRef<Cls> ref) & { return swap(ref); }

  LocalRef<Cls>& operator=(const Ref& ref) & {
    LocalRef<Cls> newRef(Ctx::mEnv, ref);
    return swap(newRef);
  }

  LocalRef<Cls>& operator=(LocalRef<GenericObject>&& ref) & {
    LocalRef<Cls> newRef(std::move(ref));
    return swap(newRef);
  }

  template <class C>
  LocalRef<Cls>& operator=(GenericLocalRef<C>&& ref) & {
    LocalRef<Cls> newRef(std::move(ref));
    return swap(newRef);
  }

  LocalRef<Cls>& operator=(decltype(nullptr)) & {
    LocalRef<Cls> newRef(Ctx::mEnv, nullptr);
    return swap(newRef);
  }
};

template <class Cls>
class GlobalRef : public Cls::Ref {
  using Ref = typename Cls::Ref;
  using JNIType = typename Ref::JNIType;

  static JNIType NewGlobalRef(JNIEnv* env, JNIType instance) {
    return JNIType(instance ? env->NewGlobalRef(instance) : nullptr);
  }

  GlobalRef& swap(GlobalRef& other) {
    auto instance = other.mInstance;
    other.mInstance = Ref::mInstance;
    Ref::mInstance = instance;
    return *this;
  }

 public:
  GlobalRef() : Ref(nullptr) {}

  // Copy constructor
  GlobalRef(const GlobalRef& ref)
      : Ref(NewGlobalRef(GetEnvForThread(), ref.mInstance)) {}

  // Move constructor
  GlobalRef(GlobalRef&& ref) : Ref(ref.mInstance) { ref.mInstance = nullptr; }

  MOZ_IMPLICIT GlobalRef(const Ref& ref)
      : Ref(NewGlobalRef(GetEnvForThread(), ref.Get())) {}

  GlobalRef(JNIEnv* env, const Ref& ref) : Ref(NewGlobalRef(env, ref.Get())) {}

  MOZ_IMPLICIT GlobalRef(const LocalRef<Cls>& ref)
      : Ref(NewGlobalRef(ref.Env(), ref.Get())) {}

  // Implicitly converts nullptr to GlobalRef.
  MOZ_IMPLICIT GlobalRef(decltype(nullptr)) : Ref(nullptr) {}

  ~GlobalRef() {
    if (Ref::mInstance) {
      Clear(GetEnvForThread());
    }
  }

  // Get the raw JNI reference that can be used as a return value.
  // Returns the same JNI type (jobject, jstring, etc.) as the underlying Ref.
  typename Ref::JNIType Forget() {
    const auto obj = Ref::Get();
    Ref::mInstance = nullptr;
    return obj;
  }

  void Clear(JNIEnv* env) {
    if (Ref::mInstance) {
      env->DeleteGlobalRef(Ref::mInstance);
      Ref::mInstance = nullptr;
    }
  }

  GlobalRef<Cls>& operator=(GlobalRef<Cls> ref) & { return swap(ref); }

  GlobalRef<Cls>& operator=(const Ref& ref) & {
    GlobalRef<Cls> newRef(ref);
    return swap(newRef);
  }

  GlobalRef<Cls>& operator=(const LocalRef<Cls>& ref) & {
    GlobalRef<Cls> newRef(ref);
    return swap(newRef);
  }

  GlobalRef<Cls>& operator=(decltype(nullptr)) & {
    GlobalRef<Cls> newRef(nullptr);
    return swap(newRef);
  }
};

template <class Cls>
class WeakRef : public Ref<Cls, jweak> {
  using Ref = Ref<Cls, jweak>;
  using JNIType = typename Ref::JNIType;

  static JNIType NewWeakRef(JNIEnv* env, JNIType instance) {
    return JNIType(instance ? env->NewWeakGlobalRef(instance) : nullptr);
  }

  WeakRef& swap(WeakRef& other) {
    auto instance = other.mInstance;
    other.mInstance = Ref::mInstance;
    Ref::mInstance = instance;
    return *this;
  }

 public:
  WeakRef() : Ref(nullptr) {}

  // Copy constructor
  WeakRef(const WeakRef& ref)
      : Ref(NewWeakRef(GetEnvForThread(), ref.mInstance)) {}

  // Move constructor
  WeakRef(WeakRef&& ref) : Ref(ref.mInstance) { ref.mInstance = nullptr; }

  MOZ_IMPLICIT WeakRef(const Ref& ref)
      : Ref(NewWeakRef(GetEnvForThread(), ref.Get())) {}

  WeakRef(JNIEnv* env, const Ref& ref) : Ref(NewWeakRef(env, ref.Get())) {}

  MOZ_IMPLICIT WeakRef(const LocalRef<Cls>& ref)
      : Ref(NewWeakRef(ref.Env(), ref.Get())) {}

  // Implicitly converts nullptr to WeakRef.
  MOZ_IMPLICIT WeakRef(decltype(nullptr)) : Ref(nullptr) {}

  ~WeakRef() {
    if (Ref::mInstance) {
      Clear(GetEnvForThread());
    }
  }

  // Get the raw JNI reference that can be used as a return value.
  // Returns the same JNI type (jobject, jstring, etc.) as the underlying Ref.
  typename Ref::JNIType Forget() {
    const auto obj = Ref::Get();
    Ref::mInstance = nullptr;
    return obj;
  }

  void Clear(JNIEnv* env) {
    if (Ref::mInstance) {
      env->DeleteWeakGlobalRef(Ref::mInstance);
      Ref::mInstance = nullptr;
    }
  }

  WeakRef<Cls>& operator=(WeakRef<Cls> ref) & { return swap(ref); }

  WeakRef<Cls>& operator=(const Ref& ref) & {
    WeakRef<Cls> newRef(ref);
    return swap(newRef);
  }

  WeakRef<Cls>& operator=(const LocalRef<Cls>& ref) & {
    WeakRef<Cls> newRef(ref);
    return swap(newRef);
  }

  WeakRef<Cls>& operator=(decltype(nullptr)) & {
    WeakRef<Cls> newRef(nullptr);
    return swap(newRef);
  }

  void operator->() const = delete;
  void operator*() const = delete;
};

template <class Cls>
class DependentRef : public Cls::Ref {
  using Ref = typename Cls::Ref;

 public:
  explicit DependentRef(typename Ref::JNIType instance) : Ref(instance) {}

  DependentRef(const DependentRef& ref) : Ref(ref.Get()) {}
};

class StringParam;

template <>
class TypedObject<jstring> : public ObjectBase<TypedObject<jstring>, jstring> {
  using Base = ObjectBase<TypedObject<jstring>, jstring>;

 public:
  using Param = const StringParam&;

  explicit TypedObject(const Context& ctx) : Base(ctx) {}

  size_t Length() const {
    const size_t ret = Base::Env()->GetStringLength(Base::Instance());
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    return ret;
  }

  nsString ToString() const {
    const jchar* const str =
        Base::Env()->GetStringChars(Base::Instance(), nullptr);
    const jsize len = Base::Env()->GetStringLength(Base::Instance());

    nsString result(reinterpret_cast<const char16_t*>(str), len);
    Base::Env()->ReleaseStringChars(Base::Instance(), str);
    return result;
  }

  nsCString ToCString() const { return NS_ConvertUTF16toUTF8(ToString()); }

  // Convert jstring to a nsString.
  operator nsString() const { return ToString(); }

  // Convert jstring to a nsCString.
  operator nsCString() const { return ToCString(); }
};

// Define a custom parameter type for String,
// which accepts both String::Ref and nsAString/nsACString
class StringParam : public String::Ref {
  using Ref = String::Ref;

 private:
  // Not null if we should delete ref on destruction.
  JNIEnv* const mEnv;

  static jstring GetString(JNIEnv* env, const nsAString& str) {
    const jstring result = env->NewString(
        reinterpret_cast<const jchar*>(str.BeginReading()), str.Length());
    if (!result) {
      NS_ABORT_OOM(str.Length() * sizeof(char16_t));
    }
    MOZ_CATCH_JNI_EXCEPTION(env);
    return result;
  }

  static jstring GetString(JNIEnv* env, const nsAString& str,
                           const fallible_t&) {
    const jstring result = env->NewString(
        reinterpret_cast<const jchar*>(str.BeginReading()), str.Length());
    if (env->ExceptionCheck()) {
#ifdef MOZ_CHECK_JNI
      env->ExceptionDescribe();
#endif
      env->ExceptionClear();
    }
    return result;
  }

  static jstring GetString(JNIEnv* env, const nsACString& str,
                           const fallible_t& aFallible) {
    nsAutoString utf16;
    if (!CopyUTF8toUTF16(str, utf16, aFallible)) {
      return nullptr;
    }
    return GetString(env, utf16, aFallible);
  }

 public:
  MOZ_IMPLICIT StringParam(decltype(nullptr)) : Ref(nullptr), mEnv(nullptr) {}

  MOZ_IMPLICIT StringParam(const Ref& ref) : Ref(ref.Get()), mEnv(nullptr) {}

  MOZ_IMPLICIT StringParam(const nsAString& str, JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, str)), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const nsAString& str, JNIEnv* env,
                           const fallible_t& aFallible)
      : Ref(GetString(env, str, aFallible)), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const nsLiteralString& str,
                           JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, str)), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const char16_t* str, JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, nsDependentString(str))), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const nsACString& str, JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, NS_ConvertUTF8toUTF16(str))), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const nsACString& str, JNIEnv* env,
                           const fallible_t& aFallible)
      : Ref(GetString(env, str, aFallible)), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const nsLiteralCString& str,
                           JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, NS_ConvertUTF8toUTF16(str))), mEnv(env) {}

  MOZ_IMPLICIT StringParam(const char* str, JNIEnv* env = Ref::FindEnv())
      : Ref(GetString(env, NS_ConvertUTF8toUTF16(str))), mEnv(env) {}

  StringParam(StringParam&& other) : Ref(other.Get()), mEnv(other.mEnv) {
    other.mInstance = nullptr;
  }

  ~StringParam() {
    if (mEnv && Get()) {
      mEnv->DeleteLocalRef(Get());
    }
  }

  operator String::LocalRef() const {
    // We can't return our existing ref because the returned
    // LocalRef could be freed first, so we need a new local ref.
    return String::LocalRef(mEnv ? mEnv : Ref::FindEnv(), *this);
  }
};

namespace detail {
template <typename T>
struct TypeAdapter;
}

// Ref specialization for arrays.
template <typename JNIType, class ElementType>
class ArrayRefBase : public ObjectBase<TypedObject<JNIType>, JNIType> {
 protected:
  using Base = ObjectBase<TypedObject<JNIType>, JNIType>;

 public:
  explicit ArrayRefBase(const Context<TypedObject<JNIType>, JNIType>& ctx)
      : Base(ctx) {}

  static typename Base::LocalRef New(const ElementType* data, size_t length) {
    using JNIElemType = typename detail::TypeAdapter<ElementType>::JNIType;
    static_assert(sizeof(ElementType) == sizeof(JNIElemType),
                  "Size of native type must match size of JNI type");
    JNIEnv* const jenv = mozilla::jni::GetEnvForThread();
    auto result = (jenv->*detail::TypeAdapter<ElementType>::NewArray)(length);
    MOZ_CATCH_JNI_EXCEPTION(jenv);
    (jenv->*detail::TypeAdapter<ElementType>::SetArray)(
        result, jsize(0), length, reinterpret_cast<const JNIElemType*>(data));
    MOZ_CATCH_JNI_EXCEPTION(jenv);
    return Base::LocalRef::Adopt(jenv, result);
  }

  size_t Length() const {
    const size_t ret = Base::Env()->GetArrayLength(Base::Instance());
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    return ret;
  }

  ElementType GetElement(size_t index) const {
    using JNIElemType = typename detail::TypeAdapter<ElementType>::JNIType;
    static_assert(sizeof(ElementType) == sizeof(JNIElemType),
                  "Size of native type must match size of JNI type");

    ElementType ret;
    (Base::Env()->*detail::TypeAdapter<ElementType>::GetArray)(
        Base::Instance(), jsize(index), 1,
        reinterpret_cast<JNIElemType*>(&ret));
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    return ret;
  }

  nsTArray<ElementType> GetElements() const {
    using JNIElemType = typename detail::TypeAdapter<ElementType>::JNIType;
    static_assert(sizeof(ElementType) == sizeof(JNIElemType),
                  "Size of native type must match size of JNI type");

    const size_t len = size_t(Base::Env()->GetArrayLength(Base::Instance()));

    nsTArray<ElementType> array(len);
    array.SetLength(len);
    CopyTo(array.Elements(), len);
    return array;
  }

  // returns number of elements copied
  size_t CopyTo(ElementType* buffer, size_t size) const {
    using JNIElemType = typename detail::TypeAdapter<ElementType>::JNIType;
    static_assert(sizeof(ElementType) == sizeof(JNIElemType),
                  "Size of native type must match size of JNI type");

    const size_t len = size_t(Base::Env()->GetArrayLength(Base::Instance()));
    const size_t amountToCopy = (len > size ? size : len);
    (Base::Env()->*detail::TypeAdapter<ElementType>::GetArray)(
        Base::Instance(), 0, jsize(amountToCopy),
        reinterpret_cast<JNIElemType*>(buffer));
    return amountToCopy;
  }

  ElementType operator[](size_t index) const { return GetElement(index); }

  operator nsTArray<ElementType>() const { return GetElements(); }
};

#define DEFINE_PRIMITIVE_ARRAY_REF_HEADER(JNIType, ElementType)                \
  template <>                                                                  \
  class TypedObject<JNIType> : public ArrayRefBase<JNIType, ElementType> {     \
   public:                                                                     \
    explicit TypedObject(const Context& ctx)                                   \
        : ArrayRefBase<JNIType, ElementType>(ctx) {}                           \
    static typename Base::LocalRef From(const nsTArray<ElementType>& aArray) { \
      return New(aArray.Elements(), aArray.Length());                          \
    }

#define DEFINE_PRIMITIVE_ARRAY_REF_FOOTER }

#define DEFINE_PRIMITIVE_ARRAY_REF_FROM_IMPLICIT_CONVERSION(ElementType,     \
                                                            ConvertFromType) \
  static typename Base::LocalRef From(                                       \
      const nsTArray<ConvertFromType>& aArray) {                             \
    return New(reinterpret_cast<const ElementType*>(aArray.Elements()),      \
               aArray.Length());                                             \
  }

#define DEFINE_PRIMITIVE_ARRAY_REF(JNIType, ElementType)  \
  DEFINE_PRIMITIVE_ARRAY_REF_HEADER(JNIType, ElementType) \
  DEFINE_PRIMITIVE_ARRAY_REF_FOOTER

#define DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION(           \
    JNIType, ElementType, ConvertFromType)                             \
  DEFINE_PRIMITIVE_ARRAY_REF_HEADER(JNIType, ElementType)              \
  DEFINE_PRIMITIVE_ARRAY_REF_FROM_IMPLICIT_CONVERSION(ElementType,     \
                                                      ConvertFromType) \
  DEFINE_PRIMITIVE_ARRAY_REF_FOOTER

DEFINE_PRIMITIVE_ARRAY_REF(jbooleanArray, bool);
DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION(jbyteArray, int8_t,
                                                    uint8_t);
DEFINE_PRIMITIVE_ARRAY_REF(jcharArray, char16_t);
DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION(jshortArray, int16_t,
                                                    uint16_t);
DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION(jintArray, int32_t,
                                                    uint32_t);
DEFINE_PRIMITIVE_ARRAY_REF(jfloatArray, float);
DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION(jlongArray, int64_t,
                                                    uint64_t);
DEFINE_PRIMITIVE_ARRAY_REF(jdoubleArray, double);

#undef DEFINE_PRIMITIVE_ARRAY_REF
#undef DEFINE_PRIMITIVE_ARRAY_REF_WITH_IMPLICIT_CONVERSION
#undef DEFINE_PRIMITIVE_ARRAY_HEADER
#undef DEFINE_PRIMITIVE_ARRAY_FROM_IMPLICIT_CONVERSION
#undef DEFINE_PRIMITIVE_ARRAY_FOOTER

class ByteBuffer : public ObjectBase<ByteBuffer, jobject> {
 public:
  explicit ByteBuffer(const Context& ctx)
      : ObjectBase<ByteBuffer, jobject>(ctx) {}

  static LocalRef New(void* data, size_t capacity) {
    JNIEnv* const env = GetEnvForThread();
    const auto ret =
        LocalRef::Adopt(env, env->NewDirectByteBuffer(data, jlong(capacity)));
    MOZ_CATCH_JNI_EXCEPTION(env);
    return ret;
  }

  void* Address() {
    void* const ret = Env()->GetDirectBufferAddress(Instance());
    MOZ_CATCH_JNI_EXCEPTION(Env());
    return ret;
  }

  size_t Capacity() {
    const size_t ret = size_t(Env()->GetDirectBufferCapacity(Instance()));
    MOZ_CATCH_JNI_EXCEPTION(Env());
    return ret;
  }
};

template <>
const char ObjectBase<ByteBuffer, jobject>::name[];

template <>
class TypedObject<jobjectArray>
    : public ObjectBase<TypedObject<jobjectArray>, jobjectArray> {
  using Base = ObjectBase<TypedObject<jobjectArray>, jobjectArray>;

 public:
  template <class Cls = Object>
  static Base::LocalRef New(size_t length,
                            typename Cls::Param initialElement = nullptr) {
    JNIEnv* const env = GetEnvForThread();
    jobjectArray array = env->NewObjectArray(
        jsize(length), typename Cls::Context(env, nullptr).ClassRef(),
        initialElement.Get());
    MOZ_CATCH_JNI_EXCEPTION(env);
    return Base::LocalRef::Adopt(env, array);
  }

  explicit TypedObject(const Context& ctx) : Base(ctx) {}

  size_t Length() const {
    const size_t ret = Base::Env()->GetArrayLength(Base::Instance());
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    return ret;
  }

  Object::LocalRef GetElement(size_t index) const {
    auto ret = Object::LocalRef::Adopt(
        Base::Env(),
        Base::Env()->GetObjectArrayElement(Base::Instance(), jsize(index)));
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    return ret;
  }

  nsTArray<Object::LocalRef> GetElements() const {
    const jsize len = size_t(Base::Env()->GetArrayLength(Base::Instance()));

    nsTArray<Object::LocalRef> array((size_t(len)));
    for (jsize i = 0; i < len; i++) {
      array.AppendElement(Object::LocalRef::Adopt(
          Base::Env(),
          Base::Env()->GetObjectArrayElement(Base::Instance(), i)));
      MOZ_CATCH_JNI_EXCEPTION(Base::Env());
    }
    return array;
  }

  Object::LocalRef operator[](size_t index) const { return GetElement(index); }

  operator nsTArray<Object::LocalRef>() const { return GetElements(); }

  void SetElement(size_t index, Object::Param element) const {
    Base::Env()->SetObjectArrayElement(Base::Instance(), jsize(index),
                                       element.Get());
    MOZ_CATCH_JNI_EXCEPTION(Base::Env());
  }
};

// Support conversion from LocalRef<T>* to LocalRef<Object>*:
//   LocalRef<Foo> foo;
//   Foo::GetFoo(&foo); // error because parameter type is LocalRef<Object>*.
//   Foo::GetFoo(ReturnTo(&foo)); // OK because ReturnTo converts the argument.
template <class Cls>
class ReturnToLocal {
 private:
  LocalRef<Cls>* const localRef;
  LocalRef<Object> objRef;

 public:
  explicit ReturnToLocal(LocalRef<Cls>* ref) : localRef(ref) {}
  operator LocalRef<Object>*() { return &objRef; }

  ~ReturnToLocal() {
    if (objRef) {
      *localRef = std::move(objRef);
    }
  }
};

template <class Cls>
ReturnToLocal<Cls> ReturnTo(LocalRef<Cls>* ref) {
  return ReturnToLocal<Cls>(ref);
}

// Support conversion from GlobalRef<T>* to LocalRef<Object/T>*:
//   GlobalRef<Foo> foo;
//   Foo::GetFoo(&foo); // error because parameter type is LocalRef<Foo>*.
//   Foo::GetFoo(ReturnTo(&foo)); // OK because ReturnTo converts the argument.
template <class Cls>
class ReturnToGlobal {
 private:
  GlobalRef<Cls>* const globalRef;
  LocalRef<Object> objRef;
  LocalRef<Cls> clsRef;

 public:
  explicit ReturnToGlobal(GlobalRef<Cls>* ref) : globalRef(ref) {}
  operator LocalRef<Object>*() { return &objRef; }
  operator LocalRef<Cls>*() { return &clsRef; }

  ~ReturnToGlobal() {
    if (objRef) {
      *globalRef = (clsRef = std::move(objRef));
    } else if (clsRef) {
      *globalRef = clsRef;
    }
  }
};

template <class Cls>
ReturnToGlobal<Cls> ReturnTo(GlobalRef<Cls>* ref) {
  return ReturnToGlobal<Cls>(ref);
}

// Make a LocalRef<T> from any other Ref<T>
template <typename Cls, typename JNIType>
LocalRef<Cls> ToLocalRef(const Ref<Cls, JNIType>& aRef) {
  return LocalRef<Cls>(aRef);
}

}  // namespace jni
}  // namespace mozilla

#endif  // mozilla_jni_Refs_h__