Add m-esr52 at 52.6.0

1 files changed, 707 insertions, 0 deletions

diff --git a/widget/android/jni/Natives.h b/widget/android/jni/Natives.h
new file mode 100644
index 000000000..511d96a87
--- /dev/null
+++ b/widget/android/jni/Natives.h
@@ -0,0 +1,707 @@
+#ifndef mozilla_jni_Natives_h__
+#define mozilla_jni_Natives_h__
+
+#include <jni.h>
+
+#include "mozilla/IndexSequence.h"
+#include "mozilla/Move.h"
+#include "mozilla/Tuple.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/WeakPtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/jni/Accessors.h"
+#include "mozilla/jni/Refs.h"
+#include "mozilla/jni/Types.h"
+#include "mozilla/jni/Utils.h"
+
+namespace mozilla {
+namespace jni {
+
+/**
+ * C++ classes implementing instance (non-static) native methods can choose
+ * from one of two ownership models, when associating a C++ object with a Java
+ * instance.
+ *
+ * * If the C++ class inherits from mozilla::SupportsWeakPtr, weak pointers
+ *   will be used. The Java instance will store and own the pointer to a
+ *   WeakPtr object. The C++ class itself is otherwise not owned or directly
+ *   referenced. To attach a Java instance to a C++ instance, pass in a pointer
+ *   to the C++ class (i.e. MyClass*).
+ *
+ *   class MyClass : public SupportsWeakPtr<MyClass>
+ *                 , public MyJavaClass::Natives<MyClass>
+ *   {
+ *       // ...
+ *
+ *   public:
+ *       MOZ_DECLARE_WEAKREFERENCE_TYPENAME(MyClass)
+ *       using MyJavaClass::Natives<MyClass>::Dispose;
+ *
+ *       void AttachTo(const MyJavaClass::LocalRef& instance)
+ *       {
+ *           MyJavaClass::Natives<MyClass>::AttachInstance(instance, this);
+ *
+ *           // "instance" does NOT own "this", so the C++ object
+ *           // lifetime is separate from the Java object lifetime.
+ *       }
+ *   };
+ *
+ * * If the C++ class doesn't inherit from mozilla::SupportsWeakPtr, the Java
+ *   instance will store and own a pointer to the C++ object itself. This
+ *   pointer must not be stored or deleted elsewhere. To attach a Java instance
+ *   to a C++ instance, pass in a reference to a UniquePtr of the C++ class
+ *   (i.e. UniquePtr<MyClass>).
+ *
+ *   class MyClass : public MyJavaClass::Natives<MyClass>
+ *   {
+ *       // ...
+ *
+ *   public:
+ *       using MyJavaClass::Natives<MyClass>::Dispose;
+ *
+ *       static void AttachTo(const MyJavaClass::LocalRef& instance)
+ *       {
+ *           MyJavaClass::Natives<MyClass>::AttachInstance(
+ *                   instance, mozilla::MakeUnique<MyClass>());
+ *
+ *           // "instance" owns the newly created C++ object, so the C++
+ *           // object is destroyed as soon as instance.dispose() is called.
+ *       }
+ *   };
+ */
+
+namespace detail {
+
+inline uintptr_t CheckNativeHandle(JNIEnv* env, uintptr_t handle)
+{
+    if (!handle) {
+        if (!env->ExceptionCheck()) {
+            ThrowException(env, "java/lang/NullPointerException",
+                           "Null native pointer");
+        }
+        return 0;
+    }
+    return handle;
+}
+
+template<class Impl, bool UseWeakPtr = mozilla::IsBaseOf<
+                         SupportsWeakPtr<Impl>, Impl>::value /* = false */>
+struct NativePtr
+{
+    static Impl* Get(JNIEnv* env, jobject instance)
+    {
+        return reinterpret_cast<Impl*>(CheckNativeHandle(
+                env, GetNativeHandle(env, instance)));
+    }
+
+    template<class LocalRef>
+    static Impl* Get(const LocalRef& instance)
+    {
+        return Get(instance.Env(), instance.Get());
+    }
+
+    template<class LocalRef>
+    static void Set(const LocalRef& instance, UniquePtr<Impl>&& ptr)
+    {
+        Clear(instance);
+        SetNativeHandle(instance.Env(), instance.Get(),
+                          reinterpret_cast<uintptr_t>(ptr.release()));
+        MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+    }
+
+    template<class LocalRef>
+    static void Clear(const LocalRef& instance)
+    {
+        UniquePtr<Impl> ptr(reinterpret_cast<Impl*>(
+                GetNativeHandle(instance.Env(), instance.Get())));
+        MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+        if (ptr) {
+            SetNativeHandle(instance.Env(), instance.Get(), 0);
+            MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+        }
+    }
+};
+
+template<class Impl>
+struct NativePtr<Impl, /* UseWeakPtr = */ true>
+{
+    static Impl* Get(JNIEnv* env, jobject instance)
+    {
+        const auto ptr = reinterpret_cast<WeakPtr<Impl>*>(
+                CheckNativeHandle(env, GetNativeHandle(env, instance)));
+        if (!ptr) {
+            return nullptr;
+        }
+
+        Impl* const impl = *ptr;
+        if (!impl) {
+            ThrowException(env, "java/lang/NullPointerException",
+                           "Native object already released");
+        }
+        return impl;
+    }
+
+    template<class LocalRef>
+    static Impl* Get(const LocalRef& instance)
+    {
+        return Get(instance.Env(), instance.Get());
+    }
+
+    template<class LocalRef>
+    static void Set(const LocalRef& instance, Impl* ptr)
+    {
+        Clear(instance);
+        SetNativeHandle(instance.Env(), instance.Get(),
+                          reinterpret_cast<uintptr_t>(new WeakPtr<Impl>(ptr)));
+        MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+    }
+
+    template<class LocalRef>
+    static void Clear(const LocalRef& instance)
+    {
+        const auto ptr = reinterpret_cast<WeakPtr<Impl>*>(
+                GetNativeHandle(instance.Env(), instance.Get()));
+        MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+        if (ptr) {
+            SetNativeHandle(instance.Env(), instance.Get(), 0);
+            MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+            delete ptr;
+        }
+    }
+};
+
+} // namespace detail
+
+using namespace detail;
+
+/**
+ * For JNI native methods that are dispatched to a proxy, i.e. using
+ * @WrapForJNI(dispatchTo = "proxy"), the implementing C++ class must provide a
+ * OnNativeCall member. Subsequently, every native call is automatically
+ * wrapped in a functor object, and the object is passed to OnNativeCall. The
+ * OnNativeCall implementation can choose to invoke the call, save it, dispatch
+ * it to a different thread, etc. Each copy of functor may only be invoked
+ * once.
+ *
+ * class MyClass : public MyJavaClass::Natives<MyClass>
+ * {
+ *     // ...
+ *
+ *     template<class Functor>
+ *     class ProxyRunnable final : public Runnable
+ *     {
+ *         Functor mCall;
+ *     public:
+ *         ProxyRunnable(Functor&& call) : mCall(mozilla::Move(call)) {}
+ *         virtual void run() override { mCall(); }
+ *     };
+ *
+ * public:
+ *     template<class Functor>
+ *     static void OnNativeCall(Functor&& call)
+ *     {
+ *         RunOnAnotherThread(new ProxyRunnable(mozilla::Move(call)));
+ *     }
+ * };
+ */
+
+namespace detail {
+
+// ProxyArg is used to handle JNI ref arguments for proxies. Because a proxied
+// call may happen outside of the original JNI native call, we must save all
+// JNI ref arguments as global refs to avoid the arguments going out of scope.
+template<typename T>
+struct ProxyArg
+{
+    static_assert(mozilla::IsPod<T>::value, "T must be primitive type");
+
+    // Primitive types can be saved by value.
+    typedef T Type;
+    typedef typename TypeAdapter<T>::JNIType JNIType;
+
+    static void Clear(JNIEnv* env, Type&) {}
+
+    static Type From(JNIEnv* env, JNIType val)
+    {
+        return TypeAdapter<T>::ToNative(env, val);
+    }
+};
+
+template<class C, typename T>
+struct ProxyArg<Ref<C, T>>
+{
+    // Ref types need to be saved by global ref.
+    typedef typename C::GlobalRef Type;
+    typedef typename TypeAdapter<Ref<C, T>>::JNIType JNIType;
+
+    static void Clear(JNIEnv* env, Type& ref) { ref.Clear(env); }
+
+    static Type From(JNIEnv* env, JNIType val)
+    {
+        return Type(env, C::Ref::From(val));
+    }
+};
+
+template<typename C> struct ProxyArg<const C&> : ProxyArg<C> {};
+template<> struct ProxyArg<StringParam> : ProxyArg<String::Ref> {};
+template<class C> struct ProxyArg<LocalRef<C>> : ProxyArg<typename C::Ref> {};
+
+// ProxyNativeCall implements the functor object that is passed to OnNativeCall
+template<class Impl, class Owner, bool IsStatic,
+         bool HasThisArg /* has instance/class local ref in the call */,
+         typename... Args>
+class ProxyNativeCall : public AbstractCall
+{
+    // "this arg" refers to the Class::LocalRef (for static methods) or
+    // Owner::LocalRef (for instance methods) that we optionally (as indicated
+    // by HasThisArg) pass into the destination C++ function.
+    typedef typename mozilla::Conditional<IsStatic,
+            Class, Owner>::Type ThisArgClass;
+    typedef typename mozilla::Conditional<IsStatic,
+            jclass, jobject>::Type ThisArgJNIType;
+
+    // Type signature of the destination C++ function, which matches the
+    // Method template parameter in NativeStubImpl::Wrap.
+    typedef typename mozilla::Conditional<IsStatic,
+            typename mozilla::Conditional<HasThisArg,
+                    void (*) (const Class::LocalRef&, Args...),
+                    void (*) (Args...)>::Type,
+            typename mozilla::Conditional<HasThisArg,
+                    void (Impl::*) (const typename Owner::LocalRef&, Args...),
+                    void (Impl::*) (Args...)>::Type>::Type NativeCallType;
+
+    // Destination C++ function.
+    NativeCallType mNativeCall;
+    // Saved this arg.
+    typename ThisArgClass::GlobalRef mThisArg;
+    // Saved arguments.
+    mozilla::Tuple<typename ProxyArg<Args>::Type...> mArgs;
+
+    // We cannot use IsStatic and HasThisArg directly (without going through
+    // extra hoops) because GCC complains about invalid overloads, so we use
+    // another pair of template parameters, Static and ThisArg.
+
+    template<bool Static, bool ThisArg, size_t... Indices>
+    typename mozilla::EnableIf<Static && ThisArg, void>::Type
+    Call(const Class::LocalRef& cls,
+         mozilla::IndexSequence<Indices...>) const
+    {
+        (*mNativeCall)(cls, mozilla::Get<Indices>(mArgs)...);
+    }
+
+    template<bool Static, bool ThisArg, size_t... Indices>
+    typename mozilla::EnableIf<Static && !ThisArg, void>::Type
+    Call(const Class::LocalRef& cls,
+         mozilla::IndexSequence<Indices...>) const
+    {
+        (*mNativeCall)(mozilla::Get<Indices>(mArgs)...);
+    }
+
+    template<bool Static, bool ThisArg, size_t... Indices>
+    typename mozilla::EnableIf<!Static && ThisArg, void>::Type
+    Call(const typename Owner::LocalRef& inst,
+         mozilla::IndexSequence<Indices...>) const
+    {
+        Impl* const impl = NativePtr<Impl>::Get(inst);
+        MOZ_CATCH_JNI_EXCEPTION(inst.Env());
+        (impl->*mNativeCall)(inst, mozilla::Get<Indices>(mArgs)...);
+    }
+
+    template<bool Static, bool ThisArg, size_t... Indices>
+    typename mozilla::EnableIf<!Static && !ThisArg, void>::Type
+    Call(const typename Owner::LocalRef& inst,
+         mozilla::IndexSequence<Indices...>) const
+    {
+        Impl* const impl = NativePtr<Impl>::Get(inst);
+        MOZ_CATCH_JNI_EXCEPTION(inst.Env());
+        (impl->*mNativeCall)(mozilla::Get<Indices>(mArgs)...);
+    }
+
+    template<size_t... Indices>
+    void Clear(JNIEnv* env, mozilla::IndexSequence<Indices...>)
+    {
+        int dummy[] = {
+            (ProxyArg<Args>::Clear(env, Get<Indices>(mArgs)), 0)...
+        };
+        mozilla::Unused << dummy;
+    }
+
+public:
+    // The class that implements the call target.
+    typedef Impl TargetClass;
+    typedef typename ThisArgClass::Param ThisArgType;
+
+    static const bool isStatic = IsStatic;
+
+    ProxyNativeCall(ThisArgJNIType thisArg,
+                    NativeCallType nativeCall,
+                    JNIEnv* env,
+                    typename ProxyArg<Args>::JNIType... args)
+        : mNativeCall(nativeCall)
+        , mThisArg(env, ThisArgClass::Ref::From(thisArg))
+        , mArgs(ProxyArg<Args>::From(env, args)...)
+    {}
+
+    ProxyNativeCall(ProxyNativeCall&&) = default;
+    ProxyNativeCall(const ProxyNativeCall&) = default;
+
+    // Get class ref for static calls or object ref for instance calls.
+    typename ThisArgClass::Param GetThisArg() const { return mThisArg; }
+
+    // Return if target is the given function pointer / pointer-to-member.
+    // Because we can only compare pointers of the same type, we use a
+    // templated overload that is chosen only if given a different type of
+    // pointer than our target pointer type.
+    bool IsTarget(NativeCallType call) const { return call == mNativeCall; }
+    template<typename T> bool IsTarget(T&&) const { return false; }
+
+    // Redirect the call to another function / class member with the same
+    // signature as the original target. Crash if given a wrong signature.
+    void SetTarget(NativeCallType call) { mNativeCall = call; }
+    template<typename T> void SetTarget(T&&) const { MOZ_CRASH(); }
+
+    void operator()() override
+    {
+        JNIEnv* const env = GetEnvForThread();
+        typename ThisArgClass::LocalRef thisArg(env, mThisArg);
+        Call<IsStatic, HasThisArg>(
+                thisArg, typename IndexSequenceFor<Args...>::Type());
+
+        // Clear all saved global refs. We do this after the call is invoked,
+        // and not inside the destructor because we already have a JNIEnv here,
+        // so it's more efficient to clear out the saved args here. The
+        // downside is that the call can only be invoked once.
+        Clear(env, typename IndexSequenceFor<Args...>::Type());
+        mThisArg.Clear(env);
+    }
+};
+
+template<class Impl, bool HasThisArg, typename... Args>
+struct Dispatcher
+{
+    template<class Traits, bool IsStatic = Traits::isStatic,
+             typename... ProxyArgs>
+    static typename EnableIf<
+            Traits::dispatchTarget == DispatchTarget::PROXY, void>::Type
+    Run(ProxyArgs&&... args)
+    {
+        Impl::OnNativeCall(ProxyNativeCall<
+                Impl, typename Traits::Owner, IsStatic,
+                HasThisArg, Args...>(Forward<ProxyArgs>(args)...));
+    }
+
+    template<class Traits, bool IsStatic = Traits::isStatic,
+             typename ThisArg, typename... ProxyArgs>
+    static typename EnableIf<
+            Traits::dispatchTarget == DispatchTarget::GECKO, void>::Type
+    Run(ThisArg thisArg, ProxyArgs&&... args)
+    {
+        // For a static method, do not forward the "this arg" (i.e. the class
+        // local ref) if the implementation does not request it. This saves us
+        // a pair of calls to add/delete global ref.
+        DispatchToGeckoThread(MakeUnique<ProxyNativeCall<
+                Impl, typename Traits::Owner, IsStatic, HasThisArg,
+                Args...>>(HasThisArg || !IsStatic ? thisArg : nullptr,
+                          Forward<ProxyArgs>(args)...));
+    }
+
+    template<class Traits, bool IsStatic = false, typename... ProxyArgs>
+    static typename EnableIf<
+            Traits::dispatchTarget == DispatchTarget::CURRENT, void>::Type
+    Run(ProxyArgs&&... args) {}
+};
+
+} // namespace detail
+
+// Wrapper methods that convert arguments from the JNI types to the native
+// types, e.g. from jobject to jni::Object::Ref. For instance methods, the
+// wrapper methods also convert calls to calls on objects.
+//
+// We need specialization for static/non-static because the two have different
+// signatures (jobject vs jclass and Impl::*Method vs *Method).
+// We need specialization for return type, because void return type requires
+// us to not deal with the return value.
+
+// Bug 1207642 - Work around Dalvik bug by realigning stack on JNI entry
+#ifdef __i386__
+#define MOZ_JNICALL JNICALL __attribute__((force_align_arg_pointer))
+#else
+#define MOZ_JNICALL JNICALL
+#endif
+
+template<class Traits, class Impl, class Args = typename Traits::Args>
+class NativeStub;
+
+template<class Traits, class Impl, typename... Args>
+class NativeStub<Traits, Impl, jni::Args<Args...>>
+{
+    using Owner = typename Traits::Owner;
+    using ReturnType = typename Traits::ReturnType;
+
+    static constexpr bool isStatic = Traits::isStatic;
+    static constexpr bool isVoid = mozilla::IsVoid<ReturnType>::value;
+
+    struct VoidType { using JNIType = void; };
+    using ReturnJNIType = typename Conditional<
+            isVoid, VoidType, TypeAdapter<ReturnType>>::Type::JNIType;
+
+    using ReturnTypeForNonVoidInstance = typename Conditional<
+            !isStatic && !isVoid, ReturnType, VoidType>::Type;
+    using ReturnTypeForVoidInstance = typename Conditional<
+            !isStatic && isVoid, ReturnType, VoidType&>::Type;
+    using ReturnTypeForNonVoidStatic = typename Conditional<
+            isStatic && !isVoid, ReturnType, VoidType>::Type;
+    using ReturnTypeForVoidStatic = typename Conditional<
+            isStatic && isVoid, ReturnType, VoidType&>::Type;
+
+    static_assert(Traits::dispatchTarget == DispatchTarget::CURRENT || isVoid,
+                  "Dispatched calls must have void return type");
+
+public:
+    // Non-void instance method
+    template<ReturnTypeForNonVoidInstance (Impl::*Method) (Args...)>
+    static MOZ_JNICALL ReturnJNIType
+    Wrap(JNIEnv* env, jobject instance,
+         typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        Impl* const impl = NativePtr<Impl>::Get(env, instance);
+        if (!impl) {
+            // There is a pending JNI exception at this point.
+            return ReturnJNIType();
+        }
+        return TypeAdapter<ReturnType>::FromNative(env,
+                (impl->*Method)(TypeAdapter<Args>::ToNative(env, args)...));
+    }
+
+    // Non-void instance method with instance reference
+    template<ReturnTypeForNonVoidInstance (Impl::*Method)
+             (const typename Owner::LocalRef&, Args...)>
+    static MOZ_JNICALL ReturnJNIType
+    Wrap(JNIEnv* env, jobject instance,
+         typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        Impl* const impl = NativePtr<Impl>::Get(env, instance);
+        if (!impl) {
+            // There is a pending JNI exception at this point.
+            return ReturnJNIType();
+        }
+        auto self = Owner::LocalRef::Adopt(env, instance);
+        const auto res = TypeAdapter<ReturnType>::FromNative(env,
+                (impl->*Method)(self, TypeAdapter<Args>::ToNative(env, args)...));
+        self.Forget();
+        return res;
+    }
+
+    // Void instance method
+    template<ReturnTypeForVoidInstance (Impl::*Method) (Args...)>
+    static MOZ_JNICALL void
+    Wrap(JNIEnv* env, jobject instance,
+         typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+            Dispatcher<Impl, /* HasThisArg */ false, Args...>::
+                    template Run<Traits>(instance, Method, env, args...);
+            return;
+        }
+
+        Impl* const impl = NativePtr<Impl>::Get(env, instance);
+        if (!impl) {
+            // There is a pending JNI exception at this point.
+            return;
+        }
+        (impl->*Method)(TypeAdapter<Args>::ToNative(env, args)...);
+    }
+
+    // Void instance method with instance reference
+    template<ReturnTypeForVoidInstance (Impl::*Method)
+             (const typename Owner::LocalRef&, Args...)>
+    static MOZ_JNICALL void
+    Wrap(JNIEnv* env, jobject instance,
+         typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+            Dispatcher<Impl, /* HasThisArg */ true, Args...>::
+                    template Run<Traits>(instance, Method, env, args...);
+            return;
+        }
+
+        Impl* const impl = NativePtr<Impl>::Get(env, instance);
+        if (!impl) {
+            // There is a pending JNI exception at this point.
+            return;
+        }
+        auto self = Owner::LocalRef::Adopt(env, instance);
+        (impl->*Method)(self, TypeAdapter<Args>::ToNative(env, args)...);
+        self.Forget();
+    }
+
+    // Overload for DisposeNative
+    template<ReturnTypeForVoidInstance (*DisposeNative)
+             (const typename Owner::LocalRef&)>
+    static MOZ_JNICALL void
+    Wrap(JNIEnv* env, jobject instance)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+            using LocalRef = typename Owner::LocalRef;
+            Dispatcher<Impl, /* HasThisArg */ false, const LocalRef&>::
+                    template Run<Traits, /* IsStatic */ true>(
+                    /* ThisArg */ nullptr, DisposeNative, env, instance);
+            return;
+        }
+
+        auto self = Owner::LocalRef::Adopt(env, instance);
+        (Impl::DisposeNative)(self);
+        self.Forget();
+    }
+
+    // Non-void static method
+    template<ReturnTypeForNonVoidStatic (*Method) (Args...)>
+    static MOZ_JNICALL ReturnJNIType
+    Wrap(JNIEnv* env, jclass, typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        return TypeAdapter<ReturnType>::FromNative(env,
+                (*Method)(TypeAdapter<Args>::ToNative(env, args)...));
+    }
+
+    // Non-void static method with class reference
+    template<ReturnTypeForNonVoidStatic (*Method)
+             (const Class::LocalRef&, Args...)>
+    static MOZ_JNICALL ReturnJNIType
+    Wrap(JNIEnv* env, jclass cls, typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        auto clazz = Class::LocalRef::Adopt(env, cls);
+        const auto res = TypeAdapter<ReturnType>::FromNative(env,
+                (*Method)(clazz, TypeAdapter<Args>::ToNative(env, args)...));
+        clazz.Forget();
+        return res;
+    }
+
+    // Void static method
+    template<ReturnTypeForVoidStatic (*Method) (Args...)>
+    static MOZ_JNICALL void
+    Wrap(JNIEnv* env, jclass cls, typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+            Dispatcher<Impl, /* HasThisArg */ false, Args...>::
+                    template Run<Traits>(cls, Method, env, args...);
+            return;
+        }
+
+        (*Method)(TypeAdapter<Args>::ToNative(env, args)...);
+    }
+
+    // Void static method with class reference
+    template<ReturnTypeForVoidStatic (*Method)
+             (const Class::LocalRef&, Args...)>
+    static MOZ_JNICALL void
+    Wrap(JNIEnv* env, jclass cls, typename TypeAdapter<Args>::JNIType... args)
+    {
+        MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+        if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+            Dispatcher<Impl, /* HasThisArg */ true, Args...>::
+                    template Run<Traits>(cls, Method, env, args...);
+            return;
+        }
+
+        auto clazz = Class::LocalRef::Adopt(env, cls);
+        (*Method)(clazz, TypeAdapter<Args>::ToNative(env, args)...);
+        clazz.Forget();
+    }
+};
+
+// Generate a JNINativeMethod from a native
+// method's traits class and a wrapped stub.
+template<class Traits, typename Ret, typename... Args>
+constexpr JNINativeMethod MakeNativeMethod(MOZ_JNICALL Ret (*stub)(JNIEnv*, Args...))
+{
+    return {
+        Traits::name,
+        Traits::signature,
+        reinterpret_cast<void*>(stub)
+    };
+}
+
+// Class inherited by implementing class.
+template<class Cls, class Impl>
+class NativeImpl
+{
+    typedef typename Cls::template Natives<Impl> Natives;
+
+    static bool sInited;
+
+public:
+    static void Init() {
+        if (sInited) {
+            return;
+        }
+        const auto& ctx = typename Cls::Context();
+        ctx.Env()->RegisterNatives(
+                ctx.ClassRef(), Natives::methods,
+                sizeof(Natives::methods) / sizeof(Natives::methods[0]));
+        MOZ_CATCH_JNI_EXCEPTION(ctx.Env());
+        sInited = true;
+    }
+
+protected:
+
+    // Associate a C++ instance with a Java instance.
+    static void AttachNative(const typename Cls::LocalRef& instance,
+                             SupportsWeakPtr<Impl>* ptr)
+    {
+        static_assert(mozilla::IsBaseOf<SupportsWeakPtr<Impl>, Impl>::value,
+                      "Attach with UniquePtr&& when not using WeakPtr");
+        return NativePtr<Impl>::Set(instance, static_cast<Impl*>(ptr));
+    }
+
+    static void AttachNative(const typename Cls::LocalRef& instance,
+                             UniquePtr<Impl>&& ptr)
+    {
+        static_assert(!mozilla::IsBaseOf<SupportsWeakPtr<Impl>, Impl>::value,
+                      "Attach with SupportsWeakPtr* when using WeakPtr");
+        return NativePtr<Impl>::Set(instance, mozilla::Move(ptr));
+    }
+
+    // Get the C++ instance associated with a Java instance.
+    // There is always a pending exception if the return value is nullptr.
+    static Impl* GetNative(const typename Cls::LocalRef& instance) {
+        return NativePtr<Impl>::Get(instance);
+    }
+
+    static void DisposeNative(const typename Cls::LocalRef& instance) {
+        NativePtr<Impl>::Clear(instance);
+    }
+
+    NativeImpl() {
+        // Initialize on creation if not already initialized.
+        Init();
+    }
+};
+
+// Define static member.
+template<class C, class I>
+bool NativeImpl<C, I>::sInited;
+
+} // namespace jni
+} // namespace mozilla
+
+#endif // mozilla_jni_Natives_h__