// Copyright 2019 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE.chromium file. #ifndef SHELL_COMMON_GIN_HELPER_FUNCTION_TEMPLATE_H_ #define SHELL_COMMON_GIN_HELPER_FUNCTION_TEMPLATE_H_ #include "base/callback.h" #include "gin/arguments.h" #include "shell/common/error_util.h" #include "shell/common/gin_helper/destroyable.h" // This file is forked from gin/function_template.h with 2 differences: // 1. Support for additional types of arguments. // 2. Support for warning using destroyed objects. // // TODO(zcbenz): We should seek to remove this file after removing native_mate. namespace gin_helper { enum CreateFunctionTemplateFlags { HolderIsFirstArgument = 1 << 0, }; template <typename T> struct CallbackParamTraits { typedef T LocalType; }; template <typename T> struct CallbackParamTraits<const T&> { typedef T LocalType; }; template <typename T> struct CallbackParamTraits<const T*> { typedef T* LocalType; }; // CallbackHolder and CallbackHolderBase are used to pass a base::Callback from // CreateFunctionTemplate through v8 (via v8::FunctionTemplate) to // DispatchToCallback, where it is invoked. // This simple base class is used so that we can share a single object template // among every CallbackHolder instance. class CallbackHolderBase { public: v8::Local<v8::External> GetHandle(v8::Isolate* isolate); protected: explicit CallbackHolderBase(v8::Isolate* isolate); virtual ~CallbackHolderBase(); private: static void FirstWeakCallback( const v8::WeakCallbackInfo<CallbackHolderBase>& data); static void SecondWeakCallback( const v8::WeakCallbackInfo<CallbackHolderBase>& data); v8::Global<v8::External> v8_ref_; DISALLOW_COPY_AND_ASSIGN(CallbackHolderBase); }; template <typename Sig> class CallbackHolder : public CallbackHolderBase { public: CallbackHolder(v8::Isolate* isolate, const base::Callback<Sig>& callback, int flags) : CallbackHolderBase(isolate), callback(callback), flags(flags) {} base::Callback<Sig> callback; int flags = 0; private: virtual ~CallbackHolder() = default; DISALLOW_COPY_AND_ASSIGN(CallbackHolder); }; template <typename T> bool GetNextArgument(gin::Arguments* args, int create_flags, bool is_first, T* result) { if (is_first && (create_flags & HolderIsFirstArgument) != 0) { return args->GetHolder(result); } else { return args->GetNext(result); } } // For advanced use cases, we allow callers to request the unparsed Arguments // object and poke around in it directly. inline bool GetNextArgument(gin::Arguments* args, int create_flags, bool is_first, gin::Arguments** result) { *result = args; return true; } // It's common for clients to just need the isolate, so we make that easy. inline bool GetNextArgument(gin::Arguments* args, int create_flags, bool is_first, v8::Isolate** result) { *result = args->isolate(); return true; } // Allow clients to pass a util::Error to throw errors if they // don't need the full gin::Arguments inline bool GetNextArgument(gin::Arguments* args, int create_flags, bool is_first, electron::util::ErrorThrower* result) { *result = electron::util::ErrorThrower(args->isolate()); return true; } // Classes for generating and storing an argument pack of integer indices // (based on well-known "indices trick", see: http://goo.gl/bKKojn): template <size_t... indices> struct IndicesHolder {}; template <size_t requested_index, size_t... indices> struct IndicesGenerator { using type = typename IndicesGenerator<requested_index - 1, requested_index - 1, indices...>::type; }; template <size_t... indices> struct IndicesGenerator<0, indices...> { using type = IndicesHolder<indices...>; }; // Class template for extracting and storing single argument for callback // at position |index|. template <size_t index, typename ArgType> struct ArgumentHolder { using ArgLocalType = typename CallbackParamTraits<ArgType>::LocalType; ArgLocalType value; bool ok = false; ArgumentHolder(gin::Arguments* args, int create_flags) { v8::Local<v8::Object> holder; if (index == 0 && (create_flags & HolderIsFirstArgument) && args->GetHolder(&holder) && gin_helper::Destroyable::IsDestroyed(holder)) { args->ThrowTypeError("Object has been destroyed"); return; } ok = GetNextArgument(args, create_flags, index == 0, &value); if (!ok) { // Ideally we would include the expected c++ type in the error // message which we can access via typeid(ArgType).name() // however we compile with no-rtti, which disables typeid. args->ThrowError(); } } }; // Class template for converting arguments from JavaScript to C++ and running // the callback with them. template <typename IndicesType, typename... ArgTypes> class Invoker {}; template <size_t... indices, typename... ArgTypes> class Invoker<IndicesHolder<indices...>, ArgTypes...> : public ArgumentHolder<indices, ArgTypes>... { public: // Invoker<> inherits from ArgumentHolder<> for each argument. // C++ has always been strict about the class initialization order, // so it is guaranteed ArgumentHolders will be initialized (and thus, will // extract arguments from Arguments) in the right order. Invoker(gin::Arguments* args, int create_flags) : ArgumentHolder<indices, ArgTypes>(args, create_flags)..., args_(args) { // GCC thinks that create_flags is going unused, even though the // expansion above clearly makes use of it. Per jyasskin@, casting // to void is the commonly accepted way to convince the compiler // that you're actually using a parameter/varible. (void)create_flags; } bool IsOK() { return And(ArgumentHolder<indices, ArgTypes>::ok...); } template <typename ReturnType> void DispatchToCallback(base::Callback<ReturnType(ArgTypes...)> callback) { v8::MicrotasksScope script_scope(args_->isolate(), v8::MicrotasksScope::kRunMicrotasks); args_->Return(callback.Run(ArgumentHolder<indices, ArgTypes>::value...)); } // In C++, you can declare the function foo(void), but you can't pass a void // expression to foo. As a result, we must specialize the case of Callbacks // that have the void return type. void DispatchToCallback(base::Callback<void(ArgTypes...)> callback) { v8::MicrotasksScope script_scope(args_->isolate(), v8::MicrotasksScope::kRunMicrotasks); callback.Run(ArgumentHolder<indices, ArgTypes>::value...); } private: static bool And() { return true; } template <typename... T> static bool And(bool arg1, T... args) { return arg1 && And(args...); } gin::Arguments* args_; }; // DispatchToCallback converts all the JavaScript arguments to C++ types and // invokes the base::Callback. template <typename Sig> struct Dispatcher {}; template <typename ReturnType, typename... ArgTypes> struct Dispatcher<ReturnType(ArgTypes...)> { static void DispatchToCallback( const v8::FunctionCallbackInfo<v8::Value>& info) { gin::Arguments args(info); v8::Local<v8::External> v8_holder; args.GetData(&v8_holder); CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(v8_holder->Value()); typedef CallbackHolder<ReturnType(ArgTypes...)> HolderT; HolderT* holder = static_cast<HolderT*>(holder_base); using Indices = typename IndicesGenerator<sizeof...(ArgTypes)>::type; Invoker<Indices, ArgTypes...> invoker(&args, holder->flags); if (invoker.IsOK()) invoker.DispatchToCallback(holder->callback); } }; // CreateFunctionTemplate creates a v8::FunctionTemplate that will create // JavaScript functions that execute a provided C++ function or base::Callback. // JavaScript arguments are automatically converted via gin::Converter, as is // the return value of the C++ function, if any. // // NOTE: V8 caches FunctionTemplates for a lifetime of a web page for its own // internal reasons, thus it is generally a good idea to cache the template // returned by this function. Otherwise, repeated method invocations from JS // will create substantial memory leaks. See http://crbug.com/463487. template <typename Sig> v8::Local<v8::FunctionTemplate> CreateFunctionTemplate( v8::Isolate* isolate, const base::Callback<Sig> callback, int callback_flags = 0) { typedef CallbackHolder<Sig> HolderT; HolderT* holder = new HolderT(isolate, callback, callback_flags); return v8::FunctionTemplate::New(isolate, &Dispatcher<Sig>::DispatchToCallback, gin::ConvertToV8<v8::Local<v8::External>>( isolate, holder->GetHandle(isolate))); } } // namespace gin_helper #endif // SHELL_COMMON_GIN_HELPER_FUNCTION_TEMPLATE_H_