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function_template.h
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function_template.h
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// 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 <utility>
#include "base/bind.h"
#include "base/callback.h"
#include "base/optional.h"
#include "gin/arguments.h"
#include "shell/common/gin_helper/arguments.h"
#include "shell/common/gin_helper/destroyable.h"
#include "shell/common/gin_helper/error_thrower.h"
#include "shell/common/gin_helper/microtasks_scope.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);
}
}
// Support base::Optional as output, which would be empty and do not throw error
// when convertion to T fails.
template <typename T>
bool GetNextArgument(gin::Arguments* args,
int create_flags,
bool is_first,
base::Optional<T>* result) {
T converted;
// Use gin::Arguments::GetNext which always advances |next| counter.
if (args->GetNext(&converted))
result->emplace(std::move(converted));
return true;
}
// 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,
ErrorThrower* result) {
*result = ErrorThrower(args->isolate());
return true;
}
// Supports the gin_helper::Arguments.
inline bool GetNextArgument(gin::Arguments* args,
int create_flags,
bool is_first,
gin_helper::Arguments** result) {
*result = static_cast<gin_helper::Arguments*>(args);
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) {
gin_helper::MicrotasksScope microtasks_scope(args_->isolate());
args_->Return(
callback.Run(std::move(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) {
gin_helper::MicrotasksScope microtasks_scope(args_->isolate());
callback.Run(std::move(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)));
}
// Base template - used only for non-member function pointers. Other types
// either go to one of the below specializations, or go here and fail to compile
// because of base::Bind().
template <typename T, typename Enable = void>
struct CallbackTraits {
static v8::Local<v8::FunctionTemplate> CreateTemplate(v8::Isolate* isolate,
T callback) {
return gin_helper::CreateFunctionTemplate(isolate,
base::BindRepeating(callback));
}
};
// Specialization for base::Callback.
template <typename T>
struct CallbackTraits<base::Callback<T>> {
static v8::Local<v8::FunctionTemplate> CreateTemplate(
v8::Isolate* isolate,
const base::RepeatingCallback<T>& callback) {
return gin_helper::CreateFunctionTemplate(isolate, callback);
}
};
// Specialization for member function pointers. We need to handle this case
// specially because the first parameter for callbacks to MFP should typically
// come from the the JavaScript "this" object the function was called on, not
// from the first normal parameter.
template <typename T>
struct CallbackTraits<
T,
typename std::enable_if<std::is_member_function_pointer<T>::value>::type> {
static v8::Local<v8::FunctionTemplate> CreateTemplate(v8::Isolate* isolate,
T callback) {
int flags = HolderIsFirstArgument;
return gin_helper::CreateFunctionTemplate(
isolate, base::BindRepeating(callback), flags);
}
};
} // namespace gin_helper
#endif // SHELL_COMMON_GIN_HELPER_FUNCTION_TEMPLATE_H_