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// Copyright 2014 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 file.
#include <stddef.h>
#include "base/callback.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/strings/strcat.h"
#include "gin/arguments.h"
#include "gin/converter.h"
#include "gin/gin_export.h"
#include "v8/include/v8.h"
namespace gin {
struct InvokerOptions {
bool holder_is_first_argument = false;
const char* holder_type = nullptr; // Null if unknown or not applicable.
namespace internal {
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 GIN_EXPORT CallbackHolderBase {
v8::Local<v8::External> GetHandle(v8::Isolate* isolate);
explicit CallbackHolderBase(v8::Isolate* isolate);
virtual ~CallbackHolderBase();
static void FirstWeakCallback(
const v8::WeakCallbackInfo<CallbackHolderBase>& data);
static void SecondWeakCallback(
const v8::WeakCallbackInfo<CallbackHolderBase>& data);
v8::Global<v8::External> v8_ref_;
template<typename Sig>
class CallbackHolder : public CallbackHolderBase {
CallbackHolder(v8::Isolate* isolate,
base::RepeatingCallback<Sig> callback,
InvokerOptions invoker_options)
: CallbackHolderBase(isolate),
invoker_options(std::move(invoker_options)) {}
base::RepeatingCallback<Sig> callback;
InvokerOptions invoker_options;
~CallbackHolder() override {}
template <typename T>
bool GetNextArgument(Arguments* args,
const InvokerOptions& invoker_options,
bool is_first,
T* result) {
if (is_first && invoker_options.holder_is_first_argument) {
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(Arguments* args,
const InvokerOptions& invoker_options,
bool is_first,
Arguments* result) {
*result = *args;
return true;
inline bool GetNextArgument(Arguments* args,
const InvokerOptions& invoker_options,
bool is_first,
Arguments** result) {
*result = args;
return true;
// It's common for clients to just need the isolate, so we make that easy.
inline bool GetNextArgument(Arguments* args,
const InvokerOptions& invoker_options,
bool is_first,
v8::Isolate** result) {
*result = args->isolate();
return true;
// Throws an error indicating conversion failure.
GIN_EXPORT void ThrowConversionError(Arguments* args,
const InvokerOptions& invoker_options,
size_t index);
// 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;
ArgumentHolder(Arguments* args, const InvokerOptions& invoker_options)
: ok(GetNextArgument(args, invoker_options, index == 0, &value)) {
if (!ok)
ThrowConversionError(args, invoker_options, index);
// 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<std::index_sequence<indices...>, ArgTypes...>
: public ArgumentHolder<indices, ArgTypes>... {
// 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(Arguments* args, const InvokerOptions& invoker_options)
: ArgumentHolder<indices, ArgTypes>(args, invoker_options)...,
args_(args) {}
bool IsOK() {
return And(ArgumentHolder<indices, ArgTypes>::ok...);
template <typename ReturnType>
void DispatchToCallback(
base::RepeatingCallback<ReturnType(ArgTypes...)> callback) {
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::RepeatingCallback<void(ArgTypes...)> callback) {
callback.Run(ArgumentHolder<indices, ArgTypes>::value...);
static bool And() { return true; }
template <typename... T>
static bool And(bool arg1, T... args) {
return arg1 && And(args...);
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) {
Arguments args(info);
v8::Local<v8::External> v8_holder;
CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
typedef CallbackHolder<ReturnType(ArgTypes...)> HolderT;
HolderT* holder = static_cast<HolderT*>(holder_base);
using Indices = std::index_sequence_for<ArgTypes...>;
Invoker<Indices, ArgTypes...> invoker(&args, holder->invoker_options);
if (invoker.IsOK())
} // namespace internal
// 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. |invoker_options| contains
// additional parameters. If it contains a holder_type, it will be used to
// provide a useful conversion error if the holder is the first argument. If not
// provided, a generic invocation error will be used.
// 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
template <typename Sig>
v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
v8::Isolate* isolate,
base::RepeatingCallback<Sig> callback,
InvokerOptions invoker_options = {}) {
typedef internal::CallbackHolder<Sig> HolderT;
HolderT* holder =
new HolderT(isolate, std::move(callback), std::move(invoker_options));
v8::Local<v8::FunctionTemplate> tmpl = v8::FunctionTemplate::New(
isolate, &internal::Dispatcher<Sig>::DispatchToCallback,
return tmpl;
} // namespace gin