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// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef GIN_FUNCTION_TEMPLATE_H_
#define GIN_FUNCTION_TEMPLATE_H_
#include <stddef.h>
#include <type_traits>
#include <utility>
#include "base/check.h"
#include "base/functional/callback.h"
#include "base/memory/raw_ptr.h"
#include "base/observer_list.h"
#include "base/strings/strcat.h"
#include "gin/arguments.h"
#include "gin/converter.h"
#include "gin/gin_export.h"
#include "gin/per_isolate_data.h"
#include "v8/include/v8-external.h"
#include "v8/include/v8-forward.h"
#include "v8/include/v8-persistent-handle.h"
#include "v8/include/v8-template.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::RepeatingCallback from CreateFunctionTemplate through v8 (via
// v8::FunctionTemplate) to DispatchToCallback, where it is invoked.
// CallbackHolder will clean up the callback in two different scenarios:
// - If the garbage collector finds that it's garbage and collects it. (But note
// that even _if_ we become garbage, we might never get collected!)
// - If the isolate gets disposed.
//
// TODO(crbug.com/40210365): When gin::Wrappable gets migrated over to using
// cppgc, this class should also be considered for migration.
// This simple base class is used so that we can share a single object template
// among every CallbackHolder instance.
class GIN_EXPORT CallbackHolderBase {
public:
CallbackHolderBase(const CallbackHolderBase&) = delete;
CallbackHolderBase& operator=(const CallbackHolderBase&) = delete;
v8::Local<v8::External> GetHandle(v8::Isolate* isolate);
protected:
explicit CallbackHolderBase(v8::Isolate* isolate);
virtual ~CallbackHolderBase();
private:
class DisposeObserver : gin::PerIsolateData::DisposeObserver {
public:
DisposeObserver(gin::PerIsolateData* per_isolate_data,
CallbackHolderBase* holder);
~DisposeObserver() override;
void OnBeforeDispose(v8::Isolate* isolate) override;
void OnDisposed() override;
private:
const raw_ref<gin::PerIsolateData> per_isolate_data_;
const raw_ref<CallbackHolderBase> holder_;
};
static void FirstWeakCallback(
const v8::WeakCallbackInfo<CallbackHolderBase>& data);
static void SecondWeakCallback(
const v8::WeakCallbackInfo<CallbackHolderBase>& data);
v8::Global<v8::External> v8_ref_;
DisposeObserver dispose_observer_;
};
template<typename Sig>
class CallbackHolder : public CallbackHolderBase {
public:
CallbackHolder(v8::Isolate* isolate,
base::RepeatingCallback<Sig> callback,
InvokerOptions invoker_options)
: CallbackHolderBase(isolate),
callback(std::move(callback)),
invoker_options(std::move(invoker_options)) {}
CallbackHolder(const CallbackHolder&) = delete;
CallbackHolder& operator=(const CallbackHolder&) = delete;
base::RepeatingCallback<Sig> callback;
InvokerOptions invoker_options;
private:
~CallbackHolder() override = default;
};
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, typename = void>
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);
}
};
// This is required for types such as v8::LocalVector<T>, which don't have
// a default constructor. To create an element of such a type, the isolate
// has to be provided.
template <size_t index, typename ArgType>
struct ArgumentHolder<
index,
ArgType,
std::enable_if_t<!std::is_default_constructible_v<
typename CallbackParamTraits<ArgType>::LocalType> &&
std::is_constructible_v<
typename CallbackParamTraits<ArgType>::LocalType,
v8::Isolate*>>> {
using ArgLocalType = typename CallbackParamTraits<ArgType>::LocalType;
ArgLocalType value;
bool ok;
ArgumentHolder(Arguments* args, const InvokerOptions& invoker_options)
: value(args->isolate()),
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>... {
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(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(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::RepeatingCallback<void(ArgTypes...)> callback) {
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...);
}
raw_ptr<Arguments> args_;
};
// DispatchToCallback converts all the JavaScript arguments to C++ types and
// invokes the base::RepeatingCallback.
template <typename Sig>
struct Dispatcher {};
template <typename ReturnType, typename... ArgTypes>
struct Dispatcher<ReturnType(ArgTypes...)> {
static void DispatchToCallbackImpl(Arguments* args) {
v8::Local<v8::External> v8_holder;
CHECK(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 = std::index_sequence_for<ArgTypes...>;
Invoker<Indices, ArgTypes...> invoker(args, holder->invoker_options);
if (invoker.IsOK())
invoker.DispatchToCallback(holder->callback);
}
static void DispatchToCallback(
const v8::FunctionCallbackInfo<v8::Value>& info) {
Arguments args(info);
DispatchToCallbackImpl(&args);
}
static void DispatchToCallbackForProperty(
v8::Local<v8::Name>,
const v8::PropertyCallbackInfo<v8::Value>& info) {
Arguments args(info);
DispatchToCallbackImpl(&args);
}
};
} // namespace internal
// CreateFunctionTemplate creates a v8::FunctionTemplate that will create
// JavaScript functions that execute a provided C++ function or
// base::RepeatingCallback. 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 http://crbug.com/463487.
//
// The callback will be destroyed if either the function template gets garbage
// collected or _after_ the isolate is disposed. Garbage collection can never be
// relied upon. As such, any destructors for objects bound to the callback must
// not depend on the isolate being alive at the point they are called. The order
// in which callbacks are destroyed is not guaranteed.
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,
ConvertToV8<v8::Local<v8::External>>(isolate, holder->GetHandle(isolate)),
v8::Local<v8::Signature>(), 0, v8::ConstructorBehavior::kThrow);
return tmpl;
}
// CreateDataPropertyCallback creates a v8::AccessorNameGetterCallback and
// corresponding data value that will hold and execute the provided
// base::RepeatingCallback, using automatic conversions similar to
// |CreateFunctionTemplate|.
//
// It is expected that these will be passed to v8::Template::SetLazyDataProperty
// or another similar function.
template <typename Sig>
std::pair<v8::AccessorNameGetterCallback, v8::Local<v8::Value>>
CreateDataPropertyCallback(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));
return {&internal::Dispatcher<Sig>::DispatchToCallbackForProperty,
ConvertToV8<v8::Local<v8::External>>(isolate,
holder->GetHandle(isolate))};
}
} // namespace gin
#endif // GIN_FUNCTION_TEMPLATE_H_