gin/function_template.h - chromium/src - Git at Google

 // 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.

 #ifndef GIN_FUNCTION_TEMPLATE_H_
 #define GIN_FUNCTION_TEMPLATE_H_

 #include "base/callback.h"
 #include "base/logging.h"
 #include "gin/arguments.h"
 #include "gin/converter.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8.h"

 namespace gin {

 class PerIsolateData;

 enum CreateFunctionTemplateFlags {
   HolderIsFirstArgument = 1 << 0,
 };

 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 {
  public:
   v8::Handle<v8::External> GetHandle(v8::Isolate* isolate);

  protected:
   explicit CallbackHolderBase(v8::Isolate* isolate);
   virtual ~CallbackHolderBase();

  private:
   static void WeakCallback(
       const v8::WeakCallbackData<v8::External, CallbackHolderBase>& data);

   v8::Persistent<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;
  private:
   virtual ~CallbackHolder() {}

   DISALLOW_COPY_AND_ASSIGN(CallbackHolder);
 };

 template<typename T>
 bool GetNextArgument(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(Arguments* args, int create_flags, bool is_first,
                             Arguments* result) {
   *result = *args;
   return true;
 }
 inline bool GetNextArgument(Arguments* args, int create_flags, 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, int create_flags,
                             bool is_first, v8::Isolate** result) {
   *result = 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;

   ArgumentHolder(Arguments* args, int create_flags)
       : ok(GetNextArgument(args, create_flags, index == 0, &value)) {
     if (!ok)
       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(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) {
     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) {
     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...);
   }

   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::Handle<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 = typename IndicesGenerator<sizeof...(ArgTypes)>::type;
     Invoker<Indices, ArgTypes...> invoker(&args, holder->flags);
     if (invoker.IsOK())
       invoker.DispatchToCallback(holder->callback);
   }
 };

 }  // 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.
 template<typename Sig>
 v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
     v8::Isolate* isolate, const base::Callback<Sig> callback,
     int callback_flags = 0) {
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);

   return v8::FunctionTemplate::New(
       isolate,
       &internal::Dispatcher<Sig>::DispatchToCallback,
       ConvertToV8<v8::Handle<v8::External> >(isolate,
                                              holder->GetHandle(isolate)));
 }

 // CreateFunctionHandler installs a CallAsFunction handler on the given
 // object template that forwards to a provided C++ function or base::Callback.
 template<typename Sig>
 void CreateFunctionHandler(v8::Isolate* isolate,
                            v8::Local<v8::ObjectTemplate> tmpl,
                            const base::Callback<Sig> callback,
                            int callback_flags = 0) {
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);
   tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
                                  ConvertToV8<v8::Handle<v8::External> >(
                                      isolate, holder->GetHandle(isolate)));
 }

 }  // namespace gin

 #endif  // GIN_FUNCTION_TEMPLATE_H_
	// 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.

	#ifndef GIN_FUNCTION_TEMPLATE_H_
	#define GIN_FUNCTION_TEMPLATE_H_

	#include "base/callback.h"
	#include "base/logging.h"
	#include "gin/arguments.h"
	#include "gin/converter.h"
	#include "gin/gin_export.h"
	#include "v8/include/v8.h"

	namespace gin {

	class PerIsolateData;

	enum CreateFunctionTemplateFlags {
	HolderIsFirstArgument = 1 << 0,
	};

	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 {
	public:
	v8::Handle<v8::External> GetHandle(v8::Isolate* isolate);

	protected:
	explicit CallbackHolderBase(v8::Isolate* isolate);
	virtual ~CallbackHolderBase();

	private:
	static void WeakCallback(
	const v8::WeakCallbackData<v8::External, CallbackHolderBase>& data);

	v8::Persistent<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;
	private:
	virtual ~CallbackHolder() {}

	DISALLOW_COPY_AND_ASSIGN(CallbackHolder);
	};

	template<typename T>
	bool GetNextArgument(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(Arguments* args, int create_flags, bool is_first,
	Arguments* result) {
	result = args;
	return true;
	}
	inline bool GetNextArgument(Arguments* args, int create_flags, 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, int create_flags,
	bool is_first, v8::Isolate** result) {
	*result = 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;

	ArgumentHolder(Arguments* args, int create_flags)
	: ok(GetNextArgument(args, create_flags, index == 0, &value)) {
	if (!ok)
	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(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) {
	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) {
	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...);
	}

	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::Handle<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 = typename IndicesGenerator<sizeof...(ArgTypes)>::type;
	Invoker<Indices, ArgTypes...> invoker(&args, holder->flags);
	if (invoker.IsOK())
	invoker.DispatchToCallback(holder->callback);
	}
	};

	} // 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.
	template<typename Sig>
	v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
	v8::Isolate* isolate, const base::Callback<Sig> callback,
	int callback_flags = 0) {
	typedef internal::CallbackHolder<Sig> HolderT;
	HolderT* holder = new HolderT(isolate, callback, callback_flags);

	return v8::FunctionTemplate::New(
	isolate,
	&internal::Dispatcher<Sig>::DispatchToCallback,
	ConvertToV8<v8::Handle<v8::External> >(isolate,
	holder->GetHandle(isolate)));
	}

	// CreateFunctionHandler installs a CallAsFunction handler on the given
	// object template that forwards to a provided C++ function or base::Callback.
	template<typename Sig>
	void CreateFunctionHandler(v8::Isolate* isolate,
	v8::Local<v8::ObjectTemplate> tmpl,
	const base::Callback<Sig> callback,
	int callback_flags = 0) {
	typedef internal::CallbackHolder<Sig> HolderT;
	HolderT* holder = new HolderT(isolate, callback, callback_flags);
	tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
	ConvertToV8<v8::Handle<v8::External> >(
	isolate, holder->GetHandle(isolate)));
	}

	} // namespace gin

	#endif // GIN_FUNCTION_TEMPLATE_H_