cef/libcef_dll/cpptoc/cpptoc_scoped.h

// Copyright (c) 2017 The Chromium Embedded Framework 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 CEF_LIBCEF_DLL_CPPTOC_CPPTOC_SCOPED_H_
#define CEF_LIBCEF_DLL_CPPTOC_CPPTOC_SCOPED_H_
#pragma once

#include <utility>

#include "include/base/cef_logging.h"
#include "include/capi/cef_base_capi.h"
#include "include/cef_base.h"
#include "libcef_dll/wrapper_types.h"

// Wrap a C++ class with a C structure. This is used when the class
// implementation exists on this side of the DLL boundary but will have methods
// called from the other side of the DLL boundary.
template <class ClassName, class BaseName, class StructName>
class CefCppToCScoped : public CefBaseScoped {
 public:
  CefCppToCScoped(const CefCppToCScoped&) = delete;
  CefCppToCScoped& operator=(const CefCppToCScoped&) = delete;

  // Create a new wrapper instance and associated structure reference for
  // passing an object instance the other side. The wrapper object will be
  // deleted when |del| is called on the associated structure. The wrapped
  // object will be deleted when the wrapper object is deleted. For example:
  //
  // void MyMethod(CefOwnPtr<MyType> obj) {
  //   my_method(MyTypeCppToC::WrapOwn(obj));
  // }
  //
  // void my_method(my_type_t* struct) {
  //   // Delete the MyTypeCppToC wrapper and the owned MyType object.
  //   struct->del(struct);
  // }
  static StructName* WrapOwn(CefOwnPtr<BaseName> c) {
    if (!c) {
      return nullptr;
    }

    // Wrap our object with the CefCppToC class.
    ClassName* wrapper = new ClassName();
    wrapper->Initialize(c.release(), true);

    // Return the structure pointer that can now be passed to the other side.
    return wrapper->GetStruct();
  }

  // Create a new wrapper instance and associated structure reference for
  // passing an object instance to the other side. The wrapper object is owned
  // by the caller. The wrapped object is unowned and must outlive the wrapper.
  // For example:
  //
  // void MyMethod(MyType* obj) {
  //   [MyTypeWrapper, MyTypeStruct] = MyTypeCppToC::WrapRaw(obj);
  //   my_method(MyTypeStruct);
  //   // MyTypeWrapper is deleted when MyMethod() goes out of scope.
  // }
  //
  // void my_method(my_type_t* struct) {
  //   // Access |struct| here but you can't delete it.
  // }
  static std::pair<CefOwnPtr<CefBaseScoped>, StructName*> WrapRaw(
      CefRawPtr<BaseName> c) {
    if (!c) {
      return std::make_pair(nullptr, nullptr);
    }

    // Wrap our object with the CefCppToC class.
    ClassName* wrapper = new ClassName();
    wrapper->Initialize(c, false);

    // Return the owned wrapper object.
    CefOwnPtr<ClassName> wrapperPtr(wrapper);
    auto* wrapperStruct = wrapperPtr->GetStruct();
    return std::make_pair(std::move(wrapperPtr), wrapperStruct);
  }

  // Retrieve the underlying object instance for a structure reference passed
  // back from the other side. The caller takes ownership of the object. For
  // example:
  //
  // void my_method(my_type_t* struct) {
  //   CefOwnPtr<MyType> MyTypePtr = MyTypeCppToC::UnwrapOwn(struct);
  //   // |struct| has been deleted and should no longer be accessed.
  // }
  static CefOwnPtr<BaseName> UnwrapOwn(StructName* s) {
    if (!s) {
      return CefOwnPtr<BaseName>();
    }

    // Cast our structure to the wrapper structure type.
    WrapperStruct* wrapperStruct =
        GetWrapperStruct(s, /*require_exact_type=*/false);

    // If the type does not match this object then we need to unwrap as the
    // derived type.
    if (wrapperStruct->type_ != kWrapperType) {
      return UnwrapDerivedOwn(wrapperStruct->type_, s);
    }

    // We should own the underlying object currently.
    CHECK(wrapperStruct->wrapper_->owned_);
    CHECK(wrapperStruct->object_);

    // We're giving up ownership of the underlying object. Clear the pointer so
    // it doesn't get deleted.
    BaseName* object = wrapperStruct->object_;
    wrapperStruct->object_ = nullptr;

    delete wrapperStruct->wrapper_;

    // Return the underlying object instance.
    return CefOwnPtr<BaseName>(object);
  }

  // Retrieve the underlying object instance for a structure reference passed
  // back from the other side. Ownership does not change. For example:
  //
  // void my_method(my_type_t* struct) {
  //   CefRawPtr<MyType> MyTypePtr = MyTypeCppToC::UnwrapRaw(struct);
  //   // |struct| is still valid.
  // }
  static CefRawPtr<BaseName> UnwrapRaw(StructName* s) {
    if (!s) {
      return nullptr;
    }

    // Cast our structure to the wrapper structure type.
    WrapperStruct* wrapperStruct =
        GetWrapperStruct(s, /*require_exact_type=*/false);

    // If the type does not match this object then we need to unwrap as the
    // derived type.
    if (wrapperStruct->type_ != kWrapperType) {
      return UnwrapDerivedRaw(wrapperStruct->type_, s);
    }

    // Return the underlying object instance.
    return wrapperStruct->object_;
  }

  // Retrieve the same side wrapper associated with the structure. Ownership
  // does not change.
  static CefBaseScoped* GetWrapper(StructName* s) {
    DCHECK(s);
    WrapperStruct* wrapperStruct = GetWrapperStruct(s);
    return wrapperStruct->wrapper_;
  }

  // Retrieve the underlying object instance from our own structure reference
  // when the reference is passed as the required first parameter of a C API
  // function call. Ownership of the object does not change.
  static BaseName* Get(StructName* s) {
    DCHECK(s);
    WrapperStruct* wrapperStruct = GetWrapperStruct(s);
    return wrapperStruct->object_;
  }

  // If returning the structure across the DLL boundary you should call
  // AddRef() on this CefCppToC object.  On the other side of the DLL boundary,
  // call UnderlyingRelease() on the wrapping CefCToCpp object.
  StructName* GetStruct() { return &wrapper_struct_.struct_; }

 protected:
  CefCppToCScoped() {
    wrapper_struct_.type_ = kWrapperType;
    wrapper_struct_.wrapper_ = this;
    memset(GetStruct(), 0, sizeof(StructName));
  }

  virtual ~CefCppToCScoped() {
    // Only delete the underlying object if we own it.
    if (owned_ && wrapper_struct_.object_) {
      delete wrapper_struct_.object_;
    }
  }

 private:
  // Used to associate this wrapper object, the underlying object instance and
  // the structure that will be passed to the other side.
  struct WrapperStruct {
    CefWrapperType type_;
    BaseName* object_;
    CefCppToCScoped<ClassName, BaseName, StructName>* wrapper_;
    StructName struct_;
  };

  void Initialize(BaseName* obj, bool owned) {
    wrapper_struct_.object_ = obj;
    owned_ = owned;

    cef_base_scoped_t* base = reinterpret_cast<cef_base_scoped_t*>(GetStruct());
    base->size = sizeof(StructName);
    if (owned) {
      base->del = struct_del;
    }
  }

  static WrapperStruct* GetWrapperStruct(StructName* s,
                                         bool require_exact_type = true) {
    // Offset using the WrapperStruct size instead of individual member sizes
    // to avoid problems due to platform/compiler differences in structure
    // padding.
    auto* wrapperStruct = reinterpret_cast<WrapperStruct*>(
        reinterpret_cast<char*>(s) -
        (sizeof(WrapperStruct) - sizeof(StructName)));

    if (require_exact_type) {
      // Verify that the wrapper offset was calculated correctly.
      CHECK_EQ(kWrapperType, wrapperStruct->type_);
    }

    return wrapperStruct;
  }

  // Unwrap as the derived type.
  static CefOwnPtr<BaseName> UnwrapDerivedOwn(CefWrapperType type,
                                              StructName* s);
  static CefRawPtr<BaseName> UnwrapDerivedRaw(CefWrapperType type,
                                              StructName* s);

  static void CEF_CALLBACK struct_del(cef_base_scoped_t* base) {
    DCHECK(base);
    if (!base) {
      return;
    }

    WrapperStruct* wrapperStruct =
        GetWrapperStruct(reinterpret_cast<StructName*>(base));

    // Should only be deleting wrappers that own the underlying object.
    CHECK(wrapperStruct->wrapper_->owned_);
    delete wrapperStruct->wrapper_;
  }

  WrapperStruct wrapper_struct_;
  bool owned_;

  static CefWrapperType kWrapperType;
};

#endif  // CEF_LIBCEF_DLL_CPPTOC_CPPTOC_SCOPED_H_