third_party/WebKit/Source/bindings/core/v8/CallbackPromiseAdapter.h

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
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 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
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#ifndef CallbackPromiseAdapter_h
#define CallbackPromiseAdapter_h

#include "bindings/core/v8/ScriptPromiseResolver.h"
#include "public/platform/WebCallbacks.h"
#include "wtf/PtrUtil.h"
#include "wtf/TypeTraits.h"
#include <memory>
#include <utility>

namespace blink {

// CallbackPromiseAdapter is a WebCallbacks subclass and resolves / rejects the
// stored resolver when onSuccess / onError is called, respectively.
//
// Basically CallbackPromiseAdapter<S, T> is a subclass of
// WebCallbacks<S::WebType, T::WebType>. There are some exceptions:
//  - If S or T don't have WebType (e.g. S = bool), a default WebType holder
//    called trivial WebType holder is used. For example,
//    CallbackPromiseAdapter<bool, void> is a subclass of
//    WebCallbacks<bool, void>.
//  - If a WebType is std::unique_ptr<T>, its corresponding type parameter on
//    WebCallbacks is std::unique_ptr<T>, because WebCallbacks must be exposed
//    to Chromium.
//
// When onSuccess is called with a S::WebType value, the value is passed to
// S::take and the resolver is resolved with its return value. Ditto for
// onError.
//
// ScriptPromiseResolver::resolve / reject will not be called when the execution
// context is stopped.
//
// Example:
// class MyClass {
// public:
//     using WebType = std::unique_ptr<WebMyClass>;
//     static PassRefPtr<MyClass> take(ScriptPromiseResolver* resolver,
//         std::unique_ptr<WebMyClass> webInstance)
//     {
//         return MyClass::create(webInstance);
//     }
//     ...
// };
// class MyErrorClass {
// public:
//     using WebType = const WebMyErrorClass&;
//     static MyErrorClass take(ScriptPromiseResolver* resolver,
//         const WebErrorClass& webError)
//     {
//         return MyErrorClass(webError);
//     }
//     ...
// };
// std::unique_ptr<WebCallbacks<std::unique_ptr<WebMyClass>,
//                 const WebMyErrorClass&>>
//     callbacks = wrapUnique(new CallbackPromiseAdapter<MyClass, MyErrorClass>(
//     resolver));
// ...
//
// std::unique_ptr<WebCallbacks<bool, const WebMyErrorClass&>> callbacks2 =
//     wrapUnique(new CallbackPromiseAdapter<bool, MyErrorClass>(resolver));
// ...
//
//
// In order to implement the above exceptions, we have template classes below.
// OnSuccess and OnError provide onSuccess and onError implementation, and there
// are utility templates that provide the trivial WebType holder.

namespace internal {

// This template is placed outside of CallbackPromiseAdapterInternal because
// explicit specialization is forbidden in a class scope.
template <typename T>
struct CallbackPromiseAdapterTrivialWebTypeHolder {
  using WebType = T;
  static T take(ScriptPromiseResolver*, const T& x) { return x; }
};
template <>
struct CallbackPromiseAdapterTrivialWebTypeHolder<void> {
  using WebType = void;
};

class CallbackPromiseAdapterInternal {
 private:
  template <typename T>
  static T webTypeHolderMatcher(
      typename std::remove_reference<typename T::WebType>::type*);
  template <typename T>
  static CallbackPromiseAdapterTrivialWebTypeHolder<T> webTypeHolderMatcher(
      ...);
  template <typename T>
  using WebTypeHolder = decltype(webTypeHolderMatcher<T>(nullptr));

  template <typename S, typename T>
  class Base : public WebCallbacks<typename S::WebType, typename T::WebType> {
   public:
    explicit Base(ScriptPromiseResolver* resolver) : m_resolver(resolver) {}
    ScriptPromiseResolver* resolver() { return m_resolver; }

   private:
    Persistent<ScriptPromiseResolver> m_resolver;
  };

  template <typename S, typename T>
  class OnSuccess : public Base<S, T> {
   public:
    explicit OnSuccess(ScriptPromiseResolver* resolver)
        : Base<S, T>(resolver) {}
    void onSuccess(typename S::WebType result) override {
      ScriptPromiseResolver* resolver = this->resolver();
      if (!resolver->getExecutionContext() ||
          resolver->getExecutionContext()->activeDOMObjectsAreStopped())
        return;
      resolver->resolve(S::take(resolver, std::move(result)));
    }
  };
  template <typename T>
  class OnSuccess<CallbackPromiseAdapterTrivialWebTypeHolder<void>, T>
      : public Base<CallbackPromiseAdapterTrivialWebTypeHolder<void>, T> {
   public:
    explicit OnSuccess(ScriptPromiseResolver* resolver)
        : Base<CallbackPromiseAdapterTrivialWebTypeHolder<void>, T>(resolver) {}
    void onSuccess() override {
      ScriptPromiseResolver* resolver = this->resolver();
      if (!resolver->getExecutionContext() ||
          resolver->getExecutionContext()->activeDOMObjectsAreStopped())
        return;
      resolver->resolve();
    }
  };
  template <typename S, typename T>
  class OnError : public OnSuccess<S, T> {
   public:
    explicit OnError(ScriptPromiseResolver* resolver)
        : OnSuccess<S, T>(resolver) {}
    void onError(typename T::WebType e) override {
      ScriptPromiseResolver* resolver = this->resolver();
      if (!resolver->getExecutionContext() ||
          resolver->getExecutionContext()->activeDOMObjectsAreStopped())
        return;
      ScriptState::Scope scope(resolver->getScriptState());
      resolver->reject(T::take(resolver, std::move(e)));
    }
  };
  template <typename S>
  class OnError<S, CallbackPromiseAdapterTrivialWebTypeHolder<void>>
      : public OnSuccess<S, CallbackPromiseAdapterTrivialWebTypeHolder<void>> {
   public:
    explicit OnError(ScriptPromiseResolver* resolver)
        : OnSuccess<S, CallbackPromiseAdapterTrivialWebTypeHolder<void>>(
              resolver) {}
    void onError() override {
      ScriptPromiseResolver* resolver = this->resolver();
      if (!resolver->getExecutionContext() ||
          resolver->getExecutionContext()->activeDOMObjectsAreStopped())
        return;
      resolver->reject();
    }
  };

 public:
  template <typename S, typename T>
  class CallbackPromiseAdapter final
      : public OnError<WebTypeHolder<S>, WebTypeHolder<T>> {
    WTF_MAKE_NONCOPYABLE(CallbackPromiseAdapter);

   public:
    explicit CallbackPromiseAdapter(ScriptPromiseResolver* resolver)
        : OnError<WebTypeHolder<S>, WebTypeHolder<T>>(resolver) {}
  };
};

}  // namespace internal

template <typename S, typename T>
using CallbackPromiseAdapter =
    internal::CallbackPromiseAdapterInternal::CallbackPromiseAdapter<S, T>;

}  // namespace blink

#endif