headless: Implement client API generation

headless/public/internal/value_conversions.h

+// Copyright 2016 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 HEADLESS_PUBLIC_INTERNAL_VALUE_CONVERSIONS_H_
+#define HEADLESS_PUBLIC_INTERNAL_VALUE_CONVERSIONS_H_
+
+#include <memory>
+
+#include "base/memory/ptr_util.h"
+#include "headless/public/util/error_reporter.h"
+
+namespace headless {
+namespace internal {
+
+// Generic conversion from a type to a base::Value. Implemented in
+// type_conversions.h after all type-specific ToValueImpls have been defined.
+template <typename T>
+std::unique_ptr<base::Value> ToValue(const T& value);
+
+// Generic conversion from a base::Value to a type. Note that this generic
+// variant is never defined. Instead, we declare a specific template
+// specialization for all the used types.
+template <typename T>
+struct FromValue {
+  static std::unique_ptr<T> Parse(const base::Value& value,
+                                  ErrorReporter* errors);
+};
+
+// ToValueImpl is a helper used by the ToValue template for dispatching into
+// type-specific serializers. It uses a dummy |T*| argument as a way to
+// partially specialize vector types.
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(int value, T*) {
+  return base::WrapUnique(new base::FundamentalValue(value));
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(double value, T*) {
+  return base::WrapUnique(new base::FundamentalValue(value));
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(bool value, T*) {
+  return base::WrapUnique(new base::FundamentalValue(value));
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(const std::string& value, T*) {
+  return base::WrapUnique(new base::StringValue(value));
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(const base::Value& value, T*) {
+  return value.CreateDeepCopy();
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(const std::vector<T>& vector,
+                                         const std::vector<T>*) {
+  std::unique_ptr<base::ListValue> result(new base::ListValue());
+  for (const auto& it : vector)
+    result->Append(ToValue(it));
+  return std::move(result);
+}
+
+template <typename T>
+std::unique_ptr<base::Value> ToValueImpl(const std::unique_ptr<T>& value,
+                                         std::unique_ptr<T>*) {
+  return ToValue(value.get());
+}
+
+// FromValue specializations for basic types.
+template <>
+struct FromValue<bool> {
+  static bool Parse(const base::Value& value, ErrorReporter* errors) {
+    bool result = false;
+    if (!value.GetAsBoolean(&result))
+      errors->AddError("boolean value expected");
+    return result;
+  }
+};
+
+template <>
+struct FromValue<int> {
+  static int Parse(const base::Value& value, ErrorReporter* errors) {
+    int result = 0;
+    if (!value.GetAsInteger(&result))
+      errors->AddError("integer value expected");
+    return result;
+  }
+};
+
+template <>
+struct FromValue<double> {
+  static double Parse(const base::Value& value, ErrorReporter* errors) {
+    double result = 0;
+    if (!value.GetAsDouble(&result))
+      errors->AddError("double value expected");
+    return result;
+  }
+};
+
+template <>
+struct FromValue<std::string> {
+  static std::string Parse(const base::Value& value, ErrorReporter* errors) {
+    std::string result;
+    if (!value.GetAsString(&result))
+      errors->AddError("string value expected");
+    return result;
+  }
+};
+
+template <>
+struct FromValue<base::DictionaryValue> {
+  static std::unique_ptr<base::DictionaryValue> Parse(const base::Value& value,
+                                                      ErrorReporter* errors) {
+    const base::DictionaryValue* result;
+    if (!value.GetAsDictionary(&result)) {
+      errors->AddError("dictionary value expected");
+      return nullptr;
+    }
+    return result->CreateDeepCopy();
+  }
+};
+
+template <>
+struct FromValue<base::Value> {
+  static std::unique_ptr<base::Value> Parse(const base::Value& value,
+                                            ErrorReporter* errors) {
+    return value.CreateDeepCopy();
+  }
+};
+
+template <typename T>
+struct FromValue<std::unique_ptr<T>> {
+  static std::unique_ptr<T> Parse(const base::Value& value,
+                                  ErrorReporter* errors) {
+    return FromValue<T>::Parse(value, errors);
+  }
+};
+
+template <typename T>
+struct FromValue<std::vector<T>> {
+  static std::vector<T> Parse(const base::Value& value, ErrorReporter* errors) {
+    std::vector<T> result;
+    const base::ListValue* list;
+    if (!value.GetAsList(&list)) {
+      errors->AddError("list value expected");
+      return result;
+    }
+    errors->Push();
+    for (const auto& item : *list)
+      result.push_back(FromValue<T>::Parse(*item, errors));
+    errors->Pop();
+    return result;
+  }
+};
+
+}  // namespace internal
+}  // namespace headless
+
+#endif  // HEADLESS_PUBLIC_INTERNAL_VALUE_CONVERSIONS_H_