[Extensions Bindings] Add Events support

extensions/renderer/api_event_handler.cc

+// 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.
+
+#include "extensions/renderer/api_event_handler.h"
+
+#include <algorithm>
+#include <map>
+#include <memory>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "base/supports_user_data.h"
+#include "base/values.h"
+#include "content/public/child/v8_value_converter.h"
+#include "extensions/renderer/event_emitter.h"
+#include "gin/handle.h"
+#include "gin/per_context_data.h"
+
+namespace extensions {
+
+namespace {
+
+const char kExtensionAPIEventPerContextKey[] = "extension_api_events";
+
+struct APIEventPerContextData : public base::SupportsUserData::Data {
+  APIEventPerContextData(v8::Isolate* isolate) : isolate(isolate) {}
+  ~APIEventPerContextData() override {
+    v8::HandleScope scope(isolate);
+    // We explicitly clear the event data map here to remove all references to
+    // v8 objects. This helps us avoid cycles in v8 where an event listener
+    // could hold a reference to the event, which in turn holds the reference
+    // to the listener.
+    for (const auto& pair : event_data) {
+      EventEmitter* emitter = nullptr;
+      gin::Converter<EventEmitter*>::FromV8(
+          isolate, pair.second.Get(isolate), &emitter);
+      CHECK(emitter);
+      emitter->listeners()->clear();
+    }
+  }
+
+  // The associated v8::Isolate. Since this object is cleaned up at context
+  // destruction, this should always be valid.
+  v8::Isolate* isolate;
+
+  // A map from event name -> event emitter.
+  std::map<std::string, v8::Global<v8::Object>> event_data;
+};
+
+}  // namespace
+
+APIEventHandler::APIEventHandler(const binding::RunJSFunction& call_js)
+    : call_js_(call_js) {}
+APIEventHandler::~APIEventHandler() {}
+
+v8::Local<v8::Object> APIEventHandler::CreateEventInstance(
+    const std::string& event_name,
+    v8::Local<v8::Context> context) {
+  gin::PerContextData* per_context_data = gin::PerContextData::From(context);
+  DCHECK(per_context_data);
+  APIEventPerContextData* data = static_cast<APIEventPerContextData*>(
+      per_context_data->GetUserData(kExtensionAPIEventPerContextKey));
+  if (!data) {
+    auto api_data =
+        base::MakeUnique<APIEventPerContextData>(context->GetIsolate());
+    data = api_data.get();
+    per_context_data->SetUserData(kExtensionAPIEventPerContextKey,
+                                  api_data.release());
+  }
+
+  DCHECK(data->event_data.find(event_name) == data->event_data.end());
+
+  gin::Handle<EventEmitter> emitter_handle =
+      gin::CreateHandle(context->GetIsolate(), new EventEmitter());
+  CHECK(!emitter_handle.IsEmpty());
+  v8::Local<v8::Value> emitter_value = emitter_handle.ToV8();
+  CHECK(emitter_value->IsObject());
+  v8::Local<v8::Object> emitter_object =
+      v8::Local<v8::Object>::Cast(emitter_value);
+  data->event_data[event_name] =
+      v8::Global<v8::Object>(context->GetIsolate(), emitter_object);
+
+  return emitter_object;
+}
+
+void APIEventHandler::FireEventInContext(const std::string& event_name,
+                                         v8::Local<v8::Context> context,
+                                         const base::ListValue& args) {
+  gin::PerContextData* per_context_data = gin::PerContextData::From(context);
+  DCHECK(per_context_data);
+  APIEventPerContextData* data = static_cast<APIEventPerContextData*>(
+      per_context_data->GetUserData(kExtensionAPIEventPerContextKey));
+  if (!data)
+    return;
+
+  auto iter = data->event_data.find(event_name);
+  if (iter == data->event_data.end())
+    return;
+
+  // Note: since we only convert the arguments once, if a listener modifies an
+  // object (including an array), other listeners will see that modification.
+  // TODO(devlin): This is how it's always been, but should it be?
+  std::vector<v8::Local<v8::Value>> v8_args;
+  v8_args.reserve(args.GetSize());
+  std::unique_ptr<content::V8ValueConverter> converter(
+      content::V8ValueConverter::create());
+  for (const auto& arg : args)
+    v8_args.push_back(converter->ToV8Value(arg.get(), context));
+
+  EventEmitter* emitter = nullptr;
+  gin::Converter<EventEmitter*>::FromV8(
+      context->GetIsolate(), iter->second.Get(context->GetIsolate()), &emitter);
+  CHECK(emitter);
+
+  for (const auto& listener : *emitter->listeners()) {
+    call_js_.Run(listener.Get(context->GetIsolate()), context, v8_args.size(),
+                 v8_args.data());
+  }
+}
+
+size_t APIEventHandler::GetNumEventListenersForTesting(
+    const std::string& event_name,
+    v8::Local<v8::Context> context) {
+  gin::PerContextData* per_context_data = gin::PerContextData::From(context);
+  DCHECK(per_context_data);
+  APIEventPerContextData* data = static_cast<APIEventPerContextData*>(
+      per_context_data->GetUserData(kExtensionAPIEventPerContextKey));
+  DCHECK(data);
+
+  auto iter = data->event_data.find(event_name);
+  DCHECK(iter != data->event_data.end());
+  EventEmitter* emitter = nullptr;
+  gin::Converter<EventEmitter*>::FromV8(
+      context->GetIsolate(), iter->second.Get(context->GetIsolate()), &emitter);
+  CHECK(emitter);
+  return emitter->listeners()->size();
+}
+
+}  // namespace extensions