[unseasoned-pdf] Implement message posting from the plugin

Implement PostMessageSender to enable the plugin to post message events
to its embedder.

Note: The introduced implementation assumes messages are posted from the
renderer main thread, but the final implementation will be posting
messages from dedicated plugin threads.

Bug: 1109796
Change-Id: Id3737077e0ba5b82c9a8e5e6c6358e4081700b66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601112
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#851787}

pdf/BUILD.gn

@@ -275,6 +275,8 @@ if (enable_pdf) {
       "pdf_view_web_plugin.h",
       "post_message_receiver.cc",
       "post_message_receiver.h",
+      "post_message_sender.cc",
+      "post_message_sender.h",
     ]
 
     configs += [ ":pdf_common_config" ]

pdf/pdf_view_web_plugin.cc

@@ -130,6 +130,7 @@ bool PdfViewWebPlugin::Initialize(blink::WebPluginContainer* container) {
   PerProcessInitializer::GetInstance().Acquire();
   InitializeEngine(PDFiumFormFiller::ScriptOption::kNoJavaScript);
   LoadUrl(stream_url, /*is_print_preview=*/false);
+  post_message_sender_.set_container(container_);
   return true;
 }
 
@@ -142,6 +143,8 @@ void PdfViewWebPlugin::Destroy() {
   }
 
   container_ = nullptr;
+  post_message_sender_.set_container(nullptr);
+
   delete this;
 }
 

pdf/pdf_view_web_plugin.h

@@ -9,6 +9,7 @@
 #include "base/memory/weak_ptr.h"
 #include "pdf/pdf_view_plugin_base.h"
 #include "pdf/post_message_receiver.h"
+#include "pdf/post_message_sender.h"
 #include "pdf/ppapi_migration/url_loader.h"
 #include "third_party/blink/public/web/web_plugin.h"
 #include "third_party/blink/public/web/web_plugin_params.h"
@@ -146,6 +147,7 @@ class PdfViewWebPlugin final : public PdfViewPluginBase,
   blink::WebPluginContainer* container_ = nullptr;
 
   v8::Persistent<v8::Object> scriptable_receiver_;
+  PostMessageSender post_message_sender_;
 
   base::WeakPtrFactory<PdfViewWebPlugin> weak_factory_{this};
 };

pdf/post_message_sender.cc

@@ -0,0 +1,51 @@
+// Copyright 2021 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 "pdf/post_message_sender.h"
+
+#include <memory>
+
+#include "base/check_op.h"
+#include "base/values.h"
+#include "content/public/renderer/v8_value_converter.h"
+#include "third_party/blink/public/web/blink.h"
+#include "third_party/blink/public/web/web_document.h"
+#include "third_party/blink/public/web/web_dom_message_event.h"
+#include "third_party/blink/public/web/web_local_frame.h"
+#include "third_party/blink/public/web/web_plugin_container.h"
+#include "third_party/blink/public/web/web_serialized_script_value.h"
+#include "v8/include/v8.h"
+
+namespace chrome_pdf {
+
+PostMessageSender::PostMessageSender() : isolate_(blink::MainThreadIsolate()) {}
+
+PostMessageSender::~PostMessageSender() = default;
+
+// TODO(crbug.com/1109796): This method is currently called from the renderer
+// main thread, but will be called from a dedicated plugin thread in the future.
+// When that happens, the body of this method needs to be posted to the main
+// thread as a task because that's where the Blink and V8 interactions need to
+// occur.
+void PostMessageSender::Post(base::Value message) {
+  // Drop messages if there is no container.
+  if (!container_)
+    return;
+
+  v8::HandleScope handle_scope(isolate_);
+  v8::Local<v8::Context> context =
+      container_->GetDocument().GetFrame()->MainWorldScriptContext();
+  DCHECK_EQ(isolate_, context->GetIsolate());
+
+  if (!v8_value_converter_)
+    v8_value_converter_ = content::V8ValueConverter::Create();
+
+  v8::Local<v8::Value> converted_message =
+      v8_value_converter_->ToV8Value(&message, context);
+
+  container_->EnqueueMessageEvent(
+      blink::WebSerializedScriptValue::Serialize(isolate_, converted_message));
+}
+
+}  // namespace chrome_pdf

pdf/post_message_sender.h

@@ -0,0 +1,57 @@
+// Copyright 2021 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 PDF_POST_MESSAGE_SENDER_H_
+#define PDF_POST_MESSAGE_SENDER_H_
+
+#include <memory>
+
+namespace base {
+class Value;
+}  // namespace base
+
+namespace blink {
+class WebPluginContainer;
+}  // namespace blink
+
+namespace content {
+class V8ValueConverter;
+}  // namespace content
+
+namespace v8 {
+class Isolate;
+}  // namespace v8
+
+namespace chrome_pdf {
+
+// Manages messages sent from the plugin to its embedder.
+class PostMessageSender final {
+ public:
+  PostMessageSender();
+  PostMessageSender(const PostMessageSender&) = delete;
+  PostMessageSender& operator=(const PostMessageSender&) = delete;
+  ~PostMessageSender();
+
+  // Enqueues a "message" event carrying `message` to the plugin embedder.
+  // Nothing is enqueued if `container_` is null.
+  void Post(base::Value message);
+
+  // Sets the plugin container that enqueues the messages. This method should be
+  // called by the owning plugin whenever its container is set or unset to
+  // mirror the initialized lifetime of the plugin.
+  void set_container(blink::WebPluginContainer* container) {
+    container_ = container;
+  }
+
+ private:
+  std::unique_ptr<content::V8ValueConverter> v8_value_converter_;
+
+  v8::Isolate* isolate_;
+
+  blink::WebPluginContainer* container_ = nullptr;
+};
+
+}  // namespace chrome_pdf
+
+#endif  // PDF_POST_MESSAGE_SENDER_H_