worker: allow passing JS wrapper objects via postMessage

Enable JS wrapper objects to be used as transferable or cloneable
objects in `postMessage()` calls, by having them extend a C++-backed
class.

This requires a few internal changes:
- This commit adds the possibility for transferred objects to
  read/write JS values at the end of the serialization/deserialization
  phases.
- This commit adds the possibility for transferred objects to list
  sub-transferables, e.g. typically the public JS wrapper class
  would list its C++ handle in there.
- This commit adds usage of `BaseObject` in a few more places, because
  now during deserialization weakly held objects can also be involved,
  in addition to `MessagePort`s.

PR-URL: https://github.com/nodejs/node/pull/33772
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/src/node_messaging.h b/src/node_messaging.h
index 649ee201045..378468b6f44 100644
--- a/src/node_messaging.h
+++ b/src/node_messaging.h
@@ -30,6 +30,12 @@ class TransferData : public MemoryRetainer {
       Environment* env,
       v8::Local<v8::Context> context,
       std::unique_ptr<TransferData> self) = 0;
+  // FinalizeTransferWrite() is the counterpart to
+  // BaseObject::FinalizeTransferRead(). It is called right after the transfer
+  // data was created, and defaults to doing nothing. After this function,
+  // this object should not hold any more Isolate-specific data.
+  virtual v8::Maybe<bool> FinalizeTransferWrite(
+      v8::Local<v8::Context> context, v8::ValueSerializer* serializer);
 };
 
 // Represents a single communication message.
@@ -239,6 +245,52 @@ class MessagePort : public HandleWrap {
   friend class MessagePortData;
 };
 
+// Provide a base class from which JS classes that should be transferable or
+// cloneable by postMesssage() can inherit.
+// See e.g. FileHandle in internal/fs/promises.js for an example.
+class JSTransferable : public BaseObject {
+ public:
+  JSTransferable(Environment* env, v8::Local<v8::Object> obj);
+  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
+
+  TransferMode GetTransferMode() const override;
+  std::unique_ptr<TransferData> TransferForMessaging() override;
+  std::unique_ptr<TransferData> CloneForMessaging() const override;
+  v8::Maybe<std::vector<BaseObjectPtr<BaseObject>>>
+      NestedTransferables() const override;
+  v8::Maybe<bool> FinalizeTransferRead(
+      v8::Local<v8::Context> context,
+      v8::ValueDeserializer* deserializer) override;
+
+  SET_NO_MEMORY_INFO()
+  SET_MEMORY_INFO_NAME(JSTransferable)
+  SET_SELF_SIZE(JSTransferable)
+
+ private:
+  std::unique_ptr<TransferData> TransferOrClone(TransferMode mode) const;
+
+  class Data : public TransferData {
+   public:
+    Data(std::string&& deserialize_info, v8::Global<v8::Value>&& data);
+
+    BaseObjectPtr<BaseObject> Deserialize(
+        Environment* env,
+        v8::Local<v8::Context> context,
+        std::unique_ptr<TransferData> self) override;
+    v8::Maybe<bool> FinalizeTransferWrite(
+        v8::Local<v8::Context> context,
+        v8::ValueSerializer* serializer) override;
+
+    SET_NO_MEMORY_INFO()
+    SET_MEMORY_INFO_NAME(JSTransferableTransferData)
+    SET_SELF_SIZE(Data)
+
+   private:
+    std::string deserialize_info_;
+    v8::Global<v8::Value> data_;
+  };
+};
+
 v8::Local<v8::FunctionTemplate> GetMessagePortConstructorTemplate(
     Environment* env);