From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Kenton Varda <kenton@cloudflare.com>
Date: Wed, 4 Dec 2024 22:36:05 -0600
Subject: Add ValueSerializer::SetTreatProxiesAsHostObjects().

Previously, ValueSerializer would always refuse to serialize Proxy objects. This commit gives the embedder the option to handle them as host objects.

Similar to the previous patch adding `SetTreatFunctionsAsHostObjects()`, this is intended for use in an RPC system, where an arbitrary object can be "serialized" by replacing it with a stub which, when invoked, performs an RPC back to the originating isolate in order to access the original object there.

Signed-off-by: James M Snell <jsnell@cloudflare.com>

diff --git a/include/v8-value-serializer.h b/include/v8-value-serializer.h
index 141f138e08de849e3e02b3b2b346e643b9e40c70..bdcb2831c55e21c6d511f56dfc79a5076871f05a 100644
--- a/include/v8-value-serializer.h
+++ b/include/v8-value-serializer.h
@@ -204,6 +204,15 @@ class V8_EXPORT ValueSerializer {
    */
   void SetTreatFunctionsAsHostObjects(bool mode);
 
+  /**
+   * Indicate whether to treat Proxies as host objects,
+   * i.e. pass them to Delegate::WriteHostObject. This should not be
+   * called when no Delegate was passed.
+   *
+   * The default is not to treat Proxies as host objects.
+   */
+  void SetTreatProxiesAsHostObjects(bool mode);
+
   /**
    * Write raw data in various common formats to the buffer.
    * Note that integer types are written in base-128 varint format, not with a
diff --git a/src/api/api.cc b/src/api/api.cc
index 178b429ad06ea349bb43dff578b27ae46ae14da7..8754d87f1db985d4021faf9ce275783ae1229dc8 100644
--- a/src/api/api.cc
+++ b/src/api/api.cc
@@ -3592,6 +3592,10 @@ void ValueSerializer::SetTreatFunctionsAsHostObjects(bool mode) {
   private_->serializer.SetTreatFunctionsAsHostObjects(mode);
 }
 
+void ValueSerializer::SetTreatProxiesAsHostObjects(bool mode) {
+  private_->serializer.SetTreatProxiesAsHostObjects(mode);
+}
+
 Maybe<bool> ValueSerializer::WriteValue(Local<Context> context,
                                         Local<Value> value) {
   auto i_isolate = i::Isolate::Current();
diff --git a/src/objects/value-serializer.cc b/src/objects/value-serializer.cc
index 8c0bf0824b200489919f46b18d240c8c5c15a8ec..13d1a1340de579b8242bc3193c8c9002ecfd0468 100644
--- a/src/objects/value-serializer.cc
+++ b/src/objects/value-serializer.cc
@@ -339,6 +339,10 @@ void ValueSerializer::SetTreatFunctionsAsHostObjects(bool mode) {
   treat_functions_as_host_objects_ = mode;
 }
 
+void ValueSerializer::SetTreatProxiesAsHostObjects(bool mode) {
+  treat_proxies_as_host_objects_ = mode;
+}
+
 void ValueSerializer::WriteTag(SerializationTag tag) {
   uint8_t raw_tag = static_cast<uint8_t>(tag);
   WriteRawBytes(&raw_tag, sizeof(raw_tag));
@@ -610,7 +614,12 @@ Maybe<bool> ValueSerializer::WriteJSReceiver(
   InstanceType instance_type = receiver->map()->instance_type();
   if (IsCallable(*receiver)) {
     if (treat_functions_as_host_objects_) {
-      return WriteHostObject(Cast<JSObject>(receiver));
+      return WriteHostObject(receiver);
+    }
+    return ThrowDataCloneError(MessageTemplate::kDataCloneError, receiver);
+  } else if (instance_type == JS_PROXY_TYPE) {
+    if (treat_proxies_as_host_objects_) {
+      return WriteHostObject(receiver);
     }
     return ThrowDataCloneError(MessageTemplate::kDataCloneError, receiver);
   } else if (IsSpecialReceiverInstanceType(instance_type) &&
@@ -1288,7 +1297,7 @@ Maybe<bool> ValueSerializer::WriteSharedObject(
   return ThrowIfOutOfMemory();
 }
 
-Maybe<bool> ValueSerializer::WriteHostObject(DirectHandle<JSObject> object) {
+Maybe<bool> ValueSerializer::WriteHostObject(DirectHandle<JSReceiver> object) {
   WriteTag(SerializationTag::kHostObject);
   if (!delegate_) {
     isolate_->Throw(*isolate_->factory()->NewError(
diff --git a/src/objects/value-serializer.h b/src/objects/value-serializer.h
index ddc5f27a80f93bae209f3fe8731d4df4baa58ead..496aab365007a45806264c8d3b981bd7a494f903 100644
--- a/src/objects/value-serializer.h
+++ b/src/objects/value-serializer.h
@@ -111,6 +111,15 @@ class ValueSerializer {
    */
   void SetTreatFunctionsAsHostObjects(bool mode);
 
+  /*
+   * Indicate whether to treat Proxies as host objects,
+   * i.e. pass them to Delegate::WriteHostObject. This should not be
+   * called when no Delegate was passed.
+   *
+   * The default is not to treat Proxies as host objects.
+   */
+  void SetTreatProxiesAsHostObjects(bool mode);
+
  private:
   // Managing allocations of the internal buffer.
   Maybe<bool> ExpandBuffer(size_t required_capacity);
@@ -161,8 +170,7 @@ class ValueSerializer {
 #endif  // V8_ENABLE_WEBASSEMBLY
   Maybe<bool> WriteSharedObject(DirectHandle<HeapObject> object)
       V8_WARN_UNUSED_RESULT;
-  Maybe<bool> WriteHostObject(DirectHandle<JSObject> object)
-      V8_WARN_UNUSED_RESULT;
+  Maybe<bool> WriteHostObject(DirectHandle<JSReceiver> object) V8_WARN_UNUSED_RESULT;
 
   /*
    * Reads the specified keys from the object and writes key-value pairs to the
@@ -195,6 +203,7 @@ class ValueSerializer {
   bool has_custom_host_objects_ = false;
   bool treat_array_buffer_views_as_host_objects_ = false;
   bool treat_functions_as_host_objects_ = false;
+  bool treat_proxies_as_host_objects_ = false;
   bool out_of_memory_ = false;
   Zone zone_;
   uint32_t version_;