src: fix JSONParser leaking internal V8 scopes

JSONParser uses V8's JSON.parse (for now), meaning that its uses handles
and contexts. JSONParser was leaking its internal HandleScope and
Context::Scope.

Move the scope construction to the member functions to prevent those
scopes from leaking. Introduce a new private inner class
HandleAndContextScope to reduce boilerplate.

Refs: nodejs#50680 (comment)

Author: kvakil

src/json_parser.cc

@@ -5,22 +5,28 @@
 
 namespace node {
 using v8::Context;
+using v8::Global;
 using v8::Isolate;
 using v8::Local;
 using v8::Object;
 using v8::String;
 using v8::Value;
 
-JSONParser::JSONParser()
-    : handle_scope_(isolate_.get()),
-      context_(isolate_.get(), Context::New(isolate_.get())),
-      context_scope_(context_.Get(isolate_.get())) {}
+JSONParser::HandleAndContextScope::HandleAndContextScope(
+    v8::Isolate* isolate, const v8::Global<v8::Context>& context)
+    : handle_scope_(isolate), context_scope_(context.Get(isolate)) {}
+
+JSONParser::HandleAndContextScope::~HandleAndContextScope() {}
+
+JSONParser::JSONParser() {}
 
 bool JSONParser::Parse(const std::string& content) {
   DCHECK(!parsed_);
 
   Isolate* isolate = isolate_.get();
-  Local<Context> context = context_.Get(isolate);
+  v8::HandleScope handle_scope(isolate);
+  Local<Context> context = Context::New(isolate);
+  Context::Scope context_scope(context);
 
   // It's not a real script, so don't print the source line.
   errors::PrinterTryCatch bootstrapCatch(
@@ -34,16 +40,22 @@ bool JSONParser::Parse(const std::string& content) {
       !result_value->IsObject()) {
     return false;
   }
+
+  context_.Reset(isolate, context);
   content_.Reset(isolate, result_value.As<Object>());
   parsed_ = true;
+
   return true;
 }
 
 std::optional<std::string> JSONParser::GetTopLevelStringField(
     std::string_view field) {
   Isolate* isolate = isolate_.get();
+  HandleAndContextScope handle_and_context_scope(isolate, context_);
+
   Local<Context> context = context_.Get(isolate);
   Local<Object> content_object = content_.Get(isolate);
+
   Local<Value> value;
   // It's not a real script, so don't print the source line.
   errors::PrinterTryCatch bootstrapCatch(
@@ -62,6 +74,8 @@ std::optional<std::string> JSONParser::GetTopLevelStringField(
 
 std::optional<bool> JSONParser::GetTopLevelBoolField(std::string_view field) {
   Isolate* isolate = isolate_.get();
+  HandleAndContextScope handle_and_context_scope(isolate, context_);
+
   Local<Context> context = context_.Get(isolate);
   Local<Object> content_object = content_.Get(isolate);
   Local<Value> value;

src/json_parser.h

@@ -22,12 +22,22 @@ class JSONParser {
   std::optional<bool> GetTopLevelBoolField(std::string_view field);
 
  private:
+  class HandleAndContextScope {
+   public:
+    HandleAndContextScope(v8::Isolate* isolate,
+                          const v8::Global<v8::Context>& context);
+    ~HandleAndContextScope();
+
+   private:
+    v8::HandleScope handle_scope_;
+    v8::Context::Scope context_scope_;
+  };
+
   // We might want a lighter-weight JSON parser for this use case. But for now
   // using V8 is good enough.
   RAIIIsolate isolate_;
-  v8::HandleScope handle_scope_;
+
   v8::Global<v8::Context> context_;
-  v8::Context::Scope context_scope_;
   v8::Global<v8::Object> content_;
   bool parsed_ = false;
 };