Trying to expose nested map from C++ to JS

v8_nested_map.cc

#include <cassert>
#include <cstdio>
#include <cstring>
#include <fstream>
#include <iostream>
#include <map>
#include <string>
#include <vector>

#include <include/v8.h>
#include <include/libplatform/libplatform.h>

using namespace std;
using namespace v8;

class HTTPResponse {
  public:
    HTTPResponse(Isolate* isolate);
    ~HTTPResponse();
    Local<Object> WrapHTTPResponseMap();
    Isolate* GetIsolate() { return isolate_; }
    Global<ObjectTemplate> http_response_map_template_;
    map<string, string> http_response;

  private:
    static Local<ObjectTemplate> MakeHTTPResponseMapTemplate(Isolate* isolate);

    static void HTTPResponseSet(Local<Name> name, Local<Value> value,
                          const PropertyCallbackInfo<Value>& info);
    Isolate* isolate_;
};

class HTTPBody {
  public:
    HTTPBody(Isolate* isolate);
    ~HTTPBody();
    Local<Object> WrapHTTPBodyMap();
    Isolate* GetIsolate() { return isolate_; }
    map<string, string> http_body;

  private:
    static void HTTPBodySet(Local<Name> name, Local<Value> value,
                          const PropertyCallbackInfo<Value>& info);
    Isolate* isolate_;
};

// ================================================================

map<string, string>* UnwrapMap(Local<Object> obj) {
  Local<External> field = Local<External>::Cast(obj->GetInternalField(0));
  void* ptr = field->Value();
  return static_cast<map<string, string>*>(ptr);
}

string ObjectToString(Local<Value> value) {
    String::Utf8Value utf8_value(value);
    return string(*utf8_value);
}

string ToString(Isolate* isolate, Handle<Value> object) {
  HandleScope handle_scope(isolate);

  Local<Context> context = isolate->GetCurrentContext();
  Local<Object> global = context->Global();

  Local<Object> JSON = global->Get(String::NewFromUtf8(isolate, "JSON"))->ToObject();
  Local<Function> JSON_stringify =
      Local<Function>::Cast(JSON->Get(
                  String::NewFromUtf8(isolate, "stringify")));

  Local<Value> result;
  Local<Value> args[1];
  args[0] = { object };
  result = JSON_stringify->Call(context->Global(), 1, args);
  return ObjectToString(result);
}
// ================================================================

HTTPBody::HTTPBody(Isolate* isolate) {
  isolate_ = isolate;
}

HTTPBody::~HTTPBody() { }

void HTTPBody::HTTPBodySet(Local<Name> name, Local<Value> value_obj,
                           const PropertyCallbackInfo<Value>& info) {
  if (name->IsSymbol()) return;

  string key = ObjectToString(Local<String>::Cast(name));
  string value = ToString(info.GetIsolate(), value_obj);

  map<string, string>* body = UnwrapMap(info.Holder());
  (*body)[key] = value;

  cout << "ABHI: body field " << value << endl;
  info.GetReturnValue().Set(value_obj);
}

Local<Object> HTTPBody::WrapHTTPBodyMap() {
  EscapableHandleScope handle_scope(GetIsolate());

  Local<FunctionTemplate> body_map_template = FunctionTemplate::New(GetIsolate());
  body_map_template->InstanceTemplate()->SetHandler(
          NamedPropertyHandlerConfiguration(NULL, HTTPBodySet));
  body_map_template->InstanceTemplate()->SetInternalFieldCount(1);
  Local<Object> result = body_map_template->GetFunction()->NewInstance();

  Local<External> map_ptr = External::New(GetIsolate(), &http_body);
  result->SetInternalField(0, map_ptr);
  return handle_scope.Escape(result);
}

HTTPResponse::HTTPResponse(Isolate* isolate) {
  isolate_ = isolate;
}

HTTPResponse::~HTTPResponse() { }

void HTTPResponse::HTTPResponseSet(Local<Name> name, Local<Value> value_obj,
                                   const PropertyCallbackInfo<Value>& info) {
  if (name->IsSymbol()) return;

  string key = ObjectToString(Local<String>::Cast(name));
  string value = ToString(info.GetIsolate(), value_obj);

  map<string, string>* response = UnwrapMap(info.Holder());
  (*response)[key] = value;
  cout << "key: " << key << " value: " << value << endl;

  Local<External> field = Local<External>::Cast(info.Holder());
  Isolate* isolate = static_cast<Isolate*>(field->Value());

  cout << __LINE__ << endl;
  HTTPBody* body = new HTTPBody(isolate);

  cout << __LINE__ << endl;
  Local<Object> body_map = body->WrapHTTPBodyMap();
  cout << __LINE__ << endl;
  info.GetReturnValue().Set(body_map);
}

Local<ObjectTemplate> HTTPResponse::MakeHTTPResponseMapTemplate(
    Isolate* isolate) {
  EscapableHandleScope handle_scope(isolate);

  Local<ObjectTemplate> result = ObjectTemplate::New(isolate);
  result->SetInternalFieldCount(2);
  result->SetHandler(NamedPropertyHandlerConfiguration(NULL, HTTPResponseSet));
  return handle_scope.Escape(result);
}

Local<Object> HTTPResponse::WrapHTTPResponseMap() {
  EscapableHandleScope handle_scope(GetIsolate());

  if (http_response_map_template_.IsEmpty()) {
    Local<ObjectTemplate> raw_template = MakeHTTPResponseMapTemplate(GetIsolate());
    http_response_map_template_.Reset(GetIsolate(), raw_template);
  }
  Local<ObjectTemplate> templ =
      Local<ObjectTemplate>::New(GetIsolate(), http_response_map_template_);

  Local<Object> result =
      templ->NewInstance(GetIsolate()->GetCurrentContext()).ToLocalChecked();

  Local<External> map_ptr = External::New(GetIsolate(), &http_response);
  Local<External> isolate_ptr = External::New(GetIsolate(), isolate_);
  result->SetInternalField(0, map_ptr);
  result->SetInternalField(0, isolate_ptr);

  return handle_scope.Escape(result);
}

class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
 public:
  virtual void* Allocate(size_t length) {
    void* data = AllocateUninitialized(length);
    return data == NULL ? data : memset(data, 0, length);
  }
  virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
  virtual void Free(void* data, size_t) { free(data); }
};

const char* js_function =
    "function OnHTTPGet(req, res) {"
    "       res.body.query_result = 100;"
    "       res.body.row_count = 1;"
    "}";

int main(int argc, char* argv[]) {
  V8::InitializeICU();
  V8::InitializeExternalStartupData(argv[0]);
  Platform* platform = platform::CreateDefaultPlatform();
  V8::InitializePlatform(platform);
  V8::Initialize();

  ArrayBufferAllocator allocator;
  Isolate::CreateParams create_params;
  create_params.array_buffer_allocator = &allocator;
  Isolate* isolate = Isolate::New(create_params);
  {
    Isolate::Scope isolate_scope(isolate);
    HandleScope handle_scope(isolate);
    Local<Context> context = Context::New(isolate);
    Context::Scope context_scope(context);

    Local<String> source =
        String::NewFromUtf8(isolate, js_function,
                            NewStringType::kNormal).ToLocalChecked();
    Local<Script> script = Script::Compile(context, source).ToLocalChecked();
    Local<Value> result = script->Run(context).ToLocalChecked();

    const char* http_req = "{\"path\": \"/root\"}";
    HTTPResponse* response = new HTTPResponse(isolate);

    Handle<Value> args[2];
    args[0] = JSON::Parse(String::NewFromUtf8(isolate, http_req));
    args[1] = response->WrapHTTPResponseMap();

    Local<String> on_http_get =
        String::NewFromUtf8(isolate, "OnHTTPGet", NewStringType::kNormal)
        .ToLocalChecked();
    Local<Value> on_http_get_val;
    if(!context->Global()->Get(context, on_http_get).ToLocal(&on_http_get_val))
        cout << "Failed to grab OnHTTPGet function " << endl;
    if(on_http_get_val->IsFunction())
        cout << "Yes it's a function" << endl;
    Local<Function> on_http_get_fun = Local<Function>::Cast(on_http_get_val);

    cout << __LINE__ << endl;
    on_http_get_fun->Call(context->Global(), 2, args);
    cout << __LINE__ << endl;
  }

  cout << __LINE__ << endl;
  isolate->Dispose();
  V8::Dispose();
  V8::ShutdownPlatform();
  delete platform;
  return 0;
}

I line 147/148 you're writing two different values to the same internal field. I think storing the isolate pointer is not necessary, as you can just get it via info.GetIsolate() in the handler.

The actual bug is that response needs a getter, not a setter. "res.body.query_result" first gets body from res and then sets query_result on body.