src: retrieve binding data from the context

Instead of passing them through the data bound to function
templates, store references to them in a list embedded inside
the context, and store the integer index
(which is context-independent) in the function template data.
This makes the function templates more context-independent,
and makes it possible to embed binding data in non-main contexts.

Author: joyeecheung

src/README.md

@@ -402,13 +402,13 @@ Some internal bindings, such as the HTTP parser, maintain internal state that
 only affects that particular binding. In that case, one common way to store
 that state is through the use of `Environment::BindingScope`, which gives all
 new functions created within it access to an object for storing such state.
-That object is always a [`BaseObject`][].
+That object is always a `BindingDataBase`.
 
 ```c++
 // In the HTTP parser source code file:
-class BindingData : public BaseObject {
+class BindingData : public BindingDataBase {
  public:
-  BindingData(Environment* env, Local<Object> obj) : BaseObject(env, obj) {}
+  BindingData(Environment* env, Local<Object> obj) : BindingDataBase(env, obj) {}
 
   std::vector<char> parser_buffer;
   bool parser_buffer_in_use = false;
@@ -418,7 +418,7 @@ class BindingData : public BaseObject {
 
 // Available for binding functions, e.g. the HTTP Parser constructor:
 static void New(const FunctionCallbackInfo<Value>& args) {
-  BindingData* binding_data = Unwrap<BindingData>(args.Data());
+  BindingData* binding_data = BindingDataBase::Unwrap<BindingData>(args);
   new Parser(binding_data, args.This());
 }
 
@@ -429,7 +429,7 @@ void InitializeHttpParser(Local<Object> target,
                           Local<Context> context,
                           void* priv) {
   Environment* env = Environment::GetCurrent(context);
-  Environment::BindingScope<BindingData> binding_scope(env);
+  Environment::BindingScope<BindingData> binding_scope(env, context, target);
   if (!binding_scope) return;
   BindingData* binding_data = binding_scope.data;
 

src/env-inl.h

@@ -287,6 +287,10 @@ inline void Environment::AssignToContext(v8::Local<v8::Context> context,
   // Used by Environment::GetCurrent to know that we are on a node context.
   context->SetAlignedPointerInEmbedderData(
     ContextEmbedderIndex::kContextTag, Environment::kNodeContextTagPtr);
+  // Used to retrieve bindings
+  context->SetAlignedPointerInEmbedderData(
+      ContextEmbedderIndex::KBindingListIndex, &(this->bindings_));
+
 #if HAVE_INSPECTOR
   inspector_agent()->ContextCreated(context, info);
 #endif  // HAVE_INSPECTOR
@@ -318,55 +322,74 @@ inline Environment* Environment::GetCurrent(v8::Local<v8::Context> context) {
 
 inline Environment* Environment::GetCurrent(
     const v8::FunctionCallbackInfo<v8::Value>& info) {
-  return GetFromCallbackData(info.Data());
+  return BindingDataBase::Unwrap<BindingDataBase>(info)->env();
 }
 
 template <typename T>
 inline Environment* Environment::GetCurrent(
     const v8::PropertyCallbackInfo<T>& info) {
-  return GetFromCallbackData(info.Data());
+  return BindingDataBase::Unwrap<BindingDataBase>(info)->env();
 }
 
-Environment* Environment::GetFromCallbackData(v8::Local<v8::Value> val) {
-  DCHECK(val->IsObject());
-  v8::Local<v8::Object> obj = val.As<v8::Object>();
-  DCHECK_GE(obj->InternalFieldCount(),
-            BaseObject::kInternalFieldCount);
-  Environment* env = Unwrap<BaseObject>(obj)->env();
-  DCHECK(env->as_callback_data_template()->HasInstance(obj));
-  return env;
+inline BindingDataBase::BindingDataBase(Environment* env,
+                                        v8::Local<v8::Object> target)
+    : BaseObject(env, target) {}
+
+template <typename T, typename U>
+inline T* BindingDataBase::Unwrap(const v8::PropertyCallbackInfo<U>& info) {
+  return Unwrap<T>(info.GetIsolate()->GetCurrentContext(), info.Data());
 }
 
 template <typename T>
-Environment::BindingScope<T>::BindingScope(Environment* env) : env(env) {
-  v8::Local<v8::Object> callback_data;
-  if (!env->MakeBindingCallbackData<T>().ToLocal(&callback_data))
-    return;
-  data = Unwrap<T>(callback_data);
+inline T* BindingDataBase::Unwrap(
+    const v8::FunctionCallbackInfo<v8::Value>& info) {
+  return Unwrap<T>(info.GetIsolate()->GetCurrentContext(), info.Data());
+}
 
-  // No nesting allowed currently.
-  CHECK_EQ(env->current_callback_data(), env->as_callback_data());
-  env->set_current_callback_data(callback_data);
+template <typename T>
+inline T* BindingDataBase::Unwrap(v8::Local<v8::Context> context,
+                                  v8::Local<v8::Value> val) {
+  CHECK(val->IsUint32());
+  uint32_t index = val.As<v8::Uint32>()->Value();
+  std::vector<BindingDataBase*>* list =
+      static_cast<std::vector<BindingDataBase*>*>(
+          context->GetAlignedPointerFromEmbedderData(
+              ContextEmbedderIndex::KBindingListIndex));
+  CHECK_GT(list->size(), index);
+  T* result = static_cast<T*>(list->at(index));
+  return result;
 }
 
 template <typename T>
-Environment::BindingScope<T>::~BindingScope() {
-  env->set_current_callback_data(env->as_callback_data());
+inline v8::Local<v8::Uint32> BindingDataBase::New(
+    Environment* env,
+    v8::Local<v8::Context> context,
+    v8::Local<v8::Object> target) {
+  T* data = new T(env, target);
+  // This won't compile if T is not a BindingDataBase subclass.
+  BindingDataBase* item = static_cast<BindingDataBase*>(data);
+  std::vector<BindingDataBase*>* list =
+      static_cast<std::vector<BindingDataBase*>*>(
+          context->GetAlignedPointerFromEmbedderData(
+              ContextEmbedderIndex::KBindingListIndex));
+  size_t index = list->size();
+  list->push_back(item);
+  return v8::Integer::NewFromUnsigned(env->isolate(), index).As<v8::Uint32>();
 }
 
 template <typename T>
-v8::MaybeLocal<v8::Object> Environment::MakeBindingCallbackData() {
-  v8::Local<v8::Function> ctor;
-  v8::Local<v8::Object> obj;
-  if (!as_callback_data_template()->GetFunction(context()).ToLocal(&ctor) ||
-      !ctor->NewInstance(context()).ToLocal(&obj)) {
-    return v8::MaybeLocal<v8::Object>();
-  }
-  T* data = new T(this, obj);
-  // This won't compile if T is not a BaseObject subclass.
-  CHECK_EQ(data, static_cast<BaseObject*>(data));
-  data->MakeWeak();
-  return obj;
+Environment::BindingScope<T>::BindingScope(Environment* env,
+                                           v8::Local<v8::Context> context,
+                                           v8::Local<v8::Object> target)
+    : env(env) {
+  v8::Local<v8::Uint32> index = BindingDataBase::New<T>(env, context, target);
+  data = BindingDataBase::Unwrap<T>(context, index);
+  env->set_current_callback_data(index);
+}
+
+template <typename T>
+Environment::BindingScope<T>::~BindingScope() {
+  env->set_current_callback_data(env->default_callback_data());
 }
 
 inline Environment* Environment::GetThreadLocalEnv() {
@@ -1085,7 +1108,7 @@ inline v8::Local<v8::FunctionTemplate>
                                      v8::Local<v8::Signature> signature,
                                      v8::ConstructorBehavior behavior,
                                      v8::SideEffectType side_effect_type) {
-  v8::Local<v8::Object> external = current_callback_data();
+  v8::Local<v8::Value> external = current_callback_data();
   return v8::FunctionTemplate::New(isolate(), callback, external,
                                    signature, 0, behavior, side_effect_type);
 }
@@ -1276,6 +1299,7 @@ void Environment::set_process_exit_handler(
   }
   ENVIRONMENT_STRONG_PERSISTENT_TEMPLATES(V)
   ENVIRONMENT_STRONG_PERSISTENT_VALUES(V)
+  ENVIRONMENT_CALLBACK_DATA(V)
 #undef V
 
   inline v8::Local<v8::Context> Environment::context() const {

src/env.cc

@@ -50,6 +50,7 @@ using v8::String;
 using v8::Symbol;
 using v8::TracingController;
 using v8::TryCatch;
+using v8::Uint32;
 using v8::Undefined;
 using v8::Value;
 using worker::Worker;
@@ -261,9 +262,10 @@ void TrackingTraceStateObserver::UpdateTraceCategoryState() {
   USE(cb->Call(env_->context(), Undefined(isolate), arraysize(args), args));
 }
 
-class NoBindingData : public BaseObject {
+class NoBindingData : public BindingDataBase {
  public:
-  NoBindingData(Environment* env, Local<Object> obj) : BaseObject(env, obj) {}
+  NoBindingData(Environment* env, Local<Object> obj)
+      : BindingDataBase(env, obj) {}
 
   SET_NO_MEMORY_INFO()
   SET_MEMORY_INFO_NAME(NoBindingData)
@@ -273,17 +275,19 @@ class NoBindingData : public BaseObject {
 void Environment::CreateProperties() {
   HandleScope handle_scope(isolate_);
   Local<Context> ctx = context();
+
   {
     Context::Scope context_scope(ctx);
     Local<FunctionTemplate> templ = FunctionTemplate::New(isolate());
     templ->InstanceTemplate()->SetInternalFieldCount(
         BaseObject::kInternalFieldCount);
-    set_as_callback_data_template(templ);
 
-    Local<Object> obj = MakeBindingCallbackData<NoBindingData>()
-        .ToLocalChecked();
-    set_as_callback_data(obj);
-    set_current_callback_data(obj);
+    set_binding_data_ctor_template(templ);
+    Local<Function> ctor = templ->GetFunction(ctx).ToLocalChecked();
+    Local<Object> obj = ctor->NewInstance(ctx).ToLocalChecked();
+    Local<Uint32> index = BindingDataBase::New<NoBindingData>(this, ctx, obj);
+    set_default_callback_data(index);
+    set_current_callback_data(index);
   }
 
   // Store primordials setup by the per-context script in the environment.
@@ -1133,6 +1137,7 @@ void Environment::MemoryInfo(MemoryTracker* tracker) const {
 #define V(PropertyName, TypeName)                                              \
   tracker->TrackField(#PropertyName, PropertyName());
   ENVIRONMENT_STRONG_PERSISTENT_VALUES(V)
+  ENVIRONMENT_CALLBACK_DATA(V)
 #undef V
 
   // FIXME(joyeecheung): track other fields in Environment.

src/env.h

@@ -390,9 +390,9 @@ constexpr size_t kFsStatsBufferLength =
   V(zero_return_string, "ZERO_RETURN")
 
 #define ENVIRONMENT_STRONG_PERSISTENT_TEMPLATES(V)                             \
-  V(as_callback_data_template, v8::FunctionTemplate)                           \
   V(async_wrap_ctor_template, v8::FunctionTemplate)                            \
   V(async_wrap_object_ctor_template, v8::FunctionTemplate)                     \
+  V(binding_data_ctor_template, v8::FunctionTemplate)                          \
   V(compiled_fn_entry_template, v8::ObjectTemplate)                            \
   V(dir_instance_template, v8::ObjectTemplate)                                 \
   V(fd_constructor_template, v8::ObjectTemplate)                               \
@@ -419,8 +419,11 @@ constexpr size_t kFsStatsBufferLength =
   V(write_wrap_template, v8::ObjectTemplate)                                   \
   V(worker_heap_snapshot_taker_template, v8::ObjectTemplate)
 
+#define ENVIRONMENT_CALLBACK_DATA(V)                                           \
+  V(default_callback_data, v8::Uint32)                                         \
+  V(current_callback_data, v8::Uint32)
+
 #define ENVIRONMENT_STRONG_PERSISTENT_VALUES(V)                                \
-  V(as_callback_data, v8::Object)                                              \
   V(async_hooks_after_function, v8::Function)                                  \
   V(async_hooks_before_function, v8::Function)                                 \
   V(async_hooks_binding, v8::Object)                                           \
@@ -429,7 +432,6 @@ constexpr size_t kFsStatsBufferLength =
   V(async_hooks_promise_resolve_function, v8::Function)                        \
   V(buffer_prototype_object, v8::Object)                                       \
   V(crypto_key_object_constructor, v8::Function)                               \
-  V(current_callback_data, v8::Object)                                         \
   V(domain_callback, v8::Function)                                             \
   V(domexception_function, v8::Function)                                       \
   V(enhance_fatal_stack_after_inspector, v8::Function)                         \
@@ -824,6 +826,28 @@ class CleanupHookCallback {
   uint64_t insertion_order_counter_;
 };
 
+class BindingDataBase : public BaseObject {
+ public:
+  // Exposed for subclasses
+  inline BindingDataBase(Environment* env, v8::Local<v8::Object> target);
+  // Unwrap a subclass T object from a v8::Value which needs to be an
+  // v8::Uint32
+  template <typename T, typename U>
+  static inline T* Unwrap(const v8::PropertyCallbackInfo<U>& info);
+  template <typename T>
+  static inline T* Unwrap(const v8::FunctionCallbackInfo<v8::Value>& info);
+
+  template <typename T>
+  static inline T* Unwrap(v8::Local<v8::Context> context,
+                          v8::Local<v8::Value> val);
+  // Create a BindingData of subclass T, put it into the context binding list,
+  // return the index as v8::Integer
+  template <typename T>
+  static inline v8::Local<v8::Uint32> New(Environment* env,
+                                          v8::Local<v8::Context> context,
+                                          v8::Local<v8::Object> target);
+};
+
 class Environment : public MemoryRetainer {
  public:
   Environment(const Environment&) = delete;
@@ -864,14 +888,14 @@ class Environment : public MemoryRetainer {
   static inline Environment* GetCurrent(
       const v8::PropertyCallbackInfo<T>& info);
 
-  static inline Environment* GetFromCallbackData(v8::Local<v8::Value> val);
-
   // Methods created using SetMethod(), SetPrototypeMethod(), etc. inside
   // this scope can access the created T* object using
   // Unwrap<T>(args.Data()) later.
   template <typename T>
   struct BindingScope {
-    explicit inline BindingScope(Environment* env);
+    explicit inline BindingScope(Environment* env,
+                                 v8::Local<v8::Context> context,
+                                 v8::Local<v8::Object> target);
     inline ~BindingScope();
 
     T* data = nullptr;
@@ -881,9 +905,6 @@ class Environment : public MemoryRetainer {
     inline bool operator !() const { return data == nullptr; }
   };
 
-  template <typename T>
-  inline v8::MaybeLocal<v8::Object> MakeBindingCallbackData();
-
   static uv_key_t thread_local_env;
   static inline Environment* GetThreadLocalEnv();
 
@@ -1128,6 +1149,7 @@ class Environment : public MemoryRetainer {
 #define V(PropertyName, TypeName)                                             \
   inline v8::Local<TypeName> PropertyName() const;                            \
   inline void set_ ## PropertyName(v8::Local<TypeName> value);
+  ENVIRONMENT_CALLBACK_DATA(V)
   ENVIRONMENT_STRONG_PERSISTENT_VALUES(V)
   ENVIRONMENT_STRONG_PERSISTENT_TEMPLATES(V)
 #undef V
@@ -1428,6 +1450,8 @@ class Environment : public MemoryRetainer {
   void RequestInterruptFromV8();
   static void CheckImmediate(uv_check_t* handle);
 
+  std::vector<BindingDataBase*> bindings_;
+
   // Use an unordered_set, so that we have efficient insertion and removal.
   std::unordered_set<CleanupHookCallback,
                      CleanupHookCallback::Hash,
@@ -1446,6 +1470,7 @@ class Environment : public MemoryRetainer {
   void ForEachBaseObject(T&& iterator);
 
 #define V(PropertyName, TypeName) v8::Global<TypeName> PropertyName ## _;
+  ENVIRONMENT_CALLBACK_DATA(V)
   ENVIRONMENT_STRONG_PERSISTENT_VALUES(V)
   ENVIRONMENT_STRONG_PERSISTENT_TEMPLATES(V)
 #undef V

src/node_binding.cc

@@ -230,6 +230,7 @@ namespace node {
 
 using v8::Context;
 using v8::Exception;
+using v8::Function;
 using v8::FunctionCallbackInfo;
 using v8::Local;
 using v8::NewStringType;
@@ -556,8 +557,11 @@ inline struct node_module* FindModule(struct node_module* list,
 static Local<Object> InitModule(Environment* env,
                                 node_module* mod,
                                 Local<String> module) {
-  Local<Object> exports = Object::New(env->isolate());
   // Internal bindings don't have a "module" object, only exports.
+  Local<Function> ctor = env->binding_data_ctor_template()
+                             ->GetFunction(env->context())
+                             .ToLocalChecked();
+  Local<Object> exports = ctor->NewInstance(env->context()).ToLocalChecked();
   CHECK_NULL(mod->nm_register_func);
   CHECK_NOT_NULL(mod->nm_context_register_func);
   Local<Value> unused = Undefined(env->isolate());

src/node_context_data.h

@@ -25,11 +25,16 @@ namespace node {
 #define NODE_CONTEXT_TAG 35
 #endif
 
+#ifndef NODE_BINDING_LIST
+#define NODE_BINDING_LIST_INDEX 36
+#endif
+
 enum ContextEmbedderIndex {
   kEnvironment = NODE_CONTEXT_EMBEDDER_DATA_INDEX,
   kSandboxObject = NODE_CONTEXT_SANDBOX_OBJECT_INDEX,
   kAllowWasmCodeGeneration = NODE_CONTEXT_ALLOW_WASM_CODE_GENERATION_INDEX,
   kContextTag = NODE_CONTEXT_TAG,
+  KBindingListIndex = NODE_BINDING_LIST_INDEX
 };
 
 }  // namespace node

src/node_env_var.cc

@@ -379,7 +379,7 @@ static void EnvEnumerator(const PropertyCallbackInfo<Array>& info) {
 
 MaybeLocal<Object> CreateEnvVarProxy(Local<Context> context,
                                      Isolate* isolate,
-                                     Local<Object> data) {
+                                     Local<Value> data) {
   EscapableHandleScope scope(isolate);
   Local<ObjectTemplate> env_proxy_template = ObjectTemplate::New(isolate);
   env_proxy_template->SetHandler(NamedPropertyHandlerConfiguration(

src/node_file-inl.h

@@ -227,7 +227,7 @@ FSReqBase* GetReqWrap(const v8::FunctionCallbackInfo<v8::Value>& args,
     return Unwrap<FSReqBase>(value.As<v8::Object>());
   }
 
-  BindingData* binding_data = Unwrap<BindingData>(args.Data());
+  BindingData* binding_data = BindingDataBase::Unwrap<BindingData>(args);
   Environment* env = binding_data->env();
   if (value->StrictEquals(env->fs_use_promises_symbol())) {
     if (use_bigint) {