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n-api: implement wrapping using private properties
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PR-URL: nodejs#18311
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Fixes: nodejs#14367
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Gabriel Schulhof committed Apr 16, 2018
1 parent e57f34c commit 5c183d7
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Showing 3 changed files with 52 additions and 111 deletions.
2 changes: 2 additions & 0 deletions src/env.h
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,8 @@ namespace node {
V(npn_buffer_private_symbol, "node:npnBuffer") \
V(processed_private_symbol, "node:processed") \
V(selected_npn_buffer_private_symbol, "node:selectedNpnBuffer") \
V(napi_env, "node:napi:env") \
V(napi_wrapper, "node:napi:wrapper") \

// Strings are per-isolate primitives but Environment proxies them
// for the sake of convenience. Strings should be ASCII-only.
Expand Down
160 changes: 49 additions & 111 deletions src/node_api.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,6 @@
#include "node_internals.h"
#include "env-inl.h"
#include "node_api_backport.h"
#include "util.h"

static
napi_status napi_set_last_error(napi_env env, napi_status error_code,
Expand Down Expand Up @@ -53,6 +52,9 @@ struct napi_env__ {
uv_loop_t* loop = nullptr;
};

#define NAPI_PRIVATE_KEY(context, suffix) \
(node::Environment::GetCurrent((context))->napi_ ## suffix())

#define ENV_OBJECT_TEMPLATE(env, prefix, destination, field_count) \
do { \
if ((env)->prefix ## _template.IsEmpty()) { \
Expand Down Expand Up @@ -383,6 +385,10 @@ class Reference : private Finalizer {
}

public:
void* Data() {
return _finalize_data;
}

static Reference* New(napi_env env,
v8::Local<v8::Value> value,
uint32_t initial_refcount,
Expand Down Expand Up @@ -742,45 +748,6 @@ v8::Local<v8::Object> CreateAccessorCallbackData(napi_env env,
return cbdata;
}

int kWrapperFields = 3;

// Pointer used to identify items wrapped by N-API. Used by FindWrapper and
// napi_wrap().
const char napi_wrap_name[] = "N-API Wrapper";

// Search the object's prototype chain for the wrapper object. Usually the
// wrapper would be the first in the chain, but it is OK for other objects to
// be inserted in the prototype chain.
static
bool FindWrapper(v8::Local<v8::Object> obj,
v8::Local<v8::Object>* result = nullptr,
v8::Local<v8::Object>* parent = nullptr) {
v8::Local<v8::Object> wrapper = obj;

do {
v8::Local<v8::Value> proto = wrapper->GetPrototype();
if (proto.IsEmpty() || !proto->IsObject()) {
return false;
}
if (parent != nullptr) {
*parent = wrapper;
}
wrapper = proto.As<v8::Object>();
if (wrapper->InternalFieldCount() == kWrapperFields) {
v8::Local<v8::Value> external = wrapper->GetInternalField(1);
if (external->IsExternal() &&
external.As<v8::External>()->Value() == v8impl::napi_wrap_name) {
break;
}
}
} while (true);

if (result != nullptr) {
*result = wrapper;
}
return true;
}

static void DeleteEnv(napi_env env, void* data, void* hint) {
delete env;
}
Expand All @@ -797,11 +764,8 @@ napi_env GetEnv(v8::Local<v8::Context> context) {
// because we need to stop hard if either of them is empty.
//
// Re https://github.com/nodejs/node/pull/14217#discussion_r128775149
auto key = v8::Private::ForApi(isolate,
v8::String::NewFromOneByte(isolate,
reinterpret_cast<const uint8_t*>("N-API Environment"),
v8::NewStringType::kInternalized).ToLocalChecked());
auto value = global->GetPrivate(context, key).ToLocalChecked();
auto value = global->GetPrivate(context, NAPI_PRIVATE_KEY(context, env))
.ToLocalChecked();

if (value->IsExternal()) {
result = static_cast<napi_env>(value.As<v8::External>()->Value());
Expand All @@ -811,7 +775,8 @@ napi_env GetEnv(v8::Local<v8::Context> context) {

// We must also stop hard if the result of assigning the env to the global
// is either nothing or false.
CHECK(global->SetPrivate(context, key, external).FromJust());
CHECK(global->SetPrivate(context, NAPI_PRIVATE_KEY(context, env), external)
.FromJust());

// Create a self-destructing reference to external that will get rid of the
// napi_env when external goes out of scope.
Expand All @@ -821,28 +786,46 @@ napi_env GetEnv(v8::Local<v8::Context> context) {
return result;
}

enum UnwrapAction {
KeepWrap,
RemoveWrap
};

static
napi_status Unwrap(napi_env env,
napi_value js_object,
void** result,
v8::Local<v8::Object>* wrapper,
v8::Local<v8::Object>* parent = nullptr) {
UnwrapAction action) {
NAPI_PREAMBLE(env);
CHECK_ARG(env, js_object);
CHECK_ARG(env, result);
if (action == KeepWrap) {
CHECK_ARG(env, result);
}

v8::Isolate* isolate = env->isolate;
v8::Local<v8::Context> context = isolate->GetCurrentContext();

v8::Local<v8::Value> value = v8impl::V8LocalValueFromJsValue(js_object);
RETURN_STATUS_IF_FALSE(env, value->IsObject(), napi_invalid_arg);
v8::Local<v8::Object> obj = value.As<v8::Object>();

RETURN_STATUS_IF_FALSE(
env, v8impl::FindWrapper(obj, wrapper, parent), napi_invalid_arg);
auto val = obj->GetPrivate(context, NAPI_PRIVATE_KEY(context, wrapper))
.ToLocalChecked();
RETURN_STATUS_IF_FALSE(env, val->IsExternal(), napi_invalid_arg);
Reference* reference =
static_cast<v8impl::Reference*>(val.As<v8::External>()->Value());

v8::Local<v8::Value> unwrappedValue = (*wrapper)->GetInternalField(0);
RETURN_STATUS_IF_FALSE(env, unwrappedValue->IsExternal(), napi_invalid_arg);
if (result) {
*result = reference->Data();
}

*result = unwrappedValue.As<v8::External>()->Value();
if (action == RemoveWrap) {
CHECK(obj->DeletePrivate(context, NAPI_PRIVATE_KEY(context, wrapper))
.FromJust());
Reference::Delete(reference);
}

return napi_ok;
return GET_RETURN_STATUS(env);
}

static
Expand Down Expand Up @@ -2399,26 +2382,9 @@ napi_status napi_wrap(napi_env env,
v8::Local<v8::Object> obj = value.As<v8::Object>();

// If we've already wrapped this object, we error out.
RETURN_STATUS_IF_FALSE(env, !v8impl::FindWrapper(obj), napi_invalid_arg);

// Create a wrapper object with an internal field to hold the wrapped pointer
// and a second internal field to identify the owner as N-API.
v8::Local<v8::ObjectTemplate> wrapper_template;
ENV_OBJECT_TEMPLATE(env, wrap, wrapper_template, v8impl::kWrapperFields);

auto maybe_object = wrapper_template->NewInstance(context);
CHECK_MAYBE_EMPTY(env, maybe_object, napi_generic_failure);
v8::Local<v8::Object> wrapper = maybe_object.ToLocalChecked();

// Store the pointer as an external in the wrapper.
wrapper->SetInternalField(0, v8::External::New(isolate, native_object));
wrapper->SetInternalField(1, v8::External::New(isolate,
reinterpret_cast<void*>(const_cast<char*>(v8impl::napi_wrap_name))));

// Insert the wrapper into the object's prototype chain.
v8::Local<v8::Value> proto = obj->GetPrototype();
CHECK(wrapper->SetPrototype(context, proto).FromJust());
CHECK(obj->SetPrototype(context, wrapper).FromJust());
RETURN_STATUS_IF_FALSE(env,
!obj->HasPrivate(context, NAPI_PRIVATE_KEY(context, wrapper)).FromJust(),
napi_invalid_arg);

v8impl::Reference* reference = nullptr;
if (result != nullptr) {
Expand All @@ -2430,52 +2396,24 @@ napi_status napi_wrap(napi_env env,
reference = v8impl::Reference::New(
env, obj, 0, false, finalize_cb, native_object, finalize_hint);
*result = reinterpret_cast<napi_ref>(reference);
} else if (finalize_cb != nullptr) {
// Create a self-deleting reference just for the finalize callback.
reference = v8impl::Reference::New(
env, obj, 0, true, finalize_cb, native_object, finalize_hint);
} else {
// Create a self-deleting reference.
reference = v8impl::Reference::New(env, obj, 0, true, finalize_cb,
native_object, finalize_cb == nullptr ? nullptr : finalize_hint);
}

if (reference != nullptr) {
wrapper->SetInternalField(2, v8::External::New(isolate, reference));
}
CHECK(obj->SetPrivate(context, NAPI_PRIVATE_KEY(context, wrapper),
v8::External::New(isolate, reference)).FromJust());

return GET_RETURN_STATUS(env);
}

napi_status napi_unwrap(napi_env env, napi_value obj, void** result) {
// Omit NAPI_PREAMBLE and GET_RETURN_STATUS because V8 calls here cannot throw
// JS exceptions.
CHECK_ENV(env);
v8::Local<v8::Object> wrapper;
return napi_set_last_error(env, v8impl::Unwrap(env, obj, result, &wrapper));
return v8impl::Unwrap(env, obj, result, v8impl::KeepWrap);
}

napi_status napi_remove_wrap(napi_env env, napi_value obj, void** result) {
NAPI_PREAMBLE(env);
v8::Local<v8::Object> wrapper;
v8::Local<v8::Object> parent;
napi_status status = v8impl::Unwrap(env, obj, result, &wrapper, &parent);
if (status != napi_ok) {
return napi_set_last_error(env, status);
}

v8::Local<v8::Value> external = wrapper->GetInternalField(2);
if (external->IsExternal()) {
v8impl::Reference::Delete(
static_cast<v8impl::Reference*>(external.As<v8::External>()->Value()));
}

if (!parent.IsEmpty()) {
v8::Maybe<bool> maybe = parent->SetPrototype(
env->isolate->GetCurrentContext(), wrapper->GetPrototype());
CHECK_MAYBE_NOTHING(env, maybe, napi_generic_failure);
if (!maybe.FromMaybe(false)) {
return napi_set_last_error(env, napi_generic_failure);
}
}

return GET_RETURN_STATUS(env);
return v8impl::Unwrap(env, obj, result, v8impl::RemoveWrap);
}

napi_status napi_create_external(napi_env env,
Expand Down
1 change: 1 addition & 0 deletions src/node_api_backport.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
// N-API.

#include "node_internals.h"
#include "env-inl.h"

namespace node {

Expand Down

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