From 921d2b080e810dff89c78db7d7f4c2e9e92f57ec Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Fri, 21 Oct 2016 11:57:20 +0200
Subject: [PATCH] src: make cross-context MakeCallback() calls work

Check that invoking a callback on a receiver from a different context
works.

It ran afoul of an `env->context() == isolate->GetCurrentContext()`
assertion so retrieve the environment from the callback context and
the context to enter from the environment's context() method.

We could also have retrieved the environment from the receiver's context
and that would have made little practical difference.  It just seemed
more correct to get it from the callback context because that is the
actual execution context.

PR-URL: https://github.com/nodejs/node/pull/9221
Reviewed-By: Anna Henningsen <anna@addaleax.net>
---
 src/node.cc                       | 57 ++++++++++++++++---------------
 test/addons/make-callback/test.js |  4 +++
 2 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/src/node.cc b/src/node.cc
index 111b83bf70c016..9f8eac23342d7c 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -1304,45 +1304,48 @@ Local<Value> MakeCallback(Environment* env,
 
 
 Local<Value> MakeCallback(Isolate* isolate,
-                           Local<Object> recv,
-                           const char* method,
-                           int argc,
-                           Local<Value> argv[]) {
+                          Local<Object> recv,
+                          const char* method,
+                          int argc,
+                          Local<Value> argv[]) {
   EscapableHandleScope handle_scope(isolate);
-  Local<Context> context = recv->CreationContext();
-  Environment* env = Environment::GetCurrent(context);
-  Context::Scope context_scope(context);
+  Local<String> method_string = OneByteString(isolate, method);
   return handle_scope.Escape(
-      Local<Value>::New(isolate, MakeCallback(env, recv, method, argc, argv)));
+      MakeCallback(isolate, recv, method_string, argc, argv));
 }
 
 
 Local<Value> MakeCallback(Isolate* isolate,
-                           Local<Object> recv,
-                           Local<String> symbol,
-                           int argc,
-                           Local<Value> argv[]) {
+                          Local<Object> recv,
+                          Local<String> symbol,
+                          int argc,
+                          Local<Value> argv[]) {
   EscapableHandleScope handle_scope(isolate);
-  Local<Context> context = recv->CreationContext();
-  Environment* env = Environment::GetCurrent(context);
-  Context::Scope context_scope(context);
-  return handle_scope.Escape(
-      Local<Value>::New(isolate, MakeCallback(env, recv, symbol, argc, argv)));
+  Local<Value> callback_v = recv->Get(symbol);
+  if (callback_v.IsEmpty()) return Local<Value>();
+  if (!callback_v->IsFunction()) return Local<Value>();
+  Local<Function> callback = callback_v.As<Function>();
+  return handle_scope.Escape(MakeCallback(isolate, recv, callback, argc, argv));
 }
 
 
 Local<Value> MakeCallback(Isolate* isolate,
-                           Local<Object> recv,
-                           Local<Function> callback,
-                           int argc,
-                           Local<Value> argv[]) {
+                          Local<Object> recv,
+                          Local<Function> callback,
+                          int argc,
+                          Local<Value> argv[]) {
+  // Observe the following two subtleties:
+  //
+  // 1. The environment is retrieved from the callback function's context.
+  // 2. The context to enter is retrieved from the environment.
+  //
+  // Because of the AssignToContext() call in src/node_contextify.cc,
+  // the two contexts need not be the same.
   EscapableHandleScope handle_scope(isolate);
-  Local<Context> context = recv->CreationContext();
-  Environment* env = Environment::GetCurrent(context);
-  Context::Scope context_scope(context);
-  return handle_scope.Escape(Local<Value>::New(
-        isolate,
-        MakeCallback(env, recv.As<Value>(), callback, argc, argv)));
+  Environment* env = Environment::GetCurrent(callback->CreationContext());
+  Context::Scope context_scope(env->context());
+  return handle_scope.Escape(
+      MakeCallback(env, recv.As<Value>(), callback, argc, argv));
 }
 
 
diff --git a/test/addons/make-callback/test.js b/test/addons/make-callback/test.js
index 43ad014c4af478..b67d1146a6bf1b 100644
--- a/test/addons/make-callback/test.js
+++ b/test/addons/make-callback/test.js
@@ -36,6 +36,10 @@ const recv = {
 assert.strictEqual(42, makeCallback(recv, 'one'));
 assert.strictEqual(42, makeCallback(recv, 'two', 1337));
 
+// Check that callbacks on a receiver from a different context works.
+const foreignObject = vm.runInNewContext('({ fortytwo() { return 42; } })');
+assert.strictEqual(42, makeCallback(foreignObject, 'fortytwo'));
+
 // Check that the callback is made in the context of the receiver.
 const target = vm.runInNewContext(`
     (function($Object) {