src: extract common context embedder tag checks

Extract common context embedder tag checks to ContextEmbedderTag so
that verifying if a context is a node context doesn't need to access
private members of node::Environment.

PR-URL: nodejs/node#44258
Refs: nodejs/node#44179
Refs: nodejs/node#44252
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

Author: legendecas

src/env-inl.h

@@ -177,16 +177,7 @@ inline Environment* Environment::GetCurrent(v8::Isolate* isolate) {
 }
 
 inline Environment* Environment::GetCurrent(v8::Local<v8::Context> context) {
-  if (UNLIKELY(context.IsEmpty())) {
-    return nullptr;
-  }
-  if (UNLIKELY(context->GetNumberOfEmbedderDataFields() <=
-               ContextEmbedderIndex::kContextTag)) {
-    return nullptr;
-  }
-  if (UNLIKELY(context->GetAlignedPointerFromEmbedderData(
-                   ContextEmbedderIndex::kContextTag) !=
-               Environment::kNodeContextTagPtr)) {
+  if (UNLIKELY(!ContextEmbedderTag::IsNodeContext(context))) {
     return nullptr;
   }
   return static_cast<Environment*>(

src/env.cc

@@ -61,9 +61,9 @@ using v8::WeakCallbackInfo;
 using v8::WeakCallbackType;
 using worker::Worker;
 
-int const Environment::kNodeContextTag = 0x6e6f64;
-void* const Environment::kNodeContextTagPtr = const_cast<void*>(
-    static_cast<const void*>(&Environment::kNodeContextTag));
+int const ContextEmbedderTag::kNodeContextTag = 0x6e6f64;
+void* const ContextEmbedderTag::kNodeContextTagPtr = const_cast<void*>(
+    static_cast<const void*>(&ContextEmbedderTag::kNodeContextTag));
 
 void AsyncHooks::SetJSPromiseHooks(Local<Function> init,
                                    Local<Function> before,
@@ -431,11 +431,9 @@ void TrackingTraceStateObserver::UpdateTraceCategoryState() {
 
 void Environment::AssignToContext(Local<v8::Context> context,
                                   const ContextInfo& info) {
+  ContextEmbedderTag::TagNodeContext(context);
   context->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kEnvironment,
                                            this);
-  // 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_));

src/env.h

@@ -1535,9 +1535,6 @@ class Environment : public MemoryRetainer {
   uint64_t thread_id_;
   std::unordered_set<worker::Worker*> sub_worker_contexts_;
 
-  static void* const kNodeContextTagPtr;
-  static int const kNodeContextTag;
-
 #if HAVE_INSPECTOR
   std::unique_ptr<inspector::Agent> inspector_agent_;
   bool is_in_inspector_console_call_ = false;

src/node_context_data.h

@@ -3,6 +3,9 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include "util.h"
+#include "v8.h"
+
 namespace node {
 
 // Pick an index that's hopefully out of the way when we're embedded inside
@@ -21,26 +24,62 @@ namespace node {
 #define NODE_CONTEXT_ALLOW_WASM_CODE_GENERATION_INDEX 34
 #endif
 
-#ifndef NODE_CONTEXT_TAG
-#define NODE_CONTEXT_TAG 35
-#endif
-
 #ifndef NODE_BINDING_LIST
-#define NODE_BINDING_LIST_INDEX 36
+#define NODE_BINDING_LIST_INDEX 35
 #endif
 
 #ifndef NODE_CONTEXT_ALLOW_CODE_GENERATION_FROM_STRINGS_INDEX
-#define NODE_CONTEXT_ALLOW_CODE_GENERATION_FROM_STRINGS_INDEX 37
+#define NODE_CONTEXT_ALLOW_CODE_GENERATION_FROM_STRINGS_INDEX 36
+#endif
+
+// NODE_CONTEXT_TAG must be greater than any embedder indexes so that a single
+// check on the number of embedder data fields can assure the presence of all
+// embedder indexes.
+#ifndef NODE_CONTEXT_TAG
+#define NODE_CONTEXT_TAG 37
 #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,
   kAllowCodeGenerationFromStrings =
-      NODE_CONTEXT_ALLOW_CODE_GENERATION_FROM_STRINGS_INDEX
+      NODE_CONTEXT_ALLOW_CODE_GENERATION_FROM_STRINGS_INDEX,
+  kContextTag = NODE_CONTEXT_TAG,
+};
+
+class ContextEmbedderTag {
+ public:
+  static inline void TagNodeContext(v8::Local<v8::Context> context) {
+    // Used by ContextEmbedderTag::IsNodeContext to know that we are on a node
+    // context.
+    context->SetAlignedPointerInEmbedderData(
+        ContextEmbedderIndex::kContextTag,
+        ContextEmbedderTag::kNodeContextTagPtr);
+  }
+
+  static inline bool IsNodeContext(v8::Local<v8::Context> context) {
+    if (UNLIKELY(context.IsEmpty())) {
+      return false;
+    }
+    if (UNLIKELY(context->GetNumberOfEmbedderDataFields() <=
+                 ContextEmbedderIndex::kContextTag)) {
+      return false;
+    }
+    if (UNLIKELY(context->GetAlignedPointerFromEmbedderData(
+                     ContextEmbedderIndex::kContextTag) !=
+                 ContextEmbedderTag::kNodeContextTagPtr)) {
+      return false;
+    }
+    return true;
+  }
+
+ private:
+  static void* const kNodeContextTagPtr;
+  static int const kNodeContextTag;
+
+  ContextEmbedderTag() = delete;
 };
 
 }  // namespace node