http2: replace direct array usage with struct for js_fields_

PR-URL: #30534
Fixes: #30505
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_http2.cc

@@ -651,7 +651,9 @@ Http2Session::Http2Session(Environment* env,
   {
     // Make the js_fields_ property accessible to JS land.
     Local<ArrayBuffer> ab =
-        ArrayBuffer::New(env->isolate(), js_fields_, kSessionUint8FieldCount);
+        ArrayBuffer::New(env->isolate(),
+                         reinterpret_cast<uint8_t*>(&js_fields_),
+                         kSessionUint8FieldCount);
     Local<Uint8Array> uint8_arr =
         Uint8Array::New(ab, 0, kSessionUint8FieldCount);
     USE(wrap->Set(env->context(), env->fields_string(), uint8_arr));
@@ -1082,7 +1084,7 @@ int Http2Session::OnFrameNotSent(nghttp2_session* handle,
   if (error_code == NGHTTP2_ERR_SESSION_CLOSING ||
       error_code == NGHTTP2_ERR_STREAM_CLOSED ||
       error_code == NGHTTP2_ERR_STREAM_CLOSING ||
-      session->js_fields_[kSessionFrameErrorListenerCount] == 0) {
+      session->js_fields_.frame_error_listener_count == 0) {
     return 0;
   }
 
@@ -1388,7 +1390,7 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // are considered advisory only, so this has no real effect other than to
 // simply let user code know that the priority has changed.
 void Http2Session::HandlePriorityFrame(const nghttp2_frame* frame) {
-  if (js_fields_[kSessionPriorityListenerCount] == 0) return;
+  if (js_fields_.priority_listener_count == 0) return;
   Isolate* isolate = env()->isolate();
   HandleScope scope(isolate);
   Local<Context> context = env()->context();
@@ -1458,7 +1460,7 @@ void Http2Session::HandleGoawayFrame(const nghttp2_frame* frame) {
 
 // Called by OnFrameReceived when a complete ALTSVC frame has been received.
 void Http2Session::HandleAltSvcFrame(const nghttp2_frame* frame) {
-  if (!(js_fields_[kBitfield] & (1 << kSessionHasAltsvcListeners))) return;
+  if (!(js_fields_.bitfield & (1 << kSessionHasAltsvcListeners))) return;
   Isolate* isolate = env()->isolate();
   HandleScope scope(isolate);
   Local<Context> context = env()->context();
@@ -1537,7 +1539,7 @@ void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
     return;
   }
 
-  if (!(js_fields_[kBitfield] & (1 << kSessionHasPingListeners))) return;
+  if (!(js_fields_.bitfield & (1 << kSessionHasPingListeners))) return;
   // Notify the session that a ping occurred
   arg = Buffer::Copy(env(),
                       reinterpret_cast<const char*>(frame->ping.opaque_data),
@@ -1549,8 +1551,8 @@ void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
 void Http2Session::HandleSettingsFrame(const nghttp2_frame* frame) {
   bool ack = frame->hd.flags & NGHTTP2_FLAG_ACK;
   if (!ack) {
-    js_fields_[kBitfield] &= ~(1 << kSessionRemoteSettingsIsUpToDate);
-    if (!(js_fields_[kBitfield] & (1 << kSessionHasRemoteSettingsListeners)))
+    js_fields_.bitfield &= ~(1 << kSessionRemoteSettingsIsUpToDate);
+    if (!(js_fields_.bitfield & (1 << kSessionHasRemoteSettingsListeners)))
       return;
     // This is not a SETTINGS acknowledgement, notify and return
     MakeCallback(env()->http2session_on_settings_function(), 0, nullptr);

src/node_http2.h

@@ -675,15 +675,23 @@ class Http2Stream::Provider::Stream : public Http2Stream::Provider {
                         void* user_data);
 };
 
+typedef struct {
+  uint8_t bitfield;
+  uint8_t priority_listener_count;
+  uint8_t frame_error_listener_count;
+} SessionJSFields;
+
 // Indices for js_fields_, which serves as a way to communicate data with JS
 // land fast. In particular, we store information about the number/presence
 // of certain event listeners in JS, and skip calls from C++ into JS if they
 // are missing.
 enum SessionUint8Fields {
-  kBitfield,  // See below
-  kSessionPriorityListenerCount,
-  kSessionFrameErrorListenerCount,
-  kSessionUint8FieldCount
+  kBitfield = offsetof(SessionJSFields, bitfield),  // See below
+  kSessionPriorityListenerCount =
+      offsetof(SessionJSFields, priority_listener_count),
+  kSessionFrameErrorListenerCount =
+      offsetof(SessionJSFields, frame_error_listener_count),
+  kSessionUint8FieldCount = sizeof(SessionJSFields)
 };
 
 enum SessionBitfieldFlags {
@@ -972,7 +980,7 @@ class Http2Session : public AsyncWrap, public StreamListener {
   nghttp2_session* session_;
 
   // JS-accessible numeric fields, as indexed by SessionUint8Fields.
-  uint8_t js_fields_[kSessionUint8FieldCount] = {};
+  SessionJSFields js_fields_ = {};
 
   // The session type: client or server
   nghttp2_session_type session_type_;