worker: hide MessagePort init function behind symbol

This reduces unintended exposure of internals.

PR-URL: #23037
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

lib/internal/worker.js

@@ -24,7 +24,8 @@ util.inherits(MessagePort, EventEmitter);
 const {
   Worker: WorkerImpl,
   getEnvMessagePort,
-  threadId
+  threadId,
+  oninit: oninit_symbol
 } = internalBinding('worker');
 
 const isMainThread = threadId === 0;
@@ -93,7 +94,7 @@ function oninit() {
   setupPortReferencing(this, this, 'message');
 }
 
-Object.defineProperty(MessagePort.prototype, 'oninit', {
+Object.defineProperty(MessagePort.prototype, oninit_symbol, {
   enumerable: true,
   writable: false,
   value: oninit

src/env.h

@@ -113,6 +113,7 @@ struct PackageConfig {
 #define PER_ISOLATE_SYMBOL_PROPERTIES(V)                                      \
   V(handle_onclose_symbol, "handle_onclose")                                  \
   V(owner_symbol, "owner")                                                    \
+  V(oninit_symbol, "oninit")                                                  \
 
 // Strings are per-isolate primitives but Environment proxies them
 // for the sake of convenience.  Strings should be ASCII-only.
@@ -219,7 +220,6 @@ struct PackageConfig {
   V(onhandshakedone_string, "onhandshakedone")                                \
   V(onhandshakestart_string, "onhandshakestart")                              \
   V(onheaders_string, "onheaders")                                            \
-  V(oninit_string, "oninit")                                                  \
   V(onmessage_string, "onmessage")                                            \
   V(onnewsession_string, "onnewsession")                                      \
   V(onocspresponse_string, "onocspresponse")                                  \

src/node_messaging.cc

@@ -421,7 +421,7 @@ MessagePort::MessagePort(Environment* env,
   async()->data = static_cast<void*>(this);
 
   Local<Value> fn;
-  if (!wrap->Get(context, env->oninit_string()).ToLocal(&fn))
+  if (!wrap->Get(context, env->oninit_symbol()).ToLocal(&fn))
     return;
 
   if (fn->IsFunction()) {

src/node_worker.cc

@@ -501,6 +501,10 @@ void InitWorker(Local<Object> target,
               thread_id_string,
               Number::New(env->isolate(),
                           static_cast<double>(env->thread_id()))).FromJust();
+  Local<String> oninit_string = FIXED_ONE_BYTE_STRING(env->isolate(), "oninit");
+  target->Set(env->context(),
+              oninit_string,
+              env->oninit_symbol()).FromJust();
 }
 
 }  // anonymous namespace