module: bootstrap module loaders in shadow realm

This bootstraps ESM loaders in the ShadowRealm with
`ShadowRealm.prototype.importValue` as its entry point and enables
loading ESM and CJS modules in the ShadowRealm. The module is imported
without a parent URL and resolved with the current process's working
directory.

PR-URL: #48655
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>

lib/internal/bootstrap/realm.js

@@ -50,6 +50,8 @@
 
 const {
   ArrayFrom,
+  ArrayPrototypeFilter,
+  ArrayPrototypeIncludes,
   ArrayPrototypeMap,
   ArrayPrototypePush,
   ArrayPrototypeSlice,
@@ -215,8 +217,8 @@ const internalBuiltinIds = builtinIds
   .filter((id) => StringPrototypeStartsWith(id, 'internal/') && id !== selfId);
 
 // When --expose-internals is on we'll add the internal builtin ids to these.
-const canBeRequiredByUsersList = new SafeSet(publicBuiltinIds);
-const canBeRequiredByUsersWithoutSchemeList =
+let canBeRequiredByUsersList = new SafeSet(publicBuiltinIds);
+let canBeRequiredByUsersWithoutSchemeList =
   new SafeSet(publicBuiltinIds.filter((id) => !schemelessBlockList.has(id)));
 
 /**
@@ -269,6 +271,13 @@ class BuiltinModule {
     }
   }
 
+  static setRealmAllowRequireByUsers(ids) {
+    canBeRequiredByUsersList =
+      new SafeSet(ArrayPrototypeFilter(ids, (id) => ArrayPrototypeIncludes(publicBuiltinIds, id)));
+    canBeRequiredByUsersWithoutSchemeList =
+      new SafeSet(ArrayPrototypeFilter(ids, (id) => !schemelessBlockList.has(id)));
+  }
+
   // To be called during pre-execution when --expose-internals is on.
   // Enables the user-land module loader to access internal modules.
   static exposeInternals() {

lib/internal/bootstrap/shadow_realm.js

@@ -0,0 +1,21 @@
+'use strict';
+
+// This script sets up the context for shadow realms.
+
+const {
+  prepareShadowRealmExecution,
+} = require('internal/process/pre_execution');
+const {
+  BuiltinModule,
+} = require('internal/bootstrap/realm');
+
+BuiltinModule.setRealmAllowRequireByUsers([
+  /**
+   * The built-in modules exposed in the ShadowRealm must each be providing
+   * platform capabilities with no authority to cause side effects such as
+   * I/O or mutation of values that are shared across different realms within
+   * the same Node.js environment.
+   */
+]);
+
+prepareShadowRealmExecution();

lib/internal/main/worker_thread.js

@@ -136,6 +136,7 @@ port.on('message', (message) => {
     const isLoaderWorker =
       doEval === 'internal' &&
       filename === require('internal/modules/esm/utils').loaderWorkerId;
+    // Disable custom loaders in loader worker.
     setupUserModules(isLoaderWorker);
 
     if (!hasStdin)

lib/internal/modules/esm/loader.js

@@ -528,9 +528,10 @@ let emittedLoaderFlagWarning = false;
  */
 function createModuleLoader() {
   let customizations = null;
-  // Don't spawn a new worker if we're already in a worker thread created by instantiating CustomizedModuleLoader;
-  // doing so would cause an infinite loop.
-  if (!require('internal/modules/esm/utils').isLoaderWorker()) {
+  // Don't spawn a new worker if custom loaders are disabled. For instance, if
+  // we're already in a worker thread created by instantiating
+  // CustomizedModuleLoader; doing so would cause an infinite loop.
+  if (!require('internal/modules/esm/utils').forceDefaultLoader()) {
     const userLoaderPaths = getOptionValue('--experimental-loader');
     if (userLoaderPaths.length > 0) {
       if (!emittedLoaderFlagWarning) {

lib/internal/modules/esm/utils.js

@@ -4,6 +4,7 @@ const {
   ArrayIsArray,
   SafeSet,
   SafeWeakMap,
+  Symbol,
   ObjectFreeze,
 } = primordials;
 
@@ -157,6 +158,26 @@ function registerModule(referrer, registry) {
   moduleRegistries.set(idSymbol, registry);
 }
 
+/**
+ * Registers the ModuleRegistry for dynamic import() calls with a realm
+ * as the referrer. Similar to {@link registerModule}, but this function
+ * generates a new id symbol instead of using the one from the referrer
+ * object.
+ * @param {globalThis} globalThis The globalThis object of the realm.
+ * @param {ModuleRegistry} registry
+ */
+function registerRealm(globalThis, registry) {
+  let idSymbol = globalThis[host_defined_option_symbol];
+  // If the per-realm host-defined options is already registered, do nothing.
+  if (idSymbol) {
+    return;
+  }
+  // Otherwise, register the per-realm host-defined options.
+  idSymbol = Symbol('Realm globalThis');
+  globalThis[host_defined_option_symbol] = idSymbol;
+  moduleRegistries.set(idSymbol, registry);
+}
+
 /**
  * Defines the `import.meta` object for a given module.
  * @param {symbol} symbol - Reference to the module.
@@ -192,28 +213,29 @@ async function importModuleDynamicallyCallback(referrerSymbol, specifier, attrib
   throw new ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING();
 }
 
-let _isLoaderWorker = false;
+let _forceDefaultLoader = false;
 /**
  * Initializes handling of ES modules.
  * This is configured during pre-execution. Specifically it's set to true for
  * the loader worker in internal/main/worker_thread.js.
- * @param {boolean} [isLoaderWorker=false] - A boolean indicating whether the loader is a worker or not.
+ * @param {boolean} [forceDefaultLoader=false] - A boolean indicating disabling custom loaders.
  */
-function initializeESM(isLoaderWorker = false) {
-  _isLoaderWorker = isLoaderWorker;
+function initializeESM(forceDefaultLoader = false) {
+  _forceDefaultLoader = forceDefaultLoader;
   initializeDefaultConditions();
-  // Setup per-isolate callbacks that locate data or callbacks that we keep
+  // Setup per-realm callbacks that locate data or callbacks that we keep
   // track of for different ESM modules.
   setInitializeImportMetaObjectCallback(initializeImportMetaObject);
   setImportModuleDynamicallyCallback(importModuleDynamicallyCallback);
 }
 
 /**
- * Determine whether the current process is a loader worker.
- * @returns {boolean} Whether the current process is a loader worker.
+ * Determine whether custom loaders are disabled and it is forced to use the
+ * default loader.
+ * @returns {boolean}
  */
-function isLoaderWorker() {
-  return _isLoaderWorker;
+function forceDefaultLoader() {
+  return _forceDefaultLoader;
 }
 
 /**
@@ -251,10 +273,11 @@ async function initializeHooks() {
 
 module.exports = {
   registerModule,
+  registerRealm,
   initializeESM,
   initializeHooks,
   getDefaultConditions,
   getConditionsSet,
   loaderWorkerId: 'internal/modules/esm/worker',
-  isLoaderWorker,
+  forceDefaultLoader,
 };

lib/internal/process/pre_execution.js

@@ -67,6 +67,26 @@ function prepareWorkerThreadExecution() {
   });
 }
 
+function prepareShadowRealmExecution() {
+  const { registerRealm } = require('internal/modules/esm/utils');
+  // Patch the process object with legacy properties and normalizations.
+  // Do not expand argv1 as it is not available in ShadowRealm.
+  patchProcessObject(false);
+  setupDebugEnv();
+
+  // Disable custom loaders in ShadowRealm.
+  setupUserModules(true);
+  registerRealm(globalThis, {
+    __proto__: null,
+    importModuleDynamically: (specifier, _referrer, attributes) => {
+      // The handler for `ShadowRealm.prototype.importValue`.
+      const { esmLoader } = require('internal/process/esm_loader');
+      // `parentURL` is not set in the case of a ShadowRealm top-level import.
+      return esmLoader.import(specifier, undefined, attributes);
+    },
+  });
+}
+
 function prepareExecution(options) {
   const { expandArgv1, initializeModules, isMainThread } = options;
 
@@ -161,16 +181,17 @@ function setupSymbolDisposePolyfill() {
   }
 }
 
-function setupUserModules(isLoaderWorker = false) {
+function setupUserModules(forceDefaultLoader = false) {
   initializeCJSLoader();
-  initializeESMLoader(isLoaderWorker);
+  initializeESMLoader(forceDefaultLoader);
   const CJSLoader = require('internal/modules/cjs/loader');
   assert(!CJSLoader.hasLoadedAnyUserCJSModule);
-  // Loader workers are responsible for doing this themselves.
-  if (isLoaderWorker) {
-    return;
+  // Do not enable preload modules if custom loaders are disabled.
+  // For example, loader workers are responsible for doing this themselves.
+  // And preload modules are not supported in ShadowRealm as well.
+  if (!forceDefaultLoader) {
+    loadPreloadModules();
   }
-  loadPreloadModules();
   // Need to be done after --require setup.
   initializeFrozenIntrinsics();
 }
@@ -701,9 +722,9 @@ function initializeCJSLoader() {
   initializeCJS();
 }
 
-function initializeESMLoader(isLoaderWorker) {
+function initializeESMLoader(forceDefaultLoader) {
   const { initializeESM } = require('internal/modules/esm/utils');
-  initializeESM(isLoaderWorker);
+  initializeESM(forceDefaultLoader);
 
   // Patch the vm module when --experimental-vm-modules is on.
   // Please update the comments in vm.js when this block changes.
@@ -779,6 +800,7 @@ module.exports = {
   setupUserModules,
   prepareMainThreadExecution,
   prepareWorkerThreadExecution,
+  prepareShadowRealmExecution,
   markBootstrapComplete,
   loadPreloadModules,
   initializeFrozenIntrinsics,

src/async_wrap.cc

@@ -372,8 +372,9 @@ void AsyncWrap::CreatePerContextProperties(Local<Object> target,
                                            Local<Value> unused,
                                            Local<Context> context,
                                            void* priv) {
-  Environment* env = Environment::GetCurrent(context);
-  Isolate* isolate = env->isolate();
+  Realm* realm = Realm::GetCurrent(context);
+  Environment* env = realm->env();
+  Isolate* isolate = realm->isolate();
   HandleScope scope(isolate);
 
   PropertyAttribute ReadOnlyDontDelete =
@@ -446,13 +447,16 @@ void AsyncWrap::CreatePerContextProperties(Local<Object> target,
 
 #undef FORCE_SET_TARGET_FIELD
 
-  env->set_async_hooks_init_function(Local<Function>());
-  env->set_async_hooks_before_function(Local<Function>());
-  env->set_async_hooks_after_function(Local<Function>());
-  env->set_async_hooks_destroy_function(Local<Function>());
-  env->set_async_hooks_promise_resolve_function(Local<Function>());
-  env->set_async_hooks_callback_trampoline(Local<Function>());
-  env->set_async_hooks_binding(target);
+  // TODO(legendecas): async hook functions are not realm-aware yet.
+  // This simply avoid overriding principal realm's functions when a
+  // ShadowRealm initializes the binding.
+  realm->set_async_hooks_init_function(Local<Function>());
+  realm->set_async_hooks_before_function(Local<Function>());
+  realm->set_async_hooks_after_function(Local<Function>());
+  realm->set_async_hooks_destroy_function(Local<Function>());
+  realm->set_async_hooks_promise_resolve_function(Local<Function>());
+  realm->set_async_hooks_callback_trampoline(Local<Function>());
+  realm->set_async_hooks_binding(target);
 }
 
 void AsyncWrap::RegisterExternalReferences(

src/env.cc

@@ -1651,10 +1651,13 @@ void AsyncHooks::MemoryInfo(MemoryTracker* tracker) const {
 void AsyncHooks::grow_async_ids_stack() {
   async_ids_stack_.reserve(async_ids_stack_.Length() * 3);
 
-  env()->async_hooks_binding()->Set(
-      env()->context(),
-      env()->async_ids_stack_string(),
-      async_ids_stack_.GetJSArray()).Check();
+  env()
+      ->principal_realm()
+      ->async_hooks_binding()
+      ->Set(env()->context(),
+            env()->async_ids_stack_string(),
+            async_ids_stack_.GetJSArray())
+      .Check();
 }
 
 void AsyncHooks::FailWithCorruptedAsyncStack(double expected_async_id) {