worker: implement worker.moveMessagePortToContext()

This enables using `MessagePort`s in different `vm.Context`s, aiding with the isolation that the `vm` module seeks to provide. Refs: ayojs/ayo#111 PR-URL: #26497 Reviewed-By: James M Snell <jasnell@gmail.com>
nodejs · addaleax · Mar 7, 2019 · Mar 7, 2019 · Sep 9, 2017 · Mar 15, 2019
commit 23bf4ce91bb1cff44c8fb88a3aef796adec39cc0
diff --git a/doc/api/worker_threads.md b/doc/api/worker_threads.md
@@ -70,6 +70,30 @@ if (isMainThread) {
 }
 ```
 
+## worker.moveMessagePortToContext(port, contextifiedSandbox)
+<!-- YAML
+added: REPLACEME
+-->
+
+* `port` {MessagePort} The message port which will be transferred.
+* `contextifiedSandbox` {Object} A [contextified][] object as returned by the
+  `vm.createContext()` method.
+
+* Returns: {MessagePort}
+
+Transfer a `MessagePort` to a different [`vm`][] Context. The original `port`
+object will be rendered unusable, and the returned `MessagePort` instance will
+take its place.
+
+The returned `MessagePort` will be an object in the target context, and will
+inherit from its global `Object` class. Objects passed to the
+[`port.onmessage()`][] listener will also be created in the target context
+and inherit from its global `Object` class.
+
+However, the created `MessagePort` will no longer inherit from
+[`EventEmitter`][], and only [`port.onmessage()`][] can be used to receive
+events using it.
+
 ## worker.parentPort
 <!-- YAML
 added: v10.5.0
@@ -583,6 +607,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`Worker`]: #worker_threads_class_worker
 [`cluster` module]: cluster.html
 [`port.on('message')`]: #worker_threads_event_message
+[`port.onmessage()`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort/onmessage
 [`port.postMessage()`]: #worker_threads_port_postmessage_value_transferlist
 [`process.abort()`]: process.html#process_process_abort
 [`process.chdir()`]: process.html#process_process_chdir_directory
@@ -600,6 +625,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`require('worker_threads').threadId`]: #worker_threads_worker_threadid
 [`require('worker_threads').workerData`]: #worker_threads_worker_workerdata
 [`trace_events`]: tracing.html
+[`vm`]: vm.html
 [`worker.on('message')`]: #worker_threads_event_message_1
 [`worker.postMessage()`]: #worker_threads_worker_postmessage_value_transferlist
 [`worker.terminate()`]: #worker_threads_worker_terminate_callback
@@ -610,4 +636,5 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [Web Workers]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
 [browser `MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
 [child processes]: child_process.html
+[contextified]: vm.html#vm_what_does_it_mean_to_contextify_an_object
 [v8.serdes]: v8.html#v8_serialization_api
diff --git a/lib/internal/worker/io.js b/lib/internal/worker/io.js
@@ -8,6 +8,7 @@ const {
   MessagePort,
   MessageChannel,
   drainMessagePort,
+  moveMessagePortToContext,
   stopMessagePort
 } = internalBinding('messaging');
 const { threadId } = internalBinding('worker');
@@ -233,6 +234,7 @@ module.exports = {
   kIncrementsPortRef,
   kWaitingStreams,
   kStdioWantsMoreDataCallback,
+  moveMessagePortToContext,
   MessagePort,
   MessageChannel,
   setupPortReferencing,

diff --git a/lib/worker_threads.js b/lib/worker_threads.js
@@ -8,13 +8,15 @@ const {
 
 const {
   MessagePort,
-  MessageChannel
+  MessageChannel,
+  moveMessagePortToContext,
 } = require('internal/worker/io');
 
 module.exports = {
   isMainThread,
   MessagePort,
   MessageChannel,
+  moveMessagePortToContext,
   threadId,
   Worker,
   parentPort: null,

diff --git a/src/node_messaging.cc b/src/node_messaging.cc
@@ -2,11 +2,13 @@
 
 #include "async_wrap-inl.h"
 #include "debug_utils.h"
+#include "node_contextify.h"
 #include "node_buffer.h"
 #include "node_errors.h"
 #include "node_process.h"
 #include "util.h"
 
+using node::contextify::ContextifyContext;
 using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferCreationMode;
@@ -760,6 +762,35 @@ void MessagePort::Drain(const FunctionCallbackInfo<Value>& args) {
   port->OnMessage();
 }
 
+void MessagePort::MoveToContext(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  if (!args[0]->IsObject() ||
+      !env->message_port_constructor_template()->HasInstance(args[0])) {
+    return THROW_ERR_INVALID_ARG_TYPE(env,
+        "First argument needs to be a MessagePort instance");
+  }
+  MessagePort* port = Unwrap<MessagePort>(args[0].As<Object>());
+  CHECK_NOT_NULL(port);
+
+  Local<Value> context_arg = args[1];
+  ContextifyContext* context_wrapper;
+  if (!context_arg->IsObject() ||
+      (context_wrapper = ContextifyContext::ContextFromContextifiedSandbox(
+          env, context_arg.As<Object>())) == nullptr) {
+    return THROW_ERR_INVALID_ARG_TYPE(env, "Invalid context argument");
+  }
+
+  std::unique_ptr<MessagePortData> data;
+  if (!port->IsDetached())
+    data = port->Detach();
+
+  Context::Scope context_scope(context_wrapper->context());
+  MessagePort* target =
+      MessagePort::New(env, context_wrapper->context(), std::move(data));
+  if (target != nullptr)
+    args.GetReturnValue().Set(target->object());
+}
+
 void MessagePort::Entangle(MessagePort* a, MessagePort* b) {
   Entangle(a, b->data_.get());
 }
@@ -816,9 +847,9 @@ static void MessageChannel(const FunctionCallbackInfo<Value>& args) {
   MessagePort* port2 = MessagePort::New(env, context);
   MessagePort::Entangle(port1, port2);
 
-  args.This()->Set(env->context(), env->port1_string(), port1->object())
+  args.This()->Set(context, env->port1_string(), port1->object())
       .FromJust();
-  args.This()->Set(env->context(), env->port2_string(), port2->object())
+  args.This()->Set(context, env->port2_string(), port2->object())
       .FromJust();
 }
 
@@ -833,7 +864,7 @@ static void InitMessaging(Local<Object> target,
         FIXED_ONE_BYTE_STRING(env->isolate(), "MessageChannel");
     Local<FunctionTemplate> templ = env->NewFunctionTemplate(MessageChannel);
     templ->SetClassName(message_channel_string);
-    target->Set(env->context(),
+    target->Set(context,
                 message_channel_string,
                 templ->GetFunction(context).ToLocalChecked()).FromJust();
   }
@@ -847,6 +878,8 @@ static void InitMessaging(Local<Object> target,
   // the browser equivalents do not provide them.
   env->SetMethod(target, "stopMessagePort", MessagePort::Stop);
   env->SetMethod(target, "drainMessagePort", MessagePort::Drain);
+  env->SetMethod(target, "moveMessagePortToContext",
+                 MessagePort::MoveToContext);
 }
 
 }  // anonymous namespace

diff --git a/src/node_messaging.h b/src/node_messaging.h
@@ -158,12 +158,17 @@ class MessagePort : public HandleWrap {
   // Stop processing messages on this port as a receiving end.
   void Stop();
 
+  /* constructor */
   static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
+  /* prototype methods */
   static void PostMessage(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Start(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Stop(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Drain(const v8::FunctionCallbackInfo<v8::Value>& args);
 
+  /* static */
+  static void MoveToContext(const v8::FunctionCallbackInfo<v8::Value>& args);
+
   // Turns `a` and `b` into siblings, i.e. connects the sending side of one
   // to the receiving side of the other. This is not thread-safe.
   static void Entangle(MessagePort* a, MessagePort* b);

diff --git a/test/parallel/test-worker-message-port-move.js b/test/parallel/test-worker-message-port-move.js
@@ -0,0 +1,69 @@
+/* global port */
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const vm = require('vm');
+const {
+  MessagePort, MessageChannel, moveMessagePortToContext
+} = require('worker_threads');
+
+const context = vm.createContext();
+const { port1, port2 } = new MessageChannel();
+context.port = moveMessagePortToContext(port1, context);
+context.global = context;
+Object.assign(context, {
+  global: context,
+  assert,
+  MessagePort,
+  MessageChannel
+});
+
+vm.runInContext('(' + function() {
+  {
+    assert(port.postMessage instanceof Function);
+    assert(port.constructor instanceof Function);
+    for (let obj = port; obj !== null; obj = Object.getPrototypeOf(obj)) {
+      for (const key of Object.getOwnPropertyNames(obj)) {
+        if (typeof obj[key] === 'object' && obj[key] !== null) {
+          assert(obj[key] instanceof Object);
+        } else if (typeof obj[key] === 'function') {
+          assert(obj[key] instanceof Function);
+        }
+      }
+    }
+
+    assert(!(port instanceof MessagePort));
+    assert.strictEqual(port.onmessage, undefined);
+    port.onmessage = function({ data }) {
+      assert(data instanceof Object);
+      port.postMessage(data);
+    };
+    port.start();
+  }
+
+  {
+    let threw = false;
+    try {
+      port.postMessage(global);
+    } catch (e) {
+      assert.strictEqual(e.constructor.name, 'DOMException');
+      assert(e instanceof Object);
+      assert(e instanceof Error);
+      threw = true;
+    }
+    assert(threw);
+  }
+
+  {
+    const newDummyPort = new (port.constructor)();
+    assert(!(newDummyPort instanceof MessagePort));
+    assert(newDummyPort.close instanceof Function);
+    newDummyPort.close();
+  }
+} + ')()', context);
+
+port2.on('message', common.mustCall((msg) => {
+  assert(msg instanceof Object);
+  port2.close();
+}));
+port2.postMessage({});