worker: emit 'messagerror' events for failed deserialization

This is much nicer than just treating exceptions as uncaught, and
enables reporting of exceptions from the internal C++ deserialization
machinery.

PR-URL: #33772
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

Author: addaleax

doc/api/errors.md

@@ -1566,6 +1566,17 @@ behavior. See the documentation for [policy][] manifests for more information.
 An attempt was made to allocate memory (usually in the C++ layer) but it
 failed.
 
+<a id="ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE"></a>
+### `ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE`
+<!-- YAML
+added: REPLACEME
+-->
+
+A message posted to a [`MessagePort`][] could not be deserialized in the target
+[vm][] `Context`. Not all Node.js objects can be successfully instantiated in
+any context at this time, and attempting to transfer them using `postMessage()`
+can fail on the receiving side in that case.
+
 <a id="ERR_METHOD_NOT_IMPLEMENTED"></a>
 ### `ERR_METHOD_NOT_IMPLEMENTED`
 
@@ -2564,6 +2575,7 @@ such as `process.stdout.on('data')`.
 [`Class: assert.AssertionError`]: assert.html#assert_class_assert_assertionerror
 [`ERR_INVALID_ARG_TYPE`]: #ERR_INVALID_ARG_TYPE
 [`EventEmitter`]: events.html#events_class_eventemitter
+[`MessagePort`]: worker_threads.html#worker_threads_class_messageport
 [`Object.getPrototypeOf`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getPrototypeOf
 [`Object.setPrototypeOf`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/setPrototypeOf
 [`REPL`]: repl.html

doc/api/worker_threads.md

@@ -303,6 +303,15 @@ input of [`port.postMessage()`][].
 Listeners on this event will receive a clone of the `value` parameter as passed
 to `postMessage()` and no further arguments.
 
+### Event: `'messageerror'`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `error` {Error} An Error object
+
+The `'messageerror'` event is emitted when deserializing a message failed.
+
 ### `port.close()`
 <!-- YAML
 added: v10.5.0
@@ -681,6 +690,15 @@ See the [`port.on('message')`][] event for more details.
 All messages sent from the worker thread will be emitted before the
 [`'exit'` event][] is emitted on the `Worker` object.
 
+### Event: `'messageerror'`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `error` {Error} An Error object
+
+The `'messageerror'` event is emitted when deserializing a message failed.
+
 ### Event: `'online'`
 <!-- YAML
 added: v10.5.0

lib/internal/worker.js

@@ -192,7 +192,9 @@ class Worker extends EventEmitter {
       transferList.push(...options.transferList);
 
     this[kPublicPort] = port1;
-    this[kPublicPort].on('message', (message) => this.emit('message', message));
+    for (const event of ['message', 'messageerror']) {
+      this[kPublicPort].on(event, (message) => this.emit(event, message));
+    }
     setupPortReferencing(this[kPublicPort], this, 'message');
     this[kPort].postMessage({
       argv,

src/env.h

@@ -223,6 +223,7 @@ constexpr size_t kFsStatsBufferLength =
   V(done_string, "done")                                                       \
   V(duration_string, "duration")                                               \
   V(ecdh_string, "ECDH")                                                       \
+  V(emit_string, "emit")                                                       \
   V(emit_warning_string, "emitWarning")                                        \
   V(empty_object_string, "{}")                                                 \
   V(encoding_string, "encoding")                                               \
@@ -279,6 +280,7 @@ constexpr size_t kFsStatsBufferLength =
   V(message_port_constructor_string, "MessagePort")                            \
   V(message_port_string, "messagePort")                                        \
   V(message_string, "message")                                                 \
+  V(messageerror_string, "messageerror")                                       \
   V(minttl_string, "minttl")                                                   \
   V(module_string, "module")                                                   \
   V(modulus_string, "modulus")                                                 \

src/node_errors.h

@@ -41,6 +41,7 @@ void OnFatalError(const char* location, const char* message);
   V(ERR_INVALID_ARG_TYPE, TypeError)                                           \
   V(ERR_INVALID_TRANSFER_OBJECT, TypeError)                                    \
   V(ERR_MEMORY_ALLOCATION_FAILED, Error)                                       \
+  V(ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE, Error)                             \
   V(ERR_MISSING_ARGS, TypeError)                                               \
   V(ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST, TypeError)                      \
   V(ERR_MISSING_PASSPHRASE, TypeError)                                         \
@@ -92,6 +93,9 @@ void OnFatalError(const char* location, const char* message);
   V(ERR_INVALID_TRANSFER_OBJECT, "Found invalid object in transferList")       \
   V(ERR_MEMORY_ALLOCATION_FAILED, "Failed to allocate memory")                 \
   V(ERR_OSSL_EVP_INVALID_DIGEST, "Invalid digest used")                        \
+  V(ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE,                                    \
+    "A message object could not be deserialized successfully in the target "   \
+    "vm.Context")                                                              \
   V(ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST,                                 \
     "Object that needs transfer was found in message but not listed "          \
     "in transferList")                                                         \

src/node_messaging.cc

@@ -742,7 +742,17 @@ void MessagePort::OnMessage() {
     Local<Function> emit_message = PersistentToLocal::Strong(emit_message_fn_);
 
     Local<Value> payload;
-    if (!ReceiveMessage(context, true).ToLocal(&payload)) goto reschedule;
+    Local<Value> message_error;
+    {
+      // Catch any exceptions from parsing the message itself (not from
+      // emitting it) as 'messageeror' events.
+      TryCatchScope try_catch(env());
+      if (!ReceiveMessage(context, true).ToLocal(&payload)) {
+        if (try_catch.HasCaught() && !try_catch.HasTerminated())
+          message_error = try_catch.Exception();
+        goto reschedule;
+      }
+    }
     if (payload == env()->no_message_symbol()) break;
 
     if (!env()->can_call_into_js()) {
@@ -753,6 +763,16 @@ void MessagePort::OnMessage() {
 
     if (MakeCallback(emit_message, 1, &payload).IsEmpty()) {
     reschedule:
+      if (!message_error.IsEmpty()) {
+        // This should become a `messageerror` event in the sense of the
+        // EventTarget API at some point.
+        Local<Value> argv[] = {
+          env()->messageerror_string(),
+          message_error
+        };
+        USE(MakeCallback(env()->emit_string(), arraysize(argv), argv));
+      }
+
       // Re-schedule OnMessage() execution in case of failure.
       if (data_)
         TriggerAsync();
@@ -1215,8 +1235,7 @@ BaseObjectPtr<BaseObject> JSTransferable::Data::Deserialize(
   // the end of the stream, after the main message has been read.
 
   if (context != env->context()) {
-    // It would be nice to throw some kind of exception here, but how do we
-    // pass that to end users? For now, just drop the message silently.
+    THROW_ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE(env);
     return {};
   }
   HandleScope handle_scope(env->isolate());

test/parallel/test-worker-message-port-transfer-fake-js-transferable-internal.js

@@ -26,7 +26,7 @@ const { once } = require('events');
   port1.postMessage(fh, [ fh ]);
   port2.on('message', common.mustNotCall());
 
-  const [ exception ] = await once(process, 'uncaughtException');
+  const [ exception ] = await once(port2, 'messageerror');
 
   assert.strictEqual(exception.message, 'Unknown deserialize spec net:Socket');
   port2.close();

test/parallel/test-worker-message-port-transfer-fake-js-transferable.js

@@ -30,7 +30,7 @@ module.exports = {
   port1.postMessage(fh, [ fh ]);
   port2.on('message', common.mustNotCall());
 
-  const [ exception ] = await once(process, 'uncaughtException');
+  const [ exception ] = await once(port2, 'messageerror');
 
   assert.match(exception.message, /Missing internal module/);
   port2.close();

test/parallel/test-worker-message-port-transfer-filehandle.js

@@ -55,6 +55,12 @@ const { once } = require('events');
     assert.strictEqual(msgEvent.data, 'second message');
     port1.close();
   });
+  // TODO(addaleax): Switch this to a 'messageerror' event once MessagePort
+  // implements EventTarget fully and in a cross-context manner.
+  port2moved.emit = common.mustCall((name, err) => {
+    assert.strictEqual(name, 'messageerror');
+    assert.strictEqual(err.code, 'ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE');
+  });
   port2moved.start();
 
   assert.notStrictEqual(fh.fd, -1);