worker: allow passing JS wrapper objects via postMessage

Enable JS wrapper objects to be used as transferable or cloneable objects in `postMessage()` calls, by having them extend a C++-backed class. This requires a few internal changes: - This commit adds the possibility for transferred objects to read/write JS values at the end of the serialization/deserialization phases. - This commit adds the possibility for transferred objects to list sub-transferables, e.g. typically the public JS wrapper class would list its C++ handle in there. - This commit adds usage of `BaseObject` in a few more places, because now during deserialization weakly held objects can also be involved, in addition to `MessagePort`s.
addaleax · Apr 8, 2020 · Apr 9, 2020 · Jun 6, 2020 · Jun 6, 2020 · Jun 6, 2020
commit 877d631c56e6b99d9af176a2287edab850ab6e55
diff --git a/lib/internal/bootstrap/node.js b/lib/internal/bootstrap/node.js
@@ -58,6 +58,7 @@ process._exiting = false;
 
 // process.config is serialized config.gypi
 process.config = JSONParse(internalBinding('native_module').config);
+require('internal/worker/js_transferable').setup();
 
 // Bootstrappers for all threads, including worker threads and main thread
 const perThreadSetup = require('internal/process/per_thread');

diff --git a/lib/internal/worker/js_transferable.js b/lib/internal/worker/js_transferable.js
@@ -0,0 +1,31 @@
+'use strict';
+const {
+  messaging_deserialize_symbol,
+  messaging_transfer_symbol,
+  messaging_clone_symbol,
+  messaging_transfer_list_symbol
+} = internalBinding('symbols');
+const {
+  JSTransferable,
+  setDeserializerCreateObjectFunction
+} = internalBinding('messaging');
+
+function setup() {
+  // Register the handler that will be used when deserializing JS-based objects
+  // from .postMessage() calls. The format of `deserializeInfo` is generally
+  // 'module:Constructor', e.g. 'internal/fs/promises:FileHandle'.
+  setDeserializerCreateObjectFunction((deserializeInfo) => {
+    const [ module, ctor ] = deserializeInfo.split(':');
+    const Ctor = require(module)[ctor];
+    return new Ctor();
+  });
+}
+
+module.exports = {
+  setup,
+  JSTransferable,
+  kClone: messaging_clone_symbol,
+  kDeserialize: messaging_deserialize_symbol,
+  kTransfer: messaging_transfer_symbol,
+  kTransferList: messaging_transfer_list_symbol
+};
diff --git a/node.gyp b/node.gyp
@@ -220,6 +220,7 @@
       'lib/internal/vm/module.js',
       'lib/internal/worker.js',
       'lib/internal/worker/io.js',
+      'lib/internal/worker/js_transferable.js',
       'lib/internal/watchdog.js',
       'lib/internal/streams/lazy_transform.js',
       'lib/internal/streams/async_iterator.js',

diff --git a/src/base_object.h b/src/base_object.h
@@ -123,12 +123,17 @@ class BaseObject : public MemoryRetainer {
   //     make sure that they are not accidentally destroyed on the sending side.
   //     TransferForMessaging() will be called to get a representation of the
   //     object that is used for subsequent deserialization.
+  //     The NestedTransferables() method can be used to transfer other objects
+  //     along with this one, if a situation requires it.
   // - kCloneable:
   //     This object can be cloned without being modified.
   //     CloneForMessaging() will be called to get a representation of the
   //     object that is used for subsequent deserialization, unless the
   //     object is listed in transferList, in which case TransferForMessaging()
   //     is attempted first.
+  // After a successful clone, FinalizeTransferRead() is called on the receiving
+  // end, and can read deserialize JS data possibly serialized by a previous
+  // FinalizeTransferWrite() call.
   enum class TransferMode {
     kUntransferable,
     kTransferable,
@@ -137,6 +142,10 @@ class BaseObject : public MemoryRetainer {
   virtual TransferMode GetTransferMode() const;
   virtual std::unique_ptr<worker::TransferData> TransferForMessaging();
   virtual std::unique_ptr<worker::TransferData> CloneForMessaging() const;
+  virtual v8::Maybe<std::vector<BaseObjectPtrImpl<BaseObject, false>>>
+      NestedTransferables() const;
+  virtual v8::Maybe<bool> FinalizeTransferRead(
+      v8::Local<v8::Context> context, v8::ValueDeserializer* deserializer);
 
   virtual inline void OnGCCollect();
 

diff --git a/src/env.h b/src/env.h
@@ -159,6 +159,10 @@ constexpr size_t kFsStatsBufferLength =
   V(async_id_symbol, "async_id_symbol")                                        \
   V(handle_onclose_symbol, "handle_onclose")                                   \
   V(no_message_symbol, "no_message_symbol")                                    \
+  V(messaging_deserialize_symbol, "messaging_deserialize_symbol")              \
+  V(messaging_transfer_symbol, "messaging_transfer_symbol")                    \
+  V(messaging_clone_symbol, "messaging_clone_symbol")                          \
+  V(messaging_transfer_list_symbol, "messaging_transfer_list_symbol")          \
   V(oninit_symbol, "oninit")                                                   \
   V(owner_symbol, "owner_symbol")                                              \
   V(onpskexchange_symbol, "onpskexchange")                                     \
@@ -201,6 +205,7 @@ constexpr size_t kFsStatsBufferLength =
   V(crypto_rsa_pss_string, "rsa-pss")                                          \
   V(cwd_string, "cwd")                                                         \
   V(data_string, "data")                                                       \
+  V(deserialize_info_string, "deserializeInfo")                                \
   V(dest_string, "dest")                                                       \
   V(destroyed_string, "destroyed")                                             \
   V(detached_string, "detached")                                               \
@@ -453,6 +458,7 @@ constexpr size_t kFsStatsBufferLength =
   V(internal_binding_loader, v8::Function)                                     \
   V(immediate_callback_function, v8::Function)                                 \
   V(inspector_console_extension_installer, v8::Function)                       \
+  V(messaging_deserialize_create_object, v8::Function)                         \
   V(message_port, v8::Object)                                                  \
   V(native_module_require, v8::Function)                                       \
   V(performance_entry_callback, v8::Function)                                  \

diff --git a/src/node_errors.h b/src/node_errors.h
@@ -93,7 +93,8 @@ void OnFatalError(const char* location, const char* message);
   V(ERR_MEMORY_ALLOCATION_FAILED, "Failed to allocate memory")                 \
   V(ERR_OSSL_EVP_INVALID_DIGEST, "Invalid digest used")                        \
   V(ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST,                                 \
-    "MessagePort was found in message but not listed in transferList")         \
+    "Object that needs transfer was found in message but not listed "          \
+    "in transferList")                                                         \
   V(ERR_MISSING_PLATFORM_FOR_WORKER,                                           \
     "The V8 platform used by this instance of Node does not support "          \
     "creating Workers")                                                        \