js_transferable.js

'use strict';
const {
  Error,
  ObjectDefineProperties,
  ObjectGetOwnPropertyDescriptors,
  ObjectGetPrototypeOf,
  ObjectSetPrototypeOf,
  ObjectValues,
  ReflectConstruct,
  StringPrototypeSplit,
} = primordials;
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 { 0: module, 1: ctor } = StringPrototypeSplit(deserializeInfo, ':');
    const Ctor = require(module)[ctor];
    if (typeof Ctor !== 'function' ||
        typeof Ctor.prototype[messaging_deserialize_symbol] !== 'function') {
      // Not one of the official errors because one should not be able to get
      // here without messing with Node.js internals.
      // eslint-disable-next-line no-restricted-syntax
      throw new Error(`Unknown deserialize spec ${deserializeInfo}`);
    }

    return new Ctor();
  });
}

function makeTransferable(obj) {
  // If the object is already transferable, skip all this.
  if (obj instanceof JSTransferable) return obj;
  const inst = ReflectConstruct(JSTransferable, [], obj.constructor);
  const properties = ObjectGetOwnPropertyDescriptors(obj);
  const propertiesValues = ObjectValues(properties);
  for (let i = 0; i < propertiesValues.length; i++) {
    // We want to use null-prototype objects to not rely on globally mutable
    // %Object.prototype%.
    ObjectSetPrototypeOf(propertiesValues[i], null);
  }
  ObjectDefineProperties(inst, properties);
  ObjectSetPrototypeOf(inst, ObjectGetPrototypeOf(obj));
  return inst;
}

module.exports = {
  makeTransferable,
  setup,
  JSTransferable,
  kClone: messaging_clone_symbol,
  kDeserialize: messaging_deserialize_symbol,
  kTransfer: messaging_transfer_symbol,
  kTransferList: messaging_transfer_list_symbol,
};