nstdlib-nightly/lib/internal/worker/js_transferable.mjs

Node.js standard library converted to runtime-agnostic ES modules.

// Source: https://github.com/nodejs/node/blob/65eff1eb/lib/internal/worker/js_transferable.js

import {
  messaging_deserialize_symbol,
  messaging_transfer_symbol,
  messaging_clone_symbol,
  messaging_transfer_list_symbol,
} from "nstdlib/stub/binding/symbols";
import { setDeserializerCreateObjectFunction } from "nstdlib/stub/binding/messaging";
import {
  privateSymbols as __privateSymbols__,
  constants as __constants__,
} from "nstdlib/stub/binding/util";

const { transfer_mode_private_symbol } = __privateSymbols__;

const { kDisallowCloneAndTransfer, kTransferable, kCloneable } = __constants__;

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 } = String.prototype.split.call(
      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();
  });
}

/**
 * Mark an object as being transferable or customized cloneable in
 * `.postMessage()`.
 * This should only applied to host objects like Web API interfaces, Node.js'
 * built-in objects.
 * Objects marked as cloneable and transferable should implement the method
 * `@@kClone` and `@@kTransfer` respectively. Method `@@kDeserialize` is
 * required to deserialize the data to a new instance.
 *
 * Example implementation of a cloneable interface (assuming its located in
 * `internal/my_interface.js`):
 *
 * ```
 * class MyInterface {
 *   constructor(...args) {
 *     markTransferMode(this, true);
 *     this.args = args;
 *   }
 *   [kDeserialize](data) {
 *     this.args = data.args;
 *   }
 *   [kClone]() {
 *     return {
 *        data: { args: this.args },
 *        deserializeInfo: 'internal/my_interface:MyInterface',
 *     }
 *   }
 * }
 *
 * module.exports = {
 *   MyInterface,
 * };
 * ```
 * @param {object} obj Host objects that can be either cloned or transferred.
 * @param {boolean} [cloneable] if the object can be cloned and `@@kClone` is
 *                              implemented.
 * @param {boolean} [transferable] if the object can be transferred and
 *                                 `@@kTransfer` is implemented.
 */
function markTransferMode(obj, cloneable = false, transferable = false) {
  if ((typeof obj !== "object" && typeof obj !== "function") || obj === null)
    return; // This object is a primitive and therefore already untransferable.
  let mode = kDisallowCloneAndTransfer;
  if (cloneable) mode |= kCloneable;
  if (transferable) mode |= kTransferable;
  obj[transfer_mode_private_symbol] = mode;
}

export { markTransferMode };
export { setup };
export { messaging_clone_symbol as kClone };
export { messaging_deserialize_symbol as kDeserialize };
export { messaging_transfer_symbol as kTransfer };
export { messaging_transfer_list_symbol as kTransferList };