Add structuredClone global method

.eslintrc.js

@@ -362,5 +362,6 @@ module.exports = {
     btoa: 'readable',
     atob: 'readable',
     performance: 'readable',
+    structuredClone: 'readable',
   },
 };

lib/.eslintrc.yaml

@@ -57,6 +57,8 @@ rules:
       # disabled with --no-harmony-sharedarraybuffer CLI flag.
     - name: SharedArrayBuffer
       message: "Use `const { SharedArrayBuffer } = globalThis;` instead of the global."
+    - name: StructuredClone
+      message: "Use `const { structuredClone } = require('internal/structured_clone');` instead of the global."
     - name: TextDecoder
       message: "Use `const { TextDecoder } = require('internal/encoding');` instead of the global."
     - name: TextEncoder

lib/internal/bootstrap/node.js

@@ -254,6 +254,11 @@ if (!config.noBrowserGlobals) {
   // Non-standard extensions:
   defineOperation(globalThis, 'clearImmediate', timers.clearImmediate);
   defineOperation(globalThis, 'setImmediate', timers.setImmediate);
+
+  const {
+    structuredClone,
+  } = require('internal/structured_clone');
+  defineOperation(globalThis, 'structuredClone', structuredClone);
 }
 
 // Set the per-Environment callback that will be called

lib/internal/structured_clone.js

@@ -0,0 +1,21 @@
+'use strict';
+
+const {
+  MessageChannel,
+  receiveMessageOnPort,
+} = require('internal/worker/io');
+
+let channel;
+function structuredClone(value, transfer) {
+  // TODO: Improve this with a more efficient solution that avoids
+  // instantiating a MessageChannel
+  channel ??= new MessageChannel();
+  channel.port1.unref();
+  channel.port2.unref();
+  channel.port1.postMessage(value, transfer);
+  return receiveMessageOnPort(channel.port2).message;
+}
+
+module.exports = {
+  structuredClone
+};

test/fixtures/wpt/LICENSE.md

@@ -1,6 +1,6 @@
 # The 3-Clause BSD License
 
-Copyright 2019 web-platform-tests contributors
+Copyright © web-platform-tests contributors
 
 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
 

test/fixtures/wpt/README.md

@@ -18,6 +18,7 @@ Last update:
 - hr-time: https://github.com/web-platform-tests/wpt/tree/9910784394/hr-time
 - html/webappapis/atob: https://github.com/web-platform-tests/wpt/tree/f267e1dca6/html/webappapis/atob
 - html/webappapis/microtask-queuing: https://github.com/web-platform-tests/wpt/tree/2c5c3c4c27/html/webappapis/microtask-queuing
+- html/webappapis/structured-clone: https://github.com/web-platform-tests/wpt/tree/47d3fb280c/html/webappapis/structured-clone
 - html/webappapis/timers: https://github.com/web-platform-tests/wpt/tree/5873f2d8f1/html/webappapis/timers
 - interfaces: https://github.com/web-platform-tests/wpt/tree/fc086c82d5/interfaces
 - performance-timeline: https://github.com/web-platform-tests/wpt/tree/17ebc3aea0/performance-timeline

test/fixtures/wpt/html/webappapis/structured-clone/structured-clone-battery-of-tests-harness.js

@@ -0,0 +1,44 @@
+/**
+ * Runs a collection of tests that determine if an API implements structured clone
+ * correctly.
+ *
+ * The `runner` parameter has the following properties:
+ * - `setup()`: An optional function run once before testing starts
+ * - `teardown()`: An option function run once after all tests are done
+ * - `preTest()`: An optional, async function run before a test
+ * - `postTest()`: An optional, async function run after a test is done
+ * - `structuredClone(obj, transferList)`: Required function that somehow
+ *                                         structurally clones an object.
+ * - `hasDocument`: When true, disables tests that require a document. True by default.
+ */
+
+function runStructuredCloneBatteryOfTests(runner) {
+  const defaultRunner = {
+    setup() {},
+    preTest() {},
+    postTest() {},
+    teardown() {},
+    hasDocument: true
+  };
+  runner = Object.assign({}, defaultRunner, runner);
+
+  let setupPromise = runner.setup();
+  const allTests = structuredCloneBatteryOfTests.map(test => {
+
+    if (!runner.hasDocument && test.requiresDocument) {
+      return;
+    }
+
+    return new Promise(resolve => {
+      promise_test(async _ => {
+        test = await test;
+        await setupPromise;
+        await runner.preTest(test);
+        await test.f(runner)
+        await runner.postTest(test);
+        resolve();
+      }, test.description);
+    }).catch(_ => {});
+  });
+  Promise.all(allTests).then(_ => runner.teardown());
+}

test/fixtures/wpt/html/webappapis/structured-clone/structured-clone-battery-of-tests-with-transferables.js

@@ -0,0 +1,22 @@
+structuredCloneBatteryOfTests.push({
+  description: 'ArrayBuffer',
+  async f(runner) {
+    const buffer = new Uint8Array([1]).buffer;
+    const copy = await runner.structuredClone(buffer, [buffer]);
+    assert_equals(buffer.byteLength, 0);
+    assert_equals(copy.byteLength, 1);
+  }
+});
+
+structuredCloneBatteryOfTests.push({
+  description: 'MessagePort',
+  async f(runner) {
+    const {port1, port2} = new MessageChannel();
+    const copy = await runner.structuredClone(port2, [port2]);
+    const msg = new Promise(resolve => port1.onmessage = resolve);
+    copy.postMessage('ohai');
+    assert_equals((await msg).data, 'ohai');
+  }
+});
+
+// TODO: ImageBitmap