lib: initial experimental AbortController implementation

AbortController impl based very closely on:
 https://github.com/mysticatea/abort-controller

Marked experimental.
Not currently used by any of the existing promise apis.

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: #33527
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

.eslintrc.js

@@ -280,6 +280,7 @@ module.exports = {
     'node-core/no-duplicate-requires': 'error',
   },
   globals: {
+    AbortController: 'readable',
     Atomics: 'readable',
     BigInt: 'readable',
     BigInt64Array: 'readable',

doc/api/cli.md

@@ -167,6 +167,13 @@ Enable experimental Source Map V3 support for stack traces.
 Currently, overriding `Error.prepareStackTrace` is ignored when the
 `--enable-source-maps` flag is set.
 
+### `--experimental-abortcontroller`
+<!-- YAML
+added: REPLACEME
+-->
+
+Enable experimental `AbortController` and `AbortSignal` support.
+
 ### `--experimental-import-meta-resolve`
 <!-- YAML
 added:
@@ -1209,6 +1216,7 @@ Node.js options that are allowed are:
 * `--disable-proto`
 * `--enable-fips`
 * `--enable-source-maps`
+* `--experimental-abortcontroller`
 * `--experimental-import-meta-resolve`
 * `--experimental-json-modules`
 * `--experimental-loader`

doc/api/globals.md

@@ -17,6 +17,101 @@ The objects listed here are specific to Node.js. There are [built-in objects][]
 that are part of the JavaScript language itself, which are also globally
 accessible.
 
+## Class: `AbortController`
+<!--YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+<!-- type=global -->
+
+A utility class used to signal cancelation in selected `Promise`-based APIs.
+The API is based on the Web API [`AbortController`][].
+
+To use, launch Node.js using the `--experimental-abortcontroller` flag.
+
+```js
+const ac = new AbortController();
+
+ac.signal.addEventListener('abort', () => console.log('Aborted!'),
+                           { once: true });
+
+ac.abort();
+
+console.log(ac.signal.aborted);  // Prints True
+```
+
+### `abortController.abort()`
+<!-- YAML
+added: REPLACEME
+-->
+
+Triggers the abort signal, causing the `abortController.signal` to emit
+the `'abort'` event.
+
+### `abortController.signal`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {AbortSignal}
+
+### Class: `AbortSignal extends EventTarget`
+<!-- YAML
+added: REPLACEME
+-->
+
+The `AbortSignal` is used to notify observers when the
+`abortController.abort()` method is called.
+
+#### Event: `'abort'`
+<!-- YAML
+added: REPLACEME
+-->
+
+The `'abort'` event is emitted when the `abortController.abort()` method
+is called. The callback is invoked with a single object argument with a
+single `type` propety set to `'abort'`:
+
+```js
+const ac = new AbortController();
+
+// Use either the onabort property...
+ac.signal.onabort = () => console.log('aborted!');
+
+// Or the EventTarget API...
+ac.signal.addEventListener('abort', (event) => {
+  console.log(event.type);  // Prints 'abort'
+}, { once: true });
+
+ac.abort();
+```
+
+The `AbortController` with which the `AbortSignal` is associated will only
+ever trigger the `'abort'` event once. Any event listeners attached to the
+`AbortSignal` *should* use the `{ once: true }` option (or, if using the
+`EventEmitter` APIs to attach a listener, use the `once()` method) to ensure
+that the event listener is removed as soon as the `'abort'` event is handled.
+Failure to do so may result in memory leaks.
+
+#### `abortSignal.aborted`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {boolean} True after the `AbortController` has been aborted.
+
+#### `abortSignal.onabort`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Function}
+
+An optional callback function that may be set by user code to be notified
+when the `abortController.abort()` function has been called.
+
 ## Class: `Buffer`
 <!-- YAML
 added: v0.1.103
@@ -226,6 +321,7 @@ The object that acts as the namespace for all W3C
 [WebAssembly][webassembly-org] related functionality. See the
 [Mozilla Developer Network][webassembly-mdn] for usage and compatibility.
 
+[`AbortController`]: https://developer.mozilla.org/en-US/docs/Web/API/AbortController
 [`TextDecoder`]: util.html#util_class_util_textdecoder
 [`TextEncoder`]: util.html#util_class_util_textencoder
 [`URLSearchParams`]: url.html#url_class_urlsearchparams

doc/node.1

@@ -118,6 +118,9 @@ Enable FIPS-compliant crypto at startup.
 Requires Node.js to be built with
 .Sy ./configure --openssl-fips .
 .
+.It Fl -experimental-abortcontroller
+Enable experimental AbortController and AbortSignal support.
+.
 .It Fl -enable-source-maps
 Enable experimental Source Map V3 support for stack traces.
 .

lib/internal/abort_controller.js

@@ -0,0 +1,83 @@
+'use strict';
+
+// Modeled very closely on the AbortController implementation
+// in https://github.com/mysticatea/abort-controller (MIT license)
+
+const {
+  Object,
+  Symbol,
+} = primordials;
+
+const {
+  EventTarget,
+  Event
+} = require('internal/event_target');
+const {
+  customInspectSymbol,
+  emitExperimentalWarning
+} = require('internal/util');
+const { inspect } = require('internal/util/inspect');
+
+const kAborted = Symbol('kAborted');
+
+function customInspect(self, obj, depth, options) {
+  if (depth < 0)
+    return self;
+
+  const opts = Object.assign({}, options, {
+    depth: options.depth === null ? null : options.depth - 1
+  });
+
+  return `${self.constructor.name} ${inspect(obj, opts)}`;
+}
+
+class AbortSignal extends EventTarget {
+  get aborted() { return !!this[kAborted]; }
+
+  [customInspectSymbol](depth, options) {
+    return customInspect(this, {
+      aborted: this.aborted
+    }, depth, options);
+  }
+}
+
+Object.defineProperties(AbortSignal.prototype, {
+  aborted: { enumerable: true }
+});
+
+function abortSignal(signal) {
+  if (signal[kAborted]) return;
+  signal[kAborted] = true;
+  const event = new Event('abort');
+  if (typeof signal.onabort === 'function') {
+    signal.onabort(event);
+  }
+  signal.dispatchEvent(event);
+}
+
+class AbortController {
+  #signal = new AbortSignal();
+
+  constructor() {
+    emitExperimentalWarning('AbortController');
+  }
+
+  get signal() { return this.#signal; }
+  abort() { abortSignal(this.#signal); }
+
+  [customInspectSymbol](depth, options) {
+    return customInspect(this, {
+      signal: this.signal
+    }, depth, options);
+  }
+}
+
+Object.defineProperties(AbortController.prototype, {
+  signal: { enumerable: true },
+  abort: { enumerable: true }
+});
+
+module.exports = {
+  AbortController,
+  AbortSignal,
+};

lib/internal/bootstrap/pre_execution.js

@@ -3,6 +3,7 @@
 const {
   Map,
   ObjectDefineProperty,
+  ObjectDefineProperties,
   SafeWeakMap,
 } = primordials;
 
@@ -53,6 +54,7 @@ function prepareMainThreadExecution(expandArgv1 = false) {
   // (including preload modules).
   initializeClusterIPC();
 
+  initializeAbortController();
   initializeDeprecations();
   initializeWASI();
   initializeCJSLoader();
@@ -304,6 +306,30 @@ function initializeDeprecations() {
   });
 }
 
+function initializeAbortController() {
+  const abortController = getOptionValue('--experimental-abortcontroller');
+  if (abortController) {
+    const {
+      AbortController,
+      AbortSignal
+    } = require('internal/abort_controller');
+    ObjectDefineProperties(global, {
+      AbortController: {
+        writable: true,
+        enumerable: false,
+        configurable: true,
+        value: AbortController
+      },
+      AbortSignal: {
+        writable: true,
+        enumerable: false,
+        configurable: true,
+        value: AbortSignal
+      }
+    });
+  }
+}
+
 function setupChildProcessIpcChannel() {
   if (process.env.NODE_CHANNEL_FD) {
     const assert = require('internal/assert');
@@ -438,6 +464,7 @@ module.exports = {
   setupWarningHandler,
   setupDebugEnv,
   prepareMainThreadExecution,
+  initializeAbortController,
   initializeDeprecations,
   initializeESMLoader,
   initializeFrozenIntrinsics,

lib/internal/main/worker_thread.js

@@ -13,6 +13,7 @@ const {
   setupInspectorHooks,
   setupWarningHandler,
   setupDebugEnv,
+  initializeAbortController,
   initializeDeprecations,
   initializeWASI,
   initializeCJSLoader,
@@ -112,6 +113,7 @@ port.on('message', (message) => {
     if (manifestSrc) {
       require('internal/process/policy').setup(manifestSrc, manifestURL);
     }
+    initializeAbortController();
     initializeDeprecations();
     initializeWASI();
     initializeCJSLoader();

node.gyp

@@ -95,6 +95,7 @@
       'lib/wasi.js',
       'lib/worker_threads.js',
       'lib/zlib.js',
+      'lib/internal/abort_controller.js',
       'lib/internal/assert.js',
       'lib/internal/assert/assertion_error.js',
       'lib/internal/assert/calltracker.js',

src/node_options.cc

@@ -274,6 +274,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "experimental Source Map V3 support",
             &EnvironmentOptions::enable_source_maps,
             kAllowedInEnvironment);
+  AddOption("--experimental-abortcontroller",
+            "experimental AbortController support",
+            &EnvironmentOptions::experimental_abortcontroller,
+            kAllowedInEnvironment);
   AddOption("--experimental-json-modules",
             "experimental JSON interop support for the ES Module loader",
             &EnvironmentOptions::experimental_json_modules,

src/node_options.h

@@ -101,6 +101,7 @@ class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
   bool enable_source_maps = false;
+  bool experimental_abortcontroller = false;
   bool experimental_json_modules = false;
   bool experimental_modules = false;
   std::string experimental_specifier_resolution;

test/common/index.js

@@ -256,6 +256,7 @@ function platformTimeout(ms) {
 }
 
 let knownGlobals = [
+  AbortController,
   clearImmediate,
   clearInterval,
   clearTimeout,

test/parallel/test-abortcontroller.js

@@ -0,0 +1,22 @@
+// Flags: --no-warnings --experimental-abortcontroller
+'use strict';
+
+const common = require('../common');
+
+const { ok, strictEqual } = require('assert');
+
+{
+  const ac = new AbortController();
+  ok(ac.signal);
+  ac.signal.onabort = common.mustCall((event) => {
+    ok(event);
+    strictEqual(event.type, 'abort');
+  });
+  ac.signal.addEventListener('abort', common.mustCall((event) => {
+    ok(event);
+    strictEqual(event.type, 'abort');
+  }), { once: true });
+  ac.abort();
+  ac.abort();
+  ok(ac.signal.aborted);
+}