net: add experimental net/promises API

doc/api/net.md

@@ -447,6 +447,35 @@ changes:
 Calls [`server.close()`][] and returns a promise that fulfills when the
 server has closed.
 
+### `server[Symbol.asyncIterator]()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {AsyncIterator} An async iterator that yields each incoming
+  [`net.Socket`][].
+
+Returns an async iterator over the server's incoming connections, allowing them
+to be consumed with `for await...of` as an alternative to the [`'connection'`][]
+event. Iteration ends when the server emits [`'close'`][], and rejects if the
+server emits [`'error'`][].
+
+```mjs
+import { createServer } from 'node:net';
+
+const server = createServer().listen(8124);
+for await (const socket of server) {
+  socket.end('hello world!');
+}
+```
+
+Connections are buffered while the loop body is busy; the server does not stop
+accepting them, so a consumer that is slower than the connection rate can buffer
+without bound. Use [`server.maxConnections`][] to bound concurrency.
+
 ### `server.getConnections(callback)`
 
 <!-- YAML
@@ -2084,6 +2113,84 @@ net.isIPv6('::1'); // returns true
 net.isIPv6('fhqwhgads'); // returns false
 ```
 
+## `net/promises` API
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+The `net/promises` API provides a set of `net` functions that return `Promise`
+objects rather than relying on events. The API is accessible via
+`require('node:net').promises` or `require('node:net/promises')`.
+
+### `netPromises.connect(options)`
+
+### `netPromises.connect(path)`
+
+### `netPromises.connect(port[, host])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `options` {Object} Accepts the same arguments as [`net.connect()`][]. May
+  include a `signal` {AbortSignal} that can be used to abort an in-progress
+  connection attempt.
+* Returns: {Promise} Fulfills with a connected [`net.Socket`][].
+
+A promise-based alternative to [`net.connect()`][]. The returned promise is
+fulfilled with the socket once its [`'connect'`][] event fires, and is rejected
+if the connection fails or the `signal` is aborted. When the promise rejects,
+the underlying socket is destroyed.
+
+This API is named for the action it performs and awaits — connecting — to
+parallel [`netPromises.listen()`][]. It is not named `createConnection()`,
+because that name belongs to the socket-factory taxonomy of the callback API,
+which has no counterpart here.
+
+```mjs
+import { connect } from 'node:net/promises';
+
+const socket = await connect({ port: 8124 });
+socket.write('hello world!');
+socket.end();
+```
+
+### `netPromises.listen([options])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `options` {Object} Accepts the same options as [`net.createServer()`][] and
+  [`server.listen()`][], plus:
+  * `connectionListener` {Function} Automatically set as a listener for the
+    [`'connection'`][] event.
+  * `signal` {AbortSignal} An `AbortSignal` that may be used to abort the
+    server. Aborting before the server is listening rejects the returned
+    promise with an `AbortError`; aborting at any later point closes the
+    server, matching the `signal` option of [`server.listen()`][].
+* Returns: {Promise} Fulfills with a listening [`net.Server`][].
+
+Creates a [`net.Server`][] and begins listening. The returned promise is
+fulfilled with the server once its [`'listening'`][] event fires, and is
+rejected if the server fails to bind or the `signal` is aborted before it is
+listening. When the promise rejects, the server is closed.
+
+The resolved server is async iterable, so incoming connections can be consumed
+with `for await...of` (see `server[Symbol.asyncIterator]()`).
+
+```mjs
+import { listen } from 'node:net/promises';
+
+const server = await listen({ port: 8124 });
+for await (const socket of server) {
+  socket.end('hello world!');
+}
+```
+
 [IPC]: #ipc-support
 [Identifying paths for IPC connections]: #identifying-paths-for-ipc-connections
 [RFC 8305]: https://www.rfc-editor.org/rfc/rfc8305.txt
@@ -2114,6 +2221,7 @@ net.isIPv6('fhqwhgads'); // returns false
 [`net.createServer()`]: #netcreateserveroptions-connectionlistener
 [`net.getDefaultAutoSelectFamily()`]: #netgetdefaultautoselectfamily
 [`net.getDefaultAutoSelectFamilyAttemptTimeout()`]: #netgetdefaultautoselectfamilyattempttimeout
+[`netPromises.listen()`]: #netpromiseslistenoptions
 [`new net.Socket(options)`]: #new-netsocketoptions
 [`readable.setEncoding()`]: stream.md#readablesetencodingencoding
 [`server.close()`]: #serverclosecallback

lib/internal/net/promises.js

@@ -0,0 +1,86 @@
+'use strict';
+
+const { once } = require('events');
+const {
+  validateAbortSignal,
+  validateObject,
+} = require('internal/validators');
+const { AbortError } = require('internal/errors');
+const { kEmptyObject } = require('internal/util');
+
+// Lazily loaded to avoid a require cycle with the `net` module, which exposes
+// this namespace through its `promises` getter.
+let net;
+function lazyNet() {
+  net ??= require('net');
+  return net;
+}
+
+// Resolves with a connected `net.Socket` once the `'connect'` event fires, and
+// rejects if the connection fails or the optional `signal` is aborted.
+async function connect(...args) {
+  const lazy = lazyNet();
+  const options = lazy._normalizeArgs(args)[0];
+  const { signal } = options;
+  if (signal !== undefined) {
+    validateAbortSignal(signal, 'options.signal');
+    if (signal.aborted) {
+      throw new AbortError(undefined, { cause: signal.reason });
+    }
+  }
+
+  // Strip the signal so the socket does not also install its own abort
+  // handling; rejecting and destroying below fully tears the socket down.
+  const socket = lazy.connect({ ...options, signal: undefined });
+
+  try {
+    await once(socket, 'connect', signal !== undefined ? { signal } : kEmptyObject);
+  } catch (err) {
+    socket.destroy();
+    throw err;
+  }
+  return socket;
+}
+
+// Creates a server and resolves with it once it is listening, rejecting if it
+// fails to bind or the optional `signal` is aborted.
+async function listen(options = kEmptyObject) {
+  validateObject(options, 'options');
+  const { signal, connectionListener } = options;
+  if (signal !== undefined) {
+    validateAbortSignal(signal, 'options.signal');
+    if (signal.aborted) {
+      throw new AbortError(undefined, { cause: signal.reason });
+    }
+  }
+
+  const lazy = lazyNet();
+  const server = lazy.createServer(options, connectionListener);
+
+  try {
+    // Pass `signal` through to listen() so net installs its own
+    // close-on-abort handler: the signal aborts the server for its entire
+    // lifetime, not just the pending listen.
+    server.listen(options);
+    await once(server, 'listening', signal !== undefined ? { signal } : kEmptyObject);
+  } catch (err) {
+    // On abort, net's signal handler already closes the server, so closing
+    // again would be redundant; on other failures (e.g. a bind error) there
+    // is no such handler, so close it here.
+    if (!signal?.aborted) {
+      server.close();
+    }
+    throw err;
+  }
+  return server;
+}
+
+module.exports = {
+  connect,
+  listen,
+  get isIP() { return lazyNet().isIP; },
+  get isIPv4() { return lazyNet().isIPv4; },
+  get isIPv6() { return lazyNet().isIPv6; },
+  get BlockList() { return lazyNet().BlockList; },
+  get SocketAddress() { return lazyNet().SocketAddress; },
+};

lib/net.js

@@ -37,6 +37,7 @@ const {
   ObjectSetPrototypeOf,
   Symbol,
   SymbolAsyncDispose,
+  SymbolAsyncIterator,
   SymbolDispose,
 } = primordials;
 
@@ -146,6 +147,8 @@ let cluster;
 let dns;
 let BlockList;
 let SocketAddress;
+let netPromises;
+let kFirstEventParam;
 let autoSelectFamilyDefault = getOptionValue('--network-family-autoselection');
 let autoSelectFamilyAttemptTimeoutDefault = getOptionValue('--network-family-autoselection-attempt-timeout');
 
@@ -2486,6 +2489,14 @@ Server.prototype[SymbolAsyncDispose] = async function() {
   await FunctionPrototypeCall(promisify(this.close), this);
 };
 
+Server.prototype[SymbolAsyncIterator] = function() {
+  kFirstEventParam ??= require('internal/events/symbols').kFirstEventParam;
+  return EventEmitter.on(this, 'connection', {
+    close: ['close'],
+    [kFirstEventParam]: true,
+  });
+};
+
 Server.prototype._emitCloseIfDrained = function() {
   debug('SERVER _emitCloseIfDrained');
 
@@ -2576,6 +2587,10 @@ module.exports = {
   connect,
   createConnection: connect,
   createServer,
+  get promises() {
+    netPromises ??= require('internal/net/promises');
+    return netPromises;
+  },
   isIP: isIP,
   isIPv4: isIPv4,
   isIPv6: isIPv6,

lib/net/promises.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('internal/net/promises');

test/parallel/test-net-promises-connect.js

@@ -0,0 +1,62 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+const { once } = require('events');
+const { connect } = require('net/promises');
+
+(async () => {
+  // Resolves with a connected socket and round-trips data.
+  {
+    const server = net.createServer((socket) => {
+      socket.end('hello');
+    }).listen(0);
+    await once(server, 'listening');
+    const socket = await connect({ port: server.address().port });
+    assert.strictEqual(socket.connecting, false);
+    const chunks = [];
+    for await (const chunk of socket) {
+      chunks.push(chunk);
+    }
+    assert.strictEqual(Buffer.concat(chunks).toString(), 'hello');
+    server.close();
+  }
+
+  // net.promises is the same object as require('net/promises').
+  assert.strictEqual(net.promises, require('net/promises'));
+
+  // Rejects when the connection is refused.
+  {
+    const server = net.createServer().listen(0);
+    await once(server, 'listening');
+    const { port } = server.address();
+    server.close();
+    await once(server, 'close');
+    await assert.rejects(connect({ port }), { code: 'ECONNREFUSED' });
+  }
+
+  // A pre-aborted signal rejects with an AbortError.
+  {
+    await assert.rejects(
+      connect({ port: 0, signal: AbortSignal.abort() }),
+      { name: 'AbortError' });
+  }
+
+  // Aborting while connecting rejects with an AbortError.
+  {
+    const server = net.createServer().listen(0);
+    await once(server, 'listening');
+    const controller = new AbortController();
+    const promise = connect({ port: server.address().port, signal: controller.signal });
+    controller.abort();
+    await assert.rejects(promise, { name: 'AbortError' });
+    server.close();
+  }
+
+  // An invalid signal throws.
+  {
+    await assert.rejects(
+      connect({ port: 0, signal: 'INVALID_SIGNAL' }),
+      { code: 'ERR_INVALID_ARG_TYPE' });
+  }
+})().then(common.mustCall());

test/parallel/test-net-promises-listen.js

@@ -0,0 +1,71 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+const { once } = require('events');
+const { listen } = require('net/promises');
+
+(async () => {
+  // Resolves with a listening server.
+  {
+    const server = await listen({ port: 0 });
+    assert.strictEqual(server.listening, true);
+    assert.strictEqual(typeof server.address().port, 'number');
+    server.close();
+  }
+
+  // The signal aborts the server for its entire lifetime, not just the
+  // pending listen: aborting after it is listening closes the server.
+  {
+    const controller = new AbortController();
+    const server = await listen({ port: 0, signal: controller.signal });
+    assert.strictEqual(server.listening, true);
+    const closed = once(server, 'close');
+    controller.abort();
+    await closed;
+    assert.strictEqual(server.listening, false);
+  }
+
+  // The connectionListener option receives incoming connections.
+  {
+    const server = await listen({
+      port: 0,
+      connectionListener: common.mustCall((socket) => {
+        socket.end();
+        server.close();
+      }),
+    });
+    const client = net.connect(server.address().port);
+    client.resume();
+  }
+
+  // A pre-aborted signal rejects with an AbortError.
+  {
+    await assert.rejects(
+      listen({ port: 0, signal: AbortSignal.abort() }),
+      { name: 'AbortError' });
+  }
+
+  // Aborting while binding rejects with an AbortError and closes the server.
+  {
+    const controller = new AbortController();
+    const promise = listen({ port: 0, signal: controller.signal });
+    controller.abort();
+    await assert.rejects(promise, { name: 'AbortError' });
+  }
+
+  // An invalid signal throws.
+  {
+    await assert.rejects(
+      listen({ port: 0, signal: 'INVALID_SIGNAL' }),
+      { code: 'ERR_INVALID_ARG_TYPE' });
+  }
+
+  // Rejects when the address is already in use.
+  {
+    const first = await listen({ port: 0 });
+    const { port } = first.address();
+    await assert.rejects(listen({ port }), { code: 'EADDRINUSE' });
+    first.close();
+  }
+})().then(common.mustCall());