net: add autoSelectFamily global getter and setter

doc/api/cli.md

@@ -314,6 +314,15 @@ added: v6.0.0
 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built
 against FIPS-compatible OpenSSL.)
 
+### `--enable-network-family-autoselection`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Enables the family autoselection algorithm unless connection options explicitly
+disables it.
+
 ### `--enable-source-maps`
 
 <!-- YAML
@@ -1870,6 +1879,7 @@ Node.js options that are allowed are:
 * `--disable-proto`
 * `--dns-result-order`
 * `--enable-fips`
+* `--enable-network-family-autoselection`
 * `--enable-source-maps`
 * `--experimental-abortcontroller`
 * `--experimental-import-meta-resolve`

doc/api/net.md

@@ -780,6 +780,20 @@ Returns the bound `address`, the address `family` name and `port` of the
 socket as reported by the operating system:
 `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`
 
+### `socket.autoSelectFamilyAttemptedAddresses`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string\[]}
+
+This property is only present if the family autoselection algorithm is enabled in
+[`socket.connect(options)`][] and it is an array of the addresses that have been attempted.
+
+Each address is a string in the form of `$IP:$PORT`. If the connection was successful,
+then the last address is the one that the socket is currently connected to.
+
 ### `socket.bufferSize`
 
 <!-- YAML
@@ -856,6 +870,11 @@ behavior.
 <!-- YAML
 added: v0.1.90
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/45777
+    description: The default value for autoSelectFamily option can be changed
+                 at runtime using `setDefaultAutoSelectFamily` or via the
+                 command line option `--enable-network-family-autoselection`.
   - version: v19.3.0
     pr-url: https://github.com/nodejs/node/pull/44731
     description: Added the `autoSelectFamily` option.
@@ -909,12 +928,14 @@ For TCP connections, available `options` are:
   that loosely implements section 5 of [RFC 8305][].
   The `all` option passed to lookup is set to `true` and the sockets attempts to connect to all
   obtained IPv6 and IPv4 addresses, in sequence, until a connection is established.
-  The first returned AAAA address is tried first, then the first returned A address and so on.
+  The first returned AAAA address is tried first, then the first returned A address,
+  then the second returned AAAA address and so on.
   Each connection attempt is given the amount of time specified by the `autoSelectFamilyAttemptTimeout`
   option before timing out and trying the next address.
   Ignored if the `family` option is not `0` or if `localAddress` is set.
   Connection errors are not emitted if at least one connection succeeds.
-  **Default:** `false`.
+  **Default:** initially `false`, but it can be changed at runtime using [`net.setDefaultAutoSelectFamily(value)`][]
+  or via the command line option `--enable-network-family-autoselection`.
 * `autoSelectFamilyAttemptTimeout` {number}: The amount of time in milliseconds to wait
   for a connection attempt to finish before trying the next address when using the `autoSelectFamily` option.
   If set to a positive integer less than `10`, then the value `10` will be used instead.
@@ -1495,6 +1516,26 @@ immediately initiates connection with
 [`socket.connect(port[, host][, connectListener])`][`socket.connect(port)`],
 then returns the `net.Socket` that starts the connection.
 
+## `net.setDefaultAutoSelectFamily(value)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Sets the default value of the `autoSelectFamily` option of [`socket.connect(options)`][].
+
+* `value` {boolean} The new default value. The initial default value is `false`.
+
+## `net.getDefaultAutoSelectFamily()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Gets the current default value of the `autoSelectFamily` option of [`socket.connect(options)`][].
+
+* Returns: {boolean} The current default value of the `autoSelectFamily` option.
+
 ## `net.createServer([options][, connectionListener])`
 
 <!-- YAML
@@ -1673,6 +1714,7 @@ net.isIPv6('fhqwhgads'); // returns false
 [`net.createConnection(path)`]: #netcreateconnectionpath-connectlistener
 [`net.createConnection(port, host)`]: #netcreateconnectionport-host-connectlistener
 [`net.createServer()`]: #netcreateserveroptions-connectionlistener
+[`net.setDefaultAutoSelectFamily(value)`]: #netsetdefaultautoselectfamilyvalue
 [`new net.Socket(options)`]: #new-netsocketoptions
 [`readable.setEncoding()`]: stream.md#readablesetencodingencoding
 [`server.close()`]: #serverclosecallback

lib/net.js

@@ -118,12 +118,14 @@ const {
   validateString
 } = require('internal/validators');
 const kLastWriteQueueSize = Symbol('lastWriteQueueSize');
+const { getOptionValue } = require('internal/options');
 
 // Lazy loaded to improve startup performance.
 let cluster;
 let dns;
 let BlockList;
 let SocketAddress;
+let autoSelectFamilyDefault = getOptionValue('--enable-network-family-autoselection');
 
 const { clearTimeout, setTimeout } = require('timers');
 const { kTimeout } = require('internal/timers');
@@ -226,6 +228,14 @@ function connect(...args) {
   return socket.connect(normalized);
 }
 
+function getDefaultAutoSelectFamily() {
+  return autoSelectFamilyDefault;
+}
+
+function setDefaultAutoSelectFamily(value) {
+  validateBoolean(value, 'value');
+  autoSelectFamilyDefault = value;
+}
 
 // Returns an array [options, cb], where options is an object,
 // cb is either a function or null.
@@ -1092,6 +1102,8 @@ function internalConnectMultiple(context) {
   req.localAddress = localAddress;
   req.localPort = localPort;
 
+  ArrayPrototypePush(self.autoSelectFamilyAttemptedAddresses, `${address}:${port}`);
+
   if (addressType === 4) {
     err = handle.connect(req, address, port);
   } else {
@@ -1184,9 +1196,9 @@ function socketToDnsFamily(family) {
 }
 
 function lookupAndConnect(self, options) {
-  const { localAddress, localPort, autoSelectFamily } = options;
+  const { localAddress, localPort } = options;
   const host = options.host || 'localhost';
-  let { port, autoSelectFamilyAttemptTimeout } = options;
+  let { port, autoSelectFamilyAttemptTimeout, autoSelectFamily } = options;
 
   if (localAddress && !isIP(localAddress)) {
     throw new ERR_INVALID_IP_ADDRESS(localAddress);
@@ -1205,11 +1217,14 @@ function lookupAndConnect(self, options) {
   }
   port |= 0;
 
-  if (autoSelectFamily !== undefined) {
-    validateBoolean(autoSelectFamily);
+
+  if (autoSelectFamily != null) {
+    validateBoolean(autoSelectFamily, 'options.autoSelectFamily');
+  } else {
+    autoSelectFamily = autoSelectFamilyDefault;
   }
 
-  if (autoSelectFamilyAttemptTimeout !== undefined) {
+  if (autoSelectFamilyAttemptTimeout != null) {
     validateInt32(autoSelectFamilyAttemptTimeout, 'options.autoSelectFamilyAttemptTimeout', 1);
 
     if (autoSelectFamilyAttemptTimeout < 10) {
@@ -1233,7 +1248,7 @@ function lookupAndConnect(self, options) {
     return;
   }
 
-  if (options.lookup !== undefined)
+  if (options.lookup != null)
     validateFunction(options.lookup, 'options.lookup');
 
   if (dns === undefined) dns = require('dns');
@@ -1370,6 +1385,8 @@ function lookupAndConnectMultiple(self, async_id_symbol, lookup, host, options,
         }
       }
 
+      self.autoSelectFamilyAttemptedAddresses = [];
+
       const context = {
         socket: self,
         addresses,
@@ -2223,4 +2240,6 @@ module.exports = {
   Server,
   Socket,
   Stream: Socket, // Legacy naming
+  getDefaultAutoSelectFamily,
+  setDefaultAutoSelectFamily,
 };

src/node_options.cc

@@ -346,6 +346,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "returned)",
             &EnvironmentOptions::dns_result_order,
             kAllowedInEnvvar);
+  AddOption("--enable-network-family-autoselection",
+            "Enable network address family autodetection algorithm",
+            &EnvironmentOptions::enable_network_family_autoselection,
+            kAllowedInEnvvar);
   AddOption("--enable-source-maps",
             "Source Map V3 support for stack traces",
             &EnvironmentOptions::enable_source_maps,

src/node_options.h

@@ -127,6 +127,7 @@ class EnvironmentOptions : public Options {
   bool frozen_intrinsics = false;
   int64_t heap_snapshot_near_heap_limit = 0;
   std::string heap_snapshot_signal;
+  bool enable_network_family_autoselection = false;
   uint64_t max_http_header_size = 16 * 1024;
   bool deprecation = true;
   bool force_async_hooks_checks = true;

test/parallel/test-net-autoselectfamily-commandline-option.js

@@ -0,0 +1,108 @@
+'use strict';
+
+// Flags: --enable-network-family-autoselection
+
+const common = require('../common');
+const { parseDNSPacket, writeDNSPacket } = require('../common/dns');
+
+const assert = require('assert');
+const dgram = require('dgram');
+const { Resolver } = require('dns');
+const { createConnection, createServer } = require('net');
+
+// Test that happy eyeballs algorithm can be enable from command line.
+
+let autoSelectFamilyAttemptTimeout = common.platformTimeout(250);
+if (common.isWindows) {
+  // Some of the windows machines in the CI need more time to establish connection
+  autoSelectFamilyAttemptTimeout = common.platformTimeout(1500);
+}
+
+function _lookup(resolver, hostname, options, cb) {
+  resolver.resolve(hostname, 'ANY', (err, replies) => {
+    assert.notStrictEqual(options.family, 4);
+
+    if (err) {
+      return cb(err);
+    }
+
+    const hosts = replies
+      .map((r) => ({ address: r.address, family: r.type === 'AAAA' ? 6 : 4 }))
+      .sort((a, b) => b.family - a.family);
+
+    if (options.all === true) {
+      return cb(null, hosts);
+    }
+
+    return cb(null, hosts[0].address, hosts[0].family);
+  });
+}
+
+function createDnsServer(ipv6Addr, ipv4Addr, cb) {
+  // Create a DNS server which replies with a AAAA and a A record for the same host
+  const socket = dgram.createSocket('udp4');
+
+  socket.on('message', common.mustCall((msg, { address, port }) => {
+    const parsed = parseDNSPacket(msg);
+    const domain = parsed.questions[0].domain;
+    assert.strictEqual(domain, 'example.org');
+
+    socket.send(writeDNSPacket({
+      id: parsed.id,
+      questions: parsed.questions,
+      answers: [
+        { type: 'AAAA', address: ipv6Addr, ttl: 123, domain: 'example.org' },
+        { type: 'A', address: ipv4Addr, ttl: 123, domain: 'example.org' },
+      ]
+    }), port, address);
+  }));
+
+  socket.bind(0, () => {
+    const resolver = new Resolver();
+    resolver.setServers([`127.0.0.1:${socket.address().port}`]);
+
+    cb({ dnsServer: socket, lookup: _lookup.bind(null, resolver) });
+  });
+}
+
+// Test that IPV4 is reached if IPV6 is not reachable
+{
+  createDnsServer('::1', '127.0.0.1', common.mustCall(function({ dnsServer, lookup }) {
+    const ipv4Server = createServer((socket) => {
+      socket.on('data', common.mustCall(() => {
+        socket.write('response-ipv4');
+        socket.end();
+      }));
+    });
+
+    ipv4Server.listen(0, '127.0.0.1', common.mustCall(() => {
+      const port = ipv4Server.address().port;
+
+      const connection = createConnection({
+        host: 'example.org',
+        port: port,
+        lookup,
+        autoSelectFamilyAttemptTimeout,
+      });
+
+      let response = '';
+      connection.setEncoding('utf-8');
+
+      connection.on('ready', common.mustCall(() => {
+        assert.deepStrictEqual(connection.autoSelectFamilyAttemptedAddresses, [`::1:${port}`, `127.0.0.1:${port}`]);
+      }));
+
+      connection.on('data', (chunk) => {
+        response += chunk;
+      });
+
+      connection.on('end', common.mustCall(() => {
+        assert.strictEqual(response, 'response-ipv4');
+        ipv4Server.close();
+        dnsServer.close();
+      }));
+
+      connection.write('request');
+    }));
+  }));
+}

test/parallel/test-net-happy-eyeballs.js → test/parallel/test-net-autoselectfamily.js

@@ -74,9 +74,11 @@ function createDnsServer(ipv6Addr, ipv4Addr, cb) {
     });
 
     ipv4Server.listen(0, '127.0.0.1', common.mustCall(() => {
+      const port = ipv4Server.address().port;
+
       const connection = createConnection({
         host: 'example.org',
-        port: ipv4Server.address().port,
+        port: port,
         lookup,
         autoSelectFamily: true,
         autoSelectFamilyAttemptTimeout,
@@ -85,6 +87,10 @@ function createDnsServer(ipv6Addr, ipv4Addr, cb) {
       let response = '';
       connection.setEncoding('utf-8');
 
+      connection.on('ready', common.mustCall(() => {
+        assert.deepStrictEqual(connection.autoSelectFamilyAttemptedAddresses, [`::1:${port}`, `127.0.0.1:${port}`]);
+      }));
+
       connection.on('data', (chunk) => {
         response += chunk;
       });
@@ -132,6 +138,10 @@ if (common.hasIPv6) {
         let response = '';
         connection.setEncoding('utf-8');
 
+        connection.on('ready', common.mustCall(() => {
+          assert.deepStrictEqual(connection.autoSelectFamilyAttemptedAddresses, [`::1:${port}`]);
+        }));
+
         connection.on('data', (chunk) => {
           response += chunk;
         });
@@ -162,6 +172,7 @@ if (common.hasIPv6) {
 
     connection.on('ready', common.mustNotCall());
     connection.on('error', common.mustCall((error) => {
+      assert.deepStrictEqual(connection.autoSelectFamilyAttemptedAddresses, ['::1:10', '127.0.0.1:10']);
       assert.strictEqual(error.constructor.name, 'AggregateError');
       assert.strictEqual(error.errors.length, 2);
 
@@ -199,6 +210,8 @@ if (common.hasIPv6) {
 
       connection.on('ready', common.mustNotCall());
       connection.on('error', common.mustCall((error) => {
+        assert.strictEqual(connection.autoSelectFamilyAttemptedAddresses, undefined);
+
         if (common.hasIPv6) {
           assert.strictEqual(error.code, 'ECONNREFUSED');
           assert.strictEqual(error.message, `connect ECONNREFUSED ::1:${port}`);