dns: allow --dns-verbatim to change default dns verbatim

Allow the "--dns-verbatim" option to change the default value of verbatim
in `dns.lookup()`. This is useful when running Node.js in ipv6-only
environments to avoid possible ENETUNREACH errors.

doc/api/cli.md

@@ -181,6 +181,17 @@ Make built-in language features like `eval` and `new Function` that generate
 code from strings throw an exception instead. This does not affect the Node.js
 `vm` module.
 
+### `--dns-verbatim=value`
+<!-- YAML
+added: REPLACEME
+-->
+
+Set the default value of `verbatim` in [`dns.lookup()`][]. The value may be:
+* `0` to indicate `false`
+* `1` to indicate `true`
+
+Other values will be ignored.
+
 ### `--enable-fips`
 <!-- YAML
 added: v6.0.0
@@ -1371,6 +1382,7 @@ Node.js options that are allowed are:
 * `--conditions`
 * `--diagnostic-dir`
 * `--disable-proto`
+* `--dns-verbatim`
 * `--enable-fips`
 * `--enable-source-maps`
 * `--experimental-abortcontroller`
@@ -1728,6 +1740,7 @@ $ node --max-old-space-size=1536 index.js
 [`NODE_OPTIONS`]: #cli_node_options_options
 [`NO_COLOR`]: https://no-color.org
 [`SlowBuffer`]: buffer.md#buffer_class_slowbuffer
+[`dns.lookup()`]: dns.md#dns_dns_lookup_hostname_options_callback
 [`process.setUncaughtExceptionCaptureCallback()`]: process.md#process_process_setuncaughtexceptioncapturecallback_fn
 [`tls.DEFAULT_MAX_VERSION`]: tls.md#tls_tls_default_max_version
 [`tls.DEFAULT_MIN_VERSION`]: tls.md#tls_tls_default_min_version

lib/dns.js

@@ -41,6 +41,7 @@ const {
   Resolver,
   validateHints,
   emitInvalidHostnameWarning,
+  getDefaultVerbatim,
 } = require('internal/dns/utils');
 const {
   ERR_INVALID_ARG_TYPE,
@@ -96,7 +97,7 @@ function lookup(hostname, options, callback) {
   let hints = 0;
   let family = -1;
   let all = false;
-  let verbatim = false;
+  let verbatim = getDefaultVerbatim();
 
   // Parse arguments
   if (hostname) {

lib/internal/dns/promises.js

@@ -1,5 +1,4 @@
 'use strict';
-
 const {
   ArrayPrototypeMap,
   ObjectCreate,
@@ -14,6 +13,7 @@ const {
   validateHints,
   validateTimeout,
   emitInvalidHostnameWarning,
+  getDefaultVerbatim,
 } = require('internal/dns/utils');
 const { codes, dnsException } = require('internal/errors');
 const { toASCII } = require('internal/idna');
@@ -103,7 +103,7 @@ function lookup(hostname, options) {
   var hints = 0;
   var family = -1;
   var all = false;
-  var verbatim = false;
+  var verbatim = getDefaultVerbatim();
 
   // Parse arguments
   if (hostname && typeof hostname !== 'string') {

lib/internal/dns/utils.js

@@ -13,6 +13,7 @@ const {
 
 const errors = require('internal/errors');
 const { isIP } = require('internal/net');
+const { getOptionValue } = require('internal/options');
 const {
   validateArray,
   validateInt32,
@@ -184,6 +185,26 @@ function emitInvalidHostnameWarning(hostname) {
   );
 }
 
+let defaultVerbatim = null;
+
+function getDefaultVerbatim() {
+  if (defaultVerbatim !== null) {
+    return defaultVerbatim;
+  }
+
+  const option = getOptionValue('--dns-verbatim');
+  switch (option) {
+    case '1':
+      defaultVerbatim = true;
+      break;
+    case '0':
+    default:
+      defaultVerbatim = false;
+  }
+
+  return defaultVerbatim;
+}
+
 module.exports = {
   bindDefaultResolver,
   getDefaultResolver,
@@ -192,4 +213,5 @@ module.exports = {
   validateTimeout,
   Resolver,
   emitInvalidHostnameWarning,
+  getDefaultVerbatim,
 };

src/node_options.cc

@@ -297,6 +297,11 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             " (default: current working directory)",
             &EnvironmentOptions::diagnostic_dir,
             kAllowedInEnvironment);
+  AddOption("--dns-verbatim",
+            "set to 1 or 0 to enable or disable "
+            "verbatim in dns.lookup by default",
+            &EnvironmentOptions::dns_verbatim,
+            kAllowedInEnvironment);
   AddOption("--enable-source-maps",
             "Source Map V3 support for stack traces",
             &EnvironmentOptions::enable_source_maps,

src/node_options.h

@@ -101,6 +101,7 @@ class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
   std::vector<std::string> conditions;
+  std::string dns_verbatim;
   bool enable_source_maps = false;
   bool experimental_json_modules = false;
   bool experimental_modules = false;

test/parallel/test-dns-default-verbatim-false.js

@@ -0,0 +1,32 @@
+// Flags: --expose-internals --dns-verbatim=0
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { internalBinding } = require('internal/test/binding');
+const cares = internalBinding('cares_wrap');
+
+// Test that --dns-verbatim=0 works as expected.
+
+const originalGetaddrinfo = cares.getaddrinfo;
+const calls = [];
+cares.getaddrinfo = (...args) => {
+  calls.push(args);
+  originalGetaddrinfo(...args);
+};
+
+const dns = require('dns');
+const dnsPromises = dns.promises;
+
+let verbatim;
+
+dns.lookup('example.org', common.mustCall(_err => {
+  assert.strictEqual(calls.length, 1);
+  verbatim = calls[0][4];
+  assert.strictEqual(verbatim, false);
+
+  dnsPromises.lookup('example.org').then(() => {
+    assert.strictEqual(calls.length, 2);
+    verbatim = calls[1][4];
+    assert.strictEqual(verbatim, false);
+  }).catch(common.mustNotCall);
+}));

test/parallel/test-dns-default-verbatim-true.js

@@ -0,0 +1,32 @@
+// Flags: --expose-internals --dns-verbatim=1
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { internalBinding } = require('internal/test/binding');
+const cares = internalBinding('cares_wrap');
+
+// Test that --dns-verbatim=1 works as expected.
+
+const originalGetaddrinfo = cares.getaddrinfo;
+const calls = [];
+cares.getaddrinfo = (...args) => {
+  calls.push(args);
+  originalGetaddrinfo(...args);
+};
+
+const dns = require('dns');
+const dnsPromises = dns.promises;
+
+let verbatim;
+
+dns.lookup('example.org', common.mustCall(_err => {
+  assert.strictEqual(calls.length, 1);
+  verbatim = calls[0][4];
+  assert.strictEqual(verbatim, true);
+
+  dnsPromises.lookup('example.org').then(() => {
+    assert.strictEqual(calls.length, 2);
+    verbatim = calls[1][4];
+    assert.strictEqual(verbatim, true);
+  }).catch(common.mustNotCall);
+}));