From a163c21f43ac5dfdc10479002974465318116cb4 Mon Sep 17 00:00:00 2001
From: "S. M. Mohiuddin Khan Shiam" <mohiuddin.khan.shiam@gmail.com>
Date: Fri, 13 Jun 2025 03:48:20 +0600
Subject: [PATCH] dns: allow Resolver#setLocalAddress() to accept IPv6-only (or
 IPv4-only) addresses
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## Title
dns: allow `resolver.setLocalAddress()` to accept IPv6-only or IPv4-only addresses

## Description
`ResolverBase.prototype.setLocalAddress()` previously **required** the first argument (`ipv4`) to be a non-empty string, throwing `ERR_INVALID_ARG_TYPE` whenever a user tried to set **only** an IPv6 local address:

```js
const r = new (require('dns').Resolver)();
r.setLocalAddress(undefined, '::1'); // ❌ TypeError

This broke documented API behaviour and prevented IPv6-only configurations.

Changes
lib/internal/dns/utils.js
Imported ERR_MISSING_ARGS.
Updated
setLocalAddress()
:
If both ipv4 and ipv6 are undefined, throw ERR_MISSING_ARGS('ipv4', 'ipv6').
Validate each address only when provided.
Preserve snapshot-state logic.
Result
setLocalAddress()
 now works correctly with any of:

resolver.setLocalAddress('0.0.0.0'); // IPv4-only
resolver.setLocalAddress(undefined, '::1'); // IPv6-only
resolver.setLocalAddress('0.0.0.0', '::1'); // both

Restores compliance with public documentation and unblocks IPv6-only deployments.
---
 lib/internal/dns/utils.js | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/internal/dns/utils.js b/lib/internal/dns/utils.js
index 85918f0d43d5..57f371cc554a 100644
--- a/lib/internal/dns/utils.js
+++ b/lib/internal/dns/utils.js
@@ -16,6 +16,7 @@ const {
     ERR_DNS_SET_SERVERS_FAILED,
     ERR_INVALID_ARG_VALUE,
     ERR_INVALID_IP_ADDRESS,
+    ERR_MISSING_ARGS,
   },
 } = require('internal/errors');
 const { isIP } = require('internal/net');
@@ -162,10 +163,15 @@ class ResolverBase {
     }
   }
 
-
   setLocalAddress(ipv4, ipv6) {
-    validateString(ipv4, 'ipv4');
+    // Allow setting either IPv4 or IPv6 (or both). Throw if both are omitted.
+    if (ipv4 === undefined && ipv6 === undefined) {
+      throw new ERR_MISSING_ARGS('ipv4', 'ipv6');
+    }
 
+    if (ipv4 !== undefined) {
+      validateString(ipv4, 'ipv4');
+    }
     if (ipv6 !== undefined) {
       validateString(ipv6, 'ipv6');
     }