From 47e87859e279c9c5cd45c95caede137d005282b5 Mon Sep 17 00:00:00 2001
From: goingforstudying-ctrl <goingforstudying@gmail.com>
Date: Mon, 1 Jun 2026 12:54:58 +0000
Subject: [PATCH 1/2] fs: normalize encoding before utf8 fast path check

The fs.readFileSync and fs.writeFileSync fast paths for utf8 encoding
only checked for 'utf8' and 'utf-8', but normalizeEncoding also accepts
'UTF8' and 'UTF-8'. This meant that using those encodings would bypass
the fast path and go through the slower generic path.

Fix by normalizing the encoding before checking if it's utf8.

Fixes: https://github.com/nodejs/node/issues/49888
---
 lib/fs.js | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/fs.js b/lib/fs.js
index 043e29211a1580..8247f9b8911a84 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -94,6 +94,7 @@ const {
   SideEffectFreeRegExpPrototypeExec,
   defineLazyProperties,
   isWindows,
+  normalizeEncoding,
   isMacOS,
 } = require('internal/util');
 const {
@@ -489,7 +490,8 @@ function readFileSync(path, options) {
   }
   options = getOptions(options, { flag: 'r' });
 
-  if (options.encoding === 'utf8' || options.encoding === 'utf-8') {
+  const encoding = normalizeEncoding(options.encoding) || options.encoding;
+  if (encoding === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }
@@ -2845,7 +2847,8 @@ function writeFileSync(path, data, options) {
   const flag = options.flag || 'w';
 
   // C++ fast path for string data and UTF8 encoding
-  if (typeof data === 'string' && (options.encoding === 'utf8' || options.encoding === 'utf-8')) {
+  const encoding = normalizeEncoding(options.encoding) || options.encoding;
+  if (typeof data === 'string' && encoding === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }

From 24b8fef2fa1fc571de002b3d4aaa045f4f578953 Mon Sep 17 00:00:00 2001
From: goingforstudying-ctrl <goingforstudying@gmail.com>
Date: Wed, 3 Jun 2026 17:11:54 -0400
Subject: [PATCH 2/2] fix: add null check for encoding before normalizeEncoding

Address review feedback from mertcanaltin to handle cases where
options.encoding is null/undefined. Only use the utf8 fast path
when a real utf8 encoding is provided.
---
 lib/fs.js | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/lib/fs.js b/lib/fs.js
index 8247f9b8911a84..d9677c0fd41713 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -490,8 +490,7 @@ function readFileSync(path, options) {
   }
   options = getOptions(options, { flag: 'r' });
 
-  const encoding = normalizeEncoding(options.encoding) || options.encoding;
-  if (encoding === 'utf8') {
+  if (options.encoding && normalizeEncoding(options.encoding) === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }
@@ -2847,8 +2846,7 @@ function writeFileSync(path, data, options) {
   const flag = options.flag || 'w';
 
   // C++ fast path for string data and UTF8 encoding
-  const encoding = normalizeEncoding(options.encoding) || options.encoding;
-  if (typeof data === 'string' && encoding === 'utf8') {
+  if (typeof data === 'string' && options.encoding && normalizeEncoding(options.encoding) === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }