From 231d5e4437163a2b99e87793d2766bf1ae283f38 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Tue, 15 Oct 2024 10:22:15 -0700
Subject: [PATCH] buffer: make Buffer work with resizable ArrayBuffer

Fixes: https://github.com/nodejs/node/issues/52195
PR-URL: https://github.com/nodejs/node/pull/55377
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
---
 lib/buffer.js                          |  4 +---
 test/parallel/test-buffer-resizable.js | 29 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 test/parallel/test-buffer-resizable.js

diff --git a/lib/buffer.js b/lib/buffer.js
index 2c56b6c504d..756657e9108 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -504,9 +504,7 @@ function fromArrayBuffer(obj, byteOffset, length) {
   if (maxLength < 0)
     throw new ERR_BUFFER_OUT_OF_BOUNDS('offset');
 
-  if (length === undefined) {
-    length = maxLength;
-  } else {
+  if (length !== undefined) {
     // Convert length to non-negative integer.
     length = +length;
     if (length > 0) {
diff --git a/test/parallel/test-buffer-resizable.js b/test/parallel/test-buffer-resizable.js
new file mode 100644
index 00000000000..dcfe6385b68
--- /dev/null
+++ b/test/parallel/test-buffer-resizable.js
@@ -0,0 +1,29 @@
+// Flags: --no-warnings
+'use strict';
+
+require('../common');
+const { Buffer } = require('node:buffer');
+const { strictEqual } = require('node:assert');
+const { describe, it } = require('node:test');
+
+describe('Using resizable ArrayBuffer with Buffer...', () => {
+  it('works as expected', () => {
+    const ab = new ArrayBuffer(10, { maxByteLength: 20 });
+    const buffer = Buffer.from(ab, 1);
+    strictEqual(buffer.byteLength, 9);
+    ab.resize(15);
+    strictEqual(buffer.byteLength, 14);
+    ab.resize(5);
+    strictEqual(buffer.byteLength, 4);
+  });
+
+  it('works with the deprecated constructor also', () => {
+    const ab = new ArrayBuffer(10, { maxByteLength: 20 });
+    const buffer = new Buffer(ab, 1);
+    strictEqual(buffer.byteLength, 9);
+    ab.resize(15);
+    strictEqual(buffer.byteLength, 14);
+    ab.resize(5);
+    strictEqual(buffer.byteLength, 4);
+  });
+});