From 86e0292733d6d08bf338b68fd50863aef17b1e44 Mon Sep 17 00:00:00 2001
From: ud2 <sjx233@qq.com>
Date: Thu, 27 Jun 2024 05:11:56 +0800
Subject: [PATCH] perf(ext/node): improve `Buffer.from(buffer)` (#24352)

Benchmark code from #24341.

```shellsession
$ deno run --allow-hrtime bench.mjs
6479.111583
$ target/release/deno run --allow-hrtime bench.mjs
962.753875
$ node bench.mjs
855.174875
```
---
 ext/node/polyfills/internal/buffer.mjs | 10 ++++------
 tests/unit_node/buffer_test.ts         | 11 +++++++----
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/ext/node/polyfills/internal/buffer.mjs b/ext/node/polyfills/internal/buffer.mjs
index a051965a391fae..c3249455583f34 100644
--- a/ext/node/polyfills/internal/buffer.mjs
+++ b/ext/node/polyfills/internal/buffer.mjs
@@ -220,12 +220,9 @@ function fromString(string, encoding) {
   return buf;
 }
 
-function fromArrayLike(array) {
-  const length = array.length < 0 ? 0 : checked(array.length) | 0;
-  const buf = createBuffer(length);
-  for (let i = 0; i < length; i += 1) {
-    buf[i] = array[i] & 255;
-  }
+function fromArrayLike(obj) {
+  const buf = new Uint8Array(obj);
+  Object.setPrototypeOf(buf, Buffer.prototype);
   return buf;
 }
 
@@ -234,6 +231,7 @@ function fromObject(obj) {
     if (typeof obj.length !== "number") {
       return createBuffer(0);
     }
+
     return fromArrayLike(obj);
   }
 
diff --git a/tests/unit_node/buffer_test.ts b/tests/unit_node/buffer_test.ts
index 0005b1b5d3f380..07f5dd2c19b7db 100644
--- a/tests/unit_node/buffer_test.ts
+++ b/tests/unit_node/buffer_test.ts
@@ -534,15 +534,18 @@ Deno.test({
 });
 
 Deno.test({
-  name: "[node/buffer] Buffer from another buffer creates a Buffer",
+  name: "[node/buffer] Buffer from another buffer creates a copy",
   fn() {
-    const buffer: Buffer = Buffer.from(Buffer.from("test"));
-    assertEquals(buffer.length, 4, "Buffer length should be 4");
+    const buffer1: Buffer = Buffer.from("test");
+    const buffer2: Buffer = Buffer.from(buffer1);
+    assertEquals(buffer2.length, 4, "Buffer length should be 4");
     assertEquals(
-      buffer.toString(),
+      buffer2.toString(),
       "test",
       "Buffer to string should recover the string",
     );
+    buffer1[0] = 114;
+    assertEquals(buffer2.toString(), "test", "Buffer should be a copy");
   },
 });