From 8d0ca107520347ec1aad049088b0577398262e14 Mon Sep 17 00:00:00 2001
From: Jackson Tian <shyvo1987@gmail.com>
Date: Mon, 18 Jan 2016 15:08:12 +0800
Subject: [PATCH] buffer: make byteLength work with Buffer correctly

Make the byteLength work correctly when input is Buffer.

e.g:

```js
// The incomplete unicode string
Buffer.byteLength(new Buffer([0xe4, 0xb8, 0xad, 0xe6, 0x96]))
```
The old output: 9
The new output: 5

PR-URL: https://github.com/nodejs/node/pull/4738
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
---
 lib/buffer.js                           | 3 +++
 test/parallel/test-buffer-bytelength.js | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/lib/buffer.js b/lib/buffer.js
index f2499803004bb8..6514d0eb6dcf5d 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -262,6 +262,9 @@ function base64ByteLength(str, bytes) {
 
 
 function byteLength(string, encoding) {
+  if (string instanceof Buffer)
+    return string.length;
+
   if (typeof string !== 'string')
     string = '' + string;
 
diff --git a/test/parallel/test-buffer-bytelength.js b/test/parallel/test-buffer-bytelength.js
index 32ed6dbd67615e..ef68097157b1d8 100644
--- a/test/parallel/test-buffer-bytelength.js
+++ b/test/parallel/test-buffer-bytelength.js
@@ -10,6 +10,12 @@ assert.equal(Buffer.byteLength(NaN, 'utf8'), 3);
 assert.equal(Buffer.byteLength({}, 'binary'), 15);
 assert.equal(Buffer.byteLength(), 9);
 
+// buffer
+var incomplete = new Buffer([0xe4, 0xb8, 0xad, 0xe6, 0x96]);
+assert.equal(Buffer.byteLength(incomplete), 5);
+var ascii = new Buffer('abc');
+assert.equal(Buffer.byteLength(ascii), 3);
+
 // special case: zero length string
 assert.equal(Buffer.byteLength('', 'ascii'), 0);
 assert.equal(Buffer.byteLength('', 'HeX'), 0);