nodejs
diff --git a/Collapse file
‎lib/buffer.js‎
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+3Lines changed: 3 additions & 0 deletions b/Collapse file
‎lib/buffer.js‎
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+3Lines changed: 3 additions & 0 deletions
diff --git a/Collapse file
‎test/parallel/test-buffer-bytelength.js‎
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‎test/parallel/test-buffer-bytelength.js‎
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+6Lines changed: 6 additions & 0 deletions
@@ -258,6 +258,9 @@ function base64ByteLength(str, bytes) {
 
 
 function byteLength(string, encoding) {
+  if (string instanceof Buffer)
+    return string.length;
+
   if (typeof string !== 'string')
     string = '' + string;
 
 
@@ -10,6 +10,12 @@ assert.equal(Buffer.byteLength(NaN, 'utf8'), 3);
 assert.equal(Buffer.byteLength({}, 'raws'), 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);