net: fix socket.bytesWritten Buffers support

Buffer.byteLength() works only for string inputs. Thus, when connection
has pending Buffer to write, it should just use it's length instead of
throwing exception.

lib/net.js

@@ -667,10 +667,16 @@ Socket.prototype.__defineGetter__('bytesWritten', function() {
       encoding = this._pendingEncoding;
 
   state.buffer.forEach(function(el) {
+    if (Buffer.isBuffer(el.chunk))
+      bytes += el.chunk.length;
+    else
       bytes += Buffer.byteLength(el.chunk, el.encoding);
   });
 
   if (data)
+    if (Buffer.isBuffer(data))
+      bytes += data.length;
+    else
       bytes += Buffer.byteLength(data, encoding);
 
   return bytes;

test/simple/test-http-byteswritten.js

@@ -38,8 +38,10 @@ var httpServer = http.createServer(function(req, res) {
   // Write 1.5mb to cause some requests to buffer
   // Also, mix up the encodings a bit.
   var chunk = new Array(1024 + 1).join('7');
+  var bchunk = new Buffer(chunk);
   for (var i = 0; i < 1024; i++) {
     res.write(chunk);
+    res.write(bchunk);
     res.write(chunk, 'hex');
   }
   // Get .bytesWritten while buffer is not empty