dgram: pass the bytes sent to the send callback

Fixes #6953

lib/dgram.js

@@ -319,7 +319,7 @@ Socket.prototype.send = function(buffer,
 
 
 function afterSend(err) {
-  this.callback(err ? errnoException(err, 'send') : null);
+  this.callback(err ? errnoException(err, 'send') : null, this.buffer.length);
 }
 
 

test/simple/test-dgram-bytes-length.js

@@ -0,0 +1,31 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var dgram = require('dgram');
+
+var message = new Buffer('Some bytes');
+var client = dgram.createSocket('udp4');
+client.send(message, 0, message.length, 41234, "localhost", function(err, bytes) {
+  assert.strictEqual(bytes, message.length);
+  client.close();
+});