Allow a callback to be passed in to call a function when the message has been sent?

[domharrington]

I would like to implement metrics in a child process and exit the process when it is complete.

timer.stop()
process.exit(0)

But what happens is the process exits before the message is sent. I can see a noop is being passed in as the callback parameter:

lynx/lib/lynx.js

Line 470 in 12b17e1

socket.send(buffer, 0, buffer.length, this.port, this.host, noop);

Would be great to be able to pass in a callback to the .stop() function call so my code will be:

timer.stop(function (err) {
  process.exit(0)
})

Would you accept a pull request for this?