title: How to check a TCP port with Cocoa OSX SDK
body: <p>I would like to make a cocoa app that will check if some TCP ports are opened on a server.
  Return a little red ball if it's closed, or green if it's open...</p>
  
  <p>But I'm little bit confused, what class to use, etc.</p>
  
  <p>Thanks in advance for your help</p>