title: Check if IP address is in private network space
body: <p>I have a program in go which accepts URLs from clients and gets them using the net/http package. Before doing further processing, I would like to check if the URL maps to private (non-routable / RFC1918 networks) address space.</p>
  
  <p>The straight-forward way would be to perform an explicit DNS request and check the address for the known private ranges. After that, perform the HTTP GET request for the URL.</p>
  
  <p>Is there a better way to accomplish this? Preferably integrating with http.Client so it can be performed as a part of the GET request.</p>