code: func hostname(hostport string) string {
  	colon := strings.IndexByte(hostport, ':')
  	if colon == -1 {
  		return hostport
  	}
  	if i := strings.IndexByte(hostport, ']'); i != -1 {
  		return strings.TrimPrefix(hostport[:i], "[")
  	}
  	return hostport[:colon]
  }
docs: // contains code taken from go1.8, for purposes of backwards compatability with
  // older go versions.
  // hostname returns u.Host, without any port number.
  //
  // If Host is an IPv6 literal with a port number, Hostname returns the
  // IPv6 literal without the square brackets. IPv6 literals may include
  // a zone identifier.