--------------------

validate the url as part of this site before continuing

function string_sanitize_url( $p_url )
{
// remove risky stuff
$t_url = strip_tags( urldecode( $p_url ) );

  if ( preg_match( '?http(s)*://?', $t_url ) > 0 )
  {
     // no embedded addresses
     if ( preg_match( '?^' . config_get( 'path' ) . '?', $t_url ) == 0 )
     { 
        // URL is ok if it begins with our path, if not, replace it
        $t_url = 'index.php';
     }
  }

  if ( $t_url == '' )
  {
     $t_url = 'index.php';
  }

  // no additional parameters
  if ( strpos( $t_url, '?' ) === FALSE )
  {
     return $t_url;
  }

  // split and encode parameters
  list( $t_path, $t_param ) = split( '\?', $t_url, 2 );

  if ( $t_param == "" )
  {
     return $t_url;
  }

  $t_vals = array();
  parse_str( $t_param, $t_vals );
  $t_param = '';

  foreach($t_vals as $k => $v)
  {
     if ($t_param != '')
     {
        $t_param .= '&'; 
     }

     // compose non-empty parameters
     $t_param .= "$k=$v";
  }

  return $t_path . '?' . $t_param;

}