How to detect the visitor's IP address using HTML?

Question

How can i detect the visitors IP Address using HTML for my website? I have a contactform.html and a formsent.html. And when formsent.html sends the contact info to my email

Answer 1

HTML is a markup language, so it doesn't have any variables.

If you want to get it using PHP, you'll need to make use of the $_SERVER superglobal variable. A solution could be:

echo $_SERVER["REMOTE_ADDR"];

This actually gets the host ip, which would be your server.

echo $_SERVER["REMOTE_ADDR"];

This is the most basic however, and fails if the user is behind a proxy, as well as allowing them to trivially change it. A much much better method is to using something like:

function get_ip_address() {
  // check for shared internet/ISP IP
  if (!empty($_SERVER['HTTP_CLIENT_IP']) && $this->validate_ip($_SERVER['HTTP_CLIENT_IP']))
   return $_SERVER['HTTP_CLIENT_IP'];

  // check for IPs passing through proxies
  if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
   // check if multiple ips exist in var
    $iplist = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
    foreach ($iplist as $ip) {
     if ($this->validate_ip($ip))
      return $ip;
    }
   }

  if (!empty($_SERVER['HTTP_X_FORWARDED']) && $this->validate_ip($_SERVER['HTTP_X_FORWARDED']))
   return $_SERVER['HTTP_X_FORWARDED'];
  if (!empty($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']) && $this->validate_ip($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']))
   return $_SERVER['HTTP_X_CLUSTER_CLIENT_IP'];
  if (!empty($_SERVER['HTTP_FORWARDED_FOR']) && $this->validate_ip($_SERVER['HTTP_FORWARDED_FOR']))
   return $_SERVER['HTTP_FORWARDED_FOR'];
  if (!empty($_SERVER['HTTP_FORWARDED']) && $this->validate_ip($_SERVER['HTTP_FORWARDED']))
   return $_SERVER['HTTP_FORWARDED'];

  // return unreliable ip since all else failed
  return $_SERVER['REMOTE_ADDR'];
 }

function validate_ip($ip) {
     if (filter_var($ip, FILTER_VALIDATE_IP, 
                         FILTER_FLAG_IPV4 | 
                         FILTER_FLAG_IPV6 |
                         FILTER_FLAG_NO_PRIV_RANGE | 
                         FILTER_FLAG_NO_RES_RANGE) === false)
         return false;
     self::$ip = $ip;
     return true;
 }

(http://stackoverflow.com/questions/1634782/what-is-the-most-accurate-way-to-retrieve-a-users-correct-ip-address-in-php)

This correctly parses the HTTP_X_FORWARDED_FOR field as well as validating the IP to make sure it's of the right format, and not in a private block.