虽然这篇文章很老了，但这个话题仍然值得关注。所以我在我的项目中使用了另一个解决方案。我在这里找到了其他的解决方案，要么不完整，要么太复杂，难以理解。

if (! function_exists('get_visitor_IP'))
{
    /**
     * Get the real IP address from visitors proxy. e.g. Cloudflare
     *
     * @return string IP
     */
    function get_visitor_IP()
    {
        // Get real visitor IP behind CloudFlare network
        if (isset($_SERVER["HTTP_CF_CONNECTING_IP"])) {
            $_SERVER['REMOTE_ADDR'] = $_SERVER["HTTP_CF_CONNECTING_IP"];
            $_SERVER['HTTP_CLIENT_IP'] = $_SERVER["HTTP_CF_CONNECTING_IP"];
        }

        // Sometimes the `HTTP_CLIENT_IP` can be used by proxy servers
        $ip = @$_SERVER['HTTP_CLIENT_IP'];
        if (filter_var($ip, FILTER_VALIDATE_IP)) {
           return $ip;
        }

        // Sometimes the `HTTP_X_FORWARDED_FOR` can contain more than IPs 
        $forward_ips = @$_SERVER['HTTP_X_FORWARDED_FOR'];
        if ($forward_ips) {
            $all_ips = explode(',', $forward_ips);

            foreach ($all_ips as $ip) {
                if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)){
                    return $ip;
                }
            }
        }

        return $_SERVER['REMOTE_ADDR'];
    }
}

/**
 * Sanitizes IPv4 address according to Ilia Alshanetsky's book
 * "php|architect?s Guide to PHP Security", chapter 2, page 67.
 *
 * @param string $ip An IPv4 address
 */
public static function sanitizeIpAddress($ip = '')
{
if ($ip == '')
    {
    $rtnStr = '0.0.0.0';
    }
else
    {
    $rtnStr = long2ip(ip2long($ip));
    }

return $rtnStr;
}

//---------------------------------------------------

/**
 * Returns the sanitized HTTP_X_FORWARDED_FOR server variable.
 *
 */
public static function getXForwardedFor()
{
if (isset($_SERVER['HTTP_X_FORWARDED_FOR']))
    {
    $rtnStr = $_SERVER['HTTP_X_FORWARDED_FOR'];
    }
elseif (isset($HTTP_SERVER_VARS['HTTP_X_FORWARDED_FOR']))
    {
    $rtnStr = $HTTP_SERVER_VARS['HTTP_X_FORWARDED_FOR'];
    }
elseif (getenv('HTTP_X_FORWARDED_FOR'))
    {
    $rtnStr = getenv('HTTP_X_FORWARDED_FOR');
    }
else
    {
    $rtnStr = '';
    }

// Sanitize IPv4 address (Ilia Alshanetsky):
if ($rtnStr != '')
    {
    $rtnStr = explode(', ', $rtnStr);
    $rtnStr = self::sanitizeIpAddress($rtnStr[0]);
    }

return $rtnStr;
}

//---------------------------------------------------

/**
 * Returns the sanitized REMOTE_ADDR server variable.
 *
 */
public static function getRemoteAddr()
{
if (isset($_SERVER['REMOTE_ADDR']))
    {
    $rtnStr = $_SERVER['REMOTE_ADDR'];
    }
elseif (isset($HTTP_SERVER_VARS['REMOTE_ADDR']))
    {
    $rtnStr = $HTTP_SERVER_VARS['REMOTE_ADDR'];
    }
elseif (getenv('REMOTE_ADDR'))
    {
    $rtnStr = getenv('REMOTE_ADDR');
    }
else
    {
    $rtnStr = '';
    }

// Sanitize IPv4 address (Ilia Alshanetsky):
if ($rtnStr != '')
    {
    $rtnStr = explode(', ', $rtnStr);
    $rtnStr = self::sanitizeIpAddress($rtnStr[0]);
    }

return $rtnStr;
}

//---------------------------------------------------

/**
 * Returns the sanitized remote user and proxy IP addresses.
 *
 */
public static function getIpAndProxy()
{
$xForwarded = self::getXForwardedFor();
$remoteAddr = self::getRemoteAddr();

if ($xForwarded != '')
    {
    $ip    = $xForwarded;
    $proxy = $remoteAddr;
    }
else
    {
    $ip    = $remoteAddr;
    $proxy = '';
    }

return array($ip, $proxy);
}

我想知道也许你应该在爆炸的HTTP_X_FORWARDED_FOR以相反的顺序迭代，因为我的经验是，用户的IP地址结束在逗号分隔的列表的末尾，所以从头的开始，你更有可能得到一个返回的代理的IP地址，这可能仍然允许会话劫持，因为许多用户可能通过该代理。

最大的问题是目的是什么?

你的代码几乎是全面的，因为它可以-但我看到，如果你发现什么看起来像一个代理添加头，你使用它而不是CLIENT_IP，然而，如果你想要这个信息的审计目的，然后警告-它很容易伪造。

当然，您绝不应该使用IP地址进行任何形式的身份验证——即使这些地址也可能被欺骗。

您可以通过推出一个flash或java applet来更好地测量客户端ip地址，它通过非http端口连接回服务器(因此会显示透明代理或代理注入的报头为假的情况下)，但请记住，当客户端只能通过web代理连接或传出端口被阻塞时，将不会有来自applet的连接。

下面是一种更简洁的获取IP地址的方法:

function get_ip_address(){
    foreach (array('HTTP_CLIENT_IP', 'HTTP_X_FORWARDED_FOR', 'HTTP_X_FORWARDED', 'HTTP_X_CLUSTER_CLIENT_IP', 'HTTP_FORWARDED_FOR', 'HTTP_FORWARDED', 'REMOTE_ADDR') as $key){
        if (array_key_exists($key, $_SERVER) === true){
            foreach (explode(',', $_SERVER[$key]) as $ip){
                $ip = trim($ip); // just to be safe

                if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false){
                    return $ip;
                }
            }
        }
    }
}

你的代码似乎已经很完整了，我看不到任何可能的错误(除了通常的IP警告)，我会改变validate_ip()函数依赖于过滤器扩展:

public function validate_ip($ip)
{
    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) === false)
    {
        return false;
    }

    self::$ip = sprintf('%u', ip2long($ip)); // you seem to want this

    return true;
}

你的HTTP_X_FORWARDED_FOR代码片段也可以这样简化:

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

:

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

您可能还想验证IPv6地址。

我想出了这个函数，它不简单地返回IP地址，而是一个具有IP信息的数组。

// Example usage:
$info = ip_info();
if ( $info->proxy ) {
    echo 'Your IP is ' . $info->ip;
} else {
    echo 'Your IP is ' . $info->ip . ' and your proxy is ' . $info->proxy_ip;
}

函数如下:

/**
 * Retrieves the best guess of the client's actual IP address.
 * Takes into account numerous HTTP proxy headers due to variations
 * in how different ISPs handle IP addresses in headers between hops.
 *
 * @since 1.1.3
 *
 * @return object {
 *         IP Address details
 *
 *         string $ip The users IP address (might be spoofed, if $proxy is true)
 *         bool $proxy True, if a proxy was detected
 *         string $proxy_id The proxy-server IP address
 * }
 */
function ip_info() {
    $result = (object) array(
        'ip' => $_SERVER['REMOTE_ADDR'],
        'proxy' => false,
        'proxy_ip' => '',
    );

    /*
     * This code tries to bypass a proxy and get the actual IP address of
     * the visitor behind the proxy.
     * Warning: These values might be spoofed!
     */
    $ip_fields = array(
        'HTTP_CLIENT_IP',
        'HTTP_X_FORWARDED_FOR',
        'HTTP_X_FORWARDED',
        'HTTP_X_CLUSTER_CLIENT_IP',
        'HTTP_FORWARDED_FOR',
        'HTTP_FORWARDED',
        'REMOTE_ADDR',
    );
    foreach ( $ip_fields as $key ) {
        if ( array_key_exists( $key, $_SERVER ) === true ) {
            foreach ( explode( ',', $_SERVER[$key] ) as $ip ) {
                $ip = trim( $ip );

                if ( filter_var( $ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE ) !== false ) {
                    $forwarded = $ip;
                    break 2;
                }
            }
        }
    }

    // If we found a different IP address then REMOTE_ADDR then it's a proxy!
    if ( $forwarded != $result->ip ) {
        $result->proxy = true;
        $result->proxy_ip = $result->ip;
        $result->ip = $forwarded;
    }

    return $result;
}