How Can I Most Accurately Retrieve a User's IP Address in PHP?

What is the most accurate way to retrieve a user's correct IP address in PHP?

When it comes to retrieving a user's IP address in PHP, there are many options to choose from. However, the most accurate method depends on a number of factors.

One factor to consider is whether the user is behind a proxy. If the user is behind a proxy, their IP address may be hidden or masked. In this case, you will need to use a method that can pierce through the proxy to get the user's real IP address.

Another factor to consider is whether you want to use a whitelist or blacklist approach. A whitelist approach means that you only allow traffic from certain IP addresses. A blacklist approach means that you block traffic from certain IP addresses. The method you choose will depend on your specific needs and security requirements.

The following code is a general consensus on how to most accurately retrieve a user's real IP address using $_SERVER variables:

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;
                }
            }
        }
    }
}

This code checks a number of $_SERVER variables and tries to return the first valid IP address. This code provides a more accurate estimate of a user's real IP address, but it is still not perfect.

Words of Warning:

Bear in mind that $_SERVER['REMOTE_ADDR'] still represents the most reliable source of an IP address, despite its potential for inaccuracies. The purpose of the code above is to attempt to determine the IP address of a client sitting behind a proxy. For general purposes, it's advisable to combine this method with the IP address returned directly from $_SERVER['REMOTE_ADDR'] and store both.

For the overwhelming majority of users, the code above will provide accurate results. However, it may not be foolproof against malicious users who may try to abuse your system by injecting their own request headers. For mission-critical applications relying on IP addresses, stick to $_SERVER['REMOTE_ADDR'] and avoid catering to users behind proxies.

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