Yet another helper method for getting a user's real IP address

ip-address.php

<?php
class IP {
	/**
	 * Helper method for validating the IP address.
	 * Handled IPv4 and filters out private and reserved ranges.
	 * @param $ip_address string
	 * @return $ip_address bool|string Returns false if invalid
	 */
	protected function _validate_ip( $ip_address ) {
		return filter_var( $ip_address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4 | FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE );
	}

	/**
	 * Get the user's real ip address
	 * Change which $_SERVER variables to check for via add_filter( 'pmc_helpdesk_ip_keys' )
	 * @return $possible_ip bool|string  Returns false if no valid IP is found
	 */
	protected function _get_user_ip() {

		$possible_ip_keys = apply_filters( 'pmc_helpdesk_ip_keys', array(
			'True-Client-IP',
			'HTTP_X_FORWARDED_FOR',
			'HTTP_X_REAL_IP',
			'HTTP_CLIENT_IP',
			'HTTP_X_FORWARDED',
			'HTTP_X_CLUSTER_CLIENT_IP',
			'HTTP_FORWARDED_FOR',
			'HTTP_FORWARDED',
			'REMOTE_ADDR',
		) );

		foreach ( $possible_ip_keys as $possible_ip_key ) {
			if ( ! isset($_SERVER[$possible_ip_key]) ) {
				continue;
			}

			if ( strpos( $_SERVER[$possible_ip_key], ',' ) !== false ) {
				$possible_ips = explode( ',', $_SERVER[$possible_ip_key] );
				foreach ( $possible_ips as $possible_ip ) {
					$possible_ip = trim( $possible_ip );
					$possible_ip = $this->_validate_ip( $possible_ip );
					if ( $possible_ip ) {
						return $possible_ip;
					}
				}
			} else {
				$possible_ip = $this->_validate_ip( $_SERVER[$possible_ip_key] );
				if ( $possible_ip ) {
					return $possible_ip;
				}
			}
		}

		return false;
	}

}