PHP, Get IP behind trusted proxy

get-ip.php

<?php
/**
 * Inspired by https://raw.githubusercontent.com/zendframework/zend-http/master/src/PhpEnvironment/RemoteAddress.php
 */
//PHP 5.6
function get_ip( $trusted_proxies = [] ) {
	if ( ! empty( $trusted_proxies ) && isset( $_SERVER['REMOTE_ADDR'] ) && ! in_array( $_SERVER['REMOTE_ADDR'], $trusted_proxies ) ) {
		if ( isset( $_SERVER['HTTP_CF_CONNECTING_IP'] ) ) {
			$ip = $_SERVER['HTTP_CF_CONNECTING_IP'];
		} elseif ( isset( $_SERVER['HTTP_CLIENT_IP'] ) ) {
			$ip = $_SERVER['HTTP_CLIENT_IP'];
		} elseif ( isset( $_SERVER['HTTP_X_FORWARDED_FOR'] ) ) {
			$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
		} elseif ( isset( $_SERVER['HTTP_X_FORWARDED'] ) ) {
			$ip = $_SERVER['HTTP_X_FORWARDED'];
		} elseif ( isset( $_SERVER['HTTP_FORWARDED_FOR'] ) ) {
			$ip = $_SERVER['HTTP_FORWARDED_FOR'];
		} else ( isset( $_SERVER['HTTP_FORWARDED'] ) ) {
			   $ip = $_SERVER['HTTP_FORWARDED'];
		}
		return ( ! empty( $ip ) ) ? array_pop( array_diff( array_map( 'trim', explode( ',', $ip ) ), $trusted_proxies ) ) : 'unknown';
	} else {
		if ( isset( $_SERVER['REMOTE_ADDR'] ) && ! empty( $_SERVER['REMOTE_ADDR'] ) ) {
			$ip = $_SERVER['REMOTE_ADDR'];
		} else {
			$ip = 'unkown'
		}
	}
}


//PHP 7
function get_ip( array $trusted_proxies = [] ) : string {
	if ( ! empty( $trusted_proxies ) && isset( $_SERVER['REMOTE_ADDR'] ) && ! in_array( $_SERVER['REMOTE_ADDR'], $trusted_proxies ) ) {
		$ip = $_SERVER['HTTP_CF_CONNECTING_IP'] ?:
			  $_SERVER['HTTP_CLIENT_IP'] ?:
			  $_SERVER['HTTP_X_FORWARDED_FOR'] ?:
			  $_SERVER['HTTP_FORWARDED_FOR'] ?:
			  $_SERVER['HTTP_FORWARDED'] ?:
			  'unkown';

		return array_pop( array_diff( array_map( 'trim', explode( ',', $ip ) ), $trusted_proxies ) ) ?: 'unknown';
	} else {
		return $_SERVER['REMOTE_ADDR'] ?: 'unkown';
	}
}