Throttle client requests to avoid DoS attack (scroll down for IP-based)

abusecheck.php

<?php

/**
ABUSE CHECK
Throttle client requests to avoid DoS attack
*/
session_start();
$usage = array(5,5,5,5,10,20,30,40,50,60,120,180,240); // seconds to wait after each request
if (isset($_SESSION['use_last'])) {
  $nextin = $_SESSION['use_last']+$usage[$_SESSION['use_count']];
	if (time() < $nextin) {
		echo 'Please wait '.($nextin-time()).' seconds&hellip;';
		die();
	}else{
		$_SESSION['use_count']++;
		if ($_SESSION['use_count'] > sizeof($usage)-1) {$_SESSION['use_count']=sizeof($usage)-1;}
	}
}else{
	$_SESSION['use_count'] = 0;
}
$_SESSION['use_last'] = time();

// Execute code here

hrottlerequest.php

<?php

/*
Limit amount of requests to avoid server abuse (IP based)

require( dirname(__FILE__) . '/lib/throttlerequest.php' );
$tr = new ThrottleRequest( $_SERVER['REMOTE_ADDR'], dirname(__FILE__) . '/lib/throttlerequest-db.php');


*/
class ThrottleRequest {

	private $number_requests = 61;
	private $time_interval 	= 60;

	private $db_path 		= 'access.php';
	private $db 			= [];

	public function __construct( $ip, $path = NULL )
	{

		// if path is set
		if ( isset( $path ) )
		{
			$this->db_path = $path;
		}

		// Get DB
		if ( file_exists( $this->db_path ) )
		{
			$this->db = include( $this->db_path );
		}

		// Clean old IPs
		foreach ( $this->db as $session_ip => $session )
		{
			if ( $session['expires'] <= time() )
			{
				unset( $this->db[ $session_ip ] );
			}
		}

		// Add request
		if ( isset( $this->db[ $ip ] ) )
		{
			$this->db[ $ip ]['requests']++;
		}
		else
		{
			$this->db[ $ip ] = [
				'requests' => 1,
				'expires' => time() + $this->time_interval,
				'user_agent' => $_SERVER['HTTP_USER_AGENT'],
			];
		}

		// Save DB
		file_put_contents( $this->db_path, '<?php return ' . var_export( $this->db, true ) . ';' );

		// Check if needs to be blocked
		if ( $this->db[ $ip ]['requests'] > $this->number_requests )
		{
			header('HTTP/1.0 503 Service Temporarily Unavailable');
			header('Status: 503 Service Temporarily Unavailable');
			header('Retry-After: ' . $this->time_interval ); // seconds
			die( 'Too many requests. Please wait a few seconds.' );
		}
	}
}

ip-based.php

<?php

/*
Limit amount of requests to avoid server abuse (IP based)

require( dirname(__FILE__) . '/libs/throttlerequest.php' );
$tr = new ThrottleRequest( $config );


MySQL

CREATE TABLE `throttlerequest` (
  `ip` varchar(45) NOT NULL DEFAULT '',
  `requests` int(11) NOT NULL DEFAULT '1',
  `expires` datetime NOT NULL,
  `country` char(2) DEFAULT NULL,
  `url` varchar(255) DEFAULT NULL,
  `user_agent` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`ip`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

*/
class ThrottleRequest {

	private $number_requests = 39;
	private $time_interval 	= 20; // seconds

	private $db = null;
	private $config = null;


	public function __construct( $config, $url = '' ){

		$this->config = $config;
		$this->db = new DB( $this->config['db_user'], $this->config['db_pass'], $this->config['db_dbname'] );

		$ip = ( isset($_SERVER["HTTP_CF_CONNECTING_IP"]) ) ? $_SERVER["HTTP_CF_CONNECTING_IP"] : $_SERVER['REMOTE_ADDR'];

		// Clean old IPs
		$clean = $this->db->query("DELETE FROM throttlerequest WHERE expires <= :expires;")
			->bind(':expires', date('Y-m-d H:i:s'))
			->delete();
		$exists = $this->db->query("SELECT ip, requests FROM throttlerequest WHERE ip = :ip LIMIT 1;")
			->bind(':ip', $ip )
			->single();

		if ( $exists ){
			$result = $this->db->query("UPDATE throttlerequest SET
				requests = :requests,
				url = :url,
				user_agent = :user_agent
	 			WHERE ip = :ip
	 			LIMIT 1;")
				->bind(':requests', $exists['requests'] + 1 )
				->bind(':url', $url )
				->bind(':user_agent', $_SERVER['HTTP_USER_AGENT'] )
				->bind(':ip', $ip )
				->update();
		}else{
			$result = $this->db->query("INSERT INTO `throttlerequest` (`ip`, `requests`, `expires`, `country`, `url`, `user_agent`) VALUES (
					:ip,
					:requests,
					:expires,
					:country,
					:url,
					:user_agent
				);")
				->bind(':ip', $ip )
				->bind(':requests', 1 )
				->bind(':expires', date('Y-m-d H:i:s', time() + $this->time_interval ) )
				->bind(':country', @$_SERVER['HTTP_CF_IPCOUNTRY'] )
				->bind(':url', $url )
				->bind(':user_agent', $_SERVER['HTTP_USER_AGENT'] )
				->update();

		}

		// Check if needs to be blocked
		if ( $exists['requests'] > $this->number_requests ){
			http_response_code( 429 );
			header('Retry-After: ' . $this->time_interval );
			die( 'Too many requests, please wait a few seconds' );
		}
	}
}

throttlerequest.php

<?php

/**
 * THROTTLE REQUESTS
 *
 * Limit amount of requests to avoid server abuse
 * For increased security, rely on IP addresses instead of Sessions
 *
 * $number_requests to be made on each interval
 * $time_interval seconds each interval lasts
 *
 * throttlerequest( 10, 60 ); // 1 request every 6 seconds
 */
function throttlerequest( $number_requests = 10, $time_interval = 60 )
{
	if( !isset($_SESSION) ) { session_start(); }

	// window not started or already finished
	if ( !isset($_SESSION['window']) OR $_SESSION['window'] + $time_interval < time() )
	{
		$_SESSION['window'] = time();
		$_SESSION['count'] = 1;
	}

	// $_SESSION['window'] started
	else if ( $_SESSION['window'] + $time_interval >= time() )
	{
		$_SESSION['count']++;

		if ( $_SESSION['count'] > $number_requests )
		{
			die( 'Too many requests. Please wait a few seconds.' );
		}

	}
}
throttlerequest( 10, 60 );

Thank you @Rotzbua for the valid observation but can one use the code below to validate IP addresses first, before using it in here

Thank you @Rotzbua for the valid observation but can one use the code below to validate IP addresses first, before using it in here

/**

• To validate if an IP address is both a valid and does not fall within
• a private network range.
• @param string $ip
  */
  function isValidIpAddress($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;
  }
  return true;
  }