PacketRateLimiter.php

<?php
 
/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
 */
 
declare(strict_types=1);
 
namespace pocketmine\network\mcpe;
 
use pocketmine\network\PacketHandlingException;
use function hrtime;
use function intdiv;
use function min;
 
final class PacketRateLimiter{
    private int $budget;
    private int $lastUpdateTimeNs;
    private int $maxBudget;
 
    public function __construct(
        private string $name,
        private int $averagePerTick,
        int $maxBufferTicks,
        private int $updateFrequencyNs = 50_000_000,
    ){
        $this->maxBudget = $this->averagePerTick * $maxBufferTicks;
        $this->budget = $this->maxBudget;
        $this->lastUpdateTimeNs = hrtime(true);
    }
 
    public function decrement(int $amount = 1) : void{
        if($this->budget <= 0){
            $this->update();
            if($this->budget <= 0){
                throw new PacketHandlingException("Exceeded rate limit for \"$this->name\"");
            }
        }
        $this->budget -= $amount;
    }
 
    public function update() : void{
        $nowNs = hrtime(true);
        $timeSinceLastUpdateNs = $nowNs - $this->lastUpdateTimeNs;
        if($timeSinceLastUpdateNs > $this->updateFrequencyNs){
            $ticksSinceLastUpdate = intdiv($timeSinceLastUpdateNs, $this->updateFrequencyNs);
            /*
             * If the server takes an abnormally long time to process a tick, add the budget for time difference to
             * compensate. This extra budget may be very large, but it will disappear the next time a normal update
             * occurs. This ensures that backlogs during a large lag spike don't cause everyone to get kicked.
             * As long as all the backlogged packets are processed before the next tick, everything should be OK for
             * clients behaving normally.
             */
            $this->budget = min($this->budget, $this->maxBudget) + ($this->averagePerTick * 2 * $ticksSinceLastUpdate);
            $this->lastUpdateTimeNs = $nowNs;
        }
    }
}