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<?php |
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declare(strict_types=1); |
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namespace Yiisoft\Yii\Web\RateLimiter; |
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use Psr\SimpleCache\CacheInterface; |
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/** |
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* Counter implements generic сell rate limit algorithm (GCRA) that ensures that after reaching the limit futher |
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* increments are distributed equally. |
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* |
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* @link https://en.wikipedia.org/wiki/Generic_cell_rate_algorithm |
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*/ |
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final class Counter implements CounterInterface |
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{ |
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private const DEFAULT_TTL = 86400; |
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private const ID_PREFIX = 'rate-limiter-'; |
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private const MILLISECONDS_PER_SECOND = 1000; |
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/** |
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* @var int period to apply limit to, in milliseconds |
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*/ |
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private int $period; |
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private int $limit; |
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/** |
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* @var float maximum interval before next increment, in milliseconds |
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* In GCRA it is known as emission interval. |
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*/ |
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private float $incrementInterval; |
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private ?string $id = null; |
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private CacheInterface $storage; |
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private int $ttl = self::DEFAULT_TTL; |
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/** |
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* @var int last increment time |
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* In GCRA it's known as arrival time |
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*/ |
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private int $lastIncrementTime; |
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/** |
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* @param int $limit maximum number of increments that could be performed before increments are limited |
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* @param int $period period to apply limit to, in seconds |
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* @param CacheInterface $storage |
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*/ |
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public function __construct(int $limit, int $period, CacheInterface $storage) |
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{ |
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if ($limit < 1) { |
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throw new \InvalidArgumentException('The limit must be a positive value.'); |
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} |
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if ($period < 1) { |
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throw new \InvalidArgumentException('The period must be a positive value.'); |
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} |
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$this->limit = $limit; |
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$this->period = $period * self::MILLISECONDS_PER_SECOND; |
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$this->storage = $storage; |
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$this->incrementInterval = (float)($this->period / $this->limit); |
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} |
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public function setId(string $id): void |
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{ |
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$this->id = $id; |
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} |
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/** |
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* @param int $ttl cache TTL that is used to store counter values |
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* Default is one day. |
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* Note that period can not exceed TTL. |
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*/ |
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public function setTtl(int $ttl): void |
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{ |
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$this->ttl = $ttl; |
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} |
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public function getCacheKey(): string |
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{ |
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return self::ID_PREFIX . $this->id; |
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} |
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public function incrementAndGetState(): CounterState |
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{ |
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if ($this->id === null) { |
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throw new \LogicException('The counter ID should be set'); |
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} |
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$this->lastIncrementTime = $this->getCurrentTime(); |
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$theoreticalNextIncrementTime = $this->calculateTheoreticalNextIncrementTime( |
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$this->getLastStoredTheoreticalNextIncrementTime() |
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); |
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$remaining = $this->calculateRemaining($theoreticalNextIncrementTime); |
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$resetAfter = $this->calculateResetAfter($theoreticalNextIncrementTime); |
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if ($remaining >= 1) { |
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$this->storeTheoreticalNextIncrementTime($theoreticalNextIncrementTime); |
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} |
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return new CounterState($this->limit, $remaining, $resetAfter); |
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} |
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/** |
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* @param float $storedTheoreticalNextIncrementTime |
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* @return float theoretical increment time that would be expected from equally spaced increments at exactly rate limit |
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* In GCRA it is known as TAT, theoretical arrival time. |
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*/ |
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private function calculateTheoreticalNextIncrementTime(float $storedTheoreticalNextIncrementTime): float |
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{ |
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return max($this->lastIncrementTime, $storedTheoreticalNextIncrementTime) + $this->incrementInterval; |
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} |
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/** |
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* @param float $theoreticalNextIncrementTime |
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* @return int the number of remaining requests in the current time period |
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*/ |
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private function calculateRemaining(float $theoreticalNextIncrementTime): int |
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{ |
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$incrementAllowedAt = $theoreticalNextIncrementTime - $this->period; |
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return (int)(round($this->lastIncrementTime - $incrementAllowedAt) / $this->incrementInterval); |
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} |
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private function getLastStoredTheoreticalNextIncrementTime(): float |
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{ |
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return $this->storage->get($this->getCacheKey(), (float)$this->lastIncrementTime); |
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} |
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private function storeTheoreticalNextIncrementTime(float $theoreticalNextIncrementTime): void |
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{ |
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$this->storage->set($this->getCacheKey(), $theoreticalNextIncrementTime, $this->ttl); |
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} |
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/** |
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* @param float $theoreticalNextIncrementTime |
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* @return int timestamp to wait until the rate limit resets |
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*/ |
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private function calculateResetAfter(float $theoreticalNextIncrementTime): int |
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{ |
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return (int)($theoreticalNextIncrementTime / self::MILLISECONDS_PER_SECOND); |
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} |
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private function getCurrentTime(): int |
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{ |
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return (int)round(microtime(true) * self::MILLISECONDS_PER_SECOND); |
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} |
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} |
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yiisoft /
yii-web
