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<?php |
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declare(strict_types=1); |
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namespace Yiisoft\Yii\RateLimiter; |
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use InvalidArgumentException; |
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use Psr\SimpleCache\CacheInterface; |
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/** |
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* Counter implements generic cell rate limit algorithm (GCRA) that ensures that after reaching the limit further |
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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. |
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*/ |
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private int $periodInMilliseconds; |
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private int $limit; |
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/** |
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* @var float Maximum interval before next increment. |
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* In GCRA it is known as emission interval. |
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*/ |
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private float $incrementIntervalInMilliseconds; |
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private CacheInterface $storage; |
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private int $ttlInSeconds; |
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private string $cachePrefix; |
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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 $periodInSeconds Period to apply limit to. |
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*/ |
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public function __construct( |
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CacheInterface $storage, |
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int $limit, |
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int $periodInSeconds, |
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int $ttlInSeconds = self::DEFAULT_TTL, |
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string $cachePrefix = self::ID_PREFIX |
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) { |
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if ($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 ($periodInSeconds < 1) { |
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throw new InvalidArgumentException('The period must be a positive value.'); |
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} |
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$this->limit = $limit; |
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$this->periodInMilliseconds = $periodInSeconds * self::MILLISECONDS_PER_SECOND; |
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$this->storage = $storage; |
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$this->ttlInSeconds = $ttlInSeconds; |
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$this->cachePrefix = $cachePrefix; |
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$this->incrementIntervalInMilliseconds = (float)($this->periodInMilliseconds / $this->limit); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function hit(string $id): CounterState |
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{ |
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// Last increment time. |
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// In GCRA it's known as arrival time. |
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$lastIncrementTimeInMilliseconds = $this->currentTimeInMilliseconds(); |
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$theoreticalNextIncrementTime = $this->calculateTheoreticalNextIncrementTime( |
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$lastIncrementTimeInMilliseconds, |
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$this->getLastStoredTheoreticalNextIncrementTime($id, $lastIncrementTimeInMilliseconds) |
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); |
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$remaining = $this->calculateRemaining($lastIncrementTimeInMilliseconds, $theoreticalNextIncrementTime); |
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$resetAfter = $this->calculateResetAfter($theoreticalNextIncrementTime); |
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if ($remaining >= 1) { |
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$this->storeTheoreticalNextIncrementTime($id, $theoreticalNextIncrementTime); |
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} |
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return new CounterState($this->limit, $remaining, $resetAfter); |
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} |
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/** |
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* @return float Theoretical increment time that would be expected from equally spaced increments at exactly rate |
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* limit. In GCRA it is known as TAT, theoretical arrival time. |
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*/ |
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private function calculateTheoreticalNextIncrementTime( |
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int $lastIncrementTimeInMilliseconds, |
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float $storedTheoreticalNextIncrementTime |
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): float { |
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return max($lastIncrementTimeInMilliseconds, $storedTheoreticalNextIncrementTime) + |
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$this->incrementIntervalInMilliseconds; |
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} |
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/** |
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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(int $lastIncrementTimeInMilliseconds, float $theoreticalNextIncrementTime): int |
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{ |
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$incrementAllowedAt = $theoreticalNextIncrementTime - $this->periodInMilliseconds; |
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return (int)( |
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round($lastIncrementTimeInMilliseconds - $incrementAllowedAt) / |
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$this->incrementIntervalInMilliseconds |
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); |
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} |
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private function getLastStoredTheoreticalNextIncrementTime(string $id, int $lastIncrementTimeInMilliseconds): float |
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{ |
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return (float)$this->storage->get($this->getCacheKey($id), $lastIncrementTimeInMilliseconds); |
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} |
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private function storeTheoreticalNextIncrementTime(string $id, float $theoreticalNextIncrementTime): void |
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{ |
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$this->storage->set($this->getCacheKey($id), $theoreticalNextIncrementTime, $this->ttlInSeconds); |
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} |
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/** |
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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 currentTimeInMilliseconds(): 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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* @param string $id |
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* |
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* @return string Cache key used to store the next increment time. |
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*/ |
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private function getCacheKey(string $id): string |
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{ |
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return $this->cachePrefix . $id; |
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} |
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} |
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yiisoft /
rate-limiter
