API Rate Limiting & 쿼터 관리

-- Rate Limiting 테이블
CREATE TABLE rate_limits (
    id           BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    identifier   VARCHAR(255) NOT NULL,           -- API 키 또는 tenant_id
    endpoint     VARCHAR(100) NOT NULL DEFAULT '*', -- 엔드포인트별 제한
    tokens       DECIMAL(10,2) NOT NULL,          -- 남은 토큰
    max_tokens   INT UNSIGNED NOT NULL,              -- 최대 토큰 (버킷 크기)
    refill_rate  DECIMAL(10,4) NOT NULL,          -- 초당 토큰 충전량
    last_refill  DATETIME(3) NOT NULL,              -- 마지막 충전 시각 (밀리초)

    UNIQUE KEY uq_identifier_endpoint (identifier, endpoint),
    INDEX idx_identifier (identifier)
);
        

// RateLimiter.php - Token Bucket 기반 Rate Limiter

class RateLimiter {
    private PDO $pdo;

    // 요금제별 Rate Limit 설정
    private const PLAN_LIMITS = [
        'free'  => ['max_tokens' => 10,  'refill_rate' => 0.1667],  // 10req/분, 버스트 10
        'basic' => ['max_tokens' => 60,  'refill_rate' => 1.0],     // 60req/분, 버스트 60
        'pro'   => ['max_tokens' => 300, 'refill_rate' => 5.0],     // 300req/분, 버스트 300
    ];

    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    /**
     * 요청 허용 여부 확인 (Token Bucket)
     * 반환값: ['allowed' => bool, 'remaining' => int, ...]
     */
    public function attempt(string $identifier, string $planName, string $endpoint = '*'): array
    {
        $limits = self::PLAN_LIMITS[$planName] ?? self::PLAN_LIMITS['free'];
        $now    = microtime(true);

        $this->pdo->beginTransaction();

        try {
            // 현재 버킷 상태 조회 (행 잠금)
            $stmt = $this->pdo->prepare("
                SELECT tokens, max_tokens, refill_rate, last_refill
                FROM rate_limits
                WHERE identifier = :id AND endpoint = :ep
                FOR UPDATE
            ");
            $stmt->execute([':id' => $identifier, ':ep' => $endpoint]);
            $bucket = $stmt->fetch(PDO::FETCH_ASSOC);

            if (!$bucket) {
                // 첫 요청: 버킷 생성
                $stmt = $this->pdo->prepare("
                    INSERT INTO rate_limits (identifier, endpoint, tokens, max_tokens, refill_rate, last_refill)
                    VALUES (:id, :ep, :tokens, :max, :rate, NOW(3))
                ");
                $stmt->execute([
                    ':id'     => $identifier,
                    ':ep'     => $endpoint,
                    ':tokens' => $limits['max_tokens'] - 1, // 현재 요청분 차감
                    ':max'    => $limits['max_tokens'],
                    ':rate'   => $limits['refill_rate'],
                ]);

                $this->pdo->commit();
                return [
                    'allowed'   => true,
                    'remaining' => $limits['max_tokens'] - 1,
                    'limit'     => $limits['max_tokens'],
                    'reset'     => 60,
                ];
            }

            // 경과 시간에 따른 토큰 충전
            $lastRefill  = strtotime($bucket['last_refill']);
            $elapsed     = $now - $lastRefill;
            $newTokens   = $elapsed * (float)$bucket['refill_rate'];
            $tokens      = min(
                (float)$bucket['max_tokens'],
                (float)$bucket['tokens'] + $newTokens
            );

            if ($tokens 1) {
                // 토큰 부족: 요청 거부
                $this->pdo->commit();
                $retryAfter = (int)ceil((1 - $tokens) / (float)$bucket['refill_rate']);

                return [
                    'allowed'     => false,
                    'remaining'   => 0,
                    'limit'       => (int)$bucket['max_tokens'],
                    'retry_after' => $retryAfter,
                ];
            }

            // 토큰 소비
            $tokens -= 1;
            $stmt = $this->pdo->prepare("
                UPDATE rate_limits
                SET tokens = :tokens, last_refill = NOW(3)
                WHERE identifier = :id AND endpoint = :ep
            ");
            $stmt->execute([
                ':tokens' => $tokens,
                ':id'     => $identifier,
                ':ep'     => $endpoint,
            ]);

            $this->pdo->commit();

            return [
                'allowed'   => true,
                'remaining' => (int)floor($tokens),
                'limit'     => (int)$bucket['max_tokens'],
                'reset'     => 60,
            ];

        } catch (Exception $e) {
            $this->pdo->rollBack();
            throw $e;
        }
    }
}