5 つのレートリミットアルゴリズムを同時に動かして比較する PHP サービスを作った

interface LimiterInterface
{
    public function name(): string;
    public function check(string $key): Decision;
    public function peek(string $key): Decision;
    public function reset(?string $key = null): void;
    public function storedKeys(): int;
    public function exportState(): array;
    public function importState(array $state): void;
}

interface Clock
{
    public function now(): float;
}

public function check(string $key): Decision
{
    $now    = $this->clock->now();
    $bucket = (int) floor($now / $this->windowSeconds);

    $entry = $this->state[$key] ?? ['bucket' => $bucket, 'count' => 0];
    if ($entry['bucket'] !== $bucket) {
        $entry = ['bucket' => $bucket, 'count' => 0];
    }

    $resetAt = (float) (($bucket + 1) * $this->windowSeconds);

    if ($entry['count'] >= $this->limit) {
        $this->state[$key] = $entry;
        return new Decision(false, $this->name(), $this->limit, 0, $resetAt, $entry['count']);
    }

    $entry['count']++;
    $this->state[$key] = $entry;
    return new Decision(true, $this->name(), $this->limit,
                        $this->limit - $entry['count'], $resetAt, $entry['count']);
}

public function testEdgeBurstFlaw20RequestsIn10Seconds(): void
{
    $clock = new FakeClock(1_000_009.5); // 境界の 0.5 秒前
    $fw    = new FixedWindow($clock, 10, 10);

    $allowed = 0;
    for ($i = 0; $i < 10; $i++) {
        if ($fw->check('k')->allowed) $allowed++;
    }
    $clock->advance(0.6);
    for ($i = 0; $i < 10; $i++) {
        if ($fw->check('k')->allowed) $allowed++;
    }

    $this->assertSame(20, $allowed,
        'fixed window allows 20 requests inside a 10s span at the boundary');
}

public function check(string $key): Decision
{
    $now    = $this->clock->now();
    $cutoff = $now - $this->windowSeconds;
    $log    = $this->state[$key] ?? [];

    $drop = 0;
    foreach ($log as $t) {
        if ($t > $cutoff) break;
        $drop++;
    }
    if ($drop > 0) $log = array_slice($log, $drop);

    if (count($log) >= $this->limit) {
        $this->state[$key] = $log;
        return new Decision(false, ...);
    }

    $log[] = $now;
    $this->state[$key] = $log;
    return new Decision(true, ...);
}

$bucket      = (int) floor($now / $this->windowSeconds);
$bucketStart = (float) ($bucket * $this->windowSeconds);
$elapsed     = $now - $bucketStart;
$weight      = 1.0 - ($elapsed / $this->windowSeconds);

$estimate = (int) floor($entry['prev'] * $weight + $entry['count']);

if ($estimate >= $this->limit) {
    // deny
}

public function check(string $key): Decision
{
    $now   = $this->clock->now();
    $entry = $this->state[$key] ?? ['tokens' => (float) $this->capacity, 'last' => $now];

    $elapsed = $now - $entry['last'];
    if ($elapsed > 0) {
        $entry['tokens'] = min(
            (float) $this->capacity,
            $entry['tokens'] + $elapsed * $this->refillRate,
        );
    }
    $entry['last'] = $now;

    if ($entry['tokens'] >= 1.0) {
        $entry['tokens'] -= 1.0;
        // allowed
    }
    // denied
}

public function check(string $key): Decision
{
    $now   = $this->clock->now();
    $entry = $this->state[$key] ?? ['size' => 0.0, 'last' => $now];

    $elapsed = $now - $entry['last'];
    if ($elapsed > 0) {
        $entry['size'] = max(0.0, $entry['size'] - $elapsed * $this->leakRate);
    }
    $entry['last'] = $now;

    if ($entry['size'] + 1.0 > (float) $this->capacity) {
        // queue full → deny
    }
    $entry['size'] += 1.0;
    // allow
}

{
  "input": { "key": "0.0.0.0", "n": 15, "delay": 0.1 },
  "results": {
    "fixed_window":           { "allowed": 10, "denied": 5, "sequence": [...] },
    "sliding_window_log":     { "allowed": 10, "denied": 5, "sequence": [...] },
    "sliding_window_counter": { "allowed": 10, "denied": 5, "sequence": [...] },
    "token_bucket":           { "allowed": 11, "denied": 4, "sequence": [...] },
    "leaky_bucket":           { "allowed": 11, "denied": 4, "sequence": [...] }
  }
}

git clone https://github.com/sen-ltd/rate-limit-demo
cd rate-limit-demo
docker build -t rate-limit-demo .
docker run --rm -p 8000:8000 rate-limit-demo

# 別シェルで:
for i in $(seq 1 12); do
  curl -sS -o /dev/null -w "%{http_code} " http://localhost:8000/fixed-window
done; echo
# → 200 200 200 200 200 200 200 200 200 200 429 429

curl -sS 'http://localhost:8000/compare?n=15&delay=0.1' | jq '.results | keys'