Make RateLimiter resilient to timeShifting

jderusse · jderusse · commit 65e86142f05c · 2021-11-30T10:45:59.000+01:00
diff --git a/src/Symfony/Component/RateLimiter/Policy/Window.php b/src/Symfony/Component/RateLimiter/Policy/Window.php
@@ -68,11 +68,6 @@ public function getHitCount(): int
 
     public function getAvailableTokens(float $now)
     {
-        // if timer is in future, there are no tokens available anymore
-        if ($this->timer > $now) {
-            return 0;
-        }
-
         // if now is more than the window interval in the past, all tokens are available
         if (($now - $this->timer) > $this->intervalInSeconds) {
             return $this->maxSize;
diff --git a/src/Symfony/Component/RateLimiter/Tests/Policy/FixedWindowLimiterTest.php b/src/Symfony/Component/RateLimiter/Tests/Policy/FixedWindowLimiterTest.php
@@ -14,6 +14,7 @@
 use PHPUnit\Framework\TestCase;
 use Symfony\Bridge\PhpUnit\ClockMock;
 use Symfony\Component\RateLimiter\Policy\FixedWindowLimiter;
+use Symfony\Component\RateLimiter\Policy\Window;
 use Symfony\Component\RateLimiter\RateLimit;
 use Symfony\Component\RateLimiter\Storage\InMemoryStorage;
 use Symfony\Component\RateLimiter\Tests\Resources\DummyWindow;
@@ -90,6 +91,19 @@ public function testWrongWindowFromCache()
         $this->assertEquals(9, $rateLimit->getRemainingTokens());
     }
 
+    public function testWindowResilientToTimeShifting()
+    {
+        $serverOneClock = microtime(true) - 1;
+        $serverTwoClock = microtime(true) + 1;
+        $window = new Window('id', 300, 100, $serverTwoClock);
+        $this->assertSame(100, $window->getAvailableTokens($serverTwoClock));
+        $this->assertSame(100, $window->getAvailableTokens($serverOneClock));
+
+        $window = new Window('id', 300, 100, $serverOneClock);
+        $this->assertSame(100, $window->getAvailableTokens($serverTwoClock));
+        $this->assertSame(100, $window->getAvailableTokens($serverOneClock));
+    }
+
     private function createLimiter(): FixedWindowLimiter
     {
         return new FixedWindowLimiter('test', 10, new \DateInterval('PT1M'), $this->storage);
