Introduce a hyper-log-log-based cardinality rate limiter

service/src/test/java/org/whispersystems/textsecuregcm/limits/CardinalityRateLimiterTest.java

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+/*
+ * Copyright 2021 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.limits;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
+import org.whispersystems.textsecuregcm.redis.AbstractRedisClusterTest;
+
+import java.time.Duration;
+
+import static org.junit.Assert.*;
+
+public class CardinalityRateLimiterTest extends AbstractRedisClusterTest {
+
+    @Before
+    public void setUp() throws Exception {
+      super.setUp();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+      super.tearDown();
+    }
+
+    @Test
+    public void testValidate() {
+      final int maxCardinality = 10;
+      final CardinalityRateLimiter rateLimiter = new CardinalityRateLimiter(getRedisCluster(), "test", Duration.ofDays(1), Duration.ofDays(1), maxCardinality);
+
+      final String source = "+18005551234";
+      int validatedAttempts = 0;
+      int blockedAttempts = 0;
+
+      for (int i = 0; i < maxCardinality * 2; i++) {
+        try {
+          rateLimiter.validate(source, String.valueOf(i));
+          validatedAttempts++;
+        } catch (final RateLimitExceededException e) {
+          blockedAttempts++;
+        }
+      }
+
+      assertTrue(validatedAttempts >= maxCardinality);
+      assertTrue(blockedAttempts > 0);
+
+      final String secondSource = "+18005554321";
+
+      try {
+        rateLimiter.validate(secondSource, "test");
+      } catch (final RateLimitExceededException e) {
+        fail("New source should not trigger a rate limit exception on first attempted validation");
+      }
+    }
+}