Fix leaky bucket serialization

// FREEBIE

src/main/java/org/whispersystems/textsecuregcm/limits/LeakyBucket.java

@@ -42,7 +42,8 @@ public class LeakyBucket {
   }
 
   public boolean add(int amount) {
-    this.spaceRemaining = getUpdatedSpaceRemaining();
+    this.spaceRemaining       = getUpdatedSpaceRemaining();
+    this.lastUpdateTimeMillis = System.currentTimeMillis();
 
     if (this.spaceRemaining >= amount) {
       this.spaceRemaining -= amount;

src/test/java/org/whispersystems/textsecuregcm/tests/limits/LeakyBucketTest.java

@@ -0,0 +1,52 @@
+package org.whispersystems.textsecuregcm.tests.limits;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.Test;
+import org.whispersystems.textsecuregcm.limits.LeakyBucket;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class LeakyBucketTest {
+
+  @Test
+  public void testFull() {
+    LeakyBucket leakyBucket = new LeakyBucket(2, 1.0 / 2.0);
+
+    assertTrue(leakyBucket.add(1));
+    assertTrue(leakyBucket.add(1));
+    assertFalse(leakyBucket.add(1));
+
+    leakyBucket = new LeakyBucket(2, 1.0 / 2.0);
+
+    assertTrue(leakyBucket.add(2));
+    assertFalse(leakyBucket.add(1));
+    assertFalse(leakyBucket.add(2));
+  }
+
+  @Test
+  public void testLapseRate() throws IOException {
+    ObjectMapper mapper     = new ObjectMapper();
+    String       serialized = "{\"bucketSize\":2,\"leakRatePerMillis\":8.333333333333334E-6,\"spaceRemaining\":0,\"lastUpdateTimeMillis\":" + (System.currentTimeMillis() - TimeUnit.MINUTES.toMillis(2)) + "}";
+
+    LeakyBucket leakyBucket = LeakyBucket.fromSerialized(mapper, serialized);
+    assertTrue(leakyBucket.add(1));
+
+    String      serializedAgain  = leakyBucket.serialize(mapper);
+    LeakyBucket leakyBucketAgain = LeakyBucket.fromSerialized(mapper, serializedAgain);
+
+    assertFalse(leakyBucketAgain.add(1));
+  }
+
+  @Test
+  public void testLapseShort() throws Exception {
+    ObjectMapper mapper     = new ObjectMapper();
+    String       serialized = "{\"bucketSize\":2,\"leakRatePerMillis\":8.333333333333334E-6,\"spaceRemaining\":0,\"lastUpdateTimeMillis\":" + (System.currentTimeMillis() - TimeUnit.MINUTES.toMillis(1)) + "}";
+
+    LeakyBucket leakyBucket = LeakyBucket.fromSerialized(mapper, serialized);
+    assertFalse(leakyBucket.add(1));
+  }
+}