Add method to list active users for a given flag

.circleci/config.yml

@@ -5,5 +5,6 @@ jobs:
       - image: librato/java-ci:latest
       - image: wurstmeister/zookeeper
     steps:
+      - add_ssh_keys
       - checkout
       - run: mvn test

src/main/java/com/librato/rollout/RolloutClient.java

@@ -18,6 +18,12 @@ public interface RolloutClient {
      */
     boolean userFeatureActive(final String feature, long userId);
 
+    /**
+     * @param feature   Rollout feature
+     * @return list of active user ids
+     */
+    List<Long> activeUsers(final String feature);
+
     /**
      * @param feature Rollout feature
      * @return Percentage of given feature, or 0 if feature does not exist

src/main/java/com/librato/rollout/zk/RolloutZKClient.java

@@ -74,6 +74,13 @@ public boolean userFeatureActive(String feature, long userId, List<String> userG
         return false;
     }
 
+    @Override
+    public List<Long> activeUsers(String feature) {
+        final Entry entry = features.get().get(feature);
+        if (entry == null) return Collections.emptyList();
+        return entry.userIds;
+    }
+
     @Override
     public void start() throws Exception {
         if (!isStarted.compareAndSet(false, true)) {
@@ -156,7 +163,7 @@ public static Entry fromString(String s, String key) {
                     log.warn("Couldn't parse `{}` as a long, ignoring user id for key `{}`", id, key);
                 }
             }
-            return new Entry(percentage, userIds, groups);
+            return new Entry(percentage, Collections.unmodifiableList(userIds), Collections.unmodifiableList(groups));
         }
     }
 }

src/test/java/com/librato/rollout/RolloutZKClientTest.java

@@ -204,4 +204,25 @@ public void testInvalidUserIdAndPercentage() throws Exception {
             }
         }
     }
+
+    @Test
+    public void testGetActiveUsers() throws Exception {
+        RolloutClient client = null;
+        try {
+            client = new RolloutZKClient(framework, rolloutPath);
+            client.start();
+
+            assertTrue(client.activeUsers("nosuchfeature").isEmpty());
+
+            framework.setData().forPath(rolloutPath, "{\"feature:hello\": \"0|1|\", \"feature:another\": \"0|1,2|\",  \"feature:__features__\":\"hello,another\"}".getBytes());
+            Thread.sleep(100);
+
+            assertEquals(Lists.newArrayList(1L), client.activeUsers("hello"));
+            assertEquals(Lists.newArrayList(1L, 2L), client.activeUsers("another"));
+        } finally {
+            if (client != null) {
+                client.stop();
+            }
+        }
+    }
 }