Add 'getSubscriptions' API on Server.

Add a test for sessions without clean session flag.

broker/src/test/java/io/moquette/server/ServerIntegrationEmbeddedPublishTest.java

@@ -97,6 +97,17 @@ public class ServerIntegrationEmbeddedPublishTest {
         m_server.internalPublish(message);
     }
 
+    private void connectNoCleanSession() throws Exception {
+        MqttConnectOptions opts = new MqttConnectOptions();
+        opts.setCleanSession(false);
+        m_subscriber.connect(opts);
+    }
+
+    private void subscribeToWithQosAndNoCleanSession(String topic, int qos) throws Exception {
+        connectNoCleanSession();
+        m_subscriber.subscribe(topic, qos);
+    }
+
     private void verifyNoMessageIsReceived() throws Exception {
         MqttMessage msg = m_callback.getMessage(false);
         assertNull(msg);
@@ -276,4 +287,16 @@ public class ServerIntegrationEmbeddedPublishTest {
         MqttMessage message = m_callback.getMessage(true);
         assertTrue(message == null);
     }
+
+    @Test
+    public void testClientSubscribeWithoutCleanSession() throws Exception {
+        LOG.info("*** testClientSubscribeWithoutCleanSession ***");
+        subscribeToWithQosAndNoCleanSession("foo", 1);
+        m_subscriber.disconnect();
+        assertTrue(m_server.getSubscriptions().size() == 1);
+        connectNoCleanSession();
+        assertTrue(m_server.getSubscriptions().size() == 1);
+        internalPublishToWithQosAndRetained("foo", QOSType.MOST_ONE, false);
+        verifyMessageIsReceivedSuccessfully();
+    }
 }

broker/src/test/java/io/moquette/spi/persistence/MemorySessionStore.java

@@ -157,6 +157,15 @@ public class MemorySessionStore implements ISessionsStore {
         return null;
     }
 
+    @Override
+    public List<Subscription> getSubscriptions() {
+        List<Subscription> subscriptions = new ArrayList<>();
+        for (Map.Entry<String, Set<Subscription>> entry : m_persistentSubscriptions.entrySet()) {
+            subscriptions.addAll(entry.getValue());
+        }
+        return subscriptions;
+    }
+
     @Override
     public void inFlightAck(String clientID, int messageID) {
         Map<Integer, MessageGUID> m = this.m_inflightStore.get(clientID);