Return error via SubscriptionListener when presence events are malformed

src/main/java/com/pusher/client/channel/SubscriptionEventListener.java

@@ -33,4 +33,18 @@ public interface SubscriptionEventListener {
      *            See {@linkplain PusherEvent} for more.
      */
     void onEvent(final PusherEvent event);
+
+    /**
+     * Callback that is fired whenever an unexpected error occurs processing
+     * for this {@linkplain SubscriptionEventListener}.
+     *
+     * @param message
+     *            A description of the problem.
+     * @param e
+     *            An associated exception, if available.
+     */
+    default void onError(String message, Exception e) {
+        // No-op
+        return;
+    };
 }

src/main/java/com/pusher/client/channel/impl/PresenceChannelImpl.java

@@ -95,9 +95,20 @@ public String toString() {
 
     @SuppressWarnings({ "rawtypes", "unchecked" })
     private void handleSubscriptionSuccessfulMessage(final String message) {
+        final ChannelEventListener listener = getEventListener();
 
         // extract data from the JSON message
         final PresenceData presenceData = extractPresenceDataFrom(message);
+        if (presenceData == null) {
+            if (listener != null) {
+                listener.onError(
+                    "Subscription failed: Presence data not found",
+                    null
+                );
+            }
+            return;
+        }
+
         final List<String> ids = presenceData.ids;
         final Map<String, Object> hash = presenceData.hash;
 
@@ -109,7 +120,7 @@ private void handleSubscriptionSuccessfulMessage(final String message) {
                 idToUserMap.put(id, user);
             }
         }
-        final ChannelEventListener listener = getEventListener();
+
         if (listener != null) {
             final PresenceChannelEventListener presenceListener = (PresenceChannelEventListener)listener;
             presenceListener.onUsersInformationReceived(getName(), getUsers());

src/test/java/com/pusher/client/channel/impl/PresenceChannelImplTest.java

@@ -30,6 +30,7 @@ public class PresenceChannelImplTest extends PrivateChannelImplTest {
     private static final String AUTH_RESPONSE = "\"auth\":\"a87fe72c6f36272aa4b1:f9db294eae7\",\"channel_data\":\"{\\\"user_id\\\":\\\"5116a4519575b\\\",\\\"user_info\\\":{\\\"name\\\":\\\"Phil Leggetter\\\",\\\"twitter_id\\\":\\\"@leggetter\\\"}}\"";
     private static final String AUTH_RESPONSE_NUMERIC_ID = "\"auth\":\"a87fe72c6f36272aa4b1:f9db294eae7\",\"channel_data\":\"{\\\"user_id\\\":51169,\\\"user_info\\\":{\\\"name\\\":\\\"Phil Leggetter\\\",\\\"twitter_id\\\":\\\"@leggetter\\\"}}\"";
     private static final String USER_ID = "5116a4519575b";
+    private static final String ERROR_NO_PRESENCE_DATA = "Subscription failed: Presence data not found";
 
     @Mock
     private PresenceChannelEventListener mockEventListener;
@@ -77,6 +78,17 @@ public void testIsSubscribedMethod(){
         assertTrue(channel.isSubscribed());
     }
 
+    @Test
+    public void testInternalSubscriptionSucceededMessageWithNoPresenceDataReturnsError(){
+        final String eventName = "pusher_internal:subscription_succeeded";
+        final Map<String, Object> data = new LinkedHashMap<String, Object>();
+
+        channel.onMessage(eventName, eventJson(eventName, data, getChannelName()));
+
+        final InOrder inOrder = inOrder(mockEventListener);
+        inOrder.verify(mockEventListener).onError(eq(ERROR_NO_PRESENCE_DATA), eq(null));
+    }
+
     @Test
     @Override
     @SuppressWarnings({ "rawtypes", "unchecked" })