Return error via SubscriptionListener when presence events are malformed

Author: jonathanlloyd

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());