Messaging App for mobile devices on Android -- 2

Requirement is to develop messaging application that uses publish/subscribe paradigm. it should support publisher/subscriber mode where publisher can post messages on particular topic and same is received by subscriber who has subscribed to that topic Some of the highlights 1. Application should be password protected. 2. Concurrent user login is not permitted 3. UI should look similar to WhatsApp/Slack 4. Communication is done over websocket 5. Ability to show messages with various formatting like bold, italic. 6. Ability to view image, xls, document 7. Show user profile 8. Show messages in separate list as per topic 9. Application should run in background and show notification when new message is received. 10. Application should be compatible with various devices in landscape and portrait mode.