code: protected static SessionService create(IPublisherInfo self, String sessionId, IEventManager eventManager,
                                             ISessionUpdate callback) {
          String sendEvent = StrUtil.formatMessage(EVENT_SEND, sessionId);
          String joinEvent = StrUtil.formatMessage(EVENT_JOIN, sessionId);
          String leaveEvent = StrUtil.formatMessage(EVENT_LEAVE, sessionId);
          return new SessionService(self, sendEvent, joinEvent, leaveEvent, eventManager, callback);
      }
docs: Creates a service handler for a chat session.
  
  @param self Creator of the chat session.
  @param sessionId Unique id of the chat session.
  @param eventManager Event manager instance.
  @param callback Call back method for session-related events.
  @return The newly created service.