Demo of an MQTT application that subscribes to multiple topic filters using a subscription manager to manage multiple subscriptions, register different callbacks for each subscription, and handle wildcard topics. It establishes a TLS connection with server-only authentication, and communicates at QoS 1 level with the broker.

This demo uses an OpenSSL-based transport interface implementation to establish a server-authenticated TLS connection, and demonstrates the subscribe-publish workflow of MQTT at QoS 1 level, using a subscription manager. Before subscribing to a topic filter, the application registers the filter's unique callback with the subscription manager. After subscription, it publishes to the same topic and waits for receipt of that message to be returned from the server at QoS 1 level. Once received, the subscription manager will invoke the callback registered for the topic filter that matches the topic of the incoming PUBLISH. This subscribe-publish process is repeated for 3 different topic filters, including one wildcard filter. This cycle of publishing to the broker and receiving the same message back from the broker is repeated indefinitely.

Messages in this demo are sent at QoS 1, which guarantees at least one delivery according to the MQTT spec. See the demo workflow below: