C++ implementation of an MQTT-SN client and gateway

• Minimal MQTT-SN client and aggregating gateway, with gateway discovery supported
• Intended for the Arduino environment, client is light enough to run on an Uno easily
• Completely non-blocking, so other application tasks can happen during protocol transactions
• Modular, so that new transports and HALs/devices can be easily added by implementing the right interface
• Gateway falls back to being a local MQTT-SN broker, in the absence of an MQTT connection
• Zero dynamic allocation, up-front costs only, a plus depending on your application
• Basic functionality complete and tested. No topic wildcards, LWT or message retention supported yet
• Sleeping clients now supported, though completely untested for now

Dependencies

• A modified fork of [knolleary]'s PubSubClient provides the default MQTT client interface in examples. This can be replaced by simply sub-classing the MQTTClient class to provide your own MQTT client implementation.

• A simple generic FIFO library for holding messages

Tests

• ESP32 gateway and one ESP32 client using RFM69HW transport
• ESP32 gateway with one STM32 client (in Truestudio) using HC12 transport