wolfMQTT by wolfSSL is a lightweight messaging protocol designed for constrained environments such as M2M (Machine to Machine) and IoT (Internet of Things). It operates on the Pub/Sub messaging principle of publishing messages and subscribing to topics. wolfMQTT is a C-based client implementation of MQTT for embedded use, supporting SSL/TLS via the wolfSSL library to enhance MQTT security. It is designed to be multi-platform, space-efficient, and extensible. It supports all Packet Types, all Quality of Service (QoS) levels 0-2, and supports SSL/TLS using the wolfSSL library. This implementation provides support for MQTT v5.0 and MQTT v3.1.1. Additionally, there is also client support for MQTT-SN (Sensor Network). wolfMQTT is built for maximum portability and is generally very easy to compile on new platforms. It is written in native C89 with minimal external dependencies and has a compiled size of about 6kB. The design is space-conscious, and it includes a user manual with build instructions, example overview, and API documentation. The library is open source (GPLv2) and supports a wide range of operating environments and chipmakers.
