// the find
tuanpmt/esp_mqtt
MQTT client library for ESP8266
A port of an MQTT client library for the ESP8266 running the non-OS SDK. Targets developers doing bare-metal IoT work on ESP8266 who need a functional MQTT implementation without FreeRTOS or the Arduino ecosystem. Last touched in 2020.
Covers the full MQTT spec including all three QoS levels, LWT, authentication, and SSL — not a stripped-down subset. Multiple simultaneous broker connections is a real feature that most hobby-grade alternatives skip. The code is compact and the module structure (mqtt/, modules/, driver/) is clean enough to read and modify. SSL via 1024-bit RSA is at least present, even if the key size is dated.
Dead since 2020 and tied to the non-OS SDK, which Espressif has long since deprecated in favor of ESP-IDF and the FreeRTOS SDK — this won't compile against anything current without real porting work. SSL cert is self-signed with a 1024-bit key, which no serious broker will accept today. No reconnection logic is visible in the public API; dropped connections are your problem. The 'usage: see user_main.c' documentation is a red flag — there is no real API reference.