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MQTT (Message Queuing Telemetry Transport) Protocol

MQTT is a lightweight, publish-subscribe network protocol that transports messages between devices. It is designed for connections with remote locations where a "small code footprint" is required or the network bandwidth is limited.

Protocol Overview​

  • Architecture: Based on a Client/Broker model.
  • Transport: Typically runs over TCP/IP, but variants like MQTT-SN (for Sensor Networks) can run over UDP/Bluetooth.
  • Port: Default is 1883, while encrypted (TLS/SSL) is 8883.
  • Payload: Can carry up to 256MB of data; control headers can be as small as 2 bytes.
  • QoS (Quality of Service):
    • Level 0: At most once (Fire and forget).
    • Level 1: At least once (Acknowledged).
    • Level 2: Exactly once (Four-step handshake).

Features & Security​

  • Topic System: Uses a hierarchical structure (e.g., home/living-room/temperature).
  • Retained Messages: The broker stores the last message on a topic for new subscribers.
  • Last Will and Testament (LWT): Notifies other clients when a client unexpectedly disconnects.
  • Security: Basic authentication uses plain-text usernames and passwords. TLS/SSL is highly recommended to protect against interception and tempering.

Brokers​

Client Libraries​

  • Eclipse Paho: A collection of high-quality MQTT client libraries.
    • eclipse/paho.mqtt.golang
      • Go, EPL-2.0 / EDL-1.0
      • The standard MQTT client library for Go. Supports MQTT 3.1, 3.1.1, and V5. Supports TCP, TLS, and WebSockets.

Resources​