Arduino Client for MQTT

This library provides a client for doing simple publish/subscribe messaging with a server that supports MQTT.

Notes of this fork

This is a fork of the repository knolleary/pubsubclient v2.8, which was last updated in May 20, 2020. There was an update approach in #1045, but it's also stale.

I tried lot's of different other MQTT libs, but they need more resources than PubSubClient or lacking maintenance as well:

• https://github.com/256dpi/arduino-mqtt
• https://github.com/hideakitai/MQTTPubSubClient
• https://github.com/bertmelis/espMqttClient
• https://github.com/arduino-libraries/ArduinoMqttClient
• https://github.com/thingsboard/pubsubclient

Since there was no progress I decided to merge the most important PRs manually and publish a new major version. I also renamed to PubSubClient3 to have a similar but different name of the library.

I appreciate every contribution to this library.

Examples

The library comes with a number of example sketches. See File > Examples > PubSubClient within the Arduino application.

Full API documentation is available here: https://hmueller01.github.io/pubsubclient3/api

Limitations

• The client is based on the MQTT Version 3.1.1 specification with some limitations.

• It can publish at QoS 0, 1 or 2.

  WARNING: No retransmission is supported to keep the library as much memory friendly as possible.

  Note: Without retransmission support, the publish QoS is only meaningful when the broker sends your message to a subscriber, supposing that the subscriber subscribes with a QoS greater then or equal to the publish QoS. Consider that MQTT runs over TCP, so retransmission isn't really required in most cases, especially when publishing to the broker.

• It can subscribe at QoS 0 or QoS 1.

• The maximum message size, including header, is 256 bytes by default. This is configurable via MQTT_MAX_PACKET_SIZE in PubSubClient.h or can be changed by calling PubSubClient::setBufferSize(size).

• The keepalive interval is set to 15 seconds by default. This is configurable via MQTT_KEEPALIVE in PubSubClient.h or can be changed by calling PubSubClient::setKeepAlive(keepAlive).

• The client uses MQTT 3.1.1 by default. It can be changed to use MQTT 3.1 by changing value of MQTT_VERSION in PubSubClient.h.

Compatible Hardware

The library uses the Arduino Ethernet Client api for interacting with the underlying network hardware. This means it Just Works with a growing number of boards and shields, including:

• Arduino Ethernet
• Arduino Ethernet Shield
• Arduino YUN – use the included YunClient in place of EthernetClient, and be sure to do a Bridge.begin() first
• Arduino WiFi Shield - if you want to send packets > 90 bytes with this shield, enable the MQTT_MAX_TRANSFER_SIZE define in PubSubClient.h.
• Sparkfun WiFly Shield – library
• TI CC3000 WiFi - library
• Intel Galileo/Edison
• ESP8266
• ESP32

The library cannot currently be used with hardware based on the ENC28J60 chip – such as the Nanode or the Nuelectronics Ethernet Shield. For those, there is an alternative library available.

License

This code is released under the MIT License.