This library provides a client for doing simple publish/subscribe messaging with a server that supports MQTT.
The library comes with a number of example sketches. See File > Examples > PubSubClient within the Arduino application.
Full API documentation is available here: https://pubsubclient.knolleary.net
- It can subscribe at QoS 0 or 1.
- It can publish at QoS 0, 1 or 2. WARNING! No retransmission is supported to keep the library as much memory friendly as possible. (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)
- The maximum message size, including header, is 128 bytes by default. This
is configurable via
MQTT_MAX_PACKET_SIZEinPubSubClient.h. - The keepalive interval is set to 15 seconds by default. This is configurable
via
MQTT_KEEPALIVEinPubSubClient.h. - The client uses MQTT 3.1.1 by default. It can be changed to use MQTT 3.1 by
changing value of
MQTT_VERSIONinPubSubClient.h.
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
YunClientin place ofEthernetClient, and be sure to do aBridge.begin()first - Arduino WiFi Shield - if you want to send packets > 90 bytes with this shield,
enable the
MQTT_MAX_TRANSFER_SIZEdefine inPubSubClient.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.
This code is released under the MIT License.