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 only publish QoS 0 messages. It can subscribe at QoS 0 or QoS 1.
• The maximum message size, including header, is 128 bytes by default. This is configurable via MQTT_MAX_PACKET_SIZE in PubSubClient.h.
• The keepalive interval is set to 15 seconds by default. This is configurable via MQTT_KEEPALIVE in PubSubClient.h.
• 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.

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.

This code is released under the MIT License.