This is a fork of the main repository, which was last updated in 2020. Since we have an SDK based on this client, we decided to continue with this repository. We also believe that this library provides a lot of opportunities for people who want to build their own IoT devices. As with our other open source repositories, we appreciate every contribution to this library.

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.
• Individual buffers are used to send and receive messages. The default maximum message size in each buffer, including header, is 256 bytes. This is configurable via MQTT_MAX_PACKET_SIZE in PubSubClient.h or each buffer's size can be changed at runtime by calling PubSubClient::setBufferSize(uint16_t receive_size, uint16_t send_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.

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.