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If set to false (0) both the client and server will maintain state across restarts of the client, the server and the

connection. As state is maintained:

Message delivery will be reliable meeting the specified QOS even if the client, server or connection

are restarted.

The server will treat a subscription as durable.

If set to true (1) the client and server will not maintain state across restarts of the client, the server or the

connection. This means:

Message delivery to the specified QOS cannot be maintained if the client, server or connection are

restarted

The server will treat a subscription as non-durable

keepalive_sec: This value defines the maximum interval (in seconds) between messages being sent or received.

Setting a value here ensures that at least one message is sent between the client and the broker within every

'keep alive' period. If no data was sent within 'keepalive_sec' seconds, the Client will send a simple ping to the

broker to keep the connection alive. Setting this value to '0' disables the keep alive feature. The default value is

60 seconds.

Returns: 'True' (1) if the connection was successful, otherwise 'false' (0).

bool disconnect (void)

Disconnects from the remote MQTT broker.

Parameters: None

Returns: 'True' (1) if the disconnect was successful, otherwise 'false' (0) if an error occured (check .errno, .errstr, etc.).

Messaging

The following functions allow you to publish, subscribe and unsubscribe to MQTT topics:

bool publish ( UTF8String topic, UTF8String message, uint8_t qos =

MQTT_QOS_AT_MOST_ONCE, bool retained = false );

Published the supplied 'message' to the specified 'topic'.

Parameters:

topic: The topic where the data should be published (ex: "adafruit/data" or "home/rooms/bedroom/temp").

UTF8String is used to make it easier to work with UTF8 data.

message: The string of data to write to the specified 'topic'. UTF8String is used to make it easier to work with

UTF8 data.

qos: The quality of service level (see the MQTT spec for details). Default = 'At Most Once', meaning the message

tries to send once but isn't persisted if the send fails. Possible values are:

MQTT_QOS_AT_MOST_ONCE

MQTT_QOS_AT_LEAST_ONCE

MQTT_QOS_EXACTLY_ONCE

retained: Whether or not the published message should be 'retained' by the MQTT broker. Sending a message

with the retained bool set to 'false' (0) will clear any previously retained message from the broker. The default

value is false.