Package client provides an MQTT Client.

Package packet provides MQTT Control Packets.

ValidQoS returns true if the input QoS equals to QoS0, QoS1 or QoS2.

QoS0 represents "QoS 0: At most once delivery".

QoS1 represents "QoS 1: At least once delivery".

QoS2 represents "QoS 2: Exactly once delivery".