ConstReadonlyAUTH: 15Authentication exchange (5.0 only)
ReadonlyCONNACK: 2Connect acknowledgement
ReadonlyCONNECT: 1Client request to connect to server
ReadonlyDISCONNECT: 14Disconnect notification
ReadonlyPINGREQ: 12PING request
ReadonlyPINGRESP: 13PING response
ReadonlyPUBACK: 4Publish acknowledgement (QoS 1)
ReadonlyPUBCOMP: 7Publish complete (QoS 2 delivery part 3)
ReadonlyPUBLISH: 3Publish message
ReadonlyPUBREC: 5Publish received (QoS 2 delivery part 1)
ReadonlyPUBREL: 6Publish release (QoS 2 delivery part 2)
ReadonlySUBACK: 9Subscribe acknowledgement
ReadonlySUBSCRIBE: 8Subscribe request
ReadonlyUNSUBACK: 11Unsubscribe acknowledgement
ReadonlyUNSUBSCRIBE: 10Unsubscribe request
MQTT control packet types.
The packet type is encoded in the upper 4 bits of the fixed header's first byte.