Review / TEST spec chapter 2

[anyflow]

• [MQTT-2.2.2-1] Where a flag bit is marked as “Reserved” in Table 2.2 - Flag Bits, it is reserved for future use and MUST be set to the value listed in that table.
• [MQTT-2.2.2-2] If invalid flags are received, the receiver MUST close the Network Connection.
• [MQTT-2.3.1-1] SUBSCRIBE, UNSUBSCRIBE, and PUBLISH (in cases where QoS > 0) Control Packets MUST contain a non-zero 16-bit Packet Identifier.
• [MQTT-2.3.1-3] If a Client re-sends a particular Control Packet, then it MUST use the same Packet Identifier in subsequent re-sends of that packet. The Packet Identifier becomes available for reuse after the Client has processed the corresponding acknowledgement packet. In the case of a QoS 1 PUBLISH this is the corresponding PUBACK; in the case of QO2 it is PUBCOMP. For SUBSCRIBE or UNSUBSCRIBE it is the corresponding SUBACK or UNSUBACK.
• [MQTT-2.3.1-6] A PUBACK, PUBREC or PUBREL Packet MUST contain the same Packet Identifier as the PUBLISH Packet that was originally sent.
• [MQTT-2.3.1-5] A PUBLISH Packet MUST NOT contain a Packet Identifier if its QoS value is set to 0.
• [MQTT-2.3.1-2] Each time a Client sends a new packet of one of these types it MUST assign it a currently unused Packet Identifier.
• [MQTT-2.3.1-4] The same conditions [MQTT-2.3.1-3] apply to a Server when it sends a PUBLISH with QoS >0.
• [MQTT-2.3.1-7] Similarly to [MQTT-2.3.1-6], SUBACK and UNSUBACK MUST contain the Packet Identifier that was used in the corresponding SUBSCRIBE and UNSUBSCRIBE Packet respectively.