[Feature Request] Support for all mandatory system topics

[mazoqui]

Although defined as required by the official documentation https://github.com/mqtt/mqtt.org/wiki/SYS-Topics/_history, Mosquitto broker (2.0.99) does not seem to implement the topic $SYS/broker/time (The current time on the server)

$ mosquitto_sub -h test.mosquitto.org -p 1883 -t '$SYS/broker/version' -v -d -q 2 -C 1
Client mosqsub|6354-mint sending CONNECT
Client mosqsub|6354-mint received CONNACK
Client mosqsub|6354-mint sending SUBSCRIBE (Mid: 1, Topic: $SYS/broker/version, QoS: 2)
Client mosqsub|6354-mint received SUBACK
Subscribed (mid: 1): 2
Client mosqsub|6354-mint received PUBLISH (d0, q2, r1, m1, '$SYS/broker/version', ... (24 bytes))
Client mosqsub|6354-mint sending PUBREC (Mid: 1)
Client mosqsub|6354-mint received PUBREL (Mid: 1)
$SYS/broker/version mosquitto version 2.0.99
Client mosqsub|6354-mint sending DISCONNECT
Client mosqsub|6354-mint sending PUBCOMP (Mid: 1)

$ mosquitto_sub -h test.mosquitto.org -p 1883 -t '$SYS/broker/time' -v -d -q 2 -C 1
Client mosqsub|7600-mint sending CONNECT
Client mosqsub|7600-mint received CONNACK
Client mosqsub|7600-mint sending SUBSCRIBE (Mid: 1, Topic: $SYS/broker/time, QoS: 2)
Client mosqsub|7600-mint received SUBACK
Subscribed (mid: 1): 2

[karlp]

it literally says at that top that that page is attempting to standardize what would be required. Also, there's no requirement (yet) on what should be in that message.

[mazoqui]

I understand your interpretation, but the document does not claim to be an attempt at standardization, but rather a clearly debated vision of what may or may not be optional. I just believe that since Mosquitto is one of the most used brokers, even cited as a reference in the document itself, it should implement the standardization discussed since 2014