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Show the flow of bytes and control packets through various subsystems

An Access Control List system is required to allow MQTT clients to only PUBLISH and SUBSCRIBE to topics if the packets pass the ACL.

If there are no ACL's for a client then an implicit deny is enforced for both PUBLISH and SUBSCRIBES packets. The ACL will have the following format

PUBLISH sensor/1234/# ALLOW
PUBLISH sensor/1236/# ALLOW

SUBSCRIBE sensor/# ALLOW

PUBLISH sensor/1234/# DENY

The DENY's overrule all permissions irrespective of the position in the ACL.

PUBLISH sensor/1234/2 will be denied because there is an explicit DENY (PUBLISH sensor/1234/# DENY), even though there is an explicit ALLOW (PUBLISH sensor/1234/# ALLOW)

A client can subscribe to SUBSCRIBE # and will only get packets for topics which pass the ACL.