Development of support for MQTT 5 is ongoing and making good progress, but has been substantially delayed due to other non-Mosquitto work having to take priority.

It is possible to test the current state of MQTT 5 support by using the mqtt5 branch of the repository. Please note that this is very much a work in progress, so parts are incomplete and interfaces may yet change. The client library in particular has had to have an increase in functions available in order to provide the features needed whilst providing backwards compatibility. Part of the plan for the 2.0 release, which will follow after 1.6, is to consolidate the libmosquitto API with breaking changes. There are more details on the roadmap.

Current features include:

  • Support for all incoming and outgoing packets, although not everything is processed.
  • Support for sending and receiving all properties, with not all properties processed.
  • Client support for setting properties
  • Request/response support (client cannot process incoming correlation data)
  • Retain availability
  • Message expiry interval support
  • Server support for assigned client identifiers
  • Payload format indicator support
  • Content-type support
  • Basic topic alias support from client to broker
  • Lots of new tests

Both mosquitto_pub and mosquitto_sub support setting properties on the command line, for example:

mosquitto_sub -t topic -v -D connect session-expiry-interval 60 -D connect user-property key value -D subscribe user-property sub-key sub-value
mosquitto_pub -t topic -m '{"key":"value"}' -D publish content-type "application/json"
./ | mosquitto_pub -t topic -l  -D publish topic-alias 1

Further updates will be posted when more features are available.