MQTT 5 Test Release

The work on MQTT v5 support in Mosquitto has reached a point where it may be of interest to a range of people. It is not yet complete, but wider testing and feedback would be appreciated.

The source is available at mosquitto-mqtt5-test1.tar.gz and can be compiled as normal.

Supported features

  • Session expiry
  • Message expiry
  • Reason code on all ACKs (not all reason codes are used)
  • Reason string on all ACKs (no reason strings are provided by the broker however)
  • Payload format and content type
  • Request / response pattern
  • Subscription ID
  • Topic alias
  • Flow control
  • User properties
  • Optional server feature availability
  • Subscription options
  • Server keep alive
  • Assigned Client ID

Unsupported features

  • Shared subscriptions
  • Extended authentication
  • Server reference
  • Not all reason codes are used by the broker
  • Bridges do not use MQTT v5
  • On disk persistence does not include MQTT 5 property support
  • The broker will not create topic aliases

Version 1.5.7 released

This is a bugfix release.


  • Fix build failure when using WITH_ADNS=yes
  • Ensure that an error occurs if per_listener_settings true is given after other security options. Closes #1149.
  • Fix include_dir not sorting config files before loading. This was partially fixed in 1.5 previously.
  • Improve documentation around the include_dir option. Closes #1154.
  • Fix case where old unreferenced msg_store messages were being saved to the persistence file, bloating its size unnecessarily. Closes #389.


  • Fix mosquitto_topic_matches_sub() not returning MOSQ_ERR_INVAL for invalid subscriptions like topic/#abc. This only affects the return value, not the match/no match result, which was already correct.


  • Don't require C99 compiler.
  • Add rewritten build test script and remove some build warnings.