Release v0.48.2 · LabOverWire/mqtt-lib

[mqtt5 0.48.2] - 2026-10-19

Retained wills, and every other retained message the broker stores, are held to max_retained_message_size and max_retained_messages (#227). The limits were checked only for a retained PUBLISH from a client, so a client could store retained messages of any size, on any number of topics, by reconnecting with a different retained will each time. The router now applies both limits under the same lock that stores the message, so they hold for every path that stores one, including wills and bridged messages. A message over a limit is still delivered to current subscribers but not stored. The broker's own $SYS messages are exempt, and a retained message a client sends on a $SYS topic is held to both limits. Limits changed by a config reload apply to clients that are already connected. A retained PUBLISH over a limit is still refused with 0x97 (Quota exceeded). A retained will over max_retained_message_size is refused at CONNECT, since the broker must publish a will it has accepted as retained (MQTT-3.1.2-8, MQTT-3.1.2-15): MQTT 5 clients get CONNACK 0x97, and MQTT 3.1.1 connections are closed without a CONNACK, since no 3.1.1 return code applies (MQTT 3.1.1 MQTT-3.2.2-6).

Retained and queued messages reach MQTT 3.1.1 subscribers without MQTT 5 properties in the payload (#213). A retained message, or a message queued for an offline 3.1.1 session, was sent with an MQTT 5 properties block, which a 3.1.1 subscriber reads as the start of the payload. With the broker's x-mqtt-client-id user property, that put the property bytes in front of every such payload. Live delivery was already correct. The broker now encodes every outbound PUBLISH for the protocol version of the connection it is sent on.

With max_retained_message_size set in the --config file, mqttv5 broker refuses a CONNECT whose retained will is larger: MQTT 5 clients get CONNACK 0x97 (Quota exceeded), and MQTT 3.1.1 connections are closed without a CONNACK. See mqtt5 0.48.2.

Docker images built with the opentelemetry feature are published with an -otel tag suffix, such as latest-otel. Only those images accept the --otel-* broker flags.

Requires mqtt5 0.48.2, so mqttv5 broker gets its retained message fixes. See mqtt5 0.48.2.

Retained and queued messages reach MQTT 3.1.1 subscribers without MQTT 5 properties in the payload (#213). The wasm broker sent retained messages, and messages queued for an offline 3.1.1 session, with an MQTT 5 properties block, which a 3.1.1 subscriber reads as the start of the payload. It now encodes every outbound PUBLISH for the protocol version of the connection it is sent on.