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Reject MQTT5 PUBLISH with Topic Alias 0 - #326
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popduke merged 2 commits intoNov 5, 2026
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Fixes #325
Summary
The MQTT 5.0 specification does not permit a Topic Alias of 0 ([MQTT-3.3.2-8]).
MQTT5ProtocolHelper.validatePubMessageonly rejected aliases greater thanMaxTopicAlias, so a PUBLISH with Topic Alias 0 was routed and alias 0 was stored in the receiver alias map.This change disconnects the client with reason code 0x94 (Topic Alias invalid) and reports a
ProtocolViolationevent with statementMQTT5-3.3.2-8, the same handling as an alias above the maximum.Tests
TransientSessionHandlerTest.c2sPubWithZeroTopicAlias. It sends a QoS 1 PUBLISH with Topic Alias 0 and checks for DISCONNECT 0x94, a closed channel, no dist call, and aPROTOCOL_VIOLATIONevent.