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Fix TopicUtil accepting shared subscription with empty filter - #317
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Reject \/g/ and \/g/ where the filter part is empty. Previously isValidTopicFilter returned true because the scan loop was skipped when i == length. Add explicit empty-filter guard after skipping the share separator per MQTT-4.8.2-2. Fixes apache#288
popduke
approved these changes
Nov 3, 2026
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Summary
Reject
$share/g/and$oshare/g/where the filter part is empty.Previously
TopicUtil.isValidTopicFilterreturnedtruefor these inputs because after skipping the share-name separator,iwas advanced totopicFilter.length()and the main scan loop was skipped entirely.Fix
Add explicit empty-filter guard after skipping the separator, per MQTT-4.8.2-2.
Fixes #288
Verification
TopicUtilsTest:$share/g/now asserts false, added$oshare/g/coverage.$share/g//remains true.TopicUtilsTest: 7 tests run, 0 failures.