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eclipse / paho.mqtt.java

Eclipse Paho Java MQTT client library. Paho is an Eclipse IoT project.
https://eclipse.org/paho
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MQTTv5 - Client should throw error if it receives an unknown topic alias. #479

Closed jpwsutton closed 6 years ago

jpwsutton commented 6 years ago

If the client has not enabled topic aliases, but receives a message with a topic alias set, the message will just 'disappear' and not get sent to the callback. We need to throw an error and also pass the message through if we have a global callback.

borgendale commented 6 years ago

Topic alias is not just enabled or disabled. The client gives the server the max value of a topic alias. The server can use topic alias 1 to max and any other value is a protocol error. The server is not required to send a topic alias even if the client has requested the use of topic alias. Note also that the topic alias max is a separate value in the two directions. The server sends the client a topic alias max on CONNACK.

One more thing, when a message arrives from the server with a topic alias but with a zero length topic name, the messageArraived() callback is being sent a zero length string for the topic argument, and not the saved topic name based on the topic alias.