Downgrade QoS 2 subscribers to QoS 1

[michaelklishin]

Currently we fail with an error. MQTT 3.1 allows for downgrades and has a non-existent error notifications story, so a much better idea would be to downgrade QoS 2 requests to QoS 1.

[michaelklishin]

This is technically fixed in master but we haven't updated the docs yet => re-opening.

[michaelklishin]

Docs updated in rabbitmq/rabbitmq-website#147. Thank you, @hairyhum.

[grassy-noel]

Does the QOS2->QOS1 downgrade still work as per the Web-site docs?
My experience with 3.6.14 on Windows and 3.70 on Linux is that the connection drops.

Windows - Mosquitto

"C:\Program Files (x86)\mosquitto\mosquitto_pub.exe" -h localhost -p 1883 -t home.garden.fountain -m "test message" -q 2
Error: The connection was lost.

MQTT-fx using Paho works with QOS0 and QOS1

2017-12-14 05:29:42,987 INFO --- MqttFX ClientModel : attempt to add PublishTopic
2017-12-14 05:29:42,987 INFO --- MqttFX ClientModel : addPublishTopic : home.garden.fountain
2017-12-14 05:29:42,988 INFO --- MqttFX ClientModel : sucessfully published message Test @ QOS0 to topic home.garden.fountain (QoS 0, Retained false)
2017-12-14 05:29:52,956 INFO --- PublishController : publish
2017-12-14 05:29:52,957 INFO --- MqttFX ClientModel : attempt to add PublishTopic
2017-12-14 05:29:52,958 INFO --- MqttFX ClientModel : sucessfully published message Test @ QOS0 to topic home.garden.fountain (QoS 0, Retained false)
2017-12-14 05:30:06,316 INFO --- PublishController : publish
2017-12-14 05:30:06,320 INFO --- MqttFX ClientModel : attempt to add PublishTopic
2017-12-14 05:30:06,321 INFO --- MqttFX ClientModel : sucessfully published message Test @ QOS1 to topic home.garden.fountain (QoS 1, Retained false)
2017-12-14 05:30:07,066 INFO --- PublishController : publish
2017-12-14 05:30:07,068 INFO --- MqttFX ClientModel : attempt to add PublishTopic
2017-12-14 05:30:07,068 INFO --- MqttFX ClientModel : sucessfully published message Test @ QOS1 to topic home.garden.fountain (QoS 1, Retained false)
2017-12-14 05:30:14,853 INFO --- PublishController : publish
2017-12-14 05:30:14,857 INFO --- MqttFX ClientModel : Broker connection lost: Retrying...
2017-12-14 05:30:14,857 ERROR --- MqttFX ClientModel : Error publishing to topic: home.garden.fountain
org.eclipse.paho.client.mqttv3.MqttException: Connection lost
at org.eclipse.paho.client.mqttv3.internal.CommsReceiver.run(CommsReceiver.java:146) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_131]
Caused by: java.io.EOFException
at java.io.DataInputStream.readByte(Unknown Source) ~[?:1.8.0_131]
at org.eclipse.paho.client.mqttv3.internal.wire.MqttInputStream.readMqttWireMessage(MqttInputStream.java:65) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
at org.eclipse.paho.client.mqttv3.internal.CommsReceiver.run(CommsReceiver.java:107) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
... 1 more
2017-12-14 05:30:16,063 INFO --- PublishController : publish
2017-12-14 05:30:16,066 ERROR --- MqttFX ClientModel : Error publishing to topic: home.garden.fountain
org.eclipse.paho.client.mqttv3.MqttException: Connection lost
at org.eclipse.paho.client.mqttv3.internal.CommsReceiver.run(CommsReceiver.java:146) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_131]
Caused by: java.io.EOFException
at java.io.DataInputStream.readByte(Unknown Source) ~[?:1.8.0_131]
at org.eclipse.paho.client.mqttv3.internal.wire.MqttInputStream.readMqttWireMessage(MqttInputStream.java:65) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
at org.eclipse.paho.client.mqttv3.internal.CommsReceiver.run(CommsReceiver.java:107) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]
... 1 more
2017-12-14 05:30:16,067 INFO --- MqttFX ClientModel : Broker connection lost: Retrying...
2017-12-14 05:30:16,352 INFO --- PublishController : publish
2017-12-14 05:30:16,352 ERROR --- MqttFX ClientModel : Error publishing to topic: home.garden.fountain
org.eclipse.paho.client.mqttv3.MqttException: Client is not connected
at org.eclipse.paho.client.mqttv3.internal.ExceptionHelper.createMqttException(ExceptionHelper.java:31) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:?]

[michaelklishin]

@grassy-noel our team does not use Github issues for investigations. Please start a rabbitmq-users thread, provide a list of steps to reproduce and server logs.