node-red: MQTT-Node: Messages are lost on connection problems, despite QOS-Level 1

What are the steps to reproduce?

Generate this simple testflow Subscripe topic on another machine via mosquitto_sub -h <MQTT Server-Address> -t /testtopic -q 1

In the following 0;19 means 0am and 19 minutes. Thats just for better redoing the steps.

0:19 Click inject. You’ll see that you receive the timestamp.

0:20 On NodeRed host do sudo iptables -A OUTPUT -d <IP of MQTT Server>/32 -j DROP to simulate network problems. Click 5 times inject node.

Wait until MQTT Node shows connections problems

0:21 click 5 times inject node

0:22 do sudo iptables -D OUTPUT -d <IP of MQTT Server>/32 -j DROP to reestablish connection. Don’t wait. Immediately after executing that command click inject Node 5 times.

What happens?

MQTT Client shows

1612739965989 --> 0:19
1612740005045 --> 0:20
1612740006033 --> 0:20
1612740006913 --> 0:20
1612740007707 --> 0:20
1612740008476 --> 0:20

So a lot of messages are lost. It seems all messages are lost that are received while not in connected state.

What do you expect to happen?

I expected that all messages are received. Maybe duplicate because of QOS1, but definitely no dropped messages. Or if dropped messages, then there should be thrown an error with you can catch by a Catch-Node.

Please tell us about your environment:

• Node-RED version: v1.2.6
• Node.js version: v12.20.0
• npm version:
• Platform/OS: Linux 5.4.79-v7l+ arm LE
• Browser: Firefox