fix: built-in MQTT bridge handling of QoS 0 messages published to the cloud topic

[reubenmiller]

Proposed changes

Messages with packet id 0 should be handled differently as they won't receive a PubAck or PubRec control messages hence it will never be removed from the hashmap and future messages with packet id 0 are ignored.

This should resolve the last incident seen on the OSADL slot 2 device, as the tedge mapper went unresponsive after requesting a file from the device, which most likely invoked a JWT request, which never was answered. Note, that the problem is limited to publishing messages directly to the cloud topic with QoS 0, as publishing a message to the te/# topics will be republished to the c8y/# topics with QoS > 0 (something automatically done by the bridge, to ensure reliable cloud communication).

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

• built-in bridge connection not sending or receiving messages from the cloud #2960

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 78.0%. Comparing base (e419058) to head (bf9ed50).
Report is 54 commits behind head on main.

Files	Patch %	Lines
crates/extensions/tedge_mqtt_bridge/src/lib.rs	25.0%	6 Missing ⚠️

Additional details and impacted files

Files	Coverage Δ
crates/extensions/tedge_mqtt_bridge/src/lib.rs	88.0% <25.0%> (-1.5%)	⬇️

... and 46 files with indirect coverage changes

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
488	0	2	488	100	1h28m51.960845s

[gligorisaev]

The added test was reviewed and it is passing

[albinsuresh]

LGTM. At least the change that skips caching of QoS 0 messages.