ISSUE-20020: [Bug] [pulsar-function-go] - bounds check issue on user metrics causing go function crash for stats command

[sijie]

Original Issue: apache#20020

---

Search before asking

• I searched in the issues and found nothing similar.

Version

issuing a pulsar-admin functions stats check on a go function will cause it to crash if no user metrics are defined. This is because it makes a similar assumption to the other metrics calls that the result of gi.getFilteredMetricFamilies will have a len of at least 1. If there are no user metrics, it will not, and it will cause the agent to restart.

PR incoming

Minimal reproduce step

1. create go function w/o user metrics
2. pulsar-admin functions stats --fqfn tenant/namespace/functionname
3. function will crash/restart

What did you expect to see?

Actual stats

What did you see instead?

stats of zero. function restart

Anything else?

No response

Are you willing to submit a PR?

Considering as this is basically my fault, yes I am willing to submit a PR.

• I'm willing to submit a PR!