metrics-exporter-prometheus crashes if port 9000 blocked

[bryanlarsen]

If you have something already using port 9000, metrics-exporter-prometheus crashes at https://github.com/metrics-rs/metrics/blob/ca453d31009e1809161a0644943bbf5a8b3eb2e6/metrics-exporter-prometheus/src/exporter/builder.rs#L61, even if you never call install(), and even if you use with_http_listener to tell it to use a different port.

More info: https://github.com/Ptrskay3/axum-prometheus/issues/66

[tobz]

:wave:

I saw and responded on the linked issue, but just to dive in a little here:

If you have something already using port 9000, metrics-exporter-prometheus crashes..

This is expected since we can't bind to a port already in use.

, even if you never call install(), and even if you use with_http_listener to tell it to use a different port.

Now this part makes me pause. Do you have a reproduction for the "even if you tell it to use a different port" part? I'm not actually seeing how that would be possible.

[Ptrskay3]

I definitely can't reproduce that last part.

Changed the default http listener in axum-prometheus to:

 let (recorder, _) = PrometheusBuilder::new()
            .upkeep_timeout(Duration::from_secs(5))
            .with_http_listener(([0, 0, 0, 0], 9001))
            .unwrap()
            .build()
            .expect("Failed to build metrics recorder");

then ran netcat -l 9000, and my examples build and work just fine. Without this change they did panic because of the 9000 port already is use.