feat: add metrics

[dapplion]

• Extends fix: port listener to ES6 class syntax #214

Adds metrics for Prometheus-like collecting engine:

• serverStatus: If server is listening or not
• connections: Current count of active connections from internal net server data structures
• listenerErrors: Total count of relevant errors by error type
• socketEvents: Total count of socket events by type

[achingbrain]

These metrics are very useful but they should be added to the built in libp2p metrics object instead of being their own thing

[dapplion]

These metrics are very useful but they should be added to the built in libp2p metrics object instead of being their own thing

Why?

[achingbrain]

So there's a central point to collect metrics from for viewing, rather than having to go and ask every component, and so each component submits metrics in the same format following the same interface.

[dapplion]

So there's a central point to collect metrics from for viewing, rather than having to go and ask every component, and so each component submits metrics in the same format following the same interface.

How can I do .inc with the built in libp2p metrics object?

[dapplion]

Updated PR to use a "metrics generator" so that consumer only needs to pass something that can create Gauge instances. This follows similar encapsulation principles as built in libp2p metrics object but with no performance penalty.

[p-shahi]

depends on libp2p/js-libp2p#1458

[mpetrunic]

@dapplion Does it make sense to close this one since #223 is merged or?

[p-shahi]

#223 adds the same metrics as this PR: tcp server status, active connections, listener errors, and socket events
However, they were added as counters and not gauges. Not sure if all these are intended to be cumulative (like active connections)

I think we'll want to add a Gauge interface to interface-metrics here and convert some counters to gauges afterwards.

[dapplion]

@dapplion Does it make sense to close this one since #223 is merged or?

#223 is flawed will comment there

[dapplion]

• Closing for feat!: add metrics #223