Fantom-foundation/go-lachesis

package prometheus

import (
    "net/http"

    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/metrics"
    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
)

var logger = log.New("module", "prometheus")

// ListenTo serves prometheus connections.
func ListenTo(endpoint string, reg metrics.Registry) {
    if reg == nil {
        reg = metrics.DefaultRegistry
    }
    reg.Each(collect)

    go func() {
        logger.Info("metrics server starts", "endpoint", endpoint)
        defer logger.Info("metrics server is stopped")

        http.HandleFunc(
            "/metrics", promhttp.Handler().ServeHTTP)
        err := http.ListenAndServe(endpoint, nil)
        if err != nil {
            logger.Info("metrics server", "err", err)
        }

        // TODO: wait for exit signal?
    }()
}

func collect(name string, metric interface{}) {
    logger.Info("metric to prometheus", "metric", name)

    collector, ok := convertToPrometheusMetric(name, metric)
    if !ok {
        return
    }

    err := prometheus.Register(collector)
    if err != nil {
        switch err.(type) {
        case prometheus.AlreadyRegisteredError:
            return
        default:
            logger.Warn(err.Error())
        }
    }
}