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path: root/metrics/exp/exp.go
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// Hook go-metrics into expvar
// on any /debug/metrics request, load all vars from the registry into expvar, and execute regular expvar handler
package exp

import (
    "expvar"
    "fmt"
    "net/http"
    "sync"

    "github.com/ethereum/go-ethereum/metrics"
    "github.com/ethereum/go-ethereum/metrics/prometheus"
)

type exp struct {
    expvarLock sync.Mutex // expvar panics if you try to register the same var twice, so we must probe it safely
    registry   metrics.Registry
}

func (exp *exp) expHandler(w http.ResponseWriter, r *http.Request) {
    // load our variables into expvar
    exp.syncToExpvar()

    // now just run the official expvar handler code (which is not publicly callable, so pasted inline)
    w.Header().Set("Content-Type", "application/json; charset=utf-8")
    fmt.Fprintf(w, "{\n")
    first := true
    expvar.Do(func(kv expvar.KeyValue) {
        if !first {
            fmt.Fprintf(w, ",\n")
        }
        first = false
        fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
    })
    fmt.Fprintf(w, "\n}\n")
}

// Exp will register an expvar powered metrics handler with http.DefaultServeMux on "/debug/vars"
func Exp(r metrics.Registry) {
    h := ExpHandler(r)
    // this would cause a panic:
    // panic: http: multiple registrations for /debug/vars
    // http.HandleFunc("/debug/vars", e.expHandler)
    // haven't found an elegant way, so just use a different endpoint
    http.Handle("/debug/metrics", h)
    http.Handle("/debug/metrics/prometheus", prometheus.Handler(r))
}

// ExpHandler will return an expvar powered metrics handler.
func ExpHandler(r metrics.Registry) http.Handler {
    e := exp{sync.Mutex{}, r}
    return http.HandlerFunc(e.expHandler)
}

func (exp *exp) getInt(name string) *expvar.Int {
    var v *expvar.Int
    exp.expvarLock.Lock()
    p := expvar.Get(name)
    if p != nil {
        v = p.(*expvar.Int)
    } else {
        v = new(expvar.Int)
        expvar.Publish(name, v)
    }
    exp.expvarLock.Unlock()
    return v
}

func (exp *exp) getFloat(name string) *expvar.Float {
    var v *expvar.Float
    exp.expvarLock.Lock()
    p := expvar.Get(name)
    if p != nil {
        v = p.(*expvar.Float)
    } else {
        v = new(expvar.Float)
        expvar.Publish(name, v)
    }
    exp.expvarLock.Unlock()
    return v
}

func (exp *exp) publishCounter(name string, metric metrics.Counter) {
    v := exp.getInt(name)
    v.Set(metric.Count())
}

func (exp *exp) publishGauge(name string, metric metrics.Gauge) {
    v := exp.getInt(name)
    v.Set(metric.Value())
}
func (exp *exp) publishGaugeFloat64(name string, metric metrics.GaugeFloat64) {
    exp.getFloat(name).Set(metric.Value())
}

func (exp *exp) publishHistogram(name string, metric metrics.Histogram) {
    h := metric.Snapshot()
    ps := h.Percentiles([]float64{0.5, 0.75, 0.95, 0.99, 0.999})
    exp.getInt(name + ".count").Set(h.Count())
    exp.getFloat(name + ".min").Set(float64(h.Min()))
    exp.getFloat(name + ".max").Set(float64(h.Max()))
    exp.getFloat(name + ".mean").Set(h.Mean())
    exp.getFloat(name + ".std-dev").Set(h.StdDev())
    exp.getFloat(name + ".50-percentile").Set(ps[0])
    exp.getFloat(name + ".75-percentile").Set(ps[1])
    exp.getFloat(name + ".95-percentile").Set(ps[2])
    exp.getFloat(name + ".99-percentile").Set(ps[3])
    exp.getFloat(name + ".999-percentile").Set(ps[4])
}

func (exp *exp) publishMeter(name string, metric metrics.Meter) {
    m := metric.Snapshot()
    exp.getInt(name + ".count").Set(m.Count())
    exp.getFloat(name + ".one-minute").Set(m.Rate1())
    exp.getFloat(name + ".five-minute").Set(m.Rate5())
    exp.getFloat(name + ".fifteen-minute").Set((m.Rate15()))
    exp.getFloat(name + ".mean").Set(m.RateMean())
}

func (exp *exp) publishTimer(name string, metric metrics.Timer) {
    t := metric.Snapshot()
    ps := t.Percentiles([]float64{0.5, 0.75, 0.95, 0.99, 0.999})
    exp.getInt(name + ".count").Set(t.Count())
    exp.getFloat(name + ".min").Set(float64(t.Min()))
    exp.getFloat(name + ".max").Set(float64(t.Max()))
    exp.getFloat(name + ".mean").Set(t.Mean())
    exp.getFloat(name + ".std-dev").Set(t.StdDev())
    exp.getFloat(name + ".50-percentile").Set(ps[0])
    exp.getFloat(name + ".75-percentile").Set(ps[1])
    exp.getFloat(name + ".95-percentile").Set(ps[2])
    exp.getFloat(name + ".99-percentile").Set(ps[3])
    exp.getFloat(name + ".999-percentile").Set(ps[4])
    exp.getFloat(name + ".one-minute").Set(t.Rate1())
    exp.getFloat(name + ".five-minute").Set(t.Rate5())
    exp.getFloat(name + ".fifteen-minute").Set(t.Rate15())
    exp.getFloat(name + ".mean-rate").Set(t.RateMean())
}

func (exp *exp) publishResettingTimer(name string, metric metrics.ResettingTimer) {
    t := metric.Snapshot()
    ps := t.Percentiles([]float64{50, 75, 95, 99})
    exp.getInt(name + ".count").Set(int64(len(t.Values())))
    exp.getFloat(name + ".mean").Set(t.Mean())
    exp.getInt(name + ".50-percentile").Set(ps[0])
    exp.getInt(name + ".75-percentile").Set(ps[1])
    exp.getInt(name + ".95-percentile").Set(ps[2])
    exp.getInt(name + ".99-percentile").Set(ps[3])
}

func (exp *exp) syncToExpvar() {
    exp.registry.Each(func(name string, i interface{}) {
        switch i := i.(type) {
        case metrics.Counter:
            exp.publishCounter(name, i)
        case metrics.Gauge:
            exp.publishGauge(name, i)
        case metrics.GaugeFloat64:
            exp.publishGaugeFloat64(name, i)
        case metrics.Histogram:
            exp.publishHistogram(name, i)
        case metrics.Meter:
            exp.publishMeter(name, i)
        case metrics.Timer:
            exp.publishTimer(name, i)
        case metrics.ResettingTimer:
            exp.publishResettingTimer(name, i)
        default:
            panic(fmt.Sprintf("unsupported type for '%s': %T", name, i))
        }
    })
}