expvar.go

/*
#golang #gem: Use expvar to expose metrics on /debug/vars.
*/
package main

import (
    "expvar"
    "fmt"
    "log"
    "net/http"
)

func addMetrics(name string, h http.Handler) http.Handler {
    calls := expvar.NewInt(fmt.Sprintf("%s.calls", name))
    // TODO: More metrics

    fn := func(w http.ResponseWriter, r *http.Request) {
        calls.Add(1)
        h.ServeHTTP(w, r)
    }

    return http.HandlerFunc(fn)
}

func healthHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "OK")
}

func main() {
    h := addMetrics("health", http.HandlerFunc(healthHandler))
    http.Handle("/health", h)

    if err := http.ListenAndServe(":8080", nil); err != nil {
        log.Fatalf("error: %s", err)
    }
}