From d6b83167c839e47b26729234b72f3b6a796e462e Mon Sep 17 00:00:00 2001
From: Vincent Bernat <vincent@bernat.im>
Date: Sun, 29 Jul 2018 16:07:58 +0200
Subject: [PATCH] exp: export healthcheck status

This will trigger the check immediately, then export its status as
".status" with value of 1 if the healthcheck is OK and 0 otherwise. If
the status is 0, the error is stored in ".error", otherwise an empty
string is used.

Fix #213
---
 cmd/metrics-example/metrics-example.go | 22 ++++++++++++++++++++-
 exp/exp.go                             | 27 ++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/cmd/metrics-example/metrics-example.go b/cmd/metrics-example/metrics-example.go
index 66f42c0..1fb24a4 100644
--- a/cmd/metrics-example/metrics-example.go
+++ b/cmd/metrics-example/metrics-example.go
@@ -2,8 +2,12 @@ package main
 
 import (
 	"errors"
+	// "fmt"
 	"github.com/rcrowley/go-metrics"
+	// "github.com/rcrowley/go-metrics/exp"
 	// "github.com/rcrowley/go-metrics/stathat"
+	// "net"
+	// "net/http"
 	"log"
 	"math/rand"
 	"os"
@@ -69,7 +73,7 @@ func main() {
 	}
 
 	hc := metrics.NewHealthcheck(func(h metrics.Healthcheck) {
-		if 0 < rand.Intn(2) {
+		if 0 == rand.Intn(2) {
 			h.Healthy()
 		} else {
 			h.Unhealthy(errors.New("baz"))
@@ -136,6 +140,22 @@ func main() {
 
 	metrics.Log(r, 60e9, log.New(os.Stderr, "metrics: ", log.Lmicroseconds))
 
+	/*
+		mux := http.NewServeMux()
+		mux.Handle("/", exp.ExpHandler(r))
+		server := &http.Server{Handler: mux}
+		addr, err := net.ResolveTCPAddr("tcp", "127.0.0.1:0")
+		if err != nil {
+			panic(err)
+		}
+		listener, err := net.ListenTCP("tcp", addr)
+		if err != nil {
+			panic(err)
+		}
+		fmt.Printf("Listening on %s\n", listener.Addr())
+		server.Serve(listener)
+	*/
+
 	/*
 		w, err := syslog.Dial("unixgram", "/dev/log", syslog.LOG_INFO, "metrics")
 		if nil != err { log.Fatalln(err) }
diff --git a/exp/exp.go b/exp/exp.go
index 11dd3f8..858b658 100644
--- a/exp/exp.go
+++ b/exp/exp.go
@@ -78,6 +78,20 @@ func (exp *exp) getFloat(name string) *expvar.Float {
 	return v
 }
 
+func (exp *exp) getString(name string) *expvar.String {
+	var v *expvar.String
+	exp.expvarLock.Lock()
+	p := expvar.Get(name)
+	if p != nil {
+		v = p.(*expvar.String)
+	} else {
+		v = new(expvar.String)
+		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())
@@ -134,6 +148,17 @@ func (exp *exp) publishTimer(name string, metric metrics.Timer) {
 	exp.getFloat(name + ".mean-rate").Set(float64(t.RateMean()))
 }
 
+func (exp *exp) publishHealthcheck(name string, metric metrics.Healthcheck) {
+	metric.Check()
+	if err := metric.Error(); err == nil {
+		exp.getInt(name + ".status").Set(1)
+		exp.getString(name + ".error").Set("")
+	} else {
+		exp.getInt(name + ".status").Set(0)
+		exp.getString(name + ".error").Set(err.Error())
+	}
+}
+
 func (exp *exp) syncToExpvar() {
 	exp.registry.Each(func(name string, i interface{}) {
 		switch i.(type) {
@@ -149,6 +174,8 @@ func (exp *exp) syncToExpvar() {
 			exp.publishMeter(name, i.(metrics.Meter))
 		case metrics.Timer:
 			exp.publishTimer(name, i.(metrics.Timer))
+		case metrics.Healthcheck:
+			exp.publishHealthcheck(name, i.(metrics.Healthcheck))
 		default:
 			panic(fmt.Sprintf("unsupported type for '%s': %T", name, i))
 		}