From 61bf99a67135ae7e12ec79e7fdbf224b7143e6b9 Mon Sep 17 00:00:00 2001
From: Dimitri Capitaine <dimitri.capitaine@corp.ovh.com>
Date: Wed, 12 Feb 2020 15:36:17 +0100
Subject: [PATCH] implement fetch metrics using prometheus common/expfmt
 instead of local http fetch

---
 go.mod                        |  1 +
 prometheus/prometheus.go      | 24 +++++++++---------------
 prometheus/prometheus_test.go | 11 +++++++++++
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/go.mod b/go.mod
index 000d5b5..3a31639 100644
--- a/go.mod
+++ b/go.mod
@@ -11,6 +11,7 @@ require (
 	github.com/opentracing/opentracing-go v1.1.0
 	github.com/pkg/errors v0.8.1 // indirect
 	github.com/prometheus/client_golang v1.1.0
+	github.com/prometheus/common v0.6.0
 	github.com/stretchr/testify v1.4.0
 	github.com/uber-go/atomic v1.4.0 // indirect
 	github.com/uber/jaeger-client-go v2.19.1-0.20191002155754-0be28c34dabf+incompatible
diff --git a/prometheus/prometheus.go b/prometheus/prometheus.go
index cb6eb42..4469144 100644
--- a/prometheus/prometheus.go
+++ b/prometheus/prometheus.go
@@ -22,7 +22,6 @@ package prometheus
 
 import (
 	"bytes"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"strconv"
@@ -33,6 +32,7 @@ import (
 	"github.com/labstack/gommon/log"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/prometheus/common/expfmt"
 )
 
 var defaultMetricPath = "/metrics"
@@ -133,10 +133,6 @@ type PushGateway struct {
 	// where JOBNAME can be any string of your choice
 	PushGatewayURL string
 
-	// Local metrics URL where metrics are fetched from, this could be ommited in the future
-	// if implemented using prometheus common/expfmt instead
-	MetricsURL string
-
 	// pushgateway job name, defaults to "echo"
 	Job string
 }
@@ -174,10 +170,9 @@ func NewPrometheus(subsystem string, skipper middleware.Skipper, customMetricsLi
 }
 
 // SetPushGateway sends metrics to a remote pushgateway exposed on pushGatewayURL
-// every pushIntervalSeconds. Metrics are fetched from metricsURL
-func (p *Prometheus) SetPushGateway(pushGatewayURL, metricsURL string, pushIntervalSeconds time.Duration) {
+// every pushIntervalSeconds. Metrics are fetched from
+func (p *Prometheus) SetPushGateway(pushGatewayURL string, pushIntervalSeconds time.Duration) {
 	p.Ppg.PushGatewayURL = pushGatewayURL
-	p.Ppg.MetricsURL = metricsURL
 	p.Ppg.PushIntervalSeconds = pushIntervalSeconds
 	p.startPushTicker()
 }
@@ -222,14 +217,13 @@ func (p *Prometheus) runServer() {
 }
 
 func (p *Prometheus) getMetrics() []byte {
-	response, err := http.Get(p.Ppg.MetricsURL)
-	if err != nil {
-		log.Errorf("Error getting metrics: %v", err)
-	}
-	defer response.Body.Close()
-	body, _ := ioutil.ReadAll(response.Body)
+	out := &bytes.Buffer{}
+	metricFamilies, _ := prometheus.DefaultGatherer.Gather()
+	for i := range metricFamilies {
+		expfmt.MetricFamilyToText(out, metricFamilies[i])
 
-	return body
+	}
+	return out.Bytes()
 }
 
 func (p *Prometheus) getPushGatewayURL() string {
diff --git a/prometheus/prometheus_test.go b/prometheus/prometheus_test.go
index 62232f0..1cf7696 100644
--- a/prometheus/prometheus_test.go
+++ b/prometheus/prometheus_test.go
@@ -121,3 +121,14 @@ func TestMetricsPathIgnored(t *testing.T) {
 	})
 	unregister(p)
 }
+
+func TestMetricsPushGateway(t *testing.T) {
+	e := echo.New()
+	p := NewPrometheus("echo", nil)
+	p.Use(e)
+
+	result := p.getMetrics()
+
+	assert.Contains(t, string(result), fmt.Sprintf("%s_request_duration", p.Subsystem))
+	unregister(p)
+}