From b29ad0afa15f8f34f9825cadc31ee97559ebcfd7 Mon Sep 17 00:00:00 2001
From: "Gabriel A. Giovanini" <mail@gabrielgio.me>
Date: Fri, 22 Mar 2024 18:28:31 +0100
Subject: feat: Add metrics

---
 main.go | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 75 insertions(+), 15 deletions(-)

(limited to 'main.go')

diff --git a/main.go b/main.go
index 945b30b..b9bed96 100644
--- a/main.go
+++ b/main.go
@@ -8,28 +8,52 @@ import (
 	"io"
 	"net/http"
 	"regexp"
+	"strconv"
 	"strings"
+	"time"
 
 	"github.com/beevik/etree"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 type ErrorRequestHandler func(w http.ResponseWriter, r *http.Request) error
 
-var RegexCollection = map[string]string{
-	"nerdcast":     "NerdCast [0-9]+[a-c]* -",
-	"empreendedor": "Empreendedor [0-9]+ -",
-	"mamicas":      "Caneca de Mamicas [0-9]+ -",
-	"english":      "Speak English [0-9]+ -",
-	"nerdcash":     "NerdCash [0-9]+ -",
-	"bunker":       "Lá do Bunker [0-9]+ -",
-	"tech":         "NerdTech [0-9]+ -",
-	"genera":       "Generacast [0-9]+ -",
-}
-
 const (
 	FeedUrl = "https://api.jovemnerd.com.br/feed-nerdcast/"
 )
 
+var (
+	RegexCollection = map[string]string{
+		"nerdcast":     "NerdCast [0-9]+[a-c]* -",
+		"empreendedor": "Empreendedor [0-9]+ -",
+		"mamicas":      "Caneca de Mamicas [0-9]+ -",
+		"english":      "Speak English [0-9]+ -",
+		"nerdcash":     "NerdCash [0-9]+ -",
+		"bunker":       "Lá do Bunker [0-9]+ -",
+		"tech":         "NerdTech [0-9]+ -",
+		"genera":       "Generacast [0-9]+ -",
+	}
+
+	feedRequest = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "feed_request",
+		Help:    "How long jovemnerd takes to answer",
+		Buckets: []float64{.01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10},
+	}, []string{"status_code"})
+
+	httpRequest = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "http_request",
+		Help:    "How long the application takes to complete the request",
+		Buckets: []float64{.01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10},
+	}, []string{"status_code", "user_agent"})
+
+	seriesCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "serie_count",
+		Help: "How often a serie is called",
+	}, []string{"serie"})
+)
+
 func getSeries(r *http.Request) []string {
 	query := r.URL.Query().Get("q")
 
@@ -59,13 +83,24 @@ func match(title string, series []string) bool {
 }
 
 func fetchXML(_ context.Context) ([]byte, error) {
+	t := time.Now()
+	c := http.StatusInternalServerError
+
+	defer func() {
+		since := time.Since(t).Seconds()
+		code := strconv.Itoa(c)
+		feedRequest.WithLabelValues(code).Observe(since)
+	}()
+
 	res, err := http.Get(FeedUrl)
 	if err != nil {
 		return nil, err
 	}
 	defer res.Body.Close()
 
-	if res.StatusCode == http.StatusOK {
+	c = res.StatusCode
+
+	if c == http.StatusOK {
 		return io.ReadAll(res.Body)
 	}
 
@@ -109,7 +144,7 @@ func filterBySeries(series []string, xml []byte, temper bool) ([]byte, error) {
 	return doc.WriteToBytes()
 }
 
-func wrap(next ErrorRequestHandler) http.HandlerFunc {
+func handleError(next ErrorRequestHandler) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if err := next(w, r); err != nil {
 			w.WriteHeader(http.StatusInternalServerError)
@@ -117,6 +152,30 @@ func wrap(next ErrorRequestHandler) http.HandlerFunc {
 	}
 }
 
+func observe(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		t := time.Now()
+
+		next(w, r)
+
+		rw := w.(*responseWriter)
+		since := time.Since(t).Seconds()
+		code := strconv.Itoa(rw.Status())
+		userAgent := r.Header.Get("user-agent")
+		httpRequest.WithLabelValues(code, userAgent).Observe(float64(since))
+
+		for _, s := range getSeries(r) {
+			seriesCount.WithLabelValues(s).Inc()
+		}
+	}
+}
+
+func wrap(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		next(NewResponseWriter(w), r)
+	}
+}
+
 func titles(w http.ResponseWriter, r *http.Request) error {
 	xml, err := fetchXML(r.Context())
 	if err != nil {
@@ -173,8 +232,9 @@ func main() {
 	flag.Parse()
 
 	mux := http.NewServeMux()
-	mux.HandleFunc("/titles", wrap(titles))
-	mux.HandleFunc("/", wrap(podcast))
+	mux.Handle("/metrics", promhttp.Handler())
+	mux.HandleFunc("/titles", wrap(handleError(titles)))
+	mux.HandleFunc("/", wrap(observe(handleError(podcast))))
 
 	server := http.Server{
 		Handler: mux,
-- 
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