metrics: Add http_requests metric

go.sum

@@ -41,6 +41,7 @@ github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXP
 github.com/prometheus/client_golang v1.0.0/go.mod h1:db9x61etRT2tGnBNRi70OPL5FsnadC4Ky3P0J6CfImo=
 github.com/prometheus/client_golang v1.1.0 h1:BQ53HtBmfOitExawJ6LokA4x8ov/z0SYYb0+HxJfRI8=
 github.com/prometheus/client_golang v1.1.0/go.mod h1:I1FGZT9+L76gKKOs5djB6ezCbFQP1xR9D75/vuwEF3g=
+github.com/prometheus/client_golang v1.2.1 h1:JnMpQc6ppsNgw9QPAGF6Dod479itz7lvlsMzzNayLOI=
 github.com/prometheus/client_model v0.0.0-20180712105110-5c3871d89910/go.mod h1:MbSGuTsp3dbXC40dX6PRTWyKYBIrTGTE9sqQNg2J8bo=
 github.com/prometheus/client_model v0.0.0-20190129233127-fd36f4220a90 h1:S/YWwWx/RA8rT8tKFRuGUZhuA90OyIBpPCXkcbwU8DE=
 github.com/prometheus/client_model v0.0.0-20190129233127-fd36f4220a90/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=

handlers.go

@@ -50,9 +50,9 @@ func (rl *rushlink) uploadFileGetHandler(w http.ResponseWriter, r *http.Request)
 		if badID {
 			renderError(w, r, http.StatusNotFound, "malformed file id")
 			return
-		} else {
-			panic(err)
 		}
+		// unexpected error
+		panic(err)
 	}
 
 	filePath := rl.fs.FilePath(fu.ID, fu.FileName)
@@ -62,9 +62,9 @@ func (rl *rushlink) uploadFileGetHandler(w http.ResponseWriter, r *http.Request)
 			log.Printf("error: %v should exist according to the database, but it doesn't", filePath)
 			renderError(w, r, http.StatusNotFound, "file not found")
 			return
-		} else {
-			panic(err)
 		}
+		// unexpected error
+		panic(err)
 	}
 	w.Header().Set("Content-Type", fu.ContentType)
 	io.Copy(w, file)

metrics.go

@@ -10,21 +10,22 @@ import (
 	"github.com/gorilla/mux"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	bolt "go.etcd.io/bbolt"
 )
 
-func StartMetricsServer(addr string, db *db.Database) {
-	var (
-		_ = promauto.NewGaugeFunc(prometheus.GaugeOpts{
-			Namespace: "rushlink",
-			Subsystem: "pastes",
-			Name:      "urls_total",
-			Help:      "The current amount of pastes in the database.",
-		}, func() float64 {
+const metricNamespace = "rushlink"
+
+var metricRequestsTotalCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
+	Namespace: metricNamespace,
+	Subsystem: "http",
+	Name:      "requests_total",
+	Help:      "How many HTTP requests processed, partitioned by status code and HTTP method.",
+}, []string{"code", "method"})
+
+func metricURLsTotal(database *db.Database) float64 {
 	var metric float64
-			if err := db.Bolt.View(func(tx *bolt.Tx) error {
+	if err := database.Bolt.View(func(tx *bolt.Tx) error {
 		bucket := tx.Bucket([]byte("pastes"))
 		if bucket == nil {
 			return errors.New("bucket 'pastes' could not be found")
@@ -36,8 +37,18 @@ func StartMetricsServer(addr string, db *db.Database) {
 		return 0
 	}
 	return metric
-		})
-	)
+}
+
+// StartMetricsServer starts sering Prometheus metrics exports on addr
+func StartMetricsServer(addr string, database *db.Database, fs *db.FileStore) {
+	prometheus.MustRegister(metricRequestsTotalCounter)
+
+	prometheus.MustRegister(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+		Namespace: metricNamespace,
+		Subsystem: "pastes",
+		Name:      "urls_total",
+		Help:      "The current amount of pastes in the database.",
+	}, func() float64 { return metricURLsTotal(database) }))
 
 	router := mux.NewRouter()
 	router.Handle("/metrics", promhttp.Handler()).Methods("GET")

router.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"net/http"
 	"runtime/debug"
+	"strconv"
 	"time"
 
 	"gitea.hashru.nl/dsprenkels/rushlink/internal/db"
@@ -37,6 +38,37 @@ func recoveryMiddleware(next http.Handler) http.Handler {
 	})
 }
 
+type statusResponseWriter struct {
+	Inner      http.ResponseWriter
+	StatusCode int
+}
+
+func (w *statusResponseWriter) Header() http.Header {
+	return w.Inner.Header()
+}
+
+func (w *statusResponseWriter) Write(buf []byte) (int, error) {
+	if w.StatusCode == 0 {
+		w.WriteHeader(http.StatusOK)
+	}
+	return w.Inner.Write(buf)
+}
+
+func (w *statusResponseWriter) WriteHeader(statusCode int) {
+	w.StatusCode = statusCode
+	w.Inner.WriteHeader(statusCode)
+}
+
+func metricsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		srw := statusResponseWriter{Inner: w}
+		next.ServeHTTP(&srw, r)
+		status := strconv.Itoa(srw.StatusCode)
+		metricRequestsTotalCounter.WithLabelValues(status, r.Method).Inc()
+	})
+}
+
+// StartMainServer starts the main http server listening on addr.
 func StartMainServer(addr string, db *db.Database, fs *db.FileStore) {
 	rl := rushlink{
 		db: db,
@@ -46,6 +78,7 @@ func StartMainServer(addr string, db *db.Database, fs *db.FileStore) {
 	// Initialize Gorilla router
 	router := mux.NewRouter()
 	router.Use(recoveryMiddleware)
+	router.Use(metricsMiddleware)
 	router.HandleFunc("/", rl.indexGetHandler).Methods("GET")
 	router.HandleFunc("/", rl.newPasteHandler).Methods("POST")
 	router.HandleFunc("/{key:[A-Za-z0-9-_]{4,}}", rl.viewPasteHandler).Methods("GET")