feat: add observability metrics

internal/server/observability.go

@@ -2,13 +2,14 @@ package server
 
 import (
 	"log"
+	"mal/internal/observability"
 	"strconv"
 	"time"
 
 	"github.com/gin-gonic/gin"
 )
 
-func RequestLogger() gin.HandlerFunc {
+func RequestLogger(metrics *observability.Metrics) gin.HandlerFunc {
 	return func(c *gin.Context) {
 		start := time.Now()
 		path := c.Request.URL.Path
@@ -21,6 +22,9 @@ func RequestLogger() gin.HandlerFunc {
 			route = path
 		}
 
+		duration := time.Since(start)
+		metrics.ObserveHTTPRequest(c.Request.Method, route, c.Writer.Status(), duration)
+
 		log.Printf(
 			"http_request method=%s route=%s path=%s query=%s status=%d duration_ms=%.2f bytes=%d client_ip=%s errors=%s",
 			c.Request.Method,
@@ -28,7 +32,7 @@ func RequestLogger() gin.HandlerFunc {
 			strconv.Quote(path),
 			strconv.Quote(query),
 			c.Writer.Status(),
-			float64(time.Since(start).Microseconds())/1000,
+			float64(duration.Microseconds())/1000,
 			c.Writer.Size(),
 			strconv.Quote(c.ClientIP()),
 			strconv.Quote(c.Errors.ByType(gin.ErrorTypePrivate).String()),

internal/server/server.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"log"
+	"mal/internal/observability"
 	"net/http"
 	"os"
 	"time"
@@ -13,18 +14,20 @@ import (
 )
 
 var Module = fx.Options(
+	fx.Provide(observability.NewMetrics),
 	fx.Provide(ProvideRouter),
 	fx.Invoke(RunServer),
 )
 
-func ProvideRouter(htmlRender render.HTMLRender) *gin.Engine {
+func ProvideRouter(htmlRender render.HTMLRender, metrics *observability.Metrics) *gin.Engine {
 	if os.Getenv("GIN_MODE") == "" {
 		gin.SetMode(gin.ReleaseMode)
 	}
 	r := gin.New()
-	r.Use(CORSMiddleware(), RequestLogger(), gin.Recovery())
+	r.Use(CORSMiddleware(), RequestLogger(metrics), gin.Recovery())
 	r.Static("/static", "./static")
 	r.Static("/dist", "./dist")
+	r.GET("/metrics", gin.WrapH(metrics.Handler()))
 	r.HTMLRender = htmlRender
 	return r
 }

internal/server/server_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"io"
 	"log"
+	"mal/internal/observability"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -42,7 +43,7 @@ func TestRequestLoggerUsesMatchedRoute(t *testing.T) {
 	defer log.SetOutput(previousOutput)
 
 	router := gin.New()
-	router.Use(RequestLogger())
+	router.Use(RequestLogger(observability.NewMetrics()))
 	router.GET("/anime/:id", func(c *gin.Context) {
 		c.String(http.StatusOK, "ok")
 	})