ch19.4

cmd/api/middleware.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"errors"
+	"expvar"
 	"fmt"
 	"net"
 	"net/http"
@@ -199,3 +200,22 @@ func (app *application) enableCORS(next http.Handler) http.Handler {
 		next.ServeHTTP(w, r)
 	})
 }
+
+func (app *application) metrics(next http.Handler) http.Handler {
+	var (
+		totalRequestsReceived           = expvar.NewInt("total_requests_received")
+		totalResponseSent               = expvar.NewInt("total_responses_sent")
+		totalProcessingTimeMicroseconds = expvar.NewInt("total_processing_time_μs")
+	)
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+
+		totalRequestsReceived.Add(1)
+		next.ServeHTTP(w, r)
+		totalResponseSent.Add(1)
+
+		duration := time.Since(start).Microseconds()
+		totalProcessingTimeMicroseconds.Add(duration)
+	})
+}

cmd/api/routes.go

@@ -28,5 +28,5 @@ func (app *application) routes() http.Handler {
 
 	router.Handler(http.MethodGet, "/debug/vars", expvar.Handler())
 
-	return app.recoverPanic(app.enableCORS(app.rateLimit(app.authenticate(router))))
+	return app.metrics(app.recoverPanic(app.enableCORS(app.rateLimit(app.authenticate(router)))))
 }