Add page footer with request time display

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"embed"
 	"flag"
 	"html/template"
@@ -12,6 +13,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"time"
 )
 
 //go:embed assets
@@ -94,7 +96,23 @@ type handler struct {
 	authKey          []byte
 }
 
+// reqStartKey marks the request start time stored in the request context
+// so HTML templates can render total server-side processing time.
+type reqStartKeyT struct{}
+
+var reqStartKey = reqStartKeyT{}
+
+// elapsedMS returns the milliseconds since the request entered ServeHTTP.
+func elapsedMS(r *http.Request) int64 {
+	if start, ok := r.Context().Value(reqStartKey).(time.Time); ok {
+		return time.Since(start).Milliseconds()
+	}
+	return 0
+}
+
 func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	r = r.WithContext(context.WithValue(r.Context(), reqStartKey, time.Now()))
+
 	if !h.checkAuth(w, r) {
 		return
 	}
@@ -234,6 +252,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	if editMode {
 		t = editTmpl
 	}
+	data.RenderMS = elapsedMS(r)
 	if err := t.ExecuteTemplate(w, "layout", data); err != nil {
 		log.Printf("template error: %v", err)
 	}