Further performance optimization

main.go

@@ -175,14 +175,21 @@ type reqStartKeyT struct{}
 
 var reqStartKey = reqStartKeyT{}
 
-// elapsedMS returns the milliseconds since the request entered ServeHTTP.
-func elapsedMS(r *http.Request) int64 {
+// requestStart returns when the request entered ServeHTTP, or now if unknown.
+func requestStart(r *http.Request) time.Time {
 	if start, ok := r.Context().Value(reqStartKey).(time.Time); ok {
-		return time.Since(start).Milliseconds()
+		return start
 	}
-	return 0
+	return time.Now()
 }
 
+// renderTimer is embedded in template data. The footer calls RenderMS while
+// the template executes, so the time includes the page's own rendering (and
+// the header's maintenance widget), not just the work before it.
+type renderTimer struct{ start time.Time }
+
+func (t renderTimer) RenderMS() int64 { return time.Since(t.start).Milliseconds() }
+
 func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	r = r.WithContext(context.WithValue(r.Context(), reqStartKey, time.Now()))
 
@@ -407,7 +414,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	if editMode {
 		t = editTmpl
 	}
-	data.RenderMS = elapsedMS(r)
+	data.renderTimer = renderTimer{requestStart(r)}
 	if err := t.ExecuteTemplate(w, "layout", data); err != nil {
 		log.Printf("template error: %v", err)
 	}