feat: browser cache directives

http/raw.go

@@ -204,6 +204,11 @@ func rawDirHandler(w http.ResponseWriter, r *http.Request, d *data, file *files.
 }
 
 func rawFileHandler(w http.ResponseWriter, r *http.Request, file *files.FileInfo) (int, error) {
+	isFresh := checkEtag(w, r, file.ModTime.Unix(), file.Size)
+	if isFresh {
+		return http.StatusNotModified, nil
+	}
+
 	fd, err := file.Fs.Open(file.Path)
 	if err != nil {
 		return http.StatusInternalServerError, err