docs: private FastRequestHandler verifyBase(File base) {
          if (!base.exists()) {
              logger.warn("file base not exists: " + base);
              return AlwaysNotFound.INSTANCE;
          }
          if (!base.canRead()) {
              logger.warn("cannot read file base: " + base);
              return AlwaysForbidden.INSTANCE;
          }
          if (base.isDirectory() & (!base.canExecute())) {
              logger.warn("cannot access directory: " + base);
              return AlwaysForbidden.INSTANCE;
          }
          return null;
      }