code: protected function checkFileWritePermissions(): void
      {
          if (!$this->storage->doesSatisfyConstraints()) {
              throw new AccessDeniedException(sprintf('unable to write file: "%s"', $this->storage instanceof Storage\Disk ? $this->storage->path()->raw : get_class($this->storage)), 403, $this->storage->getConstraintViolations());
          } elseif ($this->isFile() && !$this->isWriteable()) {
              throw new AccessDeniedException(sprintf('unable to write file: "%s"', $this->storage instanceof Storage\Disk ? $this->storage->path()->raw : get_class($this->storage)), 403);
          }
      }
docs: validate constraints and check file permissions
  @return void
  @throws AccessDeniedException