streamUploadData example

$validators = $this->getUploadValidators($field_definition);

    $prepared_filename = $this->prepareFilename($filename, $validators);

    // Create the file.     $file_uri = "{$destination}/{$prepared_filename}";
    if ($destination === $settings['uri_scheme'] . '://') {
      $file_uri = "{$destination}{$prepared_filename}";
    }

    $temp_file_path = $this->streamUploadData();

    $file_uri = $this->fileSystem->getDestinationFilename($file_uri, FileSystemInterface::EXISTS_RENAME);

    // Lock based on the prepared file URI.     $lock_id = $this->generateLockIdFromFileUri($file_uri);

    if (!$this->lock->acquire($lock_id)) {
      throw new HttpException(503, sprintf('File "%s" is already locked for writing.', $file_uri), NULL, ['Retry-After' => 1]);
    }

    // Begin building file entity.

    if (!$this->fileSystem->prepareDirectory($destination, FileSystemInterface::CREATE_DIRECTORY)) {
      throw new HttpException(500, 'Destination file path is not writable');
    }

    $validators = $this->getUploadValidators($field_definition);

    $prepared_filename = $this->prepareFilename($filename, $validators);

    // Create the file.     $file_uri = "{$destination}/{$prepared_filename}";

    $temp_file_path = $this->streamUploadData();

    $file_uri = $this->fileSystem->getDestinationFilename($file_uri, FileSystemInterface::EXISTS_RENAME);

    // Lock based on the prepared file URI.     $lock_id = $this->generateLockIdFromFileUri($file_uri);

    if (!$this->lock->acquire($lock_id)) {
      throw new HttpException(503, sprintf('File "%s" is already locked for writing', $file_uri), NULL, ['Retry-After' => 1]);
    }

    // Begin building file entity.