FileFieldWidgetTest.php in Drupal 8

Namespace

Drupal\Tests\file\Functional

File

core/modules/file/tests/src/Functional/FileFieldWidgetTest.php

<?php

namespace Drupal\Tests\file\Functional;

use Drupal\Component\Render\FormattableMarkup;
use Drupal\comment\Entity\Comment;
use Drupal\comment\Tests\CommentTestTrait;
use Drupal\Component\Serialization\Json;
use Drupal\Core\Url;
use Drupal\field\Entity\FieldConfig;
use Drupal\field\Entity\FieldStorageConfig;
use Drupal\Tests\field_ui\Traits\FieldUiTestTrait;
use Drupal\user\RoleInterface;
use Drupal\file\Entity\File;
use Drupal\user\Entity\User;
use Drupal\user\UserInterface;

/**
 * Tests the file field widget with public and private files.
 *
 * @group file
 */
class FileFieldWidgetTest extends FileFieldTestBase {
  use CommentTestTrait;
  use FieldUiTestTrait;

  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'comment',
    'block',
  ];

  /**
   * {@inheritdoc}
   */
  protected $defaultTheme = 'classy';

  /**
   * {@inheritdoc}
   */
  protected function setUp() {
    parent::setUp();
    $this
      ->drupalPlaceBlock('system_breadcrumb_block');
  }

  /**
   * Creates a temporary file, for a specific user.
   *
   * @param string $data
   *   A string containing the contents of the file.
   * @param \Drupal\user\UserInterface $user
   *   The user of the file owner.
   *
   * @return \Drupal\file\FileInterface
   *   A file object, or FALSE on error.
   */
  protected function createTemporaryFile($data, UserInterface $user = NULL) {
    $file = file_save_data($data, NULL, NULL);
    if ($file) {
      if ($user) {
        $file
          ->setOwner($user);
      }
      else {
        $file
          ->setOwner($this->adminUser);
      }

      // Change the file status to be temporary.
      $file
        ->setTemporary();

      // Save the changes.
      $file
        ->save();
    }
    return $file;
  }

  /**
   * Tests upload and remove buttons for a single-valued File field.
   */
  public function testSingleValuedWidget() {
    $node_storage = $this->container
      ->get('entity_type.manager')
      ->getStorage('node');
    $type_name = 'article';
    $field_name = strtolower($this
      ->randomMachineName());
    $this
      ->createFileField($field_name, 'node', $type_name);
    $test_file = $this
      ->getTestFile('text');

    // Create a new node with the uploaded file and ensure it got uploaded
    // successfully.
    $nid = $this
      ->uploadNodeFile($test_file, $field_name, $type_name);
    $node = $node_storage
      ->loadUnchanged($nid);
    $node_file = File::load($node->{$field_name}->target_id);
    $this
      ->assertFileExists($node_file
      ->getFileUri());

    // Ensure the file can be downloaded.
    $this
      ->drupalGet($node_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(200);

    // Ensure the edit page has a remove button instead of an upload button.
    $this
      ->drupalGet("node/{$nid}/edit");
    $this
      ->assertNoFieldByXPath('//input[@type="submit"]', t('Upload'), 'Node with file does not display the "Upload" button.');
    $this
      ->assertFieldByXpath('//input[@type="submit"]', t('Remove'), 'Node with file displays the "Remove" button.');
    $this
      ->drupalPostForm(NULL, [], t('Remove'));

    // Ensure the page now has an upload button instead of a remove button.
    $this
      ->assertNoFieldByXPath('//input[@type="submit"]', t('Remove'), 'After clicking the "Remove" button, it is no longer displayed.');
    $this
      ->assertFieldByXpath('//input[@type="submit"]', t('Upload'), 'After clicking the "Remove" button, the "Upload" button is displayed.');

    // Test label has correct 'for' attribute.
    $input = $this
      ->xpath('//input[@name="files[' . $field_name . '_0]"]');
    $label = $this
      ->xpath('//label[@for="' . $input[0]
      ->getAttribute('id') . '"]');
    $this
      ->assertTrue(isset($label[0]), 'Label for upload found.');

    // Save the node and ensure it does not have the file.
    $this
      ->drupalPostForm(NULL, [], t('Save'));
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertTrue(empty($node->{$field_name}->target_id), 'File was successfully removed from the node.');
  }

  /**
   * Tests upload and remove buttons for multiple multi-valued File fields.
   */
  public function testMultiValuedWidget() {
    $node_storage = $this->container
      ->get('entity_type.manager')
      ->getStorage('node');
    $type_name = 'article';

    // Use explicit names instead of random names for those fields, because of a
    // bug in drupalPostForm() with multiple file uploads in one form, where the
    // order of uploads depends on the order in which the upload elements are
    // added to the $form (which, in the current implementation of
    // FileStorage::listAll(), comes down to the alphabetical order on field
    // names).
    $field_name = 'test_file_field_1';
    $field_name2 = 'test_file_field_2';
    $cardinality = 3;
    $this
      ->createFileField($field_name, 'node', $type_name, [
      'cardinality' => $cardinality,
    ]);
    $this
      ->createFileField($field_name2, 'node', $type_name, [
      'cardinality' => $cardinality,
    ]);
    $test_file = $this
      ->getTestFile('text');

    // Visit the node creation form, and upload 3 files for each field. Since
    // the field has cardinality of 3, ensure the "Upload" button is displayed
    // until after the 3rd file, and after that, isn't displayed. Because
    // SimpleTest triggers the last button with a given name, so upload to the
    // second field first.
    $this
      ->drupalGet("node/add/{$type_name}");
    foreach ([
      $field_name2,
      $field_name,
    ] as $each_field_name) {
      for ($delta = 0; $delta < 3; $delta++) {
        $edit = [
          'files[' . $each_field_name . '_' . $delta . '][]' => \Drupal::service('file_system')
            ->realpath($test_file
            ->getFileUri()),
        ];

        // If the Upload button doesn't exist, drupalPostForm() will
        // automatically fail with an assertion message.
        $this
          ->drupalPostForm(NULL, $edit, t('Upload'));
      }
    }
    $this
      ->assertNoFieldByXpath('//input[@type="submit"]', t('Upload'), 'After uploading 3 files for each field, the "Upload" button is no longer displayed.');
    $num_expected_remove_buttons = 6;
    foreach ([
      $field_name,
      $field_name2,
    ] as $current_field_name) {

      // How many uploaded files for the current field are remaining.
      $remaining = 3;

      // Test clicking each "Remove" button. For extra robustness, test them out
      // of sequential order. They are 0-indexed, and get renumbered after each
      // iteration, so array(1, 1, 0) means:
      // - First remove the 2nd file.
      // - Then remove what is then the 2nd file (was originally the 3rd file).
      // - Then remove the first file.
      foreach ([
        1,
        1,
        0,
      ] as $delta) {

        // Ensure we have the expected number of Remove buttons, and that they
        // are numbered sequentially.
        $buttons = $this
          ->xpath('//input[@type="submit" and @value="Remove"]');
        $this
          ->assertCount($num_expected_remove_buttons, $buttons, new FormattableMarkup('There are %n "Remove" buttons displayed.', [
          '%n' => $num_expected_remove_buttons,
        ]));
        foreach ($buttons as $i => $button) {
          $key = $i >= $remaining ? $i - $remaining : $i;
          $check_field_name = $field_name2;
          if ($current_field_name == $field_name && $i < $remaining) {
            $check_field_name = $field_name;
          }
          $this
            ->assertIdentical($button
            ->getAttribute('name'), $check_field_name . '_' . $key . '_remove_button');
        }

        // "Click" the remove button (emulating either a nojs or js submission).
        $button_name = $current_field_name . '_' . $delta . '_remove_button';
        $this
          ->getSession()
          ->getPage()
          ->findButton($button_name)
          ->press();
        $num_expected_remove_buttons--;
        $remaining--;

        // Ensure an "Upload" button for the current field is displayed with the
        // correct name.
        $upload_button_name = $current_field_name . '_' . $remaining . '_upload_button';
        $buttons = $this
          ->xpath('//input[@type="submit" and @value="Upload" and @name=:name]', [
          ':name' => $upload_button_name,
        ]);
        $this
          ->assertCount(1, $buttons, 'The upload button is displayed with the correct name.');

        // Ensure only at most one button per field is displayed.
        $buttons = $this
          ->xpath('//input[@type="submit" and @value="Upload"]');
        $expected = $current_field_name == $field_name ? 1 : 2;
        $this
          ->assertCount($expected, $buttons, 'After removing a file, only one "Upload" button for each possible field is displayed.');
      }
    }

    // Ensure the page now has no Remove buttons.
    $this
      ->assertNoFieldByXPath('//input[@type="submit"]', t('Remove'), 'After removing all files, there is no "Remove" button displayed.');

    // Save the node and ensure it does not have any files.
    $this
      ->drupalPostForm(NULL, [
      'title[0][value]' => $this
        ->randomMachineName(),
    ], t('Save'));
    preg_match('/node\\/([0-9])/', $this
      ->getUrl(), $matches);
    $nid = $matches[1];
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertTrue(empty($node->{$field_name}->target_id), 'Node was successfully saved without any files.');

    // Try to upload more files than allowed on revision.
    $upload_files_node_revision = [
      $test_file,
      $test_file,
      $test_file,
      $test_file,
    ];
    foreach ($upload_files_node_revision as $i => $file) {
      $edit['files[test_file_field_1_0][' . $i . ']'] = \Drupal::service('file_system')
        ->realpath($test_file
        ->getFileUri());
    }

    // @todo: Replace after https://www.drupal.org/project/drupal/issues/2917885
    $this
      ->drupalGet('node/' . $node
      ->id() . '/edit');
    $this
      ->assertSession()
      ->fieldExists('files[test_file_field_1_0][]');
    $submit_xpath = $this
      ->assertSession()
      ->buttonExists('Save')
      ->getXpath();
    $client = $this
      ->getSession()
      ->getDriver()
      ->getClient();
    $form = $client
      ->getCrawler()
      ->filterXPath($submit_xpath)
      ->form();
    $client
      ->request($form
      ->getMethod(), $form
      ->getUri(), $form
      ->getPhpValues(), $edit);
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertEqual(count($node->{$field_name}), $cardinality, 'More files than allowed could not be saved to node.');
    $upload_files_node_creation = [
      $test_file,
      $test_file,
    ];

    // Try to upload multiple files, but fewer than the maximum.
    $nid = $this
      ->uploadNodeFiles($upload_files_node_creation, $field_name, $type_name, TRUE, []);
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertEqual(count($node->{$field_name}), count($upload_files_node_creation), 'Node was successfully saved with multiple files.');

    // Try to upload exactly the allowed number of files on revision.
    $this
      ->uploadNodeFile($test_file, $field_name, $node
      ->id(), 1, [], TRUE);
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertEqual(count($node->{$field_name}), $cardinality, 'Node was successfully revised to maximum number of files.');

    // Try to upload exactly the allowed number of files, new node.
    $upload_files = [
      $test_file,
      $test_file,
      $test_file,
    ];
    $nid = $this
      ->uploadNodeFiles($upload_files, $field_name, $type_name, TRUE, []);
    $node = $node_storage
      ->loadUnchanged($nid);
    $this
      ->assertEqual(count($node->{$field_name}), $cardinality, 'Node was successfully saved with maximum number of files.');
  }

  /**
   * Tests a file field with a "Private files" upload destination setting.
   */
  public function testPrivateFileSetting() {
    $node_storage = $this->container
      ->get('entity_type.manager')
      ->getStorage('node');

    // Grant the admin user required permissions.
    user_role_grant_permissions($this->adminUser->roles[0]->target_id, [
      'administer node fields',
    ]);
    $type_name = 'article';
    $field_name = strtolower($this
      ->randomMachineName());
    $this
      ->createFileField($field_name, 'node', $type_name);
    $field = FieldConfig::loadByName('node', $type_name, $field_name);
    $field_id = $field
      ->id();
    $test_file = $this
      ->getTestFile('text');

    // Change the field setting to make its files private, and upload a file.
    $edit = [
      'settings[uri_scheme]' => 'private',
    ];
    $this
      ->drupalPostForm("admin/structure/types/manage/{$type_name}/fields/{$field_id}/storage", $edit, t('Save field settings'));
    $nid = $this
      ->uploadNodeFile($test_file, $field_name, $type_name);
    $node = $node_storage
      ->loadUnchanged($nid);
    $node_file = File::load($node->{$field_name}->target_id);
    $this
      ->assertFileExists($node_file
      ->getFileUri());

    // Ensure the private file is available to the user who uploaded it.
    $this
      ->drupalGet($node_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(200);

    // Ensure we can't change 'uri_scheme' field settings while there are some
    // entities with uploaded files.
    $this
      ->drupalGet("admin/structure/types/manage/{$type_name}/fields/{$field_id}/storage");
    $this
      ->assertFieldByXpath('//input[@id="edit-settings-uri-scheme-public" and @disabled="disabled"]', 'public', 'Upload destination setting disabled.');

    // Delete node and confirm that setting could be changed.
    $node
      ->delete();
    $this
      ->drupalGet("admin/structure/types/manage/{$type_name}/fields/{$field_id}/storage");
    $this
      ->assertFieldByXpath('//input[@id="edit-settings-uri-scheme-public" and not(@disabled)]', 'public', 'Upload destination setting enabled.');
  }

  /**
   * Tests that download restrictions on private files work on comments.
   */
  public function testPrivateFileComment() {
    $user = $this
      ->drupalCreateUser([
      'access comments',
    ]);

    // Grant the admin user required comment permissions.
    $roles = $this->adminUser
      ->getRoles();
    user_role_grant_permissions($roles[1], [
      'administer comment fields',
      'administer comments',
    ]);

    // Revoke access comments permission from anon user, grant post to
    // authenticated.
    user_role_revoke_permissions(RoleInterface::ANONYMOUS_ID, [
      'access comments',
    ]);
    user_role_grant_permissions(RoleInterface::AUTHENTICATED_ID, [
      'post comments',
      'skip comment approval',
    ]);

    // Create a new field.
    $this
      ->addDefaultCommentField('node', 'article');
    $name = strtolower($this
      ->randomMachineName());
    $label = $this
      ->randomMachineName();
    $storage_edit = [
      'settings[uri_scheme]' => 'private',
    ];
    $this
      ->fieldUIAddNewField('admin/structure/comment/manage/comment', $name, $label, 'file', $storage_edit);

    // Manually clear cache on the tester side.
    \Drupal::service('entity_field.manager')
      ->clearCachedFieldDefinitions();

    // Create node.
    $edit = [
      'title[0][value]' => $this
        ->randomMachineName(),
    ];
    $this
      ->drupalPostForm('node/add/article', $edit, t('Save'));
    $node = $this
      ->drupalGetNodeByTitle($edit['title[0][value]']);

    // Add a comment with a file.
    $text_file = $this
      ->getTestFile('text');
    $edit = [
      'files[field_' . $name . '_' . 0 . ']' => \Drupal::service('file_system')
        ->realpath($text_file
        ->getFileUri()),
      'comment_body[0][value]' => $comment_body = $this
        ->randomMachineName(),
    ];
    $this
      ->drupalPostForm('node/' . $node
      ->id(), $edit, t('Save'));

    // Get the comment ID.
    preg_match('/comment-([0-9]+)/', $this
      ->getUrl(), $matches);
    $cid = $matches[1];

    // Log in as normal user.
    $this
      ->drupalLogin($user);
    $comment = Comment::load($cid);
    $comment_file = $comment->{'field_' . $name}->entity;
    $this
      ->assertFileExists($comment_file
      ->getFileUri());

    // Test authenticated file download.
    $url = $comment_file
      ->createFileUrl();
    $this
      ->assertNotEqual($url, NULL, 'Confirmed that the URL is valid');
    $this
      ->drupalGet($comment_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(200);

    // Ensure that the anonymous user cannot download the file.
    $this
      ->drupalLogout();
    $this
      ->drupalGet($comment_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(403);

    // Unpublishes node.
    $this
      ->drupalLogin($this->adminUser);
    $edit = [
      'status[value]' => FALSE,
    ];
    $this
      ->drupalPostForm('node/' . $node
      ->id() . '/edit', $edit, t('Save'));

    // Ensures normal user can no longer download the file.
    $this
      ->drupalLogin($user);
    $this
      ->drupalGet($comment_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(403);
  }

  /**
   * Tests validation with the Upload button.
   */
  public function testWidgetValidation() {
    $type_name = 'article';
    $field_name = strtolower($this
      ->randomMachineName());
    $this
      ->createFileField($field_name, 'node', $type_name);
    $this
      ->updateFileField($field_name, $type_name, [
      'file_extensions' => 'txt',
    ]);
    $type = 'nojs';

    // Create node and prepare files for upload.
    $node = $this
      ->drupalCreateNode([
      'type' => 'article',
    ]);
    $nid = $node
      ->id();
    $this
      ->drupalGet("node/{$nid}/edit");
    $test_file_text = $this
      ->getTestFile('text');
    $test_file_image = $this
      ->getTestFile('image');
    $name = 'files[' . $field_name . '_0]';

    // Upload file with incorrect extension, check for validation error.
    $edit[$name] = \Drupal::service('file_system')
      ->realpath($test_file_image
      ->getFileUri());
    $this
      ->drupalPostForm(NULL, $edit, t('Upload'));
    $error_message = t('Only files with the following extensions are allowed: %files-allowed.', [
      '%files-allowed' => 'txt',
    ]);
    $this
      ->assertRaw($error_message, t('Validation error when file with wrong extension uploaded (JSMode=%type).', [
      '%type' => $type,
    ]));

    // Upload file with correct extension, check that error message is removed.
    $edit[$name] = \Drupal::service('file_system')
      ->realpath($test_file_text
      ->getFileUri());
    $this
      ->drupalPostForm(NULL, $edit, t('Upload'));
    $this
      ->assertNoRaw($error_message, t('Validation error removed when file with correct extension uploaded (JSMode=%type).', [
      '%type' => $type,
    ]));
  }

  /**
   * Tests file widget element.
   */
  public function testWidgetElement() {
    $field_name = mb_strtolower($this
      ->randomMachineName());
    $html_name = str_replace('_', '-', $field_name);
    $this
      ->createFileField($field_name, 'node', 'article', [
      'cardinality' => FieldStorageConfig::CARDINALITY_UNLIMITED,
    ]);
    $file = $this
      ->getTestFile('text');
    $xpath = "//details[@data-drupal-selector='edit-{$html_name}']/div[@class='details-wrapper']/table";
    $this
      ->drupalGet('node/add/article');
    $elements = $this
      ->xpath($xpath);

    // If the field has no item, the table should not be visible.
    $this
      ->assertCount(0, $elements);

    // Upload a file.
    $edit['files[' . $field_name . '_0][]'] = $this->container
      ->get('file_system')
      ->realpath($file
      ->getFileUri());
    $this
      ->drupalPostForm(NULL, $edit, "{$field_name}_0_upload_button");
    $elements = $this
      ->xpath($xpath);

    // If the field has at least a item, the table should be visible.
    $this
      ->assertCount(1, $elements);

    // Test for AJAX error when using progress bar on file field widget.
    $http_client = $this
      ->getHttpClient();
    $key = $this
      ->randomMachineName();
    $post_request = $http_client
      ->request('POST', $this
      ->buildUrl('file/progress/' . $key), [
      'headers' => [
        'Accept' => 'application/json',
        'Content-Type' => 'application/x-www-form-urlencoded',
      ],
      'http_errors' => FALSE,
    ]);
    $this
      ->assertNotEquals(500, $post_request
      ->getStatusCode());
    $body = Json::decode($post_request
      ->getBody());
    $this
      ->assertStringContainsString('Starting upload...', $body['message']);
  }

  /**
   * Tests exploiting the temporary file removal of another user using fid.
   */
  public function testTemporaryFileRemovalExploit() {

    // Create a victim user.
    $victim_user = $this
      ->drupalCreateUser();

    // Create an attacker user.
    $attacker_user = $this
      ->drupalCreateUser([
      'access content',
      'create article content',
      'edit any article content',
    ]);

    // Log in as the attacker user.
    $this
      ->drupalLogin($attacker_user);

    // Perform tests using the newly created users.
    $this
      ->doTestTemporaryFileRemovalExploit($victim_user, $attacker_user);
  }

  /**
   * Tests exploiting the temporary file removal for anonymous users using fid.
   */
  public function testTemporaryFileRemovalExploitAnonymous() {

    // Set up an anonymous victim user.
    $victim_user = User::getAnonymousUser();

    // Set up an anonymous attacker user.
    $attacker_user = User::getAnonymousUser();

    // Set up permissions for anonymous attacker user.
    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
      'access content' => TRUE,
      'create article content' => TRUE,
      'edit any article content' => TRUE,
    ]);

    // Log out so as to be the anonymous attacker user.
    $this
      ->drupalLogout();

    // Perform tests using the newly set up anonymous users.
    $this
      ->doTestTemporaryFileRemovalExploit($victim_user, $attacker_user);
  }

  /**
   * Helper for testing exploiting the temporary file removal using fid.
   *
   * @param \Drupal\user\UserInterface $victim_user
   *   The victim user.
   * @param \Drupal\user\UserInterface $attacker_user
   *   The attacker user.
   */
  protected function doTestTemporaryFileRemovalExploit(UserInterface $victim_user, UserInterface $attacker_user) {
    $type_name = 'article';
    $field_name = 'test_file_field';
    $this
      ->createFileField($field_name, 'node', $type_name);
    $test_file = $this
      ->getTestFile('text');
    $type = 'no-js';

    // Create a temporary file owned by the victim user. This will be as if
    // they had uploaded the file, but not saved the node they were editing
    // or creating.
    $victim_tmp_file = $this
      ->createTemporaryFile('some text', $victim_user);
    $victim_tmp_file = File::load($victim_tmp_file
      ->id());
    $this
      ->assertTrue($victim_tmp_file
      ->isTemporary(), 'New file saved to disk is temporary.');
    $this
      ->assertFalse(empty($victim_tmp_file
      ->id()), 'New file has an fid.');
    $this
      ->assertEqual($victim_user
      ->id(), $victim_tmp_file
      ->getOwnerId(), 'New file belongs to the victim.');

    // Have attacker create a new node with a different uploaded file and
    // ensure it got uploaded successfully.
    $edit = [
      'title[0][value]' => $type . '-title',
    ];

    // Attach a file to a node.
    $edit['files[' . $field_name . '_0]'] = $this->container
      ->get('file_system')
      ->realpath($test_file
      ->getFileUri());
    $this
      ->drupalPostForm(Url::fromRoute('node.add', [
      'node_type' => $type_name,
    ]), $edit, t('Save'));
    $node = $this
      ->drupalGetNodeByTitle($edit['title[0][value]']);

    /** @var \Drupal\file\FileInterface $node_file */
    $node_file = File::load($node->{$field_name}->target_id);
    $this
      ->assertFileExists($node_file
      ->getFileUri());
    $this
      ->assertEqual($attacker_user
      ->id(), $node_file
      ->getOwnerId(), 'New file belongs to the attacker.');

    // Ensure the file can be downloaded.
    $this
      ->drupalGet($node_file
      ->createFileUrl());
    $this
      ->assertSession()
      ->statusCodeEquals(200);

    // "Click" the remove button (emulating either a nojs or js submission).
    // In this POST request, the attacker "guesses" the fid of the victim's
    // temporary file and uses that to remove this file.
    $this
      ->drupalGet($node
      ->toUrl('edit-form'));
    $file_id_field = $this
      ->assertSession()
      ->hiddenFieldExists($field_name . '[0][fids]');
    $file_id_field
      ->setValue((string) $victim_tmp_file
      ->id());
    $this
      ->drupalPostForm(NULL, [], 'Remove');

    // The victim's temporary file should not be removed by the attacker's
    // POST request.
    $this
      ->assertFileExists($victim_tmp_file
      ->getFileUri());
  }

}

Classes

Name	Description
FileFieldWidgetTest	Tests the file field widget with public and private files.