stream_wrappers.inc

<?php
/**
 * @file
 * Backdrop stream wrapper interface.
 *
 * Provides a Backdrop interface and classes to implement PHP stream wrappers for
 * public, private, and temporary files.
 *
 * A stream wrapper is an abstraction of a file system that allows Backdrop to
 * use the same set of methods to access both local files and remote resources.
 *
 * Note that PHP 5.2 fopen() only supports URIs of the form "scheme://target"
 * despite the fact that according to RFC 3986 a URI's scheme component
 * delimiter is in general just ":", not "://".  Because of this PHP limitation
 * and for consistency Backdrop will only accept URIs of form "scheme://target".
 *
 * @see http://www.faqs.org/rfcs/rfc3986.html
 * @see http://bugs.php.net/bug.php?id=47070
 */

/**
 * Stream wrapper bit flags that are the basis for composite types.
 *
 * Note that 0x0002 is skipped, because it was the value of a constant that has
 * since been removed.
 */

/**
 * Stream wrapper bit flag -- a filter that matches all wrappers.
 */
define('STREAM_WRAPPERS_ALL', 0x0000);

/**
 * Stream wrapper bit flag -- refers to a local file system location.
 */
define('STREAM_WRAPPERS_LOCAL', 0x0001);

/**
 * Stream wrapper bit flag -- wrapper is readable (almost always true).
 */
define('STREAM_WRAPPERS_READ', 0x0004);

/**
 * Stream wrapper bit flag -- wrapper is writeable.
 */
define('STREAM_WRAPPERS_WRITE', 0x0008);

/**
 * Stream wrapper bit flag -- exposed in the UI and potentially web accessible.
 */
define('STREAM_WRAPPERS_VISIBLE', 0x0010);

/**
 * Composite stream wrapper bit flags that are usually used as the types.
 */

/**
 * Stream wrapper type flag -- not visible in the UI or accessible via web,
 * but readable and writable. E.g. the temporary directory for uploads.
 */
define('STREAM_WRAPPERS_HIDDEN', STREAM_WRAPPERS_READ | STREAM_WRAPPERS_WRITE);

/**
 * Stream wrapper type flag -- hidden, readable and writeable using local files.
 */
define('STREAM_WRAPPERS_LOCAL_HIDDEN', STREAM_WRAPPERS_LOCAL | STREAM_WRAPPERS_HIDDEN);

/**
 * Stream wrapper type flag -- visible, readable and writeable.
 */
define('STREAM_WRAPPERS_WRITE_VISIBLE', STREAM_WRAPPERS_READ | STREAM_WRAPPERS_WRITE | STREAM_WRAPPERS_VISIBLE);

/**
 * Stream wrapper type flag -- visible and read-only.
 */
define('STREAM_WRAPPERS_READ_VISIBLE', STREAM_WRAPPERS_READ | STREAM_WRAPPERS_VISIBLE);

/**
 * Stream wrapper type flag -- the default when 'type' is omitted from
 * hook_stream_wrappers(). This does not include STREAM_WRAPPERS_LOCAL,
 * because PHP grants a greater trust level to local files (for example, they
 * can be used in an "include" statement, regardless of the "allow_url_include"
 * setting), so stream wrappers need to explicitly opt-in to this.
 */
define('STREAM_WRAPPERS_NORMAL', STREAM_WRAPPERS_WRITE_VISIBLE);

/**
 * Stream wrapper type flag -- visible, readable and writeable using local files.
 */
define('STREAM_WRAPPERS_LOCAL_NORMAL', STREAM_WRAPPERS_LOCAL | STREAM_WRAPPERS_NORMAL);

/**
 * Generic PHP stream wrapper interface.
 *
 * @see http://www.php.net/manual/class.streamwrapper.php
 */
interface StreamWrapperInterface {
  public function stream_open($uri, $mode, $options, &$opened_url);
  public function stream_close();
  public function stream_lock($operation);
  public function stream_read($count);
  public function stream_write($data);
  public function stream_eof();
  public function stream_seek($offset, $whence);
  public function stream_flush();
  public function stream_tell();
  public function stream_stat();
  public function unlink($uri);
  public function rename($from_uri, $to_uri);
  public function mkdir($uri, $mode, $options);
  public function rmdir($uri, $options);
  public function url_stat($uri, $flags);
  public function dir_opendir($uri, $options);
  public function dir_readdir();
  public function dir_rewinddir();
  public function dir_closedir();
}

/**
 * Backdrop stream wrapper extension.
 *
 * Extend the StreamWrapperInterface with methods expected by Backdrop stream
 * wrapper classes.
 */
interface BackdropStreamWrapperInterface extends StreamWrapperInterface {
  /**
   * Set the absolute stream resource URI.
   *
   * This allows you to set the URI. Generally is only called by the factory
   * method.
   *
   * @param $uri
   *   A string containing the URI that should be used for this instance.
   */
  public function setUri($uri);

  /**
   * Returns the stream resource URI.
   *
   * @return
   *   Returns the current URI of the instance.
   */
  public function getUri();

  /**
   * Returns a web accessible URL for the resource.
   *
   * This function should return a URL that can be embedded in a web page
   * and accessed from a browser. For example, the external URL of
   * "youtube://xIpLd0WQKCY" might be
   * "http://www.youtube.com/watch?v=xIpLd0WQKCY".
   *
   * @return
   *   Returns a string containing a web accessible URL for the resource.
   */
  public function getExternalUrl();

  /**
   * Returns the MIME type of the resource.
   *
   * @param $uri
   *   The URI, path, or filename.
   * @param $mapping
   *   An optional map of extensions to their mimetypes, in the form:
   *    - 'mimetypes': a list of mimetypes, keyed by an identifier,
   *    - 'extensions': the mapping itself, an associative array in which
   *      the key is the extension and the value is the mimetype identifier.
   *
   * @return
   *   Returns a string containing the MIME type of the resource.
   */
  public static function getMimeType($uri, $mapping = NULL);

  /**
   * Changes permissions of the resource.
   *
   * PHP lacks this functionality and it is not part of the official stream
   * wrapper interface. This is a custom implementation for Backdrop.
   *
   * @param $mode
   *   Integer value for the permissions. Consult PHP chmod() documentation
   *   for more information.
   *
   * @return
   *   Returns TRUE on success or FALSE on failure.
   */
  public function chmod($mode);

  /**
   * Returns canonical, absolute path of the resource.
   *
   * Implementation placeholder. PHP's realpath() does not support stream
   * wrappers. We provide this as a default so that individual wrappers may
   * implement their own solutions.
   *
   * @return
   *   Returns a string with absolute pathname on success (implemented
   *   by core wrappers), or FALSE on failure or if the registered
   *   wrapper does not provide an implementation.
   */
  public function realpath();

  /**
   * Gets the name of the directory from a given path.
   *
   * This method is usually accessed through backdrop_dirname(), which wraps
   * around the normal PHP dirname() function, which does not support stream
   * wrappers.
   *
   * @param $uri
   *   An optional URI.
   *
   * @return
   *   A string containing the directory name, or FALSE if not applicable.
   *
   * @see backdrop_dirname()
   */
  public function dirname($uri = NULL);
}

/**
 * Backdrop stream wrapper base class for local files.
 *
 * This class provides a complete stream wrapper implementation. URIs such as
 * "public://example.txt" are expanded to a normal filesystem path such as
 * "sites/example.com/files/example.txt" and then PHP filesystem functions are
 * invoked.
 *
 * BackdropLocalStreamWrapper implementations need to implement at least the
 * getDirectoryPath() and getExternalUrl() methods.
 */
abstract class BackdropLocalStreamWrapper implements BackdropStreamWrapperInterface {
  /**
   * Stream context resource.
   *
   * @var Resource
   */
  public $context;

  /**
   * A generic resource handle.
   *
   * @var Resource
   */
  public $handle = NULL;

  /**
   * Instance URI (stream).
   *
   * A stream is referenced as "scheme://target".
   *
   * @var String
   */
  protected $uri;

  /**
   * Gets the path that the wrapper is responsible for.
   * @TODO: Review this method name per http://drupal.org/node/701358
   *
   * @return
   *   String specifying the path.
   */
  abstract function getDirectoryPath();

  /**
   * Base implementation of setUri().
   */
  function setUri($uri) {
    $this->uri = $uri;
  }

  /**
   * Base implementation of getUri().
   */
  function getUri() {
    return $this->uri;
  }

  /**
   * Returns the local writable target of the resource within the stream.
   *
   * This function should be used in place of calls to realpath() or similar
   * functions when attempting to determine the location of a file. While
   * functions like realpath() may return the location of a read-only file, this
   * method may return a URI or path suitable for writing that is completely
   * separate from the URI used for reading.
   *
   * @param $uri
   *   Optional URI.
   *
   * @return
   *   Returns a string representing a location suitable for writing of a file,
   *   or FALSE if unable to write to the file such as with read-only streams.
   */
  protected function getTarget($uri = NULL) {
    if (!isset($uri)) {
      $uri = $this->uri;
    }

    list($scheme, $target) = explode('://', $uri, 2);

    // Remove erroneous leading or trailing, forward-slashes and backslashes.
    return trim($target, '\/');
  }

  /**
   * Base implementation of getMimeType().
   */
  static function getMimeType($uri, $mapping = NULL) {
    if (!isset($mapping)) {
      // The default file map, defined in file.mimetypes.inc is quite big.
      // We only load it when necessary.
      include_once BACKDROP_ROOT . '/core/includes/file.mimetypes.inc';
      $mapping = file_mimetype_mapping();
    }

    $extension = '';
    $file_parts = explode('.', backdrop_basename($uri));

    // Remove the first part: a full filename should not match an extension.
    array_shift($file_parts);

    // Iterate over the file parts, trying to find a match.
    // For my.awesome.image.jpeg, we try:
    //   - jpeg
    //   - image.jpeg, and
    //   - awesome.image.jpeg
    while ($additional_part = array_pop($file_parts)) {
      $extension = strtolower($additional_part . ($extension ? '.' . $extension : ''));
      if (isset($mapping['extensions'][$extension])) {
        return $mapping['mimetypes'][$mapping['extensions'][$extension]];
      }
    }

    return 'application/octet-stream';
  }

  /**
   * Base implementation of chmod().
   */
  function chmod($mode) {
    $output = @chmod($this->getLocalPath(), $mode);
    // We are modifying the underlying file here, so we have to clear the stat
    // cache so that PHP understands that URI has changed too.
    clearstatcache();
    return $output;
  }

  /**
   * Base implementation of realpath().
   */
  function realpath() {
    return $this->getLocalPath();
  }

  /**
   * Returns the canonical absolute path of the URI, if possible.
   *
   * @param string $uri
   *   (optional) The stream wrapper URI to be converted to a canonical
   *   absolute path. This may point to a directory or another type of file.
   *
   * @return string|false
   *   If $uri is not set, returns the canonical absolute path of the URI
   *   previously set by the BackdropStreamWrapperInterface::setUri() function.
   *   If $uri is set and valid for this class, returns its canonical absolute
   *   path, as determined by the realpath() function. If $uri is set but not
   *   valid, returns FALSE.
   */
  protected function getLocalPath($uri = NULL) {
    if (!isset($uri)) {
      $uri = $this->uri;
    }
    $path = $this->getDirectoryPath() . '/' . $this->getTarget($uri);
    $realpath = realpath($path);
    if (!$realpath) {
      // This file does not yet exist.
      $realpath = realpath(dirname($path)) . '/' . backdrop_basename($path);
    }
    $directory = realpath($this->getDirectoryPath());
    if (!$realpath || !$directory || strpos($realpath, $directory) !== 0) {
      return FALSE;
    }
    return $realpath;
  }

  /**
   * Support for fopen(), file_get_contents(), file_put_contents() etc.
   *
   * @param $uri
   *   A string containing the URI to the file to open.
   * @param $mode
   *   The file mode ("r", "wb" etc.).
   * @param $options
   *   A bit mask of STREAM_USE_PATH and STREAM_REPORT_ERRORS.
   * @param $opened_path
   *   A string containing the path actually opened.
   *
   * @return
   *   Returns TRUE if file was opened successfully.
   *
   * @see http://php.net/manual/streamwrapper.stream-open.php
   */
  public function stream_open($uri, $mode, $options, &$opened_path) {
    $this->uri = $uri;
    $path = $this->getLocalPath();
    if ($path) {
      $this->handle = ($options & STREAM_REPORT_ERRORS) ? fopen($path, $mode) : @fopen($path, $mode);
    }
    else {
      $this->handle = NULL;
    }

    if ((bool) $this->handle && $options & STREAM_USE_PATH) {
      $opened_path = $path;
    }

    return (bool) $this->handle;
  }

  /**
   * Support for flock().
   *
   * @param $operation
   *   One of the following:
   *   - LOCK_SH to acquire a shared lock (reader).
   *   - LOCK_EX to acquire an exclusive lock (writer).
   *   - LOCK_UN to release a lock (shared or exclusive).
   *   - LOCK_NB if you don't want flock() to block while locking (not
   *     supported on Windows).
   *
   * @return
   *   Always returns TRUE at the present time.
   *
   * @see http://php.net/manual/streamwrapper.stream-lock.php
   */
  public function stream_lock($operation) {
    if (in_array($operation, array(LOCK_SH, LOCK_EX, LOCK_UN, LOCK_NB))) {
      return flock($this->handle, $operation);
    }

    return TRUE;
  }

  /**
   * Support for fread(), file_get_contents() etc.
   *
   * @param $count
   *   Maximum number of bytes to be read.
   *
   * @return
   *   The string that was read, or FALSE in case of an error.
   *
   * @see http://php.net/manual/streamwrapper.stream-read.php
   */
  public function stream_read($count) {
    return fread($this->handle, $count);
  }

  /**
   * Support for fwrite(), file_put_contents() etc.
   *
   * @param $data
   *   The string to be written.
   *
   * @return
   *   The number of bytes written (integer).
   *
   * @see http://php.net/manual/streamwrapper.stream-write.php
   */
  public function stream_write($data) {
    return fwrite($this->handle, $data);
  }

  /**
   * Support for feof().
   *
   * @return
   *   TRUE if end-of-file has been reached.
   *
   * @see http://php.net/manual/streamwrapper.stream-eof.php
   */
  public function stream_eof() {
    return feof($this->handle);
  }

  /**
   * Support for fseek().
   *
   * @param $offset
   *   The byte offset to got to.
   * @param $whence
   *   SEEK_SET, SEEK_CUR, or SEEK_END.
   *
   * @return
   *   TRUE on success.
   *
   * @see http://php.net/manual/streamwrapper.stream-seek.php
   */
  public function stream_seek($offset, $whence) {
    // fseek returns 0 on success and -1 on a failure.
    // stream_seek   1 on success and  0 on a failure.
    return !fseek($this->handle, $offset, $whence);
  }

  /**
   * Support for fflush().
   *
   * @return
   *   TRUE if data was successfully stored (or there was no data to store).
   *
   * @see http://php.net/manual/streamwrapper.stream-flush.php
   */
  public function stream_flush() {
    return fflush($this->handle);
  }

  /**
   * Support for ftell().
   *
   * @return
   *   The current offset in bytes from the beginning of file.
   *
   * @see http://php.net/manual/streamwrapper.stream-tell.php
   */
  public function stream_tell() {
    return ftell($this->handle);
  }

  /**
   * Support for fstat().
   *
   * @return
   *   An array with file status, or FALSE in case of an error - see fstat()
   *   for a description of this array.
   *
   * @see http://php.net/manual/streamwrapper.stream-stat.php
   */
  public function stream_stat() {
    return fstat($this->handle);
  }

  /**
   * Support for fclose().
   *
   * @return
   *   TRUE if stream was successfully closed.
   *
   * @see http://php.net/manual/streamwrapper.stream-close.php
   */
  public function stream_close() {
    return fclose($this->handle);
  }

  /**
   * Sets metadata on the stream.
   *
   * WARNING: Do not call this method directly! It will be called internally by
   * PHP itself when one of the following functions is called on a stream URL:
   *
   * @param string $uri
   *   A string containing the URI to the file to set metadata on.
   * @param int $option
   *   One of:
   *   - STREAM_META_TOUCH: The method was called in response to touch().
   *   - STREAM_META_OWNER_NAME: The method was called in response to chown()
   *     with string parameter.
   *   - STREAM_META_OWNER: The method was called in response to chown().
   *   - STREAM_META_GROUP_NAME: The method was called in response to chgrp().
   *   - STREAM_META_GROUP: The method was called in response to chgrp().
   *   - STREAM_META_ACCESS: The method was called in response to chmod().
   * @param mixed $value
   *   If option is:
   *   - STREAM_META_TOUCH: Array consisting of two arguments of the touch()
   *     function.
   *   - STREAM_META_OWNER_NAME or STREAM_META_GROUP_NAME: The name of the owner
   *     user/group as string.
   *   - STREAM_META_OWNER or STREAM_META_GROUP: The value of the owner
   *     user/group as integer.
   *   - STREAM_META_ACCESS: The argument of the chmod() as integer.
   *
   * @return bool
   *   Returns TRUE on success or FALSE on failure. If $option is not
   *   implemented, FALSE should be returned.
   *
   * @see touch()
   * @see chmod()
   * @see chown()
   * @see chgrp()
   * @link http://php.net/manual/streamwrapper.stream-metadata.php
   */
  public function stream_metadata($uri, $option, $value) {
    $target = $this->getLocalPath($uri);
    $return = FALSE;
    switch ($option) {
      case STREAM_META_TOUCH:
        if (!empty($value)) {
          $return = touch($target, $value[0], $value[1]);
        }
        else {
          $return = touch($target);
        }
        break;

      case STREAM_META_OWNER_NAME:
      case STREAM_META_OWNER:
        $return = chown($target, $value);
        break;

      case STREAM_META_GROUP_NAME:
      case STREAM_META_GROUP:
        $return = chgrp($target, $value);
        break;

      case STREAM_META_ACCESS:
        $return = chmod($target, $value);
        break;
    }
    if ($return) {
      // For convenience clear the file status cache of the underlying file,
      // since metadata operations are often followed by file status checks.
      clearstatcache(TRUE, $target);
    }
    return $return;
  }

  /**
   * Truncate stream.
   *
   * Will respond to truncation; e.g., through ftruncate().
   *
   * @param int $new_size
   *   The new size.
   *
   * @return bool
   *   TRUE on success, FALSE otherwise.
   */
  public function stream_truncate($new_size) {
    return ftruncate($this->handle, $new_size);
  }

  /**
   * Retrieve the underlying stream resource.
   *
   * This method is called in response to stream_select().
   *
   * @param int $cast_as
   *   Can be STREAM_CAST_FOR_SELECT when stream_select() is calling
   *   stream_cast() or STREAM_CAST_AS_STREAM when stream_cast() is called for
   *   other uses.
   *
   * @return resource|false
   *   The underlying stream resource or FALSE if stream_select() is not
   *   supported.
   *
   * @see stream_select()
   * @link http://php.net/manual/streamwrapper.stream-cast.php
   */
  public function stream_cast($cast_as) {
    return $this->handle ? $this->handle : FALSE;
  }

  /**
   * Change stream options.
   *
   * This method is called to set options on the stream.
   *
   * Since Windows systems do not allow it and it is not needed for most use
   * cases anyway, this method is not supported on local files and will trigger
   * an error and return false. If needed, custom subclasses can provide
   * OS-specific implementations for advanced use cases.
   *
   * @param int $option
   *   One of:
   *   - STREAM_OPTION_BLOCKING: The method was called in response to
   *     stream_set_blocking().
   *   - STREAM_OPTION_READ_TIMEOUT: The method was called in response to
   *     stream_set_timeout().
   *   - STREAM_OPTION_WRITE_BUFFER: The method was called in response to
   *     stream_set_write_buffer().
   * @param int $arg1
   *   If option is:
   *   - STREAM_OPTION_BLOCKING: The requested blocking mode:
   *     - 1 means blocking.
   *     - 0 means not blocking.
   *   - STREAM_OPTION_READ_TIMEOUT: The timeout in seconds.
   *   - STREAM_OPTION_WRITE_BUFFER: The buffer mode, STREAM_BUFFER_NONE or
   *     STREAM_BUFFER_FULL.
   * @param int $arg2
   *   If option is:
   *   - STREAM_OPTION_BLOCKING: This option is not set.
   *   - STREAM_OPTION_READ_TIMEOUT: The timeout in microseconds.
   *   - STREAM_OPTION_WRITE_BUFFER: The requested buffer size.
   *
   * @return bool
   *   TRUE on success, FALSE otherwise. If $option is not implemented, FALSE
   *   should be returned.
   */
  public function stream_set_option($option, $arg1, $arg2) {
    trigger_error('stream_set_option() not supported for local file based stream wrappers', E_USER_WARNING);
    return FALSE;
  }

  /**
   * Support for unlink().
   *
   * @param $uri
   *   A string containing the URI to the resource to delete.
   *
   * @return
   *   TRUE if resource was successfully deleted.
   *
   * @see http://php.net/manual/streamwrapper.unlink.php
   */
  public function unlink($uri) {
    $this->uri = $uri;
    return backdrop_unlink($this->getLocalPath());
  }

  /**
   * Support for rename().
   *
   * @param $from_uri,
   *   The URI to the file to rename.
   * @param $to_uri
   *   The new URI for file.
   *
   * @return
   *   TRUE if file was successfully renamed.
   *
   * @see http://php.net/manual/streamwrapper.rename.php
   */
  public function rename($from_uri, $to_uri) {
    return rename($this->getLocalPath($from_uri), $this->getLocalPath($to_uri));
  }

  /**
   * Gets the name of the directory from a given path.
   *
   * This method is usually accessed through backdrop_dirname(), which wraps
   * around the PHP dirname() function because it does not support stream
   * wrappers.
   *
   * @param $uri
   *   A URI or path.
   *
   * @return
   *   A string containing the directory name.
   *
   * @see backdrop_dirname()
   */
  public function dirname($uri = NULL) {
    list($scheme, $target) = explode('://', $uri, 2);
    $target  = $this->getTarget($uri);
    $dirname = dirname($target);

    if ($dirname == '.') {
      $dirname = '';
    }

    return $scheme . '://' . $dirname;
  }

  /**
   * Support for mkdir().
   *
   * @param $uri
   *   A string containing the URI to the directory to create.
   * @param $mode
   *   Permission flags - see mkdir().
   * @param $options
   *   A bit mask of STREAM_REPORT_ERRORS and STREAM_MKDIR_RECURSIVE.
   *
   * @return
   *   TRUE if directory was successfully created.
   *
   * @see http://php.net/manual/streamwrapper.mkdir.php
   */
  public function mkdir($uri, $mode, $options) {
    $this->uri = $uri;
    $recursive = (bool) ($options & STREAM_MKDIR_RECURSIVE);
    if ($recursive) {
      // $this->getLocalPath() fails if $uri has multiple levels of directories
      // that do not yet exist.
      $local_path = $this->getDirectoryPath() . '/' . $this->getTarget($uri);
    }
    else {
      $local_path = $this->getLocalPath($uri);
    }
    if ($options & STREAM_REPORT_ERRORS) {
      return mkdir($local_path, $mode, $recursive);
    }
    else {
      return @mkdir($local_path, $mode, $recursive);
    }
  }

  /**
   * Support for rmdir().
   *
   * @param $uri
   *   A string containing the URI to the directory to delete.
   * @param $options
   *   A bit mask of STREAM_REPORT_ERRORS.
   *
   * @return
   *   TRUE if directory was successfully removed.
   *
   * @see http://php.net/manual/streamwrapper.rmdir.php
   */
  public function rmdir($uri, $options) {
    $this->uri = $uri;
    if ($options & STREAM_REPORT_ERRORS) {
      return backdrop_rmdir($this->getLocalPath());
    }
    else {
      return @backdrop_rmdir($this->getLocalPath());
    }
  }

  /**
   * Support for stat().
   *
   * @param $uri
   *   A string containing the URI to get information about.
   * @param $flags
   *   A bit mask of STREAM_URL_STAT_LINK and STREAM_URL_STAT_QUIET.
   *
   * @return
   *   An array with file status, or FALSE in case of an error - see fstat()
   *   for a description of this array.
   *
   * @see http://php.net/manual/streamwrapper.url-stat.php
   */
  public function url_stat($uri, $flags) {
    $this->uri = $uri;
    $path = $this->getLocalPath();
    // Suppress warnings if requested or if the file or directory does not
    // exist. This is consistent with PHP's plain filesystem stream wrapper.
    if ($flags & STREAM_URL_STAT_QUIET || !file_exists($path)) {
      return @stat($path);
    }
    else {
      return stat($path);
    }
  }

  /**
   * Support for opendir().
   *
   * @param $uri
   *   A string containing the URI to the directory to open.
   * @param $options
   *   Unknown (parameter is not documented in PHP Manual).
   *
   * @return
   *   TRUE on success.
   *
   * @see http://php.net/manual/streamwrapper.dir-opendir.php
   */
  public function dir_opendir($uri, $options) {
    $this->uri = $uri;
    $this->handle = opendir($this->getLocalPath());

    return (bool) $this->handle;
  }

  /**
   * Support for readdir().
   *
   * @return
   *   The next filename, or FALSE if there are no more files in the directory.
   *
   * @see http://php.net/manual/streamwrapper.dir-readdir.php
   */
  public function dir_readdir() {
    return readdir($this->handle);
  }

  /**
   * Support for rewinddir().
   *
   * @return
   *   TRUE on success.
   *
   * @see http://php.net/manual/streamwrapper.dir-rewinddir.php
   */
  public function dir_rewinddir() {
    rewinddir($this->handle);
    // We do not really have a way to signal a failure as rewinddir() does not
    // have a return value and there is no way to read a directory handler
    // without advancing to the next file.
    return TRUE;
  }

  /**
   * Support for closedir().
   *
   * @return
   *   TRUE on success.
   *
   * @see http://php.net/manual/streamwrapper.dir-closedir.php
   */
  public function dir_closedir() {
    closedir($this->handle);
    // We do not really have a way to signal a failure as closedir() does not
    // have a return value.
    return TRUE;
  }
}

/**
 * Backdrop public (public://) stream wrapper class.
 *
 * Provides support for storing publicly accessible files with the Backdrop file
 * interface.
 */
class BackdropPublicStreamWrapper extends BackdropLocalStreamWrapper {
  /**
   * Implements abstract public function getDirectoryPath()
   */
  public function getDirectoryPath() {
    return config_get('system.core', 'file_public_path');
  }

  /**
   * Overrides getExternalUrl().
   *
   * Return the HTML URI of a public file.
   */
  function getExternalUrl() {
    $path = str_replace('\\', '/', $this->getTarget());
    return $GLOBALS['base_url'] . '/' . self::getDirectoryPath() . '/' . backdrop_encode_path($path);
  }

  /**
   * {@inheritdoc}
   */
  protected function getLocalPath($uri = NULL) {
    $path = parent::getLocalPath($uri);

    $private_path = config_get('system.core', 'file_private_path');
    if ($private_path) {
      $private_path = realpath($private_path);
      if ($private_path && strpos($path, $private_path) === 0) {
        return FALSE;
      }
    }

    return $path;
  }
}

/**
 * Backdrop private (private://) stream wrapper class.
 *
 * Provides support for storing privately accessible files with the Backdrop file
 * interface.
 */
class BackdropPrivateStreamWrapper extends BackdropLocalStreamWrapper {
  /**
   * Implements abstract public function getDirectoryPath()
   */
  public function getDirectoryPath() {
    return config_get('system.core', 'file_private_path');
  }

  /**
   * Overrides getExternalUrl().
   *
   * Return the HTML URI of a private file.
   */
  function getExternalUrl() {
    $path = str_replace('\\', '/', $this->getTarget());
    return url('system/files/' . $path, array('absolute' => TRUE));
  }
}

/**
 * Backdrop temporary (temporary://) stream wrapper class.
 *
 * Provides support for storing temporarily accessible files with the Backdrop
 * file interface.
 *
 * Extends BackdropPublicStreamWrapper.
 */
class BackdropTemporaryStreamWrapper extends BackdropLocalStreamWrapper {
  /**
   * Implements abstract public function getDirectoryPath()
   */
  public function getDirectoryPath() {
    $temp = config_get('system.core', 'file_temporary_path');
    if (empty($temp)) {
      $temp = file_directory_temp();
    }
    return $temp;
  }

  /**
   * Overrides getExternalUrl().
   */
  public function getExternalUrl() {
    $path = str_replace('\\', '/', $this->getTarget());
    return url('system/temporary/' . $path, array('absolute' => TRUE));
  }
}