class FileExampleSessionStreamWrapper

Example stream wrapper class to handle session:// streams.

This is just an example, as it could have horrible results if much information were placed in the $_SESSION variable. However, it does demonstrate both the read and write implementation of a stream wrapper.

A "stream" is an important Unix concept for the reading and writing of files and other devices. Reading or writing a "stream" just means that you open some device, file, internet site, or whatever, and you don't have to know at all what it is. All the functions that deal with it are the same. You can read/write more from/to the stream, seek a position in the stream, or anything else without the code that does it even knowing what kind of device it is talking to. This Unix idea is extended into PHP's mindset.

The idea of "stream wrapper" is that this can be extended indefinitely. The classic example is HTTP: With PHP you can do a file_get_contents("http://backdropcms.org/add-ons") as if it were a file, because the scheme "http" is supported natively in PHP. So Backdrop adds the public:// and private:// schemes, and contrib modules can add any scheme they want to. This example adds the session:// scheme, which allows reading and writing the $_SESSION['file_example'] key as if it were a file.

Note that because this implementation uses simple PHP arrays ($_SESSION) it is limited to string values, so binary files will not work correctly. Only text files can be used.

Hierarchy

class FileExampleSessionStreamWrapper implements BackdropStreamWrapperInterface

Expanded class hierarchy of FileExampleSessionStreamWrapper

File

modules/examples/file_example/file_example_session_streams.inc, line 40: Provides a demonstration session:// stream-wrapper.

View source

class FileExampleSessionStreamWrapper implements BackdropStreamWrapperInterface {
  /**
   * Stream context resource.
   *
   * @var Resource
   */
  public $context;


  /**
   * Instance URI (stream).
   *
   * These streams will be references as 'session://example_target'
   *
   * @var String
   */
  protected $uri;

  /**
   * The content of the stream.
   *
   * Since this trivial example just uses the $_SESSION variable, this is
   * simply a reference to the contents of the related part of
   * $_SESSION['file_example'].
   */
  protected $sessionContent;

  /**
   * Pointer to where we are in a directory read.
   */
  protected $directoryPointer;

  /**
   * List of keys in a given directory.
   */
  protected $directoryKeys;

  /**
   * The pointer to the next read or write within the session variable.
   */
  protected $streamPointer;

  /**
   * Constructor method.
   */
  public function __construct() {
    $_SESSION['file_example']['.isadir.txt'] = TRUE;
  }

  /**
   * Implements setUri().
   */
  public function setUri($uri) {
    $this->uri = $uri;
  }

  /**
   * Implements getUri().
   */
  public function getUri() {
    return $this->uri;
  }

  /**
   * Implements getTarget().
   *
   * The "target" is the portion of the URI to the right of the scheme.
   * So in session://example/test.txt, the target is 'example/test.txt'.
   */
  public 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.
    // In the session:// scheme, there is never a leading slash on the target.
    return trim($target, '\/');
  }

  /**
   * Implements getMimeType().
   */
  public 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 = '';
    $file_parts = explode('.', basename($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)) {
      $extension = backdrop_strtolower($additional_part . ($extension ? '.' . $extension : ''));
      if (isset($mapping['extensions'][$extension])) {
        return $mapping['mimetypes'][$mapping['extensions'][$extension]];
      }
    }

    return 'application/octet-stream';
  }

  /**
   * Implements getDirectoryPath().
   *
   * In this case there is no directory string, so return an empty string.
   */
  public function getDirectoryPath() {
    return '';
  }

  /**
   * Overrides getExternalUrl().
   *
   * We have set up a helper function and menu entry to provide access to this
   * key via HTTP; normally it would be accessible some other way.
   */
  public function getExternalUrl() {
    $path = $this->getLocalPath();
    $url = url('examples/file_example/access_session/' . $path, array('absolute' => TRUE));

    return $url;
  }

  /**
   * We have no concept of chmod, so just return TRUE.
   */
  public function chmod($mode) {
    return TRUE;
  }

  /**
   * Implements realpath().
   */
  public function realpath() {
    return 'session://' . $this->getLocalPath();
  }

  /**
   * Returns the local path.
   *
   * Here we aren't doing anything but stashing the "file" in a key in the
   * $_SESSION variable, so there's not much to do but to create a "path"
   * which is really just a key in the $_SESSION variable. So something
   * like 'session://one/two/three.txt' becomes
   * $_SESSION['file_example']['one']['two']['three.txt'] and the actual path
   * is "one/two/three.txt".
   *
   * @param string $uri
   *   Optional URI, supplied when doing a move or rename.
   */
  protected function getLocalPath($uri = NULL) {
    if (!isset($uri)) {
      $uri = $this->uri;
    }

    $path = str_replace('session://', '', $uri);
    $path = trim($path, '/');

    return $path;
  }

  /**
   * Opens a stream, as for fopen(), file_get_contents(), file_put_contents().
   *
   * @param string $uri
   *   A string containing the URI to the file to open.
   * @param string $mode
   *   The file mode ("r", "wb" etc.).
   * @param int $options
   *   A bit mask of STREAM_USE_PATH and STREAM_REPORT_ERRORS.
   * @param string &$opened_path
   *   A string containing the path actually opened.
   *
   * @return bool
   *   Returns TRUE if file was opened successfully. (Always returns TRUE).
   *
   * @see http://php.net/manual/en/streamwrapper.stream-open.php
   */
  public function stream_open($uri, $mode, $options, &$opened_path) {
    $this->uri = $uri;
    // We make $session_content a reference to the appropriate key in the
    // $_SESSION variable. So if the local path were
    // /example/test.txt it $session_content would now be a
    // reference to $_SESSION['file_example']['example']['test.txt'].
    $this->sessionContent = &$this->uri_to_session_key($uri);

    // Reset the stream pointer since this is an open.
    $this->streamPointer = 0;

    return TRUE;
  }

  /**
   * Return a reference to the correct $_SESSION key.
   *
   * @param string $uri
   *   The uri: session://something
   * @param bool $create
   *   If TRUE, create the key
   *
   * @return array|bool
   *   A reference to the array at the end of the key-path, or
   *   FALSE if the path doesn't map to a key-path (and $create is FALSE).
   */
  protected function &uri_to_session_key($uri, $create = TRUE) {
    // Since our uri_to_session_key() method returns a reference, we
    // have to set up a failure flag variable.
    $fail = FALSE;
    $path = $this->getLocalPath($uri);
    $path_components = explode('/', $path);
    // Set up a reference to the root session:// 'directory.'
    $var = &$_SESSION['file_example'];
    // Handle case of just session://.
    if (count($path_components) < 1) {
      return $var;
    }
    // Walk through the path components and create keys in $_SESSION,
    // unless we're told not to create them.
    foreach ($path_components as $component) {
      if ($create || isset($var[$component])) {
        $var = &$var[$component];
      }
      else {
        // This path doesn't exist as keys, either because the
        // key doesn't exist, or because we're told not to create it.
        return $fail;
      }
    }

    return $var;
  }

  /**
   * Support for flock().
   *
   * The $_SESSION variable has no locking capability, so return TRUE.
   *
   * @param int $operation
   *   One of the following:
   *   - LOCK_SH to acquire a shared lock (reader).
   *   - LOCK_EX to acquire an exclusive lock (writer).
   *   - LOCK_UN to release a lock (shared or exclusive).
   *   - LOCK_NB if you don't want flock() to block while locking (not
   *     supported on Windows).
   *
   * @return bool
   *   Always returns TRUE at the present time. (no support)
   *
   * @see http://php.net/manual/en/streamwrapper.stream-lock.php
   */
  public function stream_lock($operation) {
    return TRUE;
  }

  /**
   * Support for fread(), file_get_contents() etc.
   *
   * @param int $count
   *   Maximum number of bytes to be read.
   *
   * @return string
   *   The string that was read, or FALSE in case of an error.
   *
   * @see http://php.net/manual/en/streamwrapper.stream-read.php
   */
  public function stream_read($count) {
    if (is_string($this->sessionContent)) {
      $remaining_chars = backdrop_strlen($this->sessionContent) - $this->streamPointer;
      $number_to_read = min($count, $remaining_chars);
      if ($remaining_chars > 0) {
        $buffer = backdrop_substr($this->sessionContent, $this->streamPointer, $number_to_read);
        $this->streamPointer += $number_to_read;
        return $buffer;
      }
    }

    return FALSE;
  }

  /**
   * Support for fwrite(), file_put_contents() etc.
   *
   * @param string $data
   *   The string to be written.
   *
   * @return int
   *   The number of bytes written (integer).
   *
   * @see http://php.net/manual/en/streamwrapper.stream-write.php
   */
  public function stream_write($data) {
    // Sanitize the data in a simple way since we're putting it into the
    // session variable.
    $data = check_plain($data);
    $this->sessionContent = substr_replace($this->sessionContent, $data, $this->streamPointer);
    $this->streamPointer += backdrop_strlen($data);

    return backdrop_strlen($data);
  }

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

  /**
   * Support for fseek().
   *
   * @param int $offset
   *   The byte offset to got to.
   * @param int $whence
   *   SEEK_SET, SEEK_CUR, or SEEK_END.
   *
   * @return bool
   *   TRUE on success.
   *
   * @see http://php.net/manual/en/streamwrapper.stream-seek.php
   */
  public function stream_seek($offset, $whence) {
    if (backdrop_strlen($this->sessionContent) >= $offset) {
      $this->streamPointer = $offset;
      return TRUE;
    }

    return FALSE;
  }

  /**
   * Support for fflush().
   *
   * @return bool
   *   TRUE if data was successfully stored (or there was no data to store).
   *   This always returns TRUE, as this example provides and needs no
   *   flush support.
   *
   * @see http://php.net/manual/en/streamwrapper.stream-flush.php
   */
  public function stream_flush() {
    return TRUE;
  }

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

  /**
   * Support for fstat().
   *
   * @return array
   *   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/en/streamwrapper.stream-stat.php
   */
  public function stream_stat() {
    return array(
      'size' => backdrop_strlen($this->sessionContent),
    );
  }

  /**
   * Support for fclose().
   *
   * @return bool
   *   TRUE if stream was successfully closed.
   *
   * @see http://php.net/manual/en/streamwrapper.stream-close.php
   */
  public function stream_close() {
    $this->streamPointer = 0;
    // Unassign the reference.
    unset($this->sessionContent);

    return TRUE;
  }

  /**
   * Support for unlink().
   *
   * @param string $uri
   *   A string containing the uri to the resource to delete.
   *
   * @return bool
   *   TRUE if resource was successfully deleted.
   *
   * @see http://php.net/manual/en/streamwrapper.unlink.php
   */
  public function unlink($uri) {
    $path = $this->getLocalPath($uri);
    $path_components = preg_split('/\//', $path);
    $fail = FALSE;
    $unset = '$_SESSION[\'file_example\']';
    foreach ($path_components as $component) {
      $unset .= '[\'' . $component . '\']';
    }
    // TODO: Is there a better way to delete from an array?
    // backdrop_array_get_nested_value() doesn't work because it only returns
    // a reference; unsetting a reference only unsets the reference.
    eval("unset($unset);");

    return TRUE;
  }

  /**
   * Support for rename().
   *
   * @param string $from_uri
   *   The uri to the file to rename.
   * @param string $to_uri
   *   The new uri for file.
   *
   * @return bool
   *   TRUE if file was successfully renamed.
   *
   * @see http://php.net/manual/en/streamwrapper.rename.php
   */
  public function rename($from_uri, $to_uri) {
    $from_key = &$this->uri_to_session_key($from_uri);
    $to_key = &$this->uri_to_session_key($to_uri);
    if (is_dir($to_key) || is_file($to_key)) {
      return FALSE;
    }
    $to_key = $from_key;
    unset($from_key);

    return TRUE;
  }

  /**
   * Gets the name of the directory from a given path.
   *
   * @param string $uri
   *   A URI.
   *
   * @return string
   *   A string containing the directory name.
   *
   * @see backdrop_dirname()
   */
  public function dirname($uri = NULL) {
    list($scheme, $target) = explode('://', $uri, 2);
    $target = $this->getTarget($uri);
    if (strpos($target, '/')) {
      $dirname = preg_replace('@/[^/]*$@', '', $target);
    }
    else {
      $dirname = '';
    }

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

  /**
   * Support for mkdir().
   *
   * @param string $uri
   *   A string containing the URI to the directory to create.
   * @param int $mode
   *   Permission flags - see mkdir().
   * @param int $options
   *   A bit mask of STREAM_REPORT_ERRORS and STREAM_MKDIR_RECURSIVE.
   *
   * @return bool
   *   TRUE if directory was successfully created.
   *
   * @see http://php.net/manual/en/streamwrapper.mkdir.php
   */
  public function mkdir($uri, $mode, $options) {
    // If this already exists, then we can't mkdir.
    if (is_dir($uri) || is_file($uri)) {
      return FALSE;
    }

    // Create the key in $_SESSION;
    $this->uri_to_session_key($uri, TRUE);

    // Place a magic file inside it to differentiate this from an empty file.
    $marker_uri = $uri . '/.isadir.txt';
    $this->uri_to_session_key($marker_uri, TRUE);

    return TRUE;
  }

  /**
   * Support for rmdir().
   *
   * @param string $uri
   *   A string containing the URI to the directory to delete.
   * @param int $options
   *   A bit mask of STREAM_REPORT_ERRORS.
   *
   * @return bool
   *   TRUE if directory was successfully removed.
   *
   * @see http://php.net/manual/en/streamwrapper.rmdir.php
   */
  public function rmdir($uri, $options) {
    $path = $this->getLocalPath($uri);
    $path_components = preg_split('/\//', $path);
    $fail = FALSE;
    $unset = '$_SESSION[\'file_example\']';
    foreach ($path_components as $component) {
      $unset .= '[\'' . $component . '\']';
    }
    // TODO: I really don't like this eval.
    debug($unset, 'array element to be unset');
    eval("unset($unset);");

    return TRUE;
  }

  /**
   * Support for stat().
   *
   * This important function goes back to the Unix way of doing things.
   * In this example almost the entire stat array is irrelevant, but the
   * mode is very important. It tells PHP whether we have a file or a
   * directory and what the permissions are. All that is packed up in a
   * bitmask. This is not normal PHP fodder.
   *
   * @param string $uri
   *   A string containing the URI to get information about.
   * @param int $flags
   *   A bit mask of STREAM_URL_STAT_LINK and STREAM_URL_STAT_QUIET.
   *
   * @return array|bool
   *   An array with file status, or FALSE in case of an error - see fstat()
   *   for a description of this array.
   *
   * @see http://php.net/manual/en/streamwrapper.url-stat.php
   */
  public function url_stat($uri, $flags) {
    // Get a reference to the $_SESSION key for this URI.
    $key = $this->uri_to_session_key($uri, FALSE);
    // Default to fail.
    $return = FALSE;
    $mode = 0;

    // We will call an array a directory and the root is always an array.
    if (is_array($key) && array_key_exists('.isadir.txt', $key)) {
      // S_IFDIR means it's a directory.
      $mode = 0040000;
    }
    elseif ($key !== FALSE) {
      // S_IFREG means it's a file.
      $mode = 0100000;
    }

    if ($mode) {
      $size = 0;
      if ($mode == 0100000) {
        $size = backdrop_strlen($key);
      }

      // There are no protections on this, so all writable.
      $mode |= 0777;
      $return = array(
        'dev' => 0,
        'ino' => 0,
        'mode' => $mode,
        'nlink' => 0,
        'uid' => 0,
        'gid' => 0,
        'rdev' => 0,
        'size' => $size,
        'atime' => 0,
        'mtime' => 0,
        'ctime' => 0,
        'blksize' => 0,
        'blocks' => 0,
      );
    }

    return $return;
  }

  /**
   * Support for opendir().
   *
   * @param string $uri
   *   A string containing the URI to the directory to open.
   * @param int $options
   *   Whether or not to enforce safe_mode (0x04).
   *
   * @return bool
   *   TRUE on success.
   *
   * @see http://php.net/manual/en/streamwrapper.dir-opendir.php
   */
  public function dir_opendir($uri, $options) {
    $var = &$this->uri_to_session_key($uri, FALSE);
    if ($var === FALSE || !array_key_exists('.isadir.txt', $var)) {
      return FALSE;
    }

    // We grab the list of key names, flip it so that .isadir.txt can easily
    // be removed, then flip it back so we can easily walk it as a list.
    $this->directoryKeys = array_flip(array_keys($var));
    unset($this->directoryKeys['.isadir.txt']);
    $this->directoryKeys = array_keys($this->directoryKeys);
    $this->directoryPointer = 0;

    return TRUE;
  }

  /**
   * Support for readdir().
   *
   * @return string|bool
   *   The next filename, or FALSE if there are no more files in the directory.
   *
   * @see http://php.net/manual/en/streamwrapper.dir-readdir.php
   */
  public function dir_readdir() {
    if ($this->directoryPointer < count($this->directoryKeys)) {
      $next = $this->directoryKeys[$this->directoryPointer];
      $this->directoryPointer++;
      return $next;
    }

    return FALSE;
  }

  /**
   * Support for rewinddir().
   *
   * @return bool
   *   TRUE on success.
   *
   * @see http://php.net/manual/en/streamwrapper.dir-rewinddir.php
   */
  public function dir_rewinddir() {
    $this->directoryPointer = 0;

    return TRUE;
  }

  /**
   * Support for closedir().
   *
   * @return bool
   *   TRUE on success.
   *
   * @see http://php.net/manual/en/streamwrapper.dir-closedir.php
   */
  public function dir_closedir() {
    $this->directoryPointer = 0;
    unset($this->directoryKeys);

    return TRUE;
  }
}

Members

Name	Modifiers	Type	Description
FileExampleSessionStreamWrapper::$context	public	property	Stream context resource.
FileExampleSessionStreamWrapper::$directoryKeys	protected	property	List of keys in a given directory.
FileExampleSessionStreamWrapper::$directoryPointer	protected	property	Pointer to where we are in a directory read.
FileExampleSessionStreamWrapper::$sessionContent	protected	property	The content of the stream.
FileExampleSessionStreamWrapper::$streamPointer	protected	property	The pointer to the next read or write within the session variable.
FileExampleSessionStreamWrapper::$uri	protected	property	Instance URI (stream).
FileExampleSessionStreamWrapper::chmod	public	function	We have no concept of chmod, so just return TRUE. Overrides BackdropStreamWrapperInterface::chmod
FileExampleSessionStreamWrapper::dirname	public	function	Gets the name of the directory from a given path. Overrides BackdropStreamWrapperInterface::dirname
FileExampleSessionStreamWrapper::dir_closedir	public	function	Support for closedir(). Overrides StreamWrapperInterface::dir_closedir
FileExampleSessionStreamWrapper::dir_opendir	public	function	Support for opendir(). Overrides StreamWrapperInterface::dir_opendir
FileExampleSessionStreamWrapper::dir_readdir	public	function	Support for readdir(). Overrides StreamWrapperInterface::dir_readdir
FileExampleSessionStreamWrapper::dir_rewinddir	public	function	Support for rewinddir(). Overrides StreamWrapperInterface::dir_rewinddir
FileExampleSessionStreamWrapper::getDirectoryPath	public	function	Implements getDirectoryPath().
FileExampleSessionStreamWrapper::getExternalUrl	public	function	Overrides getExternalUrl(). Overrides BackdropStreamWrapperInterface::getExternalUrl
FileExampleSessionStreamWrapper::getLocalPath	protected	function	Returns the local path.
FileExampleSessionStreamWrapper::getMimeType	public static	function	Implements getMimeType(). Overrides BackdropStreamWrapperInterface::getMimeType
FileExampleSessionStreamWrapper::getTarget	public	function	Implements getTarget().
FileExampleSessionStreamWrapper::getUri	public	function	Implements getUri(). Overrides BackdropStreamWrapperInterface::getUri
FileExampleSessionStreamWrapper::mkdir	public	function	Support for mkdir(). Overrides StreamWrapperInterface::mkdir
FileExampleSessionStreamWrapper::realpath	public	function	Implements realpath(). Overrides BackdropStreamWrapperInterface::realpath
FileExampleSessionStreamWrapper::rename	public	function	Support for rename(). Overrides StreamWrapperInterface::rename
FileExampleSessionStreamWrapper::rmdir	public	function	Support for rmdir(). Overrides StreamWrapperInterface::rmdir
FileExampleSessionStreamWrapper::setUri	public	function	Implements setUri(). Overrides BackdropStreamWrapperInterface::setUri
FileExampleSessionStreamWrapper::stream_close	public	function	Support for fclose(). Overrides StreamWrapperInterface::stream_close
FileExampleSessionStreamWrapper::stream_eof	public	function	Support for feof(). Overrides StreamWrapperInterface::stream_eof
FileExampleSessionStreamWrapper::stream_flush	public	function	Support for fflush(). Overrides StreamWrapperInterface::stream_flush
FileExampleSessionStreamWrapper::stream_lock	public	function	Support for flock(). Overrides StreamWrapperInterface::stream_lock
FileExampleSessionStreamWrapper::stream_open	public	function	Opens a stream, as for fopen(), file_get_contents(), file_put_contents(). Overrides StreamWrapperInterface::stream_open
FileExampleSessionStreamWrapper::stream_read	public	function	Support for fread(), file_get_contents() etc. Overrides StreamWrapperInterface::stream_read
FileExampleSessionStreamWrapper::stream_seek	public	function	Support for fseek(). Overrides StreamWrapperInterface::stream_seek
FileExampleSessionStreamWrapper::stream_stat	public	function	Support for fstat(). Overrides StreamWrapperInterface::stream_stat
FileExampleSessionStreamWrapper::stream_tell	public	function	Support for ftell(). Overrides StreamWrapperInterface::stream_tell
FileExampleSessionStreamWrapper::stream_write	public	function	Support for fwrite(), file_put_contents() etc. Overrides StreamWrapperInterface::stream_write
FileExampleSessionStreamWrapper::unlink	public	function	Support for unlink(). Overrides StreamWrapperInterface::unlink
FileExampleSessionStreamWrapper::uri_to_session_key	protected	function	Return a reference to the correct $_SESSION key.
FileExampleSessionStreamWrapper::url_stat	public	function	Support for stat(). Overrides StreamWrapperInterface::url_stat
FileExampleSessionStreamWrapper::__construct	public	function	Constructor method.

class FileExampleSessionStreamWrapper

Hierarchy

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Members

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