What is the best way to resolve a relative path (like realpath) for non-existing files?

Question

I\'m trying to enforce a root directory in a filesystem abstraction. The problem I\'m encountering is the following:

The API lets you read and write files, not only

Answer 1

To quote Jame Zawinski:

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.

protected function getAbsoluteFilename($filename) {
  $path = [];
  foreach(explode('/', $filename) as $part) {
    // ignore parts that have no value
    if (empty($part) || $part === '.') continue;

    if ($part !== '..') {
      // cool, we found a new part
      array_push($path, $part);
    }
    else if (count($path) > 0) {
      // going back up? sure
      array_pop($path);
    } else {
      // now, here we don't like
      throw new \Exception('Climbing above the root is not permitted.');
    }
  }

  // prepend my root directory
  array_unshift($path, $this->getPath());

  return join('/', $path);
}