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

/**
 * Remove '.' and '..' path parts and make path absolute without
 * resolving symlinks.
 *
 * Examples:
 *
 *   resolvePath("test/./me/../now/", false);
 *   => test/now
 *   
 *   resolvePath("test///.///me///../now/", true);
 *   => /home/example/test/now
 *   
 *   resolvePath("test/./me/../now/", "/www/example.com");
 *   => /www/example.com/test/now
 *   
 *   resolvePath("/test/./me/../now/", "/www/example.com");
 *   => /test/now
 *
 * @access public
 * @param string $path
 * @param mixed $basePath resolve paths realtively to this path. Params:
 *                        STRING: prefix with this path;
 *                        TRUE: use current dir;
 *                        FALSE: keep relative (default)
 * @return string resolved path
 */
function resolvePath($path, $basePath=false) {
    // Make absolute path
    if (substr($path, 0, 1) !== DIRECTORY_SEPARATOR) {
        if ($basePath === true) {
            // Get PWD first to avoid getcwd() resolving symlinks if in symlinked folder
            $path=(getenv('PWD') ?: getcwd()).DIRECTORY_SEPARATOR.$path;
        } elseif (strlen($basePath)) {
            $path=$basePath.DIRECTORY_SEPARATOR.$path;
        }
    }

    // Resolve '.' and '..'
    $components=array();
    foreach(explode(DIRECTORY_SEPARATOR, rtrim($path, DIRECTORY_SEPARATOR)) as $name) {
        if ($name === '..') {
            array_pop($components);
        } elseif ($name !== '.' && !(count($components) && $name === '')) {
            // … && !(count($components) && $name === '') - we want to keep initial '/' for abs paths
            $components[]=$name;
        }
    }

    return implode(DIRECTORY_SEPARATOR, $components);
}