code: function getFileStats (cfg, filePath, callback) {
  	fs.realpath(filePath, function (err, realpath) {
  		// On Windows we can get different cases for the same disk letter :/.
  		let checkPath = realpath;
  		if (os.platform() === 'win32' && realpath) {
  			checkPath = realpath.toLowerCase();
  		}
  
  		if (err || checkPath.indexOf(cfg.documentRootReal) !== 0) {
  			return callback(err || new Error('Access denied'));
  		}
  
  		fs[cfg.followSymbolicLinks ? 'stat' : 'lstat'](filePath, function (err, stats) {
  			if (err || !stats.isFile()) {
  				return callback(err || new Error('Access denied'));
  			}
  
  			stats.path = realpath;
  
  			callback(null, stats);
  		});
  	});
  }
docs: Calls back with error or null and fs.Stats object as second parameter.
  fs.Stats object is extended with `path` property.
  
  @param {!module:serve-files~configuration} cfg
  @param {!string}                           cfg.documentRootReal
  @param {string}                            [cfg.followSymbolicLinks=false]
  @param {!string}                           filePath
  @param {@Function}                         callback