anchor.diff:      }
     }
   
  -  return (Request request) {
  +  return (Request request) async {
       var segs = [fileSystemPath]..addAll(request.url.pathSegments);
   
       var fsPath = p.joinAll(segs);
  
positive.code:       HttpHeaders.LAST_MODIFIED: formatHttpDate(fileStat.changed)
      };
  
      var contentType = mime.lookupMimeType(file.path);
      if (contentType != null) {
        headers[HttpHeaders.CONTENT_TYPE] = contentType;
      }
  
negative.code: /// handler produces a listing of the directory.
  Handler createStaticHandler(String fileSystemPath,
      {bool serveFilesOutsidePath: false, String defaultDocument,
      bool listDirectories: false, bool useMagicBytesForContentType: false}) {
    var rootDir = new Directory(fileSystemPath);
    if (!rootDir.existsSync()) {
      throw new ArgumentError('A directory corresponding to fileSystemPath '
  