static S readLineThroughUTF8Processor(UTF8Processor p, InputStream in) ctex {
  new StringBuilder input;
  bool hasLine = false;
  while (!hasLine) {
    int available=in.available();
    if (available==0) break;
    byte b[]=new byte[available];
    in.read(b);
    for i to available: {
      S s = p.processByte(b[i]);
      if (nempty(s)) {
        input.append(s);
        if (s.equals("\n")) hasLine = true;
      }
    }
  }
  ret input.toString();
}