static virtual NanoHTTPD.Response subBot_serveFileRange(File file, S mimeType, S rangeHeader) ctex {
  S rangeValue = dropPrefix("bytes=", trim(rangeHeader));
  long fileLength = file.length(), start, end;
  
  if (rangeValue.startsWith("-")) {
    end = fileLength-1;
    start = fileLength-1-parseLong(dropPrefix("-", rangeValue));
  } else {
    S[] range = rangeValue.split("-");
    start = parseLong(range[0]);
    end = range.length > 1 ? min(fileLength-1, parseLong(range[1])) : fileLength-1;
  }
  
  if (start <= end) {
    long contentLength = end-start+1;
    FileInputStream fileInputStream = new(file);
    fileInputStream.skip(start);
    virtual Response response = subBot_servePartialContent(mimeType, fileInputStream, contentLength);
    call(response, "addHeader", "Content-Range", "bytes " + start + "-" + end + "/" + fileLength);
    ret response;
  } else
    ret subBot_serveRangeNotSatisfiable(rangeHeader);
}

Began life as a copy of #1014005